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How long does it take for a diode to conduct?
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Tim Wescott
Apr 9, 2012, 9:25:28 PM4/9/12
to
Is it reasonable to expect that the turn-on (not off -- _on_) time of a
diode should be pretty much consistent with the inductance of the
package, and not much else?
A customer just sent me some O-scope traces of a circuit where a voltage
at a catch diode anode is (at least apparently) going several hundred
volts above its cathode for a microsecond before settling out to the
nominal anode voltage of the diode.
We're not sure if it's a measurement artifact because the coil has some
700A in it, or if it's a real event; I wouldn't be willing to even
believe it's a real event except that I know that funny things can happen
at high currents.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
diode should be pretty much consistent with the inductance of the
package, and not much else?
A customer just sent me some O-scope traces of a circuit where a voltage
at a catch diode anode is (at least apparently) going several hundred
volts above its cathode for a microsecond before settling out to the
nominal anode voltage of the diode.
We're not sure if it's a measurement artifact because the coil has some
700A in it, or if it's a real event; I wouldn't be willing to even
believe it's a real event except that I know that funny things can happen
at high currents.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
Jamie
Apr 9, 2012, 9:47:29 PM4/9/12
to
Tim Wescott wrote:
> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
> diode should be pretty much consistent with the inductance of the
> package, and not much else?
>
> A customer just sent me some O-scope traces of a circuit where a voltage
> at a catch diode anode is (at least apparently) going several hundred
> volts above its cathode for a microsecond before settling out to the
> nominal anode voltage of the diode.
>
> We're not sure if it's a measurement artifact because the coil has some
> 700A in it, or if it's a real event; I wouldn't be willing to even
> believe it's a real event except that I know that funny things can happen
> at high currents.
>
What the customer should do is this..
> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
> diode should be pretty much consistent with the inductance of the
> package, and not much else?
>
> A customer just sent me some O-scope traces of a circuit where a voltage
> at a catch diode anode is (at least apparently) going several hundred
> volts above its cathode for a microsecond before settling out to the
> nominal anode voltage of the diode.
>
> We're not sure if it's a measurement artifact because the coil has some
> 700A in it, or if it's a real event; I wouldn't be willing to even
> believe it's a real event except that I know that funny things can happen
> at high currents.
>
Set the scope at that peak as the trigger point and expand the
scan at that point.
If there is some descending ripples( ringing), well then we
know we are dealing with a high Q reactive circuit.
If all you see is a single peak with no descending ripples, then I
take that as a slow transition in switching.
Jamie
Phil Hobbs
Apr 9, 2012, 10:17:40 PM4/9/12
to
Tim Wescott wrote:
>
> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
> diode should be pretty much consistent with the inductance of the
> package, and not much else?
>
> A customer just sent me some O-scope traces of a circuit where a voltage
> at a catch diode anode is (at least apparently) going several hundred
> volts above its cathode for a microsecond before settling out to the
> nominal anode voltage of the diode.
>
> We're not sure if it's a measurement artifact because the coil has some
> 700A in it, or if it's a real event; I wouldn't be willing to even
> believe it's a real event except that I know that funny things can happen
> at high currents.
Slow turn-on is a fairly common diode pathology.
>
> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
> diode should be pretty much consistent with the inductance of the
> package, and not much else?
>
> A customer just sent me some O-scope traces of a circuit where a voltage
> at a catch diode anode is (at least apparently) going several hundred
> volts above its cathode for a microsecond before settling out to the
> nominal anode voltage of the diode.
>
> We're not sure if it's a measurement artifact because the coil has some
> 700A in it, or if it's a real event; I wouldn't be willing to even
> believe it's a real event except that I know that funny things can happen
> at high currents.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
Tim Wescott
Apr 9, 2012, 10:24:39 PM4/9/12
to
On Mon, 09 Apr 2012 22:17:40 -0400, Phil Hobbs wrote:
> Tim Wescott wrote:
>>
>> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
>> diode should be pretty much consistent with the inductance of the
>> package, and not much else?
>>
>> A customer just sent me some O-scope traces of a circuit where a
>> voltage at a catch diode anode is (at least apparently) going several
>> hundred volts above its cathode for a microsecond before settling out
>> to the nominal anode voltage of the diode.
>>
>> We're not sure if it's a measurement artifact because the coil has some
>> 700A in it, or if it's a real event; I wouldn't be willing to even
>> believe it's a real event except that I know that funny things can
>> happen at high currents.
>
> Slow turn-on is a fairly common diode pathology.
Augh. So -- what to do? Are there diodes that are specifically rated
> Tim Wescott wrote:
>>
>> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
>> diode should be pretty much consistent with the inductance of the
>> package, and not much else?
>>
>> A customer just sent me some O-scope traces of a circuit where a
>> voltage at a catch diode anode is (at least apparently) going several
>> hundred volts above its cathode for a microsecond before settling out
>> to the nominal anode voltage of the diode.
>>
>> We're not sure if it's a measurement artifact because the coil has some
>> 700A in it, or if it's a real event; I wouldn't be willing to even
>> believe it's a real event except that I know that funny things can
>> happen at high currents.
>
> Slow turn-on is a fairly common diode pathology.
for quick turn-on? If not, are there diodes (or diode types) that are
noted for turning on rapidly? Can multiple diodes in parallel be used to
speed up the turn-on (this seems like all sorts of wrong to me, by the
way -- but I feel I have to check).
George Herold
Apr 9, 2012, 10:35:15 PM4/9/12
to
On Apr 9, 10:17 pm, Phil Hobbs
What's the physics involved?
Would increasing the temperature help?
George H.
Would increasing the temperature help?
George H.
Phil Hobbs
Apr 9, 2012, 10:46:46 PM4/9/12
to
George Herold wrote:
>
> On Apr 9, 10:17 pm, Phil Hobbs
> <pcdhSpamMeSensel...@electrooptical.net> wrote:
> > Tim Wescott wrote:
> >
> > > Is it reasonable to expect that the turn-on (not off -- _on_) time of a
> > > diode should be pretty much consistent with the inductance of the
> > > package, and not much else?
> >
> > > A customer just sent me some O-scope traces of a circuit where a voltage
> > > at a catch diode anode is (at least apparently) going several hundred
> > > volts above its cathode for a microsecond before settling out to the
> > > nominal anode voltage of the diode.
> >
> > > We're not sure if it's a measurement artifact because the coil has some
> > > 700A in it, or if it's a real event; I wouldn't be willing to even
> > > believe it's a real event except that I know that funny things can happen
> > > at high currents.
> >
> > Slow turn-on is a fairly common diode pathology.
> >
> > Cheers
> >
> > Phil Hobbs
>
>
> On Apr 9, 10:17 pm, Phil Hobbs
> <pcdhSpamMeSensel...@electrooptical.net> wrote:
> > Tim Wescott wrote:
> >
> > > Is it reasonable to expect that the turn-on (not off -- _on_) time of a
> > > diode should be pretty much consistent with the inductance of the
> > > package, and not much else?
> >
> > > A customer just sent me some O-scope traces of a circuit where a voltage
> > > at a catch diode anode is (at least apparently) going several hundred
> > > volts above its cathode for a microsecond before settling out to the
> > > nominal anode voltage of the diode.
> >
> > > We're not sure if it's a measurement artifact because the coil has some
> > > 700A in it, or if it's a real event; I wouldn't be willing to even
> > > believe it's a real event except that I know that funny things can happen
> > > at high currents.
> >
> > Slow turn-on is a fairly common diode pathology.
> >
> > Cheers
> >
> > Phil Hobbs
>
> What's the physics involved?
> Would increasing the temperature help?
>
> George H.
I don'g actually know why that is, but some diodes overshoot a lot.
> Would increasing the temperature help?
>
> George H.
There's more info in one of Jim Williams's app notes,
http://www.linear.com/docs/27403 .
Sjouke Burry
Apr 9, 2012, 10:53:15 PM4/9/12
to
Tim Wescott <t...@seemywebsite.com> wrote in
news:T_OdnWGfG_V6BB7S...@web-ster.com:
> On Mon, 09 Apr 2012 22:17:40 -0400, Phil Hobbs wrote:
>
>> Tim Wescott wrote:
>>>
>>> Is it reasonable to expect that the turn-on (not off -- _on_) time
>>> of a diode should be pretty much consistent with the inductance of
>>> the package, and not much else?
>>>
>>> A customer just sent me some O-scope traces of a circuit where a
>>> voltage at a catch diode anode is (at least apparently) going
>>> several hundred volts above its cathode for a microsecond before
>>> settling out to the nominal anode voltage of the diode.
>>>
>>> We're not sure if it's a measurement artifact because the coil has
>>> some 700A in it, or if it's a real event; I wouldn't be willing to
>>> even believe it's a real event except that I know that funny things
>>> can happen at high currents.
>>
>> Slow turn-on is a fairly common diode pathology.
>
> Augh. So -- what to do? Are there diodes that are specifically rated
> for quick turn-on? If not, are there diodes (or diode types) that are
> noted for turning on rapidly? Can multiple diodes in parallel be used
> to speed up the turn-on (this seems like all sorts of wrong to me, by
> the way -- but I feel I have to check).
>
(part)cure: never turn the laser completely off, just slightly below
or above lasing, should mean a big decrease in capacity.
Somebody have a forward voltage versus capacity plot?
news:T_OdnWGfG_V6BB7S...@web-ster.com:
> On Mon, 09 Apr 2012 22:17:40 -0400, Phil Hobbs wrote:
>
>> Tim Wescott wrote:
>>>
>>> Is it reasonable to expect that the turn-on (not off -- _on_) time
>>> of a diode should be pretty much consistent with the inductance of
>>> the package, and not much else?
>>>
>>> A customer just sent me some O-scope traces of a circuit where a
>>> voltage at a catch diode anode is (at least apparently) going
>>> several hundred volts above its cathode for a microsecond before
>>> settling out to the nominal anode voltage of the diode.
>>>
>>> We're not sure if it's a measurement artifact because the coil has
>>> some 700A in it, or if it's a real event; I wouldn't be willing to
>>> even believe it's a real event except that I know that funny things
>>> can happen at high currents.
>>
>> Slow turn-on is a fairly common diode pathology.
>
> Augh. So -- what to do? Are there diodes that are specifically rated
> for quick turn-on? If not, are there diodes (or diode types) that are
> noted for turning on rapidly? Can multiple diodes in parallel be used
> to speed up the turn-on (this seems like all sorts of wrong to me, by
> the way -- but I feel I have to check).
>
or above lasing, should mean a big decrease in capacity.
Somebody have a forward voltage versus capacity plot?
John Larkin
Apr 9, 2012, 11:09:39 PM4/9/12
to
On Mon, 09 Apr 2012 20:25:28 -0500, Tim Wescott <t...@seemywebsite.com>
wrote:
>Is it reasonable to expect that the turn-on (not off -- _on_) time of a
>diode should be pretty much consistent with the inductance of the
>package, and not much else?
Not a PN junction diode. They take a while to conduct, the phenom
being called, strangely, "forward recovery."
We did a pulse generator that used power diodes in DSRD (drift step
recovery) mode. We applied 48 volts in the forward direction, and
waited about 100 ns for the current to ramp up to 50 amps. The rampup
looked pretty linear. Then we applied -400 volts to get them to snap.
>
>A customer just sent me some O-scope traces of a circuit where a voltage
>at a catch diode anode is (at least apparently) going several hundred
>volts above its cathode for a microsecond before settling out to the
>nominal anode voltage of the diode.
That can happen. You may need a high-voltage schottky, SiC or GaN or
whatever, or a few silicon schottkies in series.
John
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
wrote:
>Is it reasonable to expect that the turn-on (not off -- _on_) time of a
>diode should be pretty much consistent with the inductance of the
>package, and not much else?
being called, strangely, "forward recovery."
We did a pulse generator that used power diodes in DSRD (drift step
recovery) mode. We applied 48 volts in the forward direction, and
waited about 100 ns for the current to ramp up to 50 amps. The rampup
looked pretty linear. Then we applied -400 volts to get them to snap.
>
>A customer just sent me some O-scope traces of a circuit where a voltage
>at a catch diode anode is (at least apparently) going several hundred
>volts above its cathode for a microsecond before settling out to the
>nominal anode voltage of the diode.
whatever, or a few silicon schottkies in series.
John
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
miso
Apr 9, 2012, 11:28:45 PM4/9/12
to
On 4/9/2012 7:24 PM, Tim Wescott wrote:
> On Mon, 09 Apr 2012 22:17:40 -0400, Phil Hobbs wrote:
>
>> Tim Wescott wrote:
>>>
>>> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
>>> diode should be pretty much consistent with the inductance of the
>>> package, and not much else?
>>>
>>> A customer just sent me some O-scope traces of a circuit where a
>>> voltage at a catch diode anode is (at least apparently) going several
>>> hundred volts above its cathode for a microsecond before settling out
>>> to the nominal anode voltage of the diode.
>>>
>>> We're not sure if it's a measurement artifact because the coil has some
>>> 700A in it, or if it's a real event; I wouldn't be willing to even
>>> believe it's a real event except that I know that funny things can
>>> happen at high currents.
>>
>> Slow turn-on is a fairly common diode pathology.
>
> Augh. So -- what to do? Are there diodes that are specifically rated
> for quick turn-on? If not, are there diodes (or diode types) that are
> noted for turning on rapidly? Can multiple diodes in parallel be used to
> speed up the turn-on (this seems like all sorts of wrong to me, by the
> way -- but I feel I have to check).
>
There is always the issue of current hogging with paralleling diodes.
> On Mon, 09 Apr 2012 22:17:40 -0400, Phil Hobbs wrote:
>
>> Tim Wescott wrote:
>>>
>>> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
>>> diode should be pretty much consistent with the inductance of the
>>> package, and not much else?
>>>
>>> A customer just sent me some O-scope traces of a circuit where a
>>> voltage at a catch diode anode is (at least apparently) going several
>>> hundred volts above its cathode for a microsecond before settling out
>>> to the nominal anode voltage of the diode.
