Google Groups no longer supports new Usenet posts or subscriptions. Historical content remains viewable.
Dismiss
These transistors sure do scream...
251 views
Skip to first unread message
Tim Williams
Feb 20, 2017, 5:31:09 AM2/20/17
to
Playing with a switching circuit, yet I seem to have made the observation
that these things are fantastic for linear.
Infineon SPA07N60C3, but everyone has their line of SuperJunction MOSFETs.
Circuit, for posterity:
https://www.seventransistorlabs.com/Images/High%20Voltage%20Bridge.pdf
Intended load is high impedance, capacitive. It can easily source 5A peak
though.
Since the load is capacitive, it operates in hard switching. The
transistors start singing as soon as they get into the Miller plateau.
Which in this circuit, I've intentionally exaggerated (27pF D-G), to help
keep the transistor voltages matched.
A word about SuperJunction transistors: Coss tanks by two decades, over the
5 to 20V range. Very nonlinear, brutal. This is fantastic for switching
converters, because it "cushions" the switching edge, doing a better job of
snubbing than an external network ever could. By pushing all the Miller
effect to the low voltage end, switching loss can be very low.
With stacked transistors, that works against me, because they'll probably be
mismatched in the low-capacitance region. So the switching times, and
voltages, probably won't be matched, forcing much more voltage across just
one over-performing transistor.
So I increase Miller capacitance, so the rise is slower, and more linear.
And to protect against accidental turn-on or damage, due to opposite side
hard-switching or output sparks, I put zener diodes on G-S. (Back-to-back
pairs, since the drive is transformer coupled.)
I think between the zeners and the Miller cap, I've got a particularly nasty
loop that makes a wonderful oscillator. In the 200 to 400MHz region,
depending on which transistor you ask.
(Ferrite beads on the gate leads solves the oscillation, more or less.)
I'm definitely going to try an RF amplifier with these, soon. I can't do
very much power, because of thermal limitations, and bandwidth won't be
fantastic because of the high load resistance versus Coss (note that the
load resistance has to be high, i.e. the supply voltage high, and because of
power limits, the current relatively low, to stay in the low-Coss range).
The useful frequency range seemingly should be worthy of vacuum tubes,
though! Assuming lead parasitics don't trash it first, which is likely. :)
Tim
--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com
that these things are fantastic for linear.
Infineon SPA07N60C3, but everyone has their line of SuperJunction MOSFETs.
Circuit, for posterity:
https://www.seventransistorlabs.com/Images/High%20Voltage%20Bridge.pdf
Intended load is high impedance, capacitive. It can easily source 5A peak
though.
Since the load is capacitive, it operates in hard switching. The
transistors start singing as soon as they get into the Miller plateau.
Which in this circuit, I've intentionally exaggerated (27pF D-G), to help
keep the transistor voltages matched.
A word about SuperJunction transistors: Coss tanks by two decades, over the
5 to 20V range. Very nonlinear, brutal. This is fantastic for switching
converters, because it "cushions" the switching edge, doing a better job of
snubbing than an external network ever could. By pushing all the Miller
effect to the low voltage end, switching loss can be very low.
With stacked transistors, that works against me, because they'll probably be
mismatched in the low-capacitance region. So the switching times, and
voltages, probably won't be matched, forcing much more voltage across just
one over-performing transistor.
So I increase Miller capacitance, so the rise is slower, and more linear.
And to protect against accidental turn-on or damage, due to opposite side
hard-switching or output sparks, I put zener diodes on G-S. (Back-to-back
pairs, since the drive is transformer coupled.)
I think between the zeners and the Miller cap, I've got a particularly nasty
loop that makes a wonderful oscillator. In the 200 to 400MHz region,
depending on which transistor you ask.
(Ferrite beads on the gate leads solves the oscillation, more or less.)
I'm definitely going to try an RF amplifier with these, soon. I can't do
very much power, because of thermal limitations, and bandwidth won't be
fantastic because of the high load resistance versus Coss (note that the
load resistance has to be high, i.e. the supply voltage high, and because of
power limits, the current relatively low, to stay in the low-Coss range).