>>>
>>> We're not sure if it's a measurement artifact because the coil has some
>>> 700A in it, or if it's a real event; I wouldn't be willing to even
>>> believe it's a real event except that I know that funny things can
>>> happen at high currents.
>>
>> Slow turn-on is a fairly common diode pathology.
>
> Augh. So -- what to do? Are there diodes that are specifically rated
> for quick turn-on? If not, are there diodes (or diode types) that are
> noted for turning on rapidly? Can multiple diodes in parallel be used to
> speed up the turn-on (this seems like all sorts of wrong to me, by the
> way -- but I feel I have to check).
>
Given your posts in the past, I think you knew that but were in need of
a cup of coffee prior to hitting the send button. ;-)
Tim Wescott
Apr 9, 2012, 11:35:48 PM4/9/12
to
Presumably if one did it one would need current balancing resistors, and
one might leave blood on the floor before one got things working.
miso
Apr 9, 2012, 11:42:53 PM4/9/12
to
transmission line tricks, not a driver circuit.
> http://www.ce-mag.com/ce-mag.com/archive/01/03/0103CE_046.html
The turn on time is a real pain in the ass in switcher design. Not only
for efficiency issues, but the pin on the chip that touches the external
catch diode rises like a bat out of hell until the diode begins
conducting. That fast rise can lead to C*dv/dt current injection into
nearby pins on the chip. So pin layout is critical. Some designs use
internal "blanking" periods to avoid making any "decisions" by the
internet circuitry while it is expected that the diode hasn't turned on yet.
Martin Riddle
Apr 10, 2012, 12:08:30 AM4/10/12
to
"John Larkin" <jjla...@highNOTlandTHIStechnologyPART.com> wrote in
message news:jp87o7d4jjd2i613v...@4ax.com...
> On Mon, 09 Apr 2012 20:25:28 -0500, Tim Wescott <t...@seemywebsite.com>
> wrote:
>
>>Is it reasonable to expect that the turn-on (not off -- _on_) time of
>>a
>>diode should be pretty much consistent with the inductance of the
>>package, and not much else?
>
> Not a PN junction diode. They take a while to conduct, the phenom
> being called, strangely, "forward recovery."
>
> We did a pulse generator that used power diodes in DSRD (drift step
> recovery) mode. We applied 48 volts in the forward direction, and
> waited about 100 ns for the current to ramp up to 50 amps. The rampup
> looked pretty linear. Then we applied -400 volts to get them to snap.
>
>
>>
>>A customer just sent me some O-scope traces of a circuit where a
>>voltage
>>at a catch diode anode is (at least apparently) going several hundred
>>volts above its cathode for a microsecond before settling out to the
>>nominal anode voltage of the diode.
>
> That can happen. You may need a high-voltage schottky, SiC or GaN or
> whatever, or a few silicon schottkies in series.
>
> John
>
> --
>
Trr is the first thing to come to mind. Rule of thumb is the higher the
> wrote:
>
>>Is it reasonable to expect that the turn-on (not off -- _on_) time of
>>a
>>diode should be pretty much consistent with the inductance of the
>>package, and not much else?
>
> Not a PN junction diode. They take a while to conduct, the phenom
> being called, strangely, "forward recovery."
>
> We did a pulse generator that used power diodes in DSRD (drift step
> recovery) mode. We applied 48 volts in the forward direction, and
> waited about 100 ns for the current to ramp up to 50 amps. The rampup
> looked pretty linear. Then we applied -400 volts to get them to snap.
>
>
>>
>>A customer just sent me some O-scope traces of a circuit where a
>>voltage
>>at a catch diode anode is (at least apparently) going several hundred
>>volts above its cathode for a microsecond before settling out to the
>>nominal anode voltage of the diode.
>
> That can happen. You may need a high-voltage schottky, SiC or GaN or
> whatever, or a few silicon schottkies in series.
>
> John
>
> --
>
reverse voltage the slower the diode is.
The SIC diodes are very fast in any voltage.
<http://www.infineon.com/cms/en/product/Discretes-and-Standard-Products/Diodes/Silicon-Carbide-Schottky-Diodes/channel.html?channel=ff80808112ab681d0112ab6a50b304a0>
<10ns for a 600v rating
Cheers
Tim Williams
Apr 10, 2012, 12:22:33 AM4/10/12
to
"miso" <mi...@sushi.com> wrote in message
news:jm0a7l$ghc$1...@speranza.aioe.org...
from a dV/dt snubber. A dV/dt snubber, of course, works even with junction
diodes, because although the diode won't turn on instantly, it has hundreds
of volts to go before it's crashing into rails or anything, so it's forced
on, *very* quickly. There's a Unitrode appnote, I believe, which plots
transistor, snubber and total losses vs. snubber size -- there's a minima
where, when the snubber just about doubles the fall time, total losses are
about 10% lower than the unsnubbed transistor alone, despite wasting power
in the snubber resistor itself.
More snubbing reduces transistor switching losses further, but dramatically
increases snubber losses. If you can arrange your circuit to use lossless
snubbers, you can achieve even better gains of course.
Even just a wad of capacitance can help (without fancy R's or D's) -- I
recently did a discrete (external switch) buck converter, 24V supply, which
exhibited 5V undershoot on the switching node (and this with a schottky
diode) -- just putting a dumb 1nF across the diode was enough to flatten out
the C vs. V curve, swamping it to a nice smooth linear falling edge and
dropping the overshoot down to 2V. The supply rail is dI/dt snubbed (L ||
R, just a few nH really) so it doesn't impact switching losses much -- when
the MOSFET switches on, the supply dips by about half, absorbing the energy
required to charge both snubber capacitance and diode junction capacitance.
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
news:jm0a7l$ghc$1...@speranza.aioe.org...
> The turn on time is a real pain in the ass in switcher design. Not only
> for efficiency issues, but the pin on the chip that touches the external
> catch diode rises like a bat out of hell until the diode begins
> conducting. That fast rise can lead to C*dv/dt current injection into
> nearby pins on the chip. So pin layout is critical.
Not really worthwhile for small apps, but big switchers can benefit greatly
> for efficiency issues, but the pin on the chip that touches the external
> catch diode rises like a bat out of hell until the diode begins
> conducting. That fast rise can lead to C*dv/dt current injection into
> nearby pins on the chip. So pin layout is critical.
from a dV/dt snubber. A dV/dt snubber, of course, works even with junction
diodes, because although the diode won't turn on instantly, it has hundreds
of volts to go before it's crashing into rails or anything, so it's forced
on, *very* quickly. There's a Unitrode appnote, I believe, which plots
transistor, snubber and total losses vs. snubber size -- there's a minima
where, when the snubber just about doubles the fall time, total losses are
about 10% lower than the unsnubbed transistor alone, despite wasting power
in the snubber resistor itself.
More snubbing reduces transistor switching losses further, but dramatically
increases snubber losses. If you can arrange your circuit to use lossless
snubbers, you can achieve even better gains of course.
Even just a wad of capacitance can help (without fancy R's or D's) -- I
recently did a discrete (external switch) buck converter, 24V supply, which
exhibited 5V undershoot on the switching node (and this with a schottky
diode) -- just putting a dumb 1nF across the diode was enough to flatten out
the C vs. V curve, swamping it to a nice smooth linear falling edge and
dropping the overshoot down to 2V. The supply rail is dI/dt snubbed (L ||
R, just a few nH really) so it doesn't impact switching losses much -- when
the MOSFET switches on, the supply dips by about half, absorbing the energy
required to charge both snubber capacitance and diode junction capacitance.
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Jan Panteltje
Apr 10, 2012, 4:53:17 AM4/10/12
to
On a sunny day (Mon, 09 Apr 2012 20:25:28 -0500) it happened Tim Wescott
<t...@seemywebsite.com> wrote in
<T_OdnWafG_WVER7S...@web-ster.com>:
>Is it reasonable to expect that the turn-on (not off -- _on_) time of a
>diode should be pretty much consistent with the inductance of the
>package, and not much else?
>
>A customer just sent me some O-scope traces of a circuit where a voltage
>at a catch diode anode is (at least apparently) going several hundred
>volts above its cathode for a microsecond before settling out to the
>nominal anode voltage of the diode.
>
>We're not sure if it's a measurement artifact because the coil has some
>700A in it, or if it's a real event; I wouldn't be willing to even
>believe it's a real event except that I know that funny things can happen
>at high currents.
Just recently I came across just that in a diode spec sheet.
Its probably real.
<t...@seemywebsite.com> wrote in
<T_OdnWafG_WVER7S...@web-ster.com>:
>Is it reasonable to expect that the turn-on (not off -- _on_) time of a
>diode should be pretty much consistent with the inductance of the
>package, and not much else?
>
>A customer just sent me some O-scope traces of a circuit where a voltage
>at a catch diode anode is (at least apparently) going several hundred
>volts above its cathode for a microsecond before settling out to the
>nominal anode voltage of the diode.
>
>We're not sure if it's a measurement artifact because the coil has some
>700A in it, or if it's a real event; I wouldn't be willing to even
>believe it's a real event except that I know that funny things can happen
>at high currents.
Its probably real.
Wimpie
Apr 10, 2012, 9:17:41 AM4/10/12
to
El 10-04-12 10:53, Jan Panteltje escribió:
Hello Jan,
It depends on the device. High voltage diodes have a forward recovery
time (Tfr and Vfr) that results in voltage peaks that cannot be
explained by package inductance.
I would think of tens of volts, but I don't know what happens with
700A and very high dI/dt.
--
Wim
PA3DJS
www.tetech.nl
Please remove abc first in case of PM
It depends on the device. High voltage diodes have a forward recovery
time (Tfr and Vfr) that results in voltage peaks that cannot be
explained by package inductance.
I would think of tens of volts, but I don't know what happens with
700A and very high dI/dt.
--
Wim
PA3DJS
www.tetech.nl
Please remove abc first in case of PM
dagmarg...@yahoo.com
Apr 10, 2012, 10:28:15 AM4/10/12
to
On Apr 9, 11:09 pm, John Larkin
http://www.ieeta.pt/~alex/docs/ApplicationNotes/Rectifier%20Applications%20Handbook.pdf
pg. 26
"In general, Schottky technology offers switching performance because
Schottky is a majority carrier technology.
In fact, switching both forward and reverse directions are major
drawbacks of p+n n+ technology.
For example, when a p+n+n+ rectifier is switched from reverse blocking
to on–conduction as shown in Figure 23, its forward voltage drop
exceeds its steady–state forward voltage drop. This phenomenon is
called forward voltage overshoot during the turn–on transport. This is
due to the fact that during Ugh–speed switching from the off–state to
the on–state, current through the rectifier is limited by the maximum
rate at which minority carriers are injected into the junction. A high
voltage drop therefore develops across the diode for a short period of
time until minority carriers diffuse into the junction and reduce the
drift region resistance.
This process was explained in an earlier section as conductivity
modulation. The time it takes for the diode to recover to within 10%
of its steady–state forward conduction voltage is called the forward
recovery time."
--
Cheers,
James Arthur
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Mon, 09 Apr 2012 20:25:28 -0500, Tim Wescott <t...@seemywebsite.com>
> wrote:
>
> >Is it reasonable to expect that the turn-on (not off -- _on_) time of a
> >diode should be pretty much consistent with the inductance of the
> >package, and not much else?
>
> Not a PN junction diode. They take a while to conduct, the phenom
> being called, strangely, "forward recovery."
>
> We did a pulse generator that used power diodes in DSRD (drift step
> recovery) mode. We applied 48 volts in the forward direction, and
> waited about 100 ns for the current to ramp up to 50 amps. The rampup
> looked pretty linear. Then we applied -400 volts to get them to snap.
>
>
>
> >A customer just sent me some O-scope traces of a circuit where a voltage
> >at a catch diode anode is (at least apparently) going several hundred
> >volts above its cathode for a microsecond before settling out to the
> >nominal anode voltage of the diode.
>
> That can happen. You may need a high-voltage schottky, SiC or GaN or
> whatever, or a few silicon schottkies in series.
On Semi Rectifier Applications Handbook (HB-214/D)
> On Mon, 09 Apr 2012 20:25:28 -0500, Tim Wescott <t...@seemywebsite.com>
> wrote:
>
> >Is it reasonable to expect that the turn-on (not off -- _on_) time of a
> >diode should be pretty much consistent with the inductance of the
> >package, and not much else?
>
> Not a PN junction diode. They take a while to conduct, the phenom
> being called, strangely, "forward recovery."
>
> We did a pulse generator that used power diodes in DSRD (drift step
> recovery) mode. We applied 48 volts in the forward direction, and
> waited about 100 ns for the current to ramp up to 50 amps. The rampup
> looked pretty linear. Then we applied -400 volts to get them to snap.
>
>
>
> >A customer just sent me some O-scope traces of a circuit where a voltage
> >at a catch diode anode is (at least apparently) going several hundred
> >volts above its cathode for a microsecond before settling out to the
> >nominal anode voltage of the diode.
>
> That can happen. You may need a high-voltage schottky, SiC or GaN or
> whatever, or a few silicon schottkies in series.
http://www.ieeta.pt/~alex/docs/ApplicationNotes/Rectifier%20Applications%20Handbook.pdf
pg. 26
"In general, Schottky technology offers switching performance because
Schottky is a majority carrier technology.
In fact, switching both forward and reverse directions are major
drawbacks of p+n n+ technology.
For example, when a p+n+n+ rectifier is switched from reverse blocking
to on–conduction as shown in Figure 23, its forward voltage drop
exceeds its steady–state forward voltage drop. This phenomenon is
called forward voltage overshoot during the turn–on transport. This is
due to the fact that during Ugh–speed switching from the off–state to
the on–state, current through the rectifier is limited by the maximum
rate at which minority carriers are injected into the junction. A high
voltage drop therefore develops across the diode for a short period of
time until minority carriers diffuse into the junction and reduce the
drift region resistance.