The useful frequency range seemingly should be worthy of vacuum tubes,
though! Assuming lead parasitics don't trash it first, which is likely. :)
Tim
--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com
piglet
Feb 20, 2017, 8:43:24 AM2/20/17
to
On 20/02/2017 10:31, Tim Williams wrote:
> Circuit, for posterity:
> https://www.seventransistorlabs.com/Images/High%20Voltage%20Bridge.pdf
Just checking ... is the transformer phasing different for top three
> Circuit, for posterity:
> https://www.seventransistorlabs.com/Images/High%20Voltage%20Bridge.pdf
stages vs lower three stages?
piglet
Tauno Voipio
Feb 20, 2017, 9:01:49 AM2/20/17
to
being a dead short from +1500 to ground.
--
-TV
Winfield Hill
Feb 20, 2017, 9:11:09 AM2/20/17
to
Tim Williams wrote...
Tell us about your gate transformers.
What risetime and falltime are you observing?
--
Thanks,
- Win
Tell us about your gate transformers.
What risetime and falltime are you observing?
--
Thanks,
- Win
John Larkin
Feb 20, 2017, 10:54:19 AM2/20/17
to
--
John Larkin Highland Technology, Inc
lunatic fringe electronics
Tim Williams
Feb 21, 2017, 2:07:46 AM2/21/17
to
"John Larkin" <jjla...@highlandtechnology.com> wrote in message
news:k74mac1bqfdmcima5...@4ax.com...
Intended application: gate drive V_cm testing. A fairly large swing, at
reasonably high dV/dt (a few kV/us), and essentially capacitive load.
It's doing about 7kV/us, which is nice, but I was hoping for >10. Maybe
I'll drop the Miller caps to 10pF and see how she sings.
news:k74mac1bqfdmcima5...@4ax.com...
> What sort of switching speed do you need?
Pokey -- around a hundred nanoseconds.
Intended application: gate drive V_cm testing. A fairly large swing, at
reasonably high dV/dt (a few kV/us), and essentially capacitive load.
It's doing about 7kV/us, which is nice, but I was hoping for >10. Maybe
I'll drop the Miller caps to 10pF and see how she sings.
Tim Williams
Feb 21, 2017, 2:11:08 AM2/21/17
to
"Winfield Hill" <hi...@rowland.harvard.edu> wrote in message
news:o8etd...@drn.newsguy.com...
The transformer impedance is pretty crappy (kind of intentionally), so the
response is, uh, what was it... think the small-signal calculation was 3uH
leakage per secondary, 33 ohms ESR and 2nF equivalent Cg. So whatever that
works out to, as a LPF.
Drive is a pair of TC4420, so the drive resistance is lowish, but not scary
low. LL + R_G dominates.
Gate waveform something like 200ns (full rise, about half being Miller
plateau), output depends on supply voltage, but it's also about 200ns at the
full 1500V supply (imagine that: constant drive current yields constant
dV/dt? :) ).
news:o8etd...@drn.newsguy.com...
> Tell us about your gate transformers.
> What risetime and falltime are you observing?
As Piglet noted, yes, the phasing is inverse for half of the windings. ;)
> What risetime and falltime are you observing?
The transformer impedance is pretty crappy (kind of intentionally), so the
response is, uh, what was it... think the small-signal calculation was 3uH
leakage per secondary, 33 ohms ESR and 2nF equivalent Cg. So whatever that
works out to, as a LPF.
Drive is a pair of TC4420, so the drive resistance is lowish, but not scary
low. LL + R_G dominates.
Gate waveform something like 200ns (full rise, about half being Miller
plateau), output depends on supply voltage, but it's also about 200ns at the
full 1500V supply (imagine that: constant drive current yields constant
dV/dt? :) ).
John Larkin
Feb 21, 2017, 10:43:14 AM2/21/17
to
On Tue, 21 Feb 2017 01:07:40 -0600, "Tim Williams"
<tiw...@seventransistorlabs.com> wrote:
>"John Larkin" <jjla...@highlandtechnology.com> wrote in message
>news:k74mac1bqfdmcima5...@4ax.com...
>> What sort of switching speed do you need?
>
>Pokey -- around a hundred nanoseconds.
>
>Intended application: gate drive V_cm testing. A fairly large swing, at
>reasonably high dV/dt (a few kV/us), and essentially capacitive load.