This process was explained in an earlier section as conductivity
modulation. The time it takes for the diode to recover to within 10%
of its steady–state forward conduction voltage is called the forward
recovery time."
--
Cheers,
James Arthur
George Herold
Apr 10, 2012, 10:39:25 AM4/10/12
to
On Apr 9, 10:46 pm, Phil Hobbs
> hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text -
>
> - Show quoted text -
Nice app note Thanks! The appendices are a gold mine. (Why are these
practical ideas/methods so rare?)
For the Jim W. fans I recently found this nice blog.
http://readingjimwilliams.blogspot.com/
I'm only up to app note 6... so I'm not sure of later entries, but he
does a nice job till then.
George H.
>
> - Show quoted text -
Nice app note Thanks! The appendices are a gold mine. (Why are these
practical ideas/methods so rare?)
For the Jim W. fans I recently found this nice blog.
http://readingjimwilliams.blogspot.com/
I'm only up to app note 6... so I'm not sure of later entries, but he
does a nice job till then.
George H.
Tim Williams
Apr 10, 2012, 12:52:36 AM4/10/12
to
I once build an inverter prototype which (due to insufficient theory at the
time) resonated quite excellently. It rang around 15MHz, generating some
80% overshoot. At 350VDC supply, that's over 600V peak, enough to toast a
poor 600V MOSFET! The equivalent circuit was roughly 18nH (the inductance
between power planes and MOSFET terminals) and 6nF (junction + snubber
capacitance), so the peak current was quite large (~160A) relative to
ratings (70A design load current).
In order to get those boards to work, I tried squashing the overshoot with
diodes to the opposing rail. This hardly reduced the overshoot by half: by
all accounts, a full 100V spike was appearing across the diode during this
event. Even taking off ~10nH lead and bond inductance, that still leaves
~50V across the die, real voltage applied to silicon.
Though the average current was small, the peak current was still enough to
toast 6A diodes, even 12A diodes -- finally, 30A diodes survived the abuse.
What kind of failure mechanism do diodes succumb to under peak conditions --
is it an electromigration thing, perhaps? The failure is gradual and not
obviously thermal: the circuit can run happy for minutes with no significant
temp rise (~10C), then the diodes suddenly go shorted.
"Tim Wescott" <t...@seemywebsite.com> wrote in message
news:T_OdnWafG_WVER7S...@web-ster.com...
time) resonated quite excellently. It rang around 15MHz, generating some
80% overshoot. At 350VDC supply, that's over 600V peak, enough to toast a
poor 600V MOSFET! The equivalent circuit was roughly 18nH (the inductance
between power planes and MOSFET terminals) and 6nF (junction + snubber
capacitance), so the peak current was quite large (~160A) relative to
ratings (70A design load current).
In order to get those boards to work, I tried squashing the overshoot with
diodes to the opposing rail. This hardly reduced the overshoot by half: by
all accounts, a full 100V spike was appearing across the diode during this
event. Even taking off ~10nH lead and bond inductance, that still leaves
~50V across the die, real voltage applied to silicon.
Though the average current was small, the peak current was still enough to
toast 6A diodes, even 12A diodes -- finally, 30A diodes survived the abuse.
What kind of failure mechanism do diodes succumb to under peak conditions --
is it an electromigration thing, perhaps? The failure is gradual and not
obviously thermal: the circuit can run happy for minutes with no significant
temp rise (~10C), then the diodes suddenly go shorted.
"Tim Wescott" <t...@seemywebsite.com> wrote in message
news:T_OdnWafG_WVER7S...@web-ster.com...
Jamie
Apr 10, 2012, 8:45:18 PM4/10/12
to
Tim Williams wrote:
> I once build an inverter prototype which (due to insufficient theory at
> the time) resonated quite excellently. It rang around 15MHz, generating
> some 80% overshoot. At 350VDC supply, that's over 600V peak, enough to
> toast a poor 600V MOSFET! The equivalent circuit was roughly 18nH (the
> inductance between power planes and MOSFET terminals) and 6nF (junction
> + snubber capacitance), so the peak current was quite large (~160A)
> relative to ratings (70A design load current).
>
> In order to get those boards to work, I tried squashing the overshoot
> with diodes to the opposing rail. This hardly reduced the overshoot by
> half: by all accounts, a full 100V spike was appearing across the diode
> during this event. Even taking off ~10nH lead and bond inductance, that
> still leaves ~50V across the die, real voltage applied to silicon.
>
> Though the average current was small, the peak current was still enough
> to toast 6A diodes, even 12A diodes -- finally, 30A diodes survived the
> abuse. What kind of failure mechanism do diodes succumb to under peak
> conditions -- is it an electromigration thing, perhaps? The failure is
> gradual and not obviously thermal: the circuit can run happy for minutes
> with no significant temp rise (~10C), then the diodes suddenly go shorted.
>
> Tim
>
--
Or, your equipment just wasn't showing you the real signal, like a
> I once build an inverter prototype which (due to insufficient theory at
> the time) resonated quite excellently. It rang around 15MHz, generating
> some 80% overshoot. At 350VDC supply, that's over 600V peak, enough to
> toast a poor 600V MOSFET! The equivalent circuit was roughly 18nH (the
> inductance between power planes and MOSFET terminals) and 6nF (junction
> + snubber capacitance), so the peak current was quite large (~160A)
> relative to ratings (70A design load current).
>
> In order to get those boards to work, I tried squashing the overshoot
> with diodes to the opposing rail. This hardly reduced the overshoot by
> half: by all accounts, a full 100V spike was appearing across the diode
> during this event. Even taking off ~10nH lead and bond inductance, that
> still leaves ~50V across the die, real voltage applied to silicon.
>
> Though the average current was small, the peak current was still enough
> to toast 6A diodes, even 12A diodes -- finally, 30A diodes survived the
> abuse. What kind of failure mechanism do diodes succumb to under peak
> conditions -- is it an electromigration thing, perhaps? The failure is
> gradual and not obviously thermal: the circuit can run happy for minutes
> with no significant temp rise (~10C), then the diodes suddenly go shorted.
>
> Tim
>
--
digital scope for example.
You would be surprised to see what is there using a spectrum analyzer.
Jamie
Paul Probert
Apr 10, 2012, 8:30:08 PM4/10/12
to Tim Williams
On 04/09/2012 10:52 PM, Tim Williams wrote:
> I once build an inverter prototype which (due to insufficient theory at
> the time) resonated quite excellently. It rang around 15MHz, generating
> some 80% overshoot. At 350VDC supply, that's over 600V peak, enough to
> toast a poor 600V MOSFET! The equivalent circuit was roughly 18nH (the
> inductance between power planes and MOSFET terminals) and 6nF (junction
> + snubber capacitance), so the peak current was quite large (~160A)
> relative to ratings (70A design load current).
>
> In order to get those boards to work, I tried squashing the overshoot
> with diodes to the opposing rail. This hardly reduced the overshoot by
> half: by all accounts, a full 100V spike was appearing across the diode
> during this event. Even taking off ~10nH lead and bond inductance, that
> still leaves ~50V across the die, real voltage applied to silicon.
>
> Though the average current was small, the peak current was still enough
> to toast 6A diodes, even 12A diodes -- finally, 30A diodes survived the
> abuse. What kind of failure mechanism do diodes succumb to under peak
> conditions -- is it an electromigration thing, perhaps? The failure is
> gradual and not obviously thermal: the circuit can run happy for minutes
> with no significant temp rise (~10C), then the diodes suddenly go shorted.
>
> Tim
>
Your diodes were hot-spotting due to high di/dt.
> I once build an inverter prototype which (due to insufficient theory at
> the time) resonated quite excellently. It rang around 15MHz, generating
> some 80% overshoot. At 350VDC supply, that's over 600V peak, enough to
> toast a poor 600V MOSFET! The equivalent circuit was roughly 18nH (the
> inductance between power planes and MOSFET terminals) and 6nF (junction
> + snubber capacitance), so the peak current was quite large (~160A)
> relative to ratings (70A design load current).
>
> In order to get those boards to work, I tried squashing the overshoot
> with diodes to the opposing rail. This hardly reduced the overshoot by
> half: by all accounts, a full 100V spike was appearing across the diode
> during this event. Even taking off ~10nH lead and bond inductance, that
> still leaves ~50V across the die, real voltage applied to silicon.
>
> Though the average current was small, the peak current was still enough
> to toast 6A diodes, even 12A diodes -- finally, 30A diodes survived the
> abuse. What kind of failure mechanism do diodes succumb to under peak
> conditions -- is it an electromigration thing, perhaps? The failure is
> gradual and not obviously thermal: the circuit can run happy for minutes
> with no significant temp rise (~10C), then the diodes suddenly go shorted.
>
> Tim
>
Paul Probert
Tim Williams
Apr 11, 2012, 1:24:53 AM4/11/12
to
"Jamie" <jamie_ka1lpa_not_v...@charter.net> wrote in message
news:vn4hr.477$IW4...@newsfe03.iad...
the noise spectrum with a >>100MHz spec and didn't see any substantial
harmonics over 60MHz, and not just on the inverter, but on any of our boards
actually; this includes monolithic switcher chips and the FPGA, but that
really just says what everyone already knows -- or should know: ground
planes keep stray fields down. With a vengance.
It's true that a given measurement could be pretty crappy. I get that a lot
when breadboarding: a switching node might fire common-mode noise into
whatever the board is resting on; as a result, squigglies show up in every
other measurement you make, even unrelated low-level circuits. But this
isn't the case.
Two supporting factors: one, my Tek 475 wouldn't have seen anything more (as
confirmed by the spec results -- the band ends at ~60MHz), and might turn
out to have a harder time visualizing the details, due to vertical
saturation and low duty cycle as you zoom in. (I'm not afraid of DSOs, I'm
familiar with their operation and limitations.) Two, the signal literally
appears everywhere on the board in this layout: it appears on the switching
node (or Vds of both transistors); across the supply (high side drain to low
side source); and, with an inductive loop probe, it appears (in phase or
otherwise) around every opening and terminal connection. Because of this,
it can be very difficult to troubleshoot -- it isn't really associated with
any component, because it's a whole-board property.
news:vn4hr.477$IW4...@newsfe03.iad...
> Or, your equipment just wasn't showing you the real signal, like a
> digital scope for example.
>
> You would be surprised to see what is there using a spectrum analyzer.
Unfortunately we only had 100MHz scopes, a travesty I know, but I looked at
> digital scope for example.
>
> You would be surprised to see what is there using a spectrum analyzer.
the noise spectrum with a >>100MHz spec and didn't see any substantial
harmonics over 60MHz, and not just on the inverter, but on any of our boards
actually; this includes monolithic switcher chips and the FPGA, but that
really just says what everyone already knows -- or should know: ground
planes keep stray fields down. With a vengance.
It's true that a given measurement could be pretty crappy. I get that a lot
when breadboarding: a switching node might fire common-mode noise into
whatever the board is resting on; as a result, squigglies show up in every
other measurement you make, even unrelated low-level circuits. But this
isn't the case.
Two supporting factors: one, my Tek 475 wouldn't have seen anything more (as
confirmed by the spec results -- the band ends at ~60MHz), and might turn
out to have a harder time visualizing the details, due to vertical
saturation and low duty cycle as you zoom in. (I'm not afraid of DSOs, I'm
familiar with their operation and limitations.) Two, the signal literally
appears everywhere on the board in this layout: it appears on the switching
node (or Vds of both transistors); across the supply (high side drain to low
side source); and, with an inductive loop probe, it appears (in phase or
otherwise) around every opening and terminal connection. Because of this,
it can be very difficult to troubleshoot -- it isn't really associated with
any component, because it's a whole-board property.
miso
Apr 11, 2012, 3:30:36 AM4/11/12
to
> Your diodes were hot-spotting due to high di/dt.
>
> Paul Probert
Hot spot yes. I'm not sure if di/dt is an issue. I know from ESD testing
>
> Paul Probert
waffle fets, some element is always the weakest link and pops. I always
assumed there is a crystal defect there or some other abnormality to
make it pop first.
Tim Wescott
Apr 11, 2012, 4:41:31 PM4/11/12
to
On Mon, 09 Apr 2012 20:25:28 -0500, Tim Wescott wrote:
> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
> diode should be pretty much consistent with the inductance of the
> package, and not much else?
>
> A customer just sent me some O-scope traces of a circuit where a voltage
> at a catch diode anode is (at least apparently) going several hundred
> volts above its cathode for a microsecond before settling out to the
> nominal anode voltage of the diode.
>
> We're not sure if it's a measurement artifact because the coil has some
> 700A in it, or if it's a real event; I wouldn't be willing to even
> believe it's a real event except that I know that funny things can
> happen at high currents.
Heh heh heh.
> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
> diode should be pretty much consistent with the inductance of the
> package, and not much else?
>
> A customer just sent me some O-scope traces of a circuit where a voltage
> at a catch diode anode is (at least apparently) going several hundred
> volts above its cathode for a microsecond before settling out to the
> nominal anode voltage of the diode.
>
> We're not sure if it's a measurement artifact because the coil has some
> 700A in it, or if it's a real event; I wouldn't be willing to even
> believe it's a real event except that I know that funny things can
> happen at high currents.
Answer: "A long time, if it's hanging off the end of a long wire looped
through the air".
This is what I get for getting all caught up in project OVER THE PHONE,
without demanding pictures.
--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
John Larkin
Apr 11, 2012, 7:16:12 PM4/11/12
to
On Mon, 09 Apr 2012 20:25:28 -0500, Tim Wescott <t...@seemywebsite.com>
wrote:
>Is it reasonable to expect that the turn-on (not off -- _on_) time of a
>diode should be pretty much consistent with the inductance of the
>package, and not much else?
>
>A customer just sent me some O-scope traces of a circuit where a voltage
>at a catch diode anode is (at least apparently) going several hundred
>volts above its cathode for a microsecond before settling out to the
>nominal anode voltage of the diode.