>
>It's doing about 7kV/us, which is nice, but I was hoping for >10. Maybe
>I'll drop the Miller caps to 10pF and see how she sings.
>
>Tim
Another way to get insane edge speeds is avalanche transistors. A
<tiw...@seventransistorlabs.com> wrote:
>"John Larkin" <jjla...@highlandtechnology.com> wrote in message
>news:k74mac1bqfdmcima5...@4ax.com...
>> What sort of switching speed do you need?
>
>Pokey -- around a hundred nanoseconds.
>
>Intended application: gate drive V_cm testing. A fairly large swing, at
>reasonably high dV/dt (a few kV/us), and essentially capacitive load.
>
>It's doing about 7kV/us, which is nice, but I was hoping for >10. Maybe
>I'll drop the Miller caps to 10pF and see how she sings.
>
>Tim
modest stack of the Zetex SOT23 parts could switch a couple of KV in a
couple of ns.
Winfield Hill
Feb 21, 2017, 2:48:10 PM2/21/17
to
Tim Williams wrote...
You should have two sets of drivers and gate
transformers, one each for high and low sides.
Then you can create an adjustable deadtime.
Another attractive idea: pos/neg pulsing to
turn a set of MOSFETs on or off, with the gate
capacitance storing the state. Combine fast
on/off times with low switching frequencies.
--
Thanks,
- Win
You should have two sets of drivers and gate
transformers, one each for high and low sides.
Then you can create an adjustable deadtime.
Another attractive idea: pos/neg pulsing to
turn a set of MOSFETs on or off, with the gate
capacitance storing the state. Combine fast
on/off times with low switching frequencies.
--
Thanks,
- Win
Winfield Hill
Feb 21, 2017, 2:55:52 PM2/21/17
to
Tim Williams wrote...
Or 1.7kV SiC parts, C2M1000170D, for $5 each.
Skip the transformers, use one TI UCC21520.
--
Thanks,
- Win
>
> Intended application: gate drive V_cm testing.
Why not simplify by using two 1.5kV MOSFETs?
> Intended application: gate drive V_cm testing.
Or 1.7kV SiC parts, C2M1000170D, for $5 each.
Skip the transformers, use one TI UCC21520.
--
Thanks,
- Win
John Larkin
Feb 21, 2017, 3:05:23 PM2/21/17
to
On 21 Feb 2017 11:55:32 -0800, Winfield Hill
DEI/IXYS makes truly insane low-inductance-packaged HV mosfets and
gate drivers. They also have some smaller, affordable gate drivers.
I like to use transmission-line transformers to step up fast edges, to
avoid stacking fets.
--
John Larkin Highland Technology, Inc
picosecond timing precision measurement
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
gate drivers. They also have some smaller, affordable gate drivers.
I like to use transmission-line transformers to step up fast edges, to
avoid stacking fets.
--
John Larkin Highland Technology, Inc
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
John Larkin
Feb 21, 2017, 3:11:38 PM2/21/17
to
On 21 Feb 2017 11:47:50 -0800, Winfield Hill
The old RadLab radar pulsers were cool. They used the stored energy in
a transmission line to make rectangular pulses, with a single switch.
I've made some very pretty pulses with a coax line and avalanche
transistors: very small and simple circuit. I'm thinking one could
merge the pulse storage line with the step-up-transformer function.
I asked about the RadLab books in a technical bookstore near the MIT
campus. They'd never heard of them.
a transmission line to make rectangular pulses, with a single switch.
I've made some very pretty pulses with a coax line and avalanche
transistors: very small and simple circuit. I'm thinking one could
merge the pulse storage line with the step-up-transformer function.
I asked about the RadLab books in a technical bookstore near the MIT
campus. They'd never heard of them.
Winfield Hill
Feb 21, 2017, 4:16:35 PM2/21/17
to
John Larkin wrote...
a guy at Flea at MIT, and gave them to the Institute.
One book specializes in high-power radar pulses.
--
Thanks,
- Win
>
> I asked about the RadLab books in a technical bookstore
> near the MIT campus. They'd never heard of them.