>
>We're not sure if it's a measurement artifact because the coil has some
>700A in it, or if it's a real event; I wouldn't be willing to even
>believe it's a real event except that I know that funny things can happen
>at high currents.
I swear, you guys are all talk.
Here's a 1N914:
http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_a.JPG
http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_b.JPG
http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_c.JPG
It kind of looks like the area under the overshoot curve is sort of
constant.
John
--
John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser controllers
wrote:
>Is it reasonable to expect that the turn-on (not off -- _on_) time of a
>diode should be pretty much consistent with the inductance of the
>package, and not much else?
>
>A customer just sent me some O-scope traces of a circuit where a voltage
>at a catch diode anode is (at least apparently) going several hundred
>volts above its cathode for a microsecond before settling out to the
>nominal anode voltage of the diode.
>
>We're not sure if it's a measurement artifact because the coil has some
>700A in it, or if it's a real event; I wouldn't be willing to even
>believe it's a real event except that I know that funny things can happen
>at high currents.
Here's a 1N914:
http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_a.JPG
http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_b.JPG
http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_c.JPG
It kind of looks like the area under the overshoot curve is sort of
constant.
John
--
John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation
Mike Perkins
Apr 11, 2012, 7:20:23 PM4/11/12
to
On 10/04/2012 02:25, Tim Wescott wrote:
> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
> diode should be pretty much consistent with the inductance of the
> package, and not much else?
>
> A customer just sent me some O-scope traces of a circuit where a voltage
> at a catch diode anode is (at least apparently) going several hundred
> volts above its cathode for a microsecond before settling out to the
> nominal anode voltage of the diode.
>
> We're not sure if it's a measurement artifact because the coil has some
> 700A in it, or if it's a real event; I wouldn't be willing to even
> believe it's a real event except that I know that funny things can happen
> at high currents.
>
I find this threat rather interesting, as I learnt that the conduction
> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
> diode should be pretty much consistent with the inductance of the
> package, and not much else?
>
> A customer just sent me some O-scope traces of a circuit where a voltage
> at a catch diode anode is (at least apparently) going several hundred
> volts above its cathode for a microsecond before settling out to the
> nominal anode voltage of the diode.
>
> We're not sure if it's a measurement artifact because the coil has some
> 700A in it, or if it's a real event; I wouldn't be willing to even
> believe it's a real event except that I know that funny things can happen
> at high currents.
>
of a diode was instant, for either minor, or majority carrier
conduction. And if anything the potential difference across the
junction actually increased over time due to stored carriers until
equilibrium. So I've been waiting here for an explanation of why a
diode should take time to turn on, assuming of course it's not down to
lead inductance. After all with 700 Amps you don't need many nH!!
--
Mike Perkins
Video Solutions Ltd
www.videosolutions.ltd.uk
Tim Wescott
Apr 11, 2012, 7:49:26 PM4/11/12
to
listed forward recovery, t_fr was about five times t_rr.
As stated in the follow-up, the real problem was a combination of
inductance and trying to diagnose problems over the phone.
Wimpie
Apr 11, 2012, 7:59:30 PM4/11/12
to
El 12-04-12 1:16, John Larkin escribió:
Very nice pictures! I do recognize them (for a 1N4448). I first
"discovered" this in a symmetrical clipper driven from 10 MHz, peak
current about 100..200 mA.
First I blamed parasitic inductance, probe issues, common mode, etc.
But in the end I (after trying various setups) am sure it was the
forward recovery time of the diode.
Also the reverse recovery of the other diode could be seen very well,
even with a 350 MHz oscilloscope.
With kind regards,
> On Mon, 09 Apr 2012 20:25:28 -0500, Tim Wescott<t...@seemywebsite.com>
> wrote:
>
>> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
>> diode should be pretty much consistent with the inductance of the
>> package, and not much else?
>>
>> A customer just sent me some O-scope traces of a circuit where a voltage
>> at a catch diode anode is (at least apparently) going several hundred
>> volts above its cathode for a microsecond before settling out to the
>> nominal anode voltage of the diode.
>>
>> We're not sure if it's a measurement artifact because the coil has some
>> 700A in it, or if it's a real event; I wouldn't be willing to even
>> believe it's a real event except that I know that funny things can happen
>> at high currents.
>
>
> I swear, you guys are all talk.
>
> Here's a 1N914:
>
> http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_a.JPG
>
> http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_b.JPG
>
> http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_c.JPG
>
>
> It kind of looks like the area under the overshoot curve is sort of
> constant.
>
> John
>
Hello John,
> wrote:
>
>> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
>> diode should be pretty much consistent with the inductance of the
>> package, and not much else?
>>
>> A customer just sent me some O-scope traces of a circuit where a voltage
>> at a catch diode anode is (at least apparently) going several hundred
>> volts above its cathode for a microsecond before settling out to the
>> nominal anode voltage of the diode.
>>
>> We're not sure if it's a measurement artifact because the coil has some
>> 700A in it, or if it's a real event; I wouldn't be willing to even
>> believe it's a real event except that I know that funny things can happen
>> at high currents.
>
>
> I swear, you guys are all talk.
>
> Here's a 1N914:
>
> http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_a.JPG
>
> http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_b.JPG
>
> http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_c.JPG
>
>
> It kind of looks like the area under the overshoot curve is sort of
> constant.
>
> John
>
Very nice pictures! I do recognize them (for a 1N4448). I first
"discovered" this in a symmetrical clipper driven from 10 MHz, peak
current about 100..200 mA.
First I blamed parasitic inductance, probe issues, common mode, etc.
But in the end I (after trying various setups) am sure it was the
forward recovery time of the diode.
Also the reverse recovery of the other diode could be seen very well,
even with a 350 MHz oscilloscope.
With kind regards,
John Larkin
Apr 11, 2012, 8:07:15 PM4/11/12
to
On Thu, 12 Apr 2012 01:59:30 +0200, Wimpie <wima...@tetech.nl>
wrote:
reverse recovery, too...
http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_d.JPG
I should try some higher voltage diodes. They are more of a PIN
structure, so should be different.
A real step-recovery diode would be fun, too. Pity I have a day job.
John Larkin
Apr 11, 2012, 8:10:46 PM4/11/12
to
On Wed, 11 Apr 2012 18:49:26 -0500, Tim Wescott <t...@seemywebsite.com>
wrote:
>On Thu, 12 Apr 2012 00:20:23 +0100, Mike Perkins wrote:
>
>> On 10/04/2012 02:25, Tim Wescott wrote:
>>> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
>>> diode should be pretty much consistent with the inductance of the
>>> package, and not much else?
>>>
>>> A customer just sent me some O-scope traces of a circuit where a
>>> voltage at a catch diode anode is (at least apparently) going several
>>> hundred volts above its cathode for a microsecond before settling out
>>> to the nominal anode voltage of the diode.
>>>
>>> We're not sure if it's a measurement artifact because the coil has some
>>> 700A in it, or if it's a real event; I wouldn't be willing to even
>>> believe it's a real event except that I know that funny things can
>>> happen at high currents.
>>>
>>>
>> I find this threat rather interesting, as I learnt that the conduction
>> of a diode was instant, for either minor, or majority carrier
>> conduction. And if anything the potential difference across the
>> junction actually increased over time due to stored carriers until
>> equilibrium. So I've been waiting here for an explanation of why a
>> diode should take time to turn on, assuming of course it's not down to
>> lead inductance. After all with 700 Amps you don't need many nH!!
>
>I don't know _why_, but for the one diode data sheet that I found that
>listed forward recovery, t_fr was about five times t_rr.
In the forward direction, you start at zero current, so it takes a
while to pump in carriers. In the reverse direction, the diode is
nearly a short, so the generator pumps in a lot of current
immediately, which clears the carriers out. Like this:
http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_d.JPG
Something hand-wavey like that.
wrote:
>On Thu, 12 Apr 2012 00:20:23 +0100, Mike Perkins wrote:
>
>> On 10/04/2012 02:25, Tim Wescott wrote:
>>> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
>>> diode should be pretty much consistent with the inductance of the
>>> package, and not much else?
>>>
>>> A customer just sent me some O-scope traces of a circuit where a
>>> voltage at a catch diode anode is (at least apparently) going several
>>> hundred volts above its cathode for a microsecond before settling out
>>> to the nominal anode voltage of the diode.
>>>
>>> We're not sure if it's a measurement artifact because the coil has some
>>> 700A in it, or if it's a real event; I wouldn't be willing to even
>>> believe it's a real event except that I know that funny things can
>>> happen at high currents.
>>>
>>>
>> I find this threat rather interesting, as I learnt that the conduction
>> of a diode was instant, for either minor, or majority carrier
>> conduction. And if anything the potential difference across the
>> junction actually increased over time due to stored carriers until
>> equilibrium. So I've been waiting here for an explanation of why a
>> diode should take time to turn on, assuming of course it's not down to
>> lead inductance. After all with 700 Amps you don't need many nH!!
>
>I don't know _why_, but for the one diode data sheet that I found that
>listed forward recovery, t_fr was about five times t_rr.
while to pump in carriers. In the reverse direction, the diode is
nearly a short, so the generator pumps in a lot of current
immediately, which clears the carriers out. Like this:
http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_d.JPG
Something hand-wavey like that.
Mike Perkins
Apr 11, 2012, 8:32:18 PM4/11/12
to
would measure it, it's not something I would see as useful except taking
into account series inductance, not like turn-off times which are diode
type and structure dependent.
Tim Wescott
Apr 11, 2012, 9:46:44 PM4/11/12
to
elements, then you'd care deeply about t_fr. So there's reason to not
only want it measured, but guaranteed.
Jamie
Apr 11, 2012, 10:12:33 PM4/11/12
to
around a problem diode ? It's very hard to see these problems doing
common measuring. Problems with in node area's tend to hide themselves
form the common world.
Jamie
Jamie
Apr 11, 2012, 10:17:05 PM4/11/12
to
not seem to exhibit this problem.
I've never had that must issues working out these problems. Most
likely cause I have not pushed it to the limits as you are.
Jamie
Tim Williams
Apr 11, 2012, 11:53:58 PM4/11/12
to
"Jamie" <jamie_ka1lpa_not_v...@charter.net> wrote in message
news:DKqhr.7057$Nk2....@newsfe08.iad...
> I assume that you were using high speed differential probes coupled around
> a problem diode ? It's very hard to see these problems doing
> common measuring. Problems with in node area's tend to hide themselves
> form the common world.
Didn't really matter in this case -- the quality of measurements is overcome
> a problem diode ? It's very hard to see these problems doing
> common measuring. Problems with in node area's tend to hide themselves
> form the common world.
by the repeatability of the measurement. The same transient signal appears
on all nodes, regardless of probe ground clip orientation and location, and
the use of ferrite beads to cut out common-mode sneak paths (often, probe
grounds will pick up stray noise even when the probe is short-circuited).
Like I said, the signal was pretty much the same no matter where it was
measured.
As far as in-node problems, I've found that a compact inductive loop probe
does wonders. Another, very useful way of looking at it is an uncalibrated
amprobe: set your scope to integrate and it becomes a crude, freehand
Rogowski coil. I've measured the waveform of current going through vias in
this way -- it would be some feat to accomplish that with a voltage probe!
Tim Williams
Apr 11, 2012, 11:59:32 PM4/11/12
to
"Mike Perkins" <sp...@spam.com> wrote in message
news:wamdnUTrH9sqjBvS...@bt.com...
already know these things have criminal inductances, but man, the diodes are
slow, too. The co-pack diodes easily double the apparent inductance in the
package, which is already a grotesque 20nH or so.
What astonishes me is, manufacturers don't even give a crap about it. They
must not know their wires have length, or something. I'm amazed they can
even be tested to measure the datasheet parameters, what few data they have.
Hard switching just once nearly ought to explode them.
news:wamdnUTrH9sqjBvS...@bt.com...
> I find this threat rather interesting, as I learnt that the conduction of
> a diode was instant, for either minor, or majority carrier conduction.
> And if anything the potential difference across the junction actually
> increased over time due to stored carriers until equilibrium. So I've
> been waiting here for an explanation of why a diode should take time to
> turn on, assuming of course it's not down to lead inductance. After all
> with 700 Amps you don't need many nH!!
I've recently taken an IGBT module onto the bench for laboratory testing. I
> a diode was instant, for either minor, or majority carrier conduction.
> And if anything the potential difference across the junction actually
> increased over time due to stored carriers until equilibrium. So I've
> been waiting here for an explanation of why a diode should take time to
> turn on, assuming of course it's not down to lead inductance. After all
> with 700 Amps you don't need many nH!!
already know these things have criminal inductances, but man, the diodes are
slow, too. The co-pack diodes easily double the apparent inductance in the
package, which is already a grotesque 20nH or so.
What astonishes me is, manufacturers don't even give a crap about it. They
must not know their wires have length, or something. I'm amazed they can
even be tested to measure the datasheet parameters, what few data they have.
Hard switching just once nearly ought to explode them.
John Devereux
Apr 12, 2012, 4:22:54 AM4/12/12
to
already been posted:
<http://cds.linear.com/docs/Application%20Note/an122f.pdf>
--
John Devereux
Mike Perkins
Apr 12, 2012, 5:36:41 AM4/12/12
to
literature that says a native diode inherently has a mechanism where it
takes time for a junction to conduct. It leads me to conclude that a
turn-on time is package dependent, through package inductance, skin
effect or whatever other mechanism may come into play. I hear what
you're saying, and from a designer's point of view t-fr must be taken
into account, I was trying to establish its cause.
George Herold
Apr 12, 2012, 9:43:04 AM4/12/12
to
>
> - Show quoted text -
Yeah, Phil H. posted that earlier. Very similar pics to what John L.
> - Show quoted text -
just measured. I was looking through my two 'practical' solid state
books (Streetman and Sze) but could find no discussion of the forward
turn on time. (They both discuss the turn off time.)
It's interesting that different diodes (of the same type) show such
different turn on times. If I'm remembering my basic diode physics
correctly, then you have to wait for the minority carriers to diffuse
to the junction. Since the diffusion coefficient is pretty much the
same, I would speculate that the difference is due to different
'lengths' in the devices... somewhat different doping profiles??
Though I'm now speaking way above my knowledge base.
George H.
Phil Hobbs
Apr 12, 2012, 10:32:59 AM4/12/12
to
the same board won't show the same effect.
John Larkin
Apr 12, 2012, 12:01:36 PM4/12/12
to
On Thu, 12 Apr 2012 10:36:41 +0100, Mike Perkins <sp...@spam.com>
wrote:
It really, really does. See the pics I posted. The higher the voltage
rating, the wider the intrinsic region, the slower the turn-on, even
in the same package.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Multichannel arbitrary waveform generators
wrote:
rating, the wider the intrinsic region, the slower the turn-on, even
in the same package.
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
Bert Hickman
Apr 12, 2012, 12:19:02 PM4/12/12
to
www.linear.com/docs/27403
However, measurement error/inductance must be involved for a
multi-hundred volt transient.
Bert
--
Bert Hickman
Stoneridge Engineering
http://www.capturedlightning.com
***********************************************************************
World's source for "Captured Lightning" Lichtenberg Figure sculptures,
magnetically "shrunken" coins, and scarce/out of print technical books
***********************************************************************
qrk
Apr 12, 2012, 1:36:38 PM4/12/12
to
using a ground connection with a short wire, your measurement is
invalid when dealing with switching power supplies. You need to, at a
minimum, connect the probe ground sleeve directly as possible to the
common of your circuit.
John Larkin
Apr 12, 2012, 1:49:34 PM4/12/12
to
because the body diode had step-recovery behavior. I've seen SRD
effects in integrated synchronous buck switchers, too. This is
classic:
http://dl.dropbox.com/u/53724080/Diode_TurnOn/SwitcherRise.JPG
That's an LM3102. The spikes trashed opamps all over the board.
So I'd expect that people tweak doping profiles in things like body
diodes to achieve soft recovery. Slow and safe.
--
John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Photonics and fiberoptic TTL data links
Jamie
Apr 12, 2012, 6:17:21 PM4/12/12
to
Jamie
John Larkin
Apr 12, 2012, 6:59:38 PM4/12/12
to
For the first 15 ns, the lower mosfet of the synchronous switcher is
on.
From 15 to 35, both fets are off, and the output inductor current is
flowing through a body diode into ground.
At 35 ns, the upper fet turns on, but the body diode, in reverse
recovery, fights it, and the voltage stays low. Lots of current is
building up.
At 38 ns, the body diode switches off abruptly, in step-recovery mode.
Twang.
Tim Williams
Apr 13, 2012, 12:44:24 AM4/13/12
to
"qrk" <Spam...@spam.net> wrote in message
news:ae4eo79tuom4vv8je...@4ax.com...
visible signal was due entirely to the ground clip (verification, moving the
wire around in space, using different ground points). At worst, this
slightly changes the >50MHz squigglies, only by phase and amplitude give or
take 10% (or more around a switching device, if you even have a point to
clip onto in such a place).
If you're looking at high precision settling time (better than 1%), or
specifically the low level transients, you're bound to see something, but
that's kind of a gimme, and doesn't compare with the amplitude of the actual
switching nodes.
Even probing an avalanche pulse generator (tr < 2ns), I don't see much
difference -- yes, it definitely has a lot more bounce and drool with four
inches of ground lead (whereas grounding the probe collar to the circuit
yields a signal identical to the proper BNC-coupled output), but it doesn't
appreciably attenuate the really high frequency stuff. You can still see
the general wave shape, rise/fall time is not ludicrously impaired.
When I first built an avalanche pulse generator, I was pleasantly surprised.
After reading fear-mongering recommendations like yours, I thought the blip
was going to simply disappear altogether with the clip. Turns out that's
not the case! Even the cheap 10x probes that I've seen still work pretty
well up there.
On a related subject, it's easy to build an avalanche pulse generator on a
solderless breadboard, and I mean with junkbox parts -- long squiggly leads
and everything, not even any attempt to make it nice. The overall pulse
looks more like a gong, of course.
To get good clean pulses, layout is more critical. For example, the first
avalanche generator I built was along the lines of AN-94, point-to-point
around a connector. Worked okay, but drool amounted to maybe 5-10% of the
initial pulse (residual charge, reflections, that sort of thing). I tried
again, with a flatter layout over a ground plane, deadbug style, still
leaded components, with similar results. Finally, I scored a PCB by hand
and used SMT components; at last, this got a lone pulse with low rattle
(<5%) and good matching (a 50 ohm pulse line attached to the back side
discharges evenly with no over/undershoot). Matching the line is actually
non-obvious; according to the attenuator network values I ended up with, the
transistor has an "on resistance" of about 20 ohms.
news:ae4eo79tuom4vv8je...@4ax.com...
> Something doesn't sound right. You speak of "ground clip". If you're
> using a ground connection with a short wire, your measurement is
> invalid when dealing with switching power supplies. You need to, at a
> minimum, connect the probe ground sleeve directly as possible to the
> common of your circuit.
Well, no. I've never probed a circuit so bad that >50%, even >10% of the
> using a ground connection with a short wire, your measurement is
> invalid when dealing with switching power supplies. You need to, at a
> minimum, connect the probe ground sleeve directly as possible to the
> common of your circuit.
visible signal was due entirely to the ground clip (verification, moving the
wire around in space, using different ground points). At worst, this
slightly changes the >50MHz squigglies, only by phase and amplitude give or
take 10% (or more around a switching device, if you even have a point to
clip onto in such a place).
If you're looking at high precision settling time (better than 1%), or
specifically the low level transients, you're bound to see something, but
that's kind of a gimme, and doesn't compare with the amplitude of the actual
switching nodes.
Even probing an avalanche pulse generator (tr < 2ns), I don't see much
difference -- yes, it definitely has a lot more bounce and drool with four
inches of ground lead (whereas grounding the probe collar to the circuit
yields a signal identical to the proper BNC-coupled output), but it doesn't
appreciably attenuate the really high frequency stuff. You can still see
the general wave shape, rise/fall time is not ludicrously impaired.
When I first built an avalanche pulse generator, I was pleasantly surprised.
After reading fear-mongering recommendations like yours, I thought the blip
was going to simply disappear altogether with the clip. Turns out that's
not the case! Even the cheap 10x probes that I've seen still work pretty
well up there.
On a related subject, it's easy to build an avalanche pulse generator on a
solderless breadboard, and I mean with junkbox parts -- long squiggly leads
and everything, not even any attempt to make it nice. The overall pulse
looks more like a gong, of course.
To get good clean pulses, layout is more critical. For example, the first
avalanche generator I built was along the lines of AN-94, point-to-point
around a connector. Worked okay, but drool amounted to maybe 5-10% of the
initial pulse (residual charge, reflections, that sort of thing). I tried
again, with a flatter layout over a ground plane, deadbug style, still
leaded components, with similar results. Finally, I scored a PCB by hand
and used SMT components; at last, this got a lone pulse with low rattle
(<5%) and good matching (a 50 ohm pulse line attached to the back side
discharges evenly with no over/undershoot). Matching the line is actually
non-obvious; according to the attenuator network values I ended up with, the
transistor has an "on resistance" of about 20 ohms.
Tim Williams
Apr 13, 2012, 1:11:00 AM4/13/12
to
"John Larkin" <jla...@highlandtechnology.com> wrote in message
news:vv4eo7tb9v1tslstd...@4ax.com...
those 5 or so nanoseconds. Put a big fat inductor in the supply line (which
at this rate might be an inch or two of trace over a ground plane cutout).
VCC droops and dI/dt is limited, at the very least reducing the rate of
recovery, and reducing the peak amplitude if it still snaps. Finally, a
little extra capacitance on the switching node slows the transition, so if
it still snaps, at least it snaps between diode and cap, rather than the
whole supply rail.
If, after all that, it still insists on snapping, there really isn't
anything you can do about it besides shop for a device that you hope doesn't
snap.
Monolithic chips are nice and handy, but they really shoot themselves in the
foot when they expect to draw power for the controller from the same dirty
rail that's doing the switching. I'm guessing most chips would find this
supply snubbing approach...distasteful.
Other obvious solutions include intentionally slow switchers. This isn't a
bad idea when high high sensitivity and bandwidth are required; see LT
AN-70. Most power supplies cheat by reporting their noise within a cutoff
of 20MHz or whatever, whereas transients can go out to 100s of MHz. Slower
operation prevents those harmonics from being generated in the first place,
but efficiency and size are the first things to go. Of course, you've
maligned many times about the plurality of supplies required to run
everything. Sometimes you just can't win.
news:vv4eo7tb9v1tslstd...@4ax.com...
> I've blown out the gates of mosfets, at low voltages and currents,
> because the body diode had step-recovery behavior. I've seen SRD
> effects in integrated synchronous buck switchers, too. This is
> classic:
>
> http://dl.dropbox.com/u/53724080/Diode_TurnOn/SwitcherRise.JPG
>
> That's an LM3102. The spikes trashed opamps all over the board.
>
> So I'd expect that people tweak doping profiles in things like body
> diodes to achieve soft recovery. Slow and safe.
Obvious solution for this -- go ahead and let it short out the supply for
> because the body diode had step-recovery behavior. I've seen SRD
> effects in integrated synchronous buck switchers, too. This is
> classic:
>
> http://dl.dropbox.com/u/53724080/Diode_TurnOn/SwitcherRise.JPG
>
> That's an LM3102. The spikes trashed opamps all over the board.
>
> So I'd expect that people tweak doping profiles in things like body
> diodes to achieve soft recovery. Slow and safe.
those 5 or so nanoseconds. Put a big fat inductor in the supply line (which
at this rate might be an inch or two of trace over a ground plane cutout).
VCC droops and dI/dt is limited, at the very least reducing the rate of
recovery, and reducing the peak amplitude if it still snaps. Finally, a
little extra capacitance on the switching node slows the transition, so if
it still snaps, at least it snaps between diode and cap, rather than the
whole supply rail.
If, after all that, it still insists on snapping, there really isn't
anything you can do about it besides shop for a device that you hope doesn't
snap.
Monolithic chips are nice and handy, but they really shoot themselves in the
foot when they expect to draw power for the controller from the same dirty
rail that's doing the switching. I'm guessing most chips would find this
supply snubbing approach...distasteful.
Other obvious solutions include intentionally slow switchers. This isn't a
bad idea when high high sensitivity and bandwidth are required; see LT
AN-70. Most power supplies cheat by reporting their noise within a cutoff
of 20MHz or whatever, whereas transients can go out to 100s of MHz. Slower
operation prevents those harmonics from being generated in the first place,
but efficiency and size are the first things to go. Of course, you've
maligned many times about the plurality of supplies required to run
everything. Sometimes you just can't win.
josephkk
Apr 13, 2012, 1:28:24 AM4/13/12
to
On Mon, 09 Apr 2012 20:25:28 -0500, Tim Wescott <t...@seemywebsite.com>
wrote:
>Is it reasonable to expect that the turn-on (not off -- _on_) time of a
>diode should be pretty much consistent with the inductance of the
>package, and not much else?
>
>A customer just sent me some O-scope traces of a circuit where a voltage
>at a catch diode anode is (at least apparently) going several hundred
>volts above its cathode for a microsecond before settling out to the
>nominal anode voltage of the diode.
>
>We're not sure if it's a measurement artifact because the coil has some
>700A in it, or if it's a real event; I wouldn't be willing to even
>believe it's a real event except that I know that funny things can happen
>at high currents.
My first suspect for that is a measurement problem. From experience
>Is it reasonable to expect that the turn-on (not off -- _on_) time of a
>diode should be pretty much consistent with the inductance of the
>package, and not much else?
>
>A customer just sent me some O-scope traces of a circuit where a voltage
>at a catch diode anode is (at least apparently) going several hundred
>volts above its cathode for a microsecond before settling out to the
>nominal anode voltage of the diode.
>
>We're not sure if it's a measurement artifact because the coil has some
>700A in it, or if it's a real event; I wouldn't be willing to even
>believe it's a real event except that I know that funny things can happen
>at high currents.
trying to get 100 and 300 ampere pulses through 8 feet of cable (3.5 us
and 300 ns wide respectively. Even harder to measure well.
?-)
Jan Panteltje
Apr 13, 2012, 5:22:59 AM4/13/12
to
On a sunny day (Wed, 11 Apr 2012 16:16:12 -0700) it happened John Larkin
<jla...@highlandtechnology.com> wrote in
<3s3co7t3k8u529420...@4ax.com>:
>I swear, you guys are all talk.
>
>Here's a 1N914:
>
>http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_a.JPG
>
>http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_b.JPG
>
>http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_c.JPG
>
>
>It kind of looks like the area under the overshoot curve is sort of
>constant.
>
>John
I was thinking about diode turn on time, and started visualizing
the vacuum diode.
Clearly in vacuum diode it takes time for the electrons hovering
around the cathode to start moving when a large voltage is applied,
and reach the anode.
The speed is set by the voltage, and the time by the distance
between anode and cathode (in the 'perfect' diode tube).
In such a case, where the turn on time depends on the electron speed,
one would expect a faster turn on when a higher voltage is applied.
Do you also see that with those diodes?
Or is this idea not correct or does not apply to semiconductors?
<jla...@highlandtechnology.com> wrote in
<3s3co7t3k8u529420...@4ax.com>:
>I swear, you guys are all talk.
>
>Here's a 1N914:
>
>http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_a.JPG
>
>http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_b.JPG
>
>http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_c.JPG
>
>
>It kind of looks like the area under the overshoot curve is sort of
>constant.
>
>John
the vacuum diode.
Clearly in vacuum diode it takes time for the electrons hovering
around the cathode to start moving when a large voltage is applied,
and reach the anode.
The speed is set by the voltage, and the time by the distance
between anode and cathode (in the 'perfect' diode tube).