Yes, out of print. I bought the complete set from
> I asked about the RadLab books in a technical bookstore
> near the MIT campus. They'd never heard of them.
a guy at Flea at MIT, and gave them to the Institute.
One book specializes in high-power radar pulses.
--
Thanks,
- Win
Jeroen Belleman
Feb 21, 2017, 4:34:27 PM2/21/17
to
On 21/02/17 21:11, John Larkin wrote:
> On 21 Feb 2017 11:47:50 -0800, Winfield Hill
> <hi...@rowland.harvard.edu> wrote:
>
>> Tim Williams wrote...
>>>
>>> Circuit, for posterity:
>>> https://www.seventransistorlabs.com/Images/High%20Voltage%20Bridge.pdf
>>
>> You should have two sets of drivers and gate
>> transformers, one each for high and low sides.
>> Then you can create an adjustable deadtime.
>>
>> Another attractive idea: pos/neg pulsing to
>> turn a set of MOSFETs on or off, with the gate
>> capacitance storing the state. Combine fast
>> on/off times with low switching frequencies.
>
> The old RadLab radar pulsers were cool. They used the stored energy in
> a transmission line to make rectangular pulses, with a single switch.
> I've made some very pretty pulses with a coax line and avalanche
> transistors: very small and simple circuit. I'm thinking one could
> merge the pulse storage line with the step-up-transformer function.
That's what a Blumlein pulse forming network does, sort-of. The load
> On 21 Feb 2017 11:47:50 -0800, Winfield Hill
> <hi...@rowland.harvard.edu> wrote:
>
>> Tim Williams wrote...
>>>
>>> Circuit, for posterity:
>>> https://www.seventransistorlabs.com/Images/High%20Voltage%20Bridge.pdf
>>
>> You should have two sets of drivers and gate
>> transformers, one each for high and low sides.
>> Then you can create an adjustable deadtime.
>>
>> Another attractive idea: pos/neg pulsing to
>> turn a set of MOSFETs on or off, with the gate
>> capacitance storing the state. Combine fast
>> on/off times with low switching frequencies.
>
> The old RadLab radar pulsers were cool. They used the stored energy in
> a transmission line to make rectangular pulses, with a single switch.
> I've made some very pretty pulses with a coax line and avalanche
> transistors: very small and simple circuit. I'm thinking one could
> merge the pulse storage line with the step-up-transformer function.
gets to see the full charging voltage, rather than half of it.
>
> I asked about the RadLab books in a technical bookstore near the MIT
> campus. They'd never heard of them.
>
>
synthesis of PFNs.
Jeroen Belleman
mrda...@gmail.com
Feb 21, 2017, 6:11:42 PM2/21/17
to
Michael
John Larkin
Feb 21, 2017, 6:24:48 PM2/21/17
to
On 21 Feb 2017 13:16:14 -0800, Winfield Hill
It took me years to collect the full set, not cosmetically matched.
Great stuff.
Great stuff.
Tim Williams
Feb 21, 2017, 10:45:40 PM2/21/17
to
"Winfield Hill" <hi...@rowland.harvard.edu> wrote in message
news:o8i5v...@drn.newsguy.com...
> Why not simplify by using two 1.5kV MOSFETs?
> Or 1.7kV SiC parts, C2M1000170D, for $5 each.
> Skip the transformers, use one TI UCC21520.
1. Had 'em on hand.
> Or 1.7kV SiC parts, C2M1000170D, for $5 each.
> Skip the transformers, use one TI UCC21520.
2. Hadn't done a stack before. Seems to work pretty well, even with the
crappy drive!
Tim Williams
Feb 21, 2017, 10:51:12 PM2/21/17
to
"John Larkin" <jjla...@highlandtechnology.com> wrote in message
news:3tnoacd1vfrgrlgb6...@4ax.com...
> Another way to get insane edge speeds is avalanche transistors. A
> modest stack of the Zetex SOT23 parts could switch a couple of KV in a
> couple of ns.
Yup, though not too much current before life expectancy plummets. I can't
> modest stack of the Zetex SOT23 parts could switch a couple of KV in a
> couple of ns.
imagine it's too easy connecting them in parallel either (yes, they can be
triggered, with reasonable jitter, but that's a lot more bother).
I did a minor study of transistors I have laying around; few did not exhibit
latching avalanche discharge, but many were finicky (the region of base
resistance vs. collector current for pulsing behavior was small, and
inconsistent between samples). None really seemed to be more powerful and
faster than the usual tiny suspects (like 2N3904).
Avalanche also spreads out poorly -- so a very large transistor (like a 15A
1500V HOT) only 'ignites' in some random spot location, and becomes damaged
at basically the same surge current as a 2N3904. (Afterwards, instead of
collector leakage, there's C-E resistance, usually on the order of 40kohms.
Characteristic of a microscopic burn hole.)
Tim Williams
Feb 21, 2017, 10:53:43 PM2/21/17
to
<mrda...@gmail.com> wrote in message
news:21c519f7-9b06-4b72...@googlegroups.com...
No, Altium. The real deal. ;-)
(You might recognize some shapes and default colors from Win's drawings as
well; he uses an old copy of Protel, IIRC. The ground symbols haven't
changed a pixel!)
news:21c519f7-9b06-4b72...@googlegroups.com...
> Nice! Did you draw this with Autodesk's Inventor?
>
GAH! Choke!
>
No, Altium. The real deal. ;-)
(You might recognize some shapes and default colors from Win's drawings as
well; he uses an old copy of Protel, IIRC. The ground symbols haven't
changed a pixel!)
Tim Williams
Feb 21, 2017, 11:05:16 PM2/21/17
to
"John Larkin" <jjlark...@highlandtechnology.com> wrote in message
news:ic7pacphaoie5kcv7...@4ax.com...
(civil, ATC I think). He's got a handful of hydrogen thyratrons and hard
glass modulators (transmitter tetrodes, with fucking huge cathodes) from it.
We've been thinking about pulse generator applications, like making a
retro-high-tech Tesla coil.
I suspect they use hydrogen thyratrons in EFT generators, but I've not taken
one apart.
Some day, I'd like to design and build an EFT tester, just because. But
getting a hydrogen thyratron would be too easy, and not really all that
helpful. I'd rather do it with an IGBT and shock line: could be very cheap
and highly available, only needing custom wound inductors (saturable
reactors, really). Don't know how easy it will be to adjust to make a clean
pulse, though...
news:ic7pacphaoie5kcv7...@4ax.com...
> The old RadLab radar pulsers were cool. They used the stored energy in
> a transmission line to make rectangular pulses, with a single switch.
> I've made some very pretty pulses with a coax line and avalanche
> transistors: very small and simple circuit. I'm thinking one could
> merge the pulse storage line with the step-up-transformer function.
A friend of mine has been taking apart some modest-vintage radar equipment
> a transmission line to make rectangular pulses, with a single switch.
> I've made some very pretty pulses with a coax line and avalanche
> transistors: very small and simple circuit. I'm thinking one could
> merge the pulse storage line with the step-up-transformer function.
(civil, ATC I think). He's got a handful of hydrogen thyratrons and hard
glass modulators (transmitter tetrodes, with fucking huge cathodes) from it.
We've been thinking about pulse generator applications, like making a
retro-high-tech Tesla coil.
I suspect they use hydrogen thyratrons in EFT generators, but I've not taken
one apart.
Some day, I'd like to design and build an EFT tester, just because. But
getting a hydrogen thyratron would be too easy, and not really all that
helpful. I'd rather do it with an IGBT and shock line: could be very cheap
and highly available, only needing custom wound inductors (saturable
reactors, really). Don't know how easy it will be to adjust to make a clean
pulse, though...
Tim Williams
Feb 21, 2017, 11:12:38 PM2/21/17
to
"Winfield Hill" <hi...@rowland.harvard.edu> wrote in message
news:o8i5h...@drn.newsguy.com...
> You should have two sets of drivers and gate
> transformers, one each for high and low sides.
> Then you can create an adjustable deadtime.
>
> Another attractive idea: pos/neg pulsing to
> turn a set of MOSFETs on or off, with the gate
> capacitance storing the state. Combine fast
> on/off times with low switching frequencies.
What you can't see about the driver is, I've already done that. :) It's
> transformers, one each for high and low sides.
> Then you can create an adjustable deadtime.