In such a case, where the turn on time depends on the electron speed,
one would expect a faster turn on when a higher voltage is applied.
Do you also see that with those diodes?
Or is this idea not correct or does not apply to semiconductors?
Phil Hobbs
Apr 13, 2012, 8:54:40 AM4/13/12
to
displacement current--you don't have to wait for the charges to get to
the other side, either in a tube or a diode. It's the diffusion delay
that you have to deal with.
It's actually the same in a NEA photocathode, where the primary
photoelectrons can rattle around for a nanosecond or so before
escaping. (Cathodes with positive electron affinity don't show the
effect so much--if an electron takes more than a couple of bounces, it
loses enough energy that it can't escape. That gives you more speed but
lower quantum efficiency.
Jan Panteltje
Apr 13, 2012, 9:47:37 AM4/13/12
to
On a sunny day (Fri, 13 Apr 2012 08:54:40 -0400) it happened Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote in
<4F882210...@electrooptical.net>:
Is this correct? 'current' is the motion of electrons (as in Ampere electrons per units of time).
So in a tube, when electrons start accelerating in the applied field (because of the voltage),
as long as an electron does not reach the anode, no current flows.
There was a current required to charge the anode up to the voltage,
but that is a different current, and long gone to zero before the
first electron hits the anode (you basically pulled electrons from the anode making it positive,
or maybe better stuffed electrons into the cathode making it negative).
I think you can only refer to 'displacement' once something is displaced.
An electron fills a hole in the semiconductor, and as that is not empty space,
atoms are close, that probably is true displacement,
electrons move one way resulting in holes moving the other way.
But in a tube...?
A different picture:
Imagine you statically charge anode to 1000V, and cathode to 0V.
With the heater off, in a tube.
Now you have the anode voltage, and still no current.
The current only starts once the cathode gets heated, so electrons become available.
And then those take time to reach the anode, if you could heat the cathode
up all at once, even then it would take time.
Or this this view wrong?
<pcdhSpamM...@electrooptical.net> wrote in
<4F882210...@electrooptical.net>:
So in a tube, when electrons start accelerating in the applied field (because of the voltage),
as long as an electron does not reach the anode, no current flows.
There was a current required to charge the anode up to the voltage,
but that is a different current, and long gone to zero before the
first electron hits the anode (you basically pulled electrons from the anode making it positive,
or maybe better stuffed electrons into the cathode making it negative).
I think you can only refer to 'displacement' once something is displaced.
An electron fills a hole in the semiconductor, and as that is not empty space,
atoms are close, that probably is true displacement,
electrons move one way resulting in holes moving the other way.
But in a tube...?
A different picture:
Imagine you statically charge anode to 1000V, and cathode to 0V.
With the heater off, in a tube.
Now you have the anode voltage, and still no current.
The current only starts once the cathode gets heated, so electrons become available.
And then those take time to reach the anode, if you could heat the cathode
up all at once, even then it would take time.
Or this this view wrong?
John Larkin
Apr 13, 2012, 10:27:24 AM4/13/12
to
In my 1N914 pics, you can see the higher currents, and faster turn-on,
when I apply a bigger voltage step. With 1.2 volts across the diode,
it hardly conducts at all for the first 4 ns or so. At 5 volts, it
appears to be conducting before the generator rise is settled.
(When I designed the P400 output stage, I limited the slew rate to
keep within US export limits. They have recently increased the
allowable slew limits, so maybe I'll speed it up some day.)
--
John Larkin Highland Technology Inc
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Photonics and fiberoptic TTL data links
John Larkin
Apr 13, 2012, 10:29:58 AM4/13/12
to
On Fri, 13 Apr 2012 00:11:00 -0500, "Tim Williams"
<tmor...@gmail.com> wrote:
>"John Larkin" <jla...@highlandtechnology.com> wrote in message
>news:vv4eo7tb9v1tslstd...@4ax.com...
>> I've blown out the gates of mosfets, at low voltages and currents,
>> because the body diode had step-recovery behavior. I've seen SRD
>> effects in integrated synchronous buck switchers, too. This is
>> classic:
>>
>> http://dl.dropbox.com/u/53724080/Diode_TurnOn/SwitcherRise.JPG
>>
>> That's an LM3102. The spikes trashed opamps all over the board.
>>
>> So I'd expect that people tweak doping profiles in things like body
>> diodes to achieve soft recovery. Slow and safe.
>
>Obvious solution for this -- go ahead and let it short out the supply for
>those 5 or so nanoseconds. Put a big fat inductor in the supply line (which
>at this rate might be an inch or two of trace over a ground plane cutout).
>VCC droops and dI/dt is limited, at the very least reducing the rate of
>recovery, and reducing the peak amplitude if it still snaps. Finally, a
>little extra capacitance on the switching node slows the transition, so if
>it still snaps, at least it snaps between diode and cap, rather than the
>whole supply rail.
>
>If, after all that, it still insists on snapping, there really isn't
>anything you can do about it besides shop for a device that you hope doesn't
>snap.
>
An external schottky diode helps a lot. It keeps that substrate diode
<tmor...@gmail.com> wrote:
>"John Larkin" <jla...@highlandtechnology.com> wrote in message
>news:vv4eo7tb9v1tslstd...@4ax.com...
>> I've blown out the gates of mosfets, at low voltages and currents,
>> because the body diode had step-recovery behavior. I've seen SRD
>> effects in integrated synchronous buck switchers, too. This is
>> classic:
>>
>> http://dl.dropbox.com/u/53724080/Diode_TurnOn/SwitcherRise.JPG
>>
>> That's an LM3102. The spikes trashed opamps all over the board.
>>
>> So I'd expect that people tweak doping profiles in things like body
>> diodes to achieve soft recovery. Slow and safe.
>
>Obvious solution for this -- go ahead and let it short out the supply for
>those 5 or so nanoseconds. Put a big fat inductor in the supply line (which
>at this rate might be an inch or two of trace over a ground plane cutout).
>VCC droops and dI/dt is limited, at the very least reducing the rate of
>recovery, and reducing the peak amplitude if it still snaps. Finally, a
>little extra capacitance on the switching node slows the transition, so if
>it still snaps, at least it snaps between diode and cap, rather than the
>whole supply rail.
>
>If, after all that, it still insists on snapping, there really isn't
>anything you can do about it besides shop for a device that you hope doesn't
>snap.
>
from turning on.
Other synchronous switchers don't do this. National flubbed that one.
--
John Larkin Highland Technology Inc
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Photonics and fiberoptic TTL data links
George Herold
Apr 13, 2012, 10:35:50 AM4/13/12
to
On Apr 13, 9:47 am, Jan Panteltje <pNaonStpealm...@yahoo.com> wrote:
> On a sunny day (Fri, 13 Apr 2012 08:54:40 -0400) it happened Phil Hobbs
> <pcdhSpamMeSensel...@electrooptical.net> wrote in
> On a sunny day (Fri, 13 Apr 2012 08:54:40 -0400) it happened Phil Hobbs
> <4F882210.9349B...@electrooptical.net>:
>
>
>
>
>
> >Jan Panteltje wrote:
>
> >> On a sunny day (Wed, 11 Apr 2012 16:16:12 -0700) it happened John Larkin
> >> <jlar...@highlandtechnology.com> wrote in
>
>
>
>
> >Jan Panteltje wrote:
>
> >> On a sunny day (Wed, 11 Apr 2012 16:16:12 -0700) it happened John Larkin
> >> <3s3co7t3k8u529420jhr9t0mink0vum...@4ax.com>:
some other circuit), then there's an image charge on the metal plate.
As the electron moves closer the image charge grows.. this charge
comes from the circuit.. it looks like current flow. So the pulse of
charge in the circuit doesn't happen all at once when the electron
arrives at the plate, but over some time.
(At least that's how I see it.)
George H.
>
>
>
> >It's the diffusion delay
> >that you have to deal with.
>
> >It's actually the same in a NEA photocathode, where the primary
> >photoelectrons can rattle around for a nanosecond or so before
> >escaping. (Cathodes with positive electron affinity don't show the
> >effect so much--if an electron takes more than a couple of bounces, it
> >loses enough energy that it can't escape. That gives you more speed but
> >lower quantum efficiency.
>
> >Cheers
>
> >Phil Hobbs- Hide quoted text -
>
>
> >It's the diffusion delay
> >that you have to deal with.
>
> >It's actually the same in a NEA photocathode, where the primary
> >photoelectrons can rattle around for a nanosecond or so before
> >escaping. (Cathodes with positive electron affinity don't show the
> >effect so much--if an electron takes more than a couple of bounces, it
> >loses enough energy that it can't escape. That gives you more speed but
> >lower quantum efficiency.
>
> >Cheers
>
>
> - Show quoted text -- Hide quoted text -
Jan Panteltje
Apr 13, 2012, 2:13:09 PM4/13/12
to
On a sunny day (Fri, 13 Apr 2012 07:35:50 -0700 (PDT)) it happened George
Herold <ghe...@teachspin.com> wrote in
<2a41d1b7-ba8f-4645...@v22g2000vby.googlegroups.com>:
>If I've got an electron moving towards a metal plate (that's part of
>some other circuit), then there's an image charge on the metal plate.
>As the electron moves closer the image charge grows.. this charge
>comes from the circuit.. it looks like current flow. So the pulse of
>charge in the circuit doesn't happen all at once when the electron
>arrives at the plate, but over some time.
>
>(At least that's how I see it.)
>
>George H.
Its intersting, I allocated some spare brain cycles to it, as now
I am running data acquisition tests on my tritium experiment,
and it stores once every hour (it lists everything to the terminal though
each second), so I hop from one place to the other, anyways
when I started thinking about it it got really complicated fast, relativity got into play too :-)
But this:
Sure if you have a cloud of electrons (say 10000) on one electrode missing,
and a 10000 surplus on the other, then it would depend on how much actually started moving
if you take the interaction between the moving electrons in the tube and the ones
on the electrodes.
If 1 was moving and 10000 missing, no electron would leave its atom in the wires?
Actually I am not sure about that, and there is the finite time c where
things interact too.
Then I started thinking photo-detector, and that 'photons' do not only
affect the electrons, but the electrons must then also affect the photons.
All the way back to the source? With time delay? QM.?
I stopped here, and do not worry about my thoughts,
:-)
Herold <ghe...@teachspin.com> wrote in
<2a41d1b7-ba8f-4645...@v22g2000vby.googlegroups.com>:
>If I've got an electron moving towards a metal plate (that's part of
>some other circuit), then there's an image charge on the metal plate.
>As the electron moves closer the image charge grows.. this charge
>comes from the circuit.. it looks like current flow. So the pulse of
>charge in the circuit doesn't happen all at once when the electron
>arrives at the plate, but over some time.
>
>(At least that's how I see it.)
>
>George H.
I am running data acquisition tests on my tritium experiment,
and it stores once every hour (it lists everything to the terminal though
each second), so I hop from one place to the other, anyways
when I started thinking about it it got really complicated fast, relativity got into play too :-)
But this:
Sure if you have a cloud of electrons (say 10000) on one electrode missing,
and a 10000 surplus on the other, then it would depend on how much actually started moving
if you take the interaction between the moving electrons in the tube and the ones
on the electrodes.
If 1 was moving and 10000 missing, no electron would leave its atom in the wires?
Actually I am not sure about that, and there is the finite time c where
things interact too.
Then I started thinking photo-detector, and that 'photons' do not only
affect the electrons, but the electrons must then also affect the photons.
All the way back to the source? With time delay? QM.?
I stopped here, and do not worry about my thoughts,
:-)
Jan Panteltje
Apr 13, 2012, 2:13:15 PM4/13/12
to
On a sunny day (Fri, 13 Apr 2012 07:27:24 -0700) it happened John Larkin
<jjla...@highNOTlandTHIStechnologyPART.com> wrote in
<kedgo7t2v1gl08hr0...@4ax.com>:
Cool.
>(When I designed the P400 output stage, I limited the slew rate to
>keep within US export limits. They have recently increased the
>allowable slew limits, so maybe I'll speed it up some day.)
Did not know they had limits on slewrates for exports too....
Indeed it seems you can gain something here with highter voltages.
<jjla...@highNOTlandTHIStechnologyPART.com> wrote in
<kedgo7t2v1gl08hr0...@4ax.com>:
>(When I designed the P400 output stage, I limited the slew rate to
>keep within US export limits. They have recently increased the
>allowable slew limits, so maybe I'll speed it up some day.)
Indeed it seems you can gain something here with highter voltages.
Tim Williams
Apr 13, 2012, 8:21:33 PM4/13/12
to
"Jan Panteltje" <pNaonSt...@yahoo.com> wrote in message
news:jm8r9l$20t$1...@news.albasani.net...
http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00002494.pdf
Bottom page 4, transient Vf(pk) vs. dI/dt. V / (dI/dt) == inductance, so
the slope of the line is inductance. You'd expect an overall linear term
due to package inductance, but this will only be ~10nH for the TO-220 with
conservative lead lengths, and <5nH for the SMTs. Typical slope is, for
example, 10Vpk / (450 A/us) = 22nH, suggesting the junction alone represents
perhaps 10-15nH.
This isn't an actual circuit inductance for three reasons: 1. Peak voltage
is measured here, whereas an inductor will have a constant voltage across it
as long as current continues to ramp up. 2. The effect varies with dI/dt
(and probably current as well), so it's nonlinear. 3. This effect does not
store energy, it's dissipative. Still, calling it inductance, during
turn-on, is a useful conceptual model for the effect.
news:jm8r9l$20t$1...@news.albasani.net...
> In such a case, where the turn on time depends on the electron speed,
> one would expect a faster turn on when a higher voltage is applied.
> Do you also see that with those diodes?
Forward recovery looks roughly inductive. See for example,
> one would expect a faster turn on when a higher voltage is applied.
> Do you also see that with those diodes?
http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00002494.pdf
Bottom page 4, transient Vf(pk) vs. dI/dt. V / (dI/dt) == inductance, so
the slope of the line is inductance. You'd expect an overall linear term
due to package inductance, but this will only be ~10nH for the TO-220 with
conservative lead lengths, and <5nH for the SMTs. Typical slope is, for
example, 10Vpk / (450 A/us) = 22nH, suggesting the junction alone represents
perhaps 10-15nH.
This isn't an actual circuit inductance for three reasons: 1. Peak voltage
is measured here, whereas an inductor will have a constant voltage across it
as long as current continues to ramp up. 2. The effect varies with dI/dt
(and probably current as well), so it's nonlinear. 3. This effect does not
store energy, it's dissipative. Still, calling it inductance, during
turn-on, is a useful conceptual model for the effect.
Phil Hobbs
Apr 13, 2012, 8:51:58 PM4/13/12
to
Phil Hobbs
Apr 13, 2012, 8:53:08 PM4/13/12
to
josephkk
Apr 14, 2012, 4:38:00 AM4/14/12
to
>
>An electron fills a hole in the semiconductor, and as that is not empty space,
>atoms are close, that probably is true displacement,
>electrons move one way resulting in holes moving the other way.
>But in a tube...?
>
>A different picture:
>Imagine you statically charge anode to 1000V, and cathode to 0V.
>With the heater off, in a tube.
>Now you have the anode voltage, and still no current.
>The current only starts once the cathode gets heated, so electrons become available.
>And then those take time to reach the anode, if you could heat the cathode
>up all at once, even then it would take time.
Alternately, heat the cathode up and apply no anode voltage and get a
>An electron fills a hole in the semiconductor, and as that is not empty space,
>atoms are close, that probably is true displacement,
>electrons move one way resulting in holes moving the other way.
>But in a tube...?
>
>A different picture:
>Imagine you statically charge anode to 1000V, and cathode to 0V.
>With the heater off, in a tube.
>Now you have the anode voltage, and still no current.
>The current only starts once the cathode gets heated, so electrons become available.
>And then those take time to reach the anode, if you could heat the cathode
>up all at once, even then it would take time.
current.
>
>Or this this view wrong?
>
Start with a hot cathode and a space charge with an electron cloud between
>Or this this view wrong?
>
the cathode and anode and calculate from there.
josephkk
Apr 14, 2012, 4:54:22 AM4/14/12
to
the diode while there is a depleted region in place. Thus collapsing it
has to do with size, field and carrier mobility.
?-)
Jan Panteltje
Apr 14, 2012, 6:02:21 AM4/14/12
to
On a sunny day (Fri, 13 Apr 2012 19:21:33 -0500) it happened "Tim Williams"
<tmor...@gmail.com> wrote in <jmafu5$h9l$1...@dont-email.me>:
>"Jan Panteltje" <pNaonSt...@yahoo.com> wrote in message
>news:jm8r9l$20t$1...@news.albasani.net...
>> In such a case, where the turn on time depends on the electron speed,
>> one would expect a faster turn on when a higher voltage is applied.
>> Do you also see that with those diodes?
>
>Forward recovery looks roughly inductive. See for example,
>http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00002494.pdf
>Bottom page 4, transient Vf(pk) vs. dI/dt. V / (dI/dt) == inductance, so
>the slope of the line is inductance.
Wow more that 10V!
> You'd expect an overall linear term
>due to package inductance, but this will only be ~10nH for the TO-220 with
>conservative lead lengths, and <5nH for the SMTs. Typical slope is, for
>example, 10Vpk / (450 A/us) = 22nH, suggesting the junction alone represents
>perhaps 10-15nH.
>This isn't an actual circuit inductance for three reasons: 1. Peak voltage
>is measured here, whereas an inductor will have a constant voltage across it
>as long as current continues to ramp up. 2. The effect varies with dI/dt
>(and probably current as well), so it's nonlinear. 3. This effect does not
>store energy, it's dissipative. Still, calling it inductance, during
>turn-on, is a useful conceptual model for the effect.
>
>Tim
Right,
It is interesting to try to understand the processes involved in this effect.
One sure can be bitten by it!
<tmor...@gmail.com> wrote in <jmafu5$h9l$1...@dont-email.me>:
>"Jan Panteltje" <pNaonSt...@yahoo.com> wrote in message
>news:jm8r9l$20t$1...@news.albasani.net...
>> In such a case, where the turn on time depends on the electron speed,
>> one would expect a faster turn on when a higher voltage is applied.
>> Do you also see that with those diodes?
>
>Forward recovery looks roughly inductive. See for example,
>http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00002494.pdf
>Bottom page 4, transient Vf(pk) vs. dI/dt. V / (dI/dt) == inductance, so
>the slope of the line is inductance.
> You'd expect an overall linear term
>due to package inductance, but this will only be ~10nH for the TO-220 with
>conservative lead lengths, and <5nH for the SMTs. Typical slope is, for
>example, 10Vpk / (450 A/us) = 22nH, suggesting the junction alone represents
>perhaps 10-15nH.
>This isn't an actual circuit inductance for three reasons: 1. Peak voltage
>is measured here, whereas an inductor will have a constant voltage across it
>as long as current continues to ramp up. 2. The effect varies with dI/dt
>(and probably current as well), so it's nonlinear. 3. This effect does not
>store energy, it's dissipative. Still, calling it inductance, during
>turn-on, is a useful conceptual model for the effect.
>
>Tim
It is interesting to try to understand the processes involved in this effect.
One sure can be bitten by it!
Jan Panteltje
Apr 14, 2012, 6:02:29 AM4/14/12
to
On a sunny day (Fri, 13 Apr 2012 20:51:58 -0400) it happened Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote in
<4F88CA2E...@electrooptical.net>:
>Google "displacement current".
>
>Cheers
>
>Phil Hobbs
OK, yes, I needed some reading up on this, it always fascinates
me how Maxwell came to his equations:
http://en.wikipedia.org/wiki/Displacement_current
It is funny how he uses a 'medium' (ether)...
But I will not stir that pot now.
Anyways, in the thoughts about all this I came to the following conclusions,
that may be important to some, especially perhaps to those interested in optical effects.
The conclusion was, that if, late at night, (or any other time[1])
I was looking at a star, and blinked my eye, then that change
(is it collapse of the wave function?) would have an effect on that star,
and of course then on its environment like its planets too.
Looking a bit deeper and adding the 'butterfly effect', where in
a semi??? chaotic system a small change can do so much, I can,
by simply blinking my eye, destroy and create civilizations on planets
around other stars.
When we apply this deep insight into our smaller world,
you can deduce, using simple math(?) that by merely LOOKING at obama
we can destroy the entire US, let alone by voting for him.
Now this deep insight happened to me this morning,
and I thought I had to share it with you, especially Jim, who always has such nice contributions to
this newsgroup.
There was something else, but I forgot Oh, it is coming back now,
I did not stop at that depth of insight, oh no,
I realized that the fact that IF I blink my eye, and when, is set by all the subconscious influences,
and the configuration of my neural net set by evolution and past experiences,
and that in a way everything is interconnected and fixed, and what I think
about what is happening and what we are even, is just a thermal effect-
and lets go into what was it .. entropy... and we are like a thermal side effect,
and the universe will cool down and become a cold crystal without us life forms
as thermal effect moving about just to use a word.
If this is true it is challenging, and if it was how did the universe come into being then in the
first place if entropy was zero,, so there must be a bit more.
This is good, as it would worry me to end up as an ice crystal,
and what good is Maxwell on ice.
So anyways that is about as far as I came today, hope this did not damage any weights
in the old neural net, but even if it did, I had to write this,
as this is how it (universe) unfolds.
Just be careful blinking your eyes.
[1] This is not exact science, it is in the realm of philosophy.
<pcdhSpamM...@electrooptical.net> wrote in
<4F88CA2E...@electrooptical.net>:
>Google "displacement current".
>
>Cheers
>
>Phil Hobbs
me how Maxwell came to his equations:
http://en.wikipedia.org/wiki/Displacement_current
It is funny how he uses a 'medium' (ether)...
But I will not stir that pot now.
Anyways, in the thoughts about all this I came to the following conclusions,
that may be important to some, especially perhaps to those interested in optical effects.
The conclusion was, that if, late at night, (or any other time[1])
I was looking at a star, and blinked my eye, then that change
(is it collapse of the wave function?) would have an effect on that star,
and of course then on its environment like its planets too.
Looking a bit deeper and adding the 'butterfly effect', where in
a semi??? chaotic system a small change can do so much, I can,
by simply blinking my eye, destroy and create civilizations on planets
around other stars.
When we apply this deep insight into our smaller world,
you can deduce, using simple math(?) that by merely LOOKING at obama
we can destroy the entire US, let alone by voting for him.
Now this deep insight happened to me this morning,
and I thought I had to share it with you, especially Jim, who always has such nice contributions to
this newsgroup.
There was something else, but I forgot Oh, it is coming back now,
I did not stop at that depth of insight, oh no,
I realized that the fact that IF I blink my eye, and when, is set by all the subconscious influences,
and the configuration of my neural net set by evolution and past experiences,
and that in a way everything is interconnected and fixed, and what I think
about what is happening and what we are even, is just a thermal effect-
and lets go into what was it .. entropy... and we are like a thermal side effect,
and the universe will cool down and become a cold crystal without us life forms
as thermal effect moving about just to use a word.
If this is true it is challenging, and if it was how did the universe come into being then in the
first place if entropy was zero,, so there must be a bit more.
This is good, as it would worry me to end up as an ice crystal,
and what good is Maxwell on ice.
So anyways that is about as far as I came today, hope this did not damage any weights
in the old neural net, but even if it did, I had to write this,
as this is how it (universe) unfolds.
Just be careful blinking your eyes.
[1] This is not exact science, it is in the realm of philosophy.
amdx
Apr 14, 2012, 7:46:53 AM4/14/12
to
On 4/14/2012 5:02 AM, Jan Panteltje wrote:
> On a sunny day (Fri, 13 Apr 2012 20:51:58 -0400) it happened Phil Hobbs
> <pcdhSpamM...@electrooptical.net> wrote in
> <4F88CA2E...@electrooptical.net>:
>
>> Google "displacement current".
>>
>> Cheers
>>
>> Phil Hobbs
>
> OK, yes, I needed some reading up on this, it always fascinates
> me how Maxwell came to his equations:
> http://en.wikipedia.org/wiki/Displacement_current
>
> It is funny how he uses a 'medium' (ether)...
>
> But I will not stir that pot now.
>
> Anyways, in the thoughts about all this I came to the following conclusions,
> that may be important to some, especially perhaps to those interested in optical effects.
>
> The conclusion was, that if, late at night, (or any other time[1])
> I was looking at a star, and blinked my eye, then that change
> (is it collapse of the wave function?) would have an effect on that star,
> and of course then on its environment like its planets too.
> Looking a bit deeper and adding the 'butterfly effect', where in
> a semi??? chaotic system a small change can do so much, I can,
> by simply blinking my eye, destroy and create civilizations on planets
> around other stars.
>
Yes, there was a pretty young female that blinked her eye and my world
> On a sunny day (Fri, 13 Apr 2012 20:51:58 -0400) it happened Phil Hobbs
> <pcdhSpamM...@electrooptical.net> wrote in
> <4F88CA2E...@electrooptical.net>:
>
>> Google "displacement current".
>>
>> Cheers
>>
>> Phil Hobbs
>
> OK, yes, I needed some reading up on this, it always fascinates
> me how Maxwell came to his equations:
> http://en.wikipedia.org/wiki/Displacement_current
>
> It is funny how he uses a 'medium' (ether)...
>
> But I will not stir that pot now.
>
> Anyways, in the thoughts about all this I came to the following conclusions,
> that may be important to some, especially perhaps to those interested in optical effects.
>
> The conclusion was, that if, late at night, (or any other time[1])
> I was looking at a star, and blinked my eye, then that change
> (is it collapse of the wave function?) would have an effect on that star,
> and of course then on its environment like its planets too.
> Looking a bit deeper and adding the 'butterfly effect', where in
> a semi??? chaotic system a small change can do so much, I can,
> by simply blinking my eye, destroy and create civilizations on planets
> around other stars.
>
changed.
So, I have corroborating evidence for your premiss.
Mikek :-)
John Larkin
Apr 14, 2012, 10:48:11 AM4/14/12
to
On Sat, 14 Apr 2012 10:02:21 GMT, Jan Panteltje
<pNaonSt...@yahoo.com> wrote:
>On a sunny day (Fri, 13 Apr 2012 19:21:33 -0500) it happened "Tim Williams"
><tmor...@gmail.com> wrote in <jmafu5$h9l$1...@dont-email.me>:
>
>>"Jan Panteltje" <pNaonSt...@yahoo.com> wrote in message
>>news:jm8r9l$20t$1...@news.albasani.net...
>>> In such a case, where the turn on time depends on the electron speed,
>>> one would expect a faster turn on when a higher voltage is applied.
>>> Do you also see that with those diodes?
>>
>>Forward recovery looks roughly inductive. See for example,
>>http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00002494.pdf
>>Bottom page 4, transient Vf(pk) vs. dI/dt. V / (dI/dt) == inductance, so
>>the slope of the line is inductance.
>
>Wow more that 10V!
>
I've run diodes at +48 volts, on purpose. In the ones I used, current
<pNaonSt...@yahoo.com> wrote:
>On a sunny day (Fri, 13 Apr 2012 19:21:33 -0500) it happened "Tim Williams"
><tmor...@gmail.com> wrote in <jmafu5$h9l$1...@dont-email.me>:
>
>>"Jan Panteltje" <pNaonSt...@yahoo.com> wrote in message
>>news:jm8r9l$20t$1...@news.albasani.net...
>>> In such a case, where the turn on time depends on the electron speed,
>>> one would expect a faster turn on when a higher voltage is applied.
>>> Do you also see that with those diodes?
>>
>>Forward recovery looks roughly inductive. See for example,
>>http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00002494.pdf
>>Bottom page 4, transient Vf(pk) vs. dI/dt. V / (dI/dt) == inductance, so
>>the slope of the line is inductance.
>
>Wow more that 10V!
>
ramped up linearly to about 50 amps in about 100 ns.
Jon Elson
Apr 14, 2012, 2:35:34 PM4/14/12
to
Tim Wescott wrote:
> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
> diode should be pretty much consistent with the inductance of the
> package, and not much else?
>
No. I had a problem in an H-bridge servo amp where output inductance
> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
> diode should be pretty much consistent with the inductance of the
> package, and not much else?
>
caused undershoot when the high side transistor turned off. The
low-side transistor's body diode could develop more than 12 V forward
voltage for several microseconds before it started conducting.
I put an "ultra fast" diode across it to prevent the undershoot
9which was destroying the FET gate driver chip). Package inductance
had nothing to do with it, it was just the characteristics of the
diode junction, how long it took charge carriers to develop.
> A customer just sent me some O-scope traces of a circuit where a voltage
> at a catch diode anode is (at least apparently) going several hundred
> volts above its cathode for a microsecond before settling out to the
> nominal anode voltage of the diode.
>
Again, no way that can be inductance. Hundreds of V for a whole
> at a catch diode anode is (at least apparently) going several hundred
> volts above its cathode for a microsecond before settling out to the
> nominal anode voltage of the diode.
>
us?
> We're not sure if it's a measurement artifact because the coil has some
> 700A in it, or if it's a real event; I wouldn't be willing to even
> believe it's a real event except that I know that funny things can happen
> at high currents.
>
Scope probing circuits with really high Di/Dt can be a huge challenge,
> 700A in it, or if it's a real event; I wouldn't be willing to even
> believe it's a real event except that I know that funny things can happen
> at high currents.
>
so there may well be a lot of measurement artifact in that.
A current probe on the diode might be helpful to determine the
Tr of the diode. And, of course, a 700 A diode might be pretty
slow, too.
Jon
Tim Williams
Apr 14, 2012, 9:36:32 PM4/14/12
to
"Jon Elson" <el...@pico-systems.com> wrote in message
news:97ydnbYY2LjrXhTS...@giganews.com...
stuck together, or whatever?
news:97ydnbYY2LjrXhTS...@giganews.com...
> Scope probing circuits with really high Di/Dt can be a huge challenge,
> so there may well be a lot of measurement artifact in that.
> A current probe on the diode might be helpful to determine the
> Tr of the diode. And, of course, a 700 A diode might be pretty
> slow, too.
No kidding! Why can't they make them the same speed as a hundred 10A diodes
> so there may well be a lot of measurement artifact in that.
> A current probe on the diode might be helpful to determine the
> Tr of the diode. And, of course, a 700 A diode might be pretty
> slow, too.
stuck together, or whatever?
John S
Apr 16, 2012, 1:25:07 PM4/16/12
to
On 4/11/2012 6:16 PM, John Larkin wrote:
> On Mon, 09 Apr 2012 20:25:28 -0500, Tim Wescott<t...@seemywebsite.com>
> On Mon, 09 Apr 2012 20:25:28 -0500, Tim Wescott<t...@seemywebsite.com>
> wrote:
>
>> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
>> diode should be pretty much consistent with the inductance of the
>> package, and not much else?
>>
>
>> Is it reasonable to expect that the turn-on (not off -- _on_) time of a
>> diode should be pretty much consistent with the inductance of the
>> package, and not much else?
>>
>> A customer just sent me some O-scope traces of a circuit where a voltage
>> at a catch diode anode is (at least apparently) going several hundred
>> volts above its cathode for a microsecond before settling out to the
>> nominal anode voltage of the diode.
>>
>> at a catch diode anode is (at least apparently) going several hundred
>> volts above its cathode for a microsecond before settling out to the
>> nominal anode voltage of the diode.
>>
>> We're not sure if it's a measurement artifact because the coil has some
>> 700A in it, or if it's a real event; I wouldn't be willing to even
>> believe it's a real event except that I know that funny things can happen
>> at high currents.
>
>
>> 700A in it, or if it's a real event; I wouldn't be willing to even
>> believe it's a real event except that I know that funny things can happen
>> at high currents.
>
>
> I swear, you guys are all talk.
>
> Here's a 1N914:
>
> http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_a.JPG
>
> http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_b.JPG
>
> http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_c.JPG
>
>
> It kind of looks like the area under the overshoot curve is sort of
> constant.
>
> John
>
Here's a question for the gurus here. If the diode under discussion is
>
> Here's a 1N914:
>
> http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_a.JPG
>
> http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_b.JPG
>
> http://dl.dropbox.com/u/53724080/Diode_TurnOn/1N914_c.JPG
>
>
> It kind of looks like the area under the overshoot curve is sort of
> constant.
>
> John
>
used to prevent reverse current into a transistor's b-e junction, does
this phenomenon eventually cause problems with the transistor and how
can it be prevented?
Thanks.
John S
John Larkin
Apr 16, 2012, 2:33:03 PM4/16/12
to
On Mon, 16 Apr 2012 12:25:07 -0500, John S <Sop...@invalid.org>
wrote:
If it allowed the transistor b-e junction to zener, yes, the
transistor could be damaged. I can't quantify that; the duration of
zenering would be small.
Better to use a schottky, or otherwise limit the base drive.
--
John Larkin Highland Technology, Inc
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser controllers
wrote:
transistor could be damaged. I can't quantify that; the duration of
zenering would be small.
Better to use a schottky, or otherwise limit the base drive.
--
John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Photonics and fiberoptic TTL data links
Mike Perkins
Apr 18, 2012, 5:31:51 AM4/18/12
to
On 12/04/2012 17:19, Bert Hickman wrote:
> Yes...
>
> www.linear.com/docs/27403
>
> However, measurement error/inductance must be involved for a
> multi-hundred volt transient.
>
> Bert
I fully accept that it is a true phenomenon, but still can't find any
literature which gives the cause of the turn-on time, apart from
device/lead inductance.
--
Mike Perkins
Video Solutions Ltd
www.videosolutions.ltd.uk
> John Larkin wrote:
>> On Thu, 12 Apr 2012 10:36:41 +0100, Mike Perkins<sp...@spam.com>
>> wrote:
>>
>>> On 12/04/2012 02:46, Tim Wescott wrote:
>>>> On Thu, 12 Apr 2012 01:32:18 +0100, Mike Perkins wrote:
>>>>
>>>>> On 12/04/2012 00:49, Tim Wescott wrote:
>>>>>> On Thu, 12 Apr 2012 00:20:23 +0100, Mike Perkins wrote:
>>>>>>
>> On Thu, 12 Apr 2012 10:36:41 +0100, Mike Perkins<sp...@spam.com>
>> wrote:
>>
>>> On 12/04/2012 02:46, Tim Wescott wrote:
>>>> On Thu, 12 Apr 2012 01:32:18 +0100, Mike Perkins wrote:
>>>>
>>>>> On 12/04/2012 00:49, Tim Wescott wrote:
>>>>>> On Thu, 12 Apr 2012 00:20:23 +0100, Mike Perkins wrote:
>>>>>>
>>>>>>> On 10/04/2012 02:25, Tim Wescott wrote:
>>>>>>>> Is it reasonable to expect that the turn-on (not off -- _on_) time
>>>>>>>> of a diode should be pretty much consistent with the inductance of
>>>>>>>> the package, and not much else?
>>>>>>>>
>>>>>>>> A customer just sent me some O-scope traces of a circuit where a
>>>>>>>> voltage at a catch diode anode is (at least apparently) going
>>>>>>>> several hundred volts above its cathode for a microsecond before
>>>>>>>> settling out to the nominal anode voltage of the diode.
>>>>>>>>
>>>>>>>> We're not sure if it's a measurement artifact because the coil has
>>>>>>>> some 700A in it, or if it's a real event; I wouldn't be willing to
>>>>>>>> even believe it's a real event except that I know that funny things
>>>>>>>> can happen at high currents.
>>>>>>>>
>>>>>>>>
>>>>>>>> Is it reasonable to expect that the turn-on (not off -- _on_) time
>>>>>>>> of a diode should be pretty much consistent with the inductance of
>>>>>>>> the package, and not much else?
>>>>>>>>
>>>>>>>> A customer just sent me some O-scope traces of a circuit where a
>>>>>>>> voltage at a catch diode anode is (at least apparently) going
>>>>>>>> several hundred volts above its cathode for a microsecond before
>>>>>>>> settling out to the nominal anode voltage of the diode.
>>>>>>>>
>>>>>>>> We're not sure if it's a measurement artifact because the coil has
>>>>>>>> some 700A in it, or if it's a real event; I wouldn't be willing to
>>>>>>>> even believe it's a real event except that I know that funny things
>>>>>>>> can happen at high currents.
>>>>>>>>
>>>>>>>>
>
> www.linear.com/docs/27403
>
> However, measurement error/inductance must be involved for a
> multi-hundred volt transient.
>
> Bert
I fully accept that it is a true phenomenon, but still can't find any
literature which gives the cause of the turn-on time, apart from
device/lead inductance.
--
Mike Perkins
Video Solutions Ltd
www.videosolutions.ltd.uk
Mike Perkins
Apr 18, 2012, 5:32:58 AM4/18/12
to
>> turn-on time is package dependent, through package inductance, skin
>> effect or whatever other mechanism may come into play. I hear what
>> you're saying, and from a designer's point of view t-fr must be taken
>> into account, I was trying to establish its cause.
>
> No, it's a minority carrier effect. A Schottky in the same package on
> the same board won't show the same effect.
>
> Cheers
>
> Phil Hobbs
>
Can you cite any literature on this? I still haven't found any
explanation apart from device inductance.
Phil Hobbs
Apr 18, 2012, 1:42:33 PM4/18/12
to
George Herold
Apr 18, 2012, 2:31:04 PM4/18/12
to
>
> - Show quoted text -
OK since no one 'choked' on this the first time I said it.
> - Show quoted text -
I would guess it’s related to the minority diffusion time. Higher
voltage parts are ‘in general’ going to have larger intrinsic regions,
and the diffusion time should go something like the length squared.
I’m not sure exactly how this model would ‘square’ with John L’s
observation that at higher forward voltages the turn on time was
smaller. (Unless, the higher voltage means more minority carriers, so
there will be more of the ‘lucky few’ carriers that make it across in
less than the diffusion time.)
George H.
John Larkin
Apr 18, 2012, 2:45:15 PM4/18/12
to
On Wed, 18 Apr 2012 10:32:58 +0100, Mike Perkins <sp...@spam.com>
wrote:
Personally, I don't need to know how a diode or a transistor works,
because I don't design semiconductors. I use semiconductors, so I need
to know how they behave. The best way to determine that is not from
academic papers, because they won't be applicable to real-world parts
in any hard usable way; I don't know the diffusion profile of a diode
that I buy from Mouser, and I wouldn't care to do the math if I did.
So I work from data sheets, verified by experiment if there's the
possibility anything exotic or unspecified going on.
Things like a hint that a PN diode might turn on slowly, or snap on
recovery, is useful because it makes me experiment with real parts
when it might matter. The tests I did on the 1N914 were interesting,
and only took a few minutes. The effect was clearly not inductive.
Testing parts to destruction is fun and valuable, too.
wrote:
because I don't design semiconductors. I use semiconductors, so I need
to know how they behave. The best way to determine that is not from
academic papers, because they won't be applicable to real-world parts
in any hard usable way; I don't know the diffusion profile of a diode
that I buy from Mouser, and I wouldn't care to do the math if I did.
So I work from data sheets, verified by experiment if there's the
possibility anything exotic or unspecified going on.
Things like a hint that a PN diode might turn on slowly, or snap on
recovery, is useful because it makes me experiment with real parts
when it might matter. The tests I did on the 1N914 were interesting,
and only took a few minutes. The effect was clearly not inductive.
Testing parts to destruction is fun and valuable, too.
Jamie
Apr 18, 2012, 5:25:59 PM4/18/12
to
Jamie
bjacoby
Apr 19, 2012, 2:54:43 AM4/19/12
to
straight-forward explanation you are in trouble. It's not inductance,
but rather drift-velocity and recombination times of carriers in the PN
junction. Especially at the transition. Any book on the physics of
semiconductor devices should cover the effects. This is one reason
schottky diodes are so fast. They don't have the delays due to P-N
recombination times etc. They are semiconductor - metal construction.
The whole business is quite complex and highly dependent upon the
structure of the various devices. Hence generally rules of thumb in this
regard are hard to come by without some very exacting measurements.
Usually switching times are just measured and listed in device specs
rather than to dig down and examine the "why" of the actual device
structure.
Mike Perkins
Apr 19, 2012, 6:40:20 AM4/19/12
to
wasn't in denial of turn on time, but this effect didn't correspond with
what I've been taught/learnt in the past. As an engineer, whilst I use
practical numbers from datasheets and measurement I have found some
understanding of what's going on invaluable. I was also assuming that
any junction would be small and velocity sufficient to make the
measurement impossible. Clearly I am wrong. Many thank for
enlightening me.
legg
Apr 19, 2012, 9:15:46 AM4/19/12
to
On Wed, 18 Apr 2012 10:31:51 +0100, Mike Perkins <sp...@spam.com>
wrote:
<snip>
RL
wrote:
<snip>
>
>I fully accept that it is a true phenomenon, but still can't find any
>literature which gives the cause of the turn-on time, apart from
>device/lead inductance.
http://cds.linear.com/docs/Application%20Note/an122f.pdf
>I fully accept that it is a true phenomenon, but still can't find any
>literature which gives the cause of the turn-on time, apart from
>device/lead inductance.
RL
Mike Perkins
Apr 19, 2012, 9:17:30 AM4/19/12
to
existence of a turn on time, and how to measure it, it still doesn't
give a clue as to the cause. Sorry if I can't see the wood for the
trees! :-)
josephkk
Apr 24, 2012, 8:43:00 PM4/24/12
to
ratings and higher applied forward voltages. They tend to be in opposite
directions.
?-)
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