>
> Another attractive idea: pos/neg pulsing to
> turn a set of MOSFETs on or off, with the gate
> capacitance storing the state. Combine fast
> on/off times with low switching frequencies.
actually an astable driving a pair of monostables driving a pair of gate
driver ICs (TC4420). So, one side pulses up, other side stays down; other
side pulses up, one side stays down; etc. Pulse width is ~2.5us, repeat
frequency low ~kHz.
Output is square-ish as long as it's dominant capacitive. At low
frequencies, the 10M probe bleeds it down, of course, leaving a rounded
wave.
John Larkin
Feb 21, 2017, 11:44:25 PM2/21/17
to
On Tue, 21 Feb 2017 21:51:06 -0600, "Tim Williams"
<tiw...@seventransistorlabs.com> wrote:
>"John Larkin" <jjla...@highlandtechnology.com> wrote in message
>news:3tnoacd1vfrgrlgb6...@4ax.com...
>> Another way to get insane edge speeds is avalanche transistors. A
>> modest stack of the Zetex SOT23 parts could switch a couple of KV in a
>> couple of ns.
>
>Yup, though not too much current before life expectancy plummets. I can't
>imagine it's too easy connecting them in parallel either (yes, they can be
>triggered, with reasonable jitter, but that's a lot more bother).
>
They seem to have good lifetimes. You can't fire an avalanche stack at
<tiw...@seventransistorlabs.com> wrote:
>"John Larkin" <jjla...@highlandtechnology.com> wrote in message
>news:3tnoacd1vfrgrlgb6...@4ax.com...
>> Another way to get insane edge speeds is avalanche transistors. A
>> modest stack of the Zetex SOT23 parts could switch a couple of KV in a
>> couple of ns.
>
>Yup, though not too much current before life expectancy plummets. I can't
>imagine it's too easy connecting them in parallel either (yes, they can be
>triggered, with reasonable jitter, but that's a lot more bother).
>
a very high rate!
There is a Zetex appnote about using them in series and parallel. The
cool thing about a series stack is that a small pulse, TTL class, can
trigger the bottom one, and the whole stack zippers.
>I did a minor study of transistors I have laying around; few did not exhibit
>latching avalanche discharge, but many were finicky (the region of base
>resistance vs. collector current for pulsing behavior was small, and
>inconsistent between samples). None really seemed to be more powerful and
>faster than the usual tiny suspects (like 2N3904).
>
>Avalanche also spreads out poorly -- so a very large transistor (like a 15A
>1500V HOT) only 'ignites' in some random spot location, and becomes damaged
>at basically the same surge current as a 2N3904. (Afterwards, instead of
>collector leakage, there's C-E resistance, usually on the order of 40kohms.
>Characteristic of a microscopic burn hole.)
probably on an ancient diffusion line. They have really low Fts, like
40 MHz, which good avalanche transistors seem to.
Tim Williams
Feb 21, 2017, 11:47:44 PM2/21/17
to
Aaaand...it's dead. Oh well, fun while it lasted. :^)
https://www.seventransistorlabs.com/Images/HighVoltageBridge2.jpg
No visible damage, but the three high side are ~shorted.
Just a show of the last version: 10pF Miller caps, which kicked dV/dt up to
17k/us or thereabouts (that's 100ns at 1.7kV).
Tried 220 ohm damper resistors in series with the 10p's, but that wasn't
actually helpful/useful (actually, may've been harmful? no idea). (The
ringing was something else.)
Ferrite beads (type #31) on the gates, and then bigger ones on the gate
drive pairs (emphasis on the middle ones, because, guess why!), fixed the
100-400MHz screaming pretty nicely, as confirmed by near-field loop
"sniffer".
I realized early on, my conspicuous lack of high voltage, wideband probes...
well, that won't do.
So....I know!
https://www.seventransistorlabs.com/Images/HighVoltageProbe.jpg
10 x 1M 0805, in parallel with (20p + 487), and then 110k || (varicap +
49.9) at the bottom. Requires 1 meter coax and 15pF || 1M scope.
Probe circuits are traditionally drawn with "speed up caps" across the
divider resistors, and nothing else, but that's dumb. It's an impedance
equalizer, going from ~megs at DC, down to whatever the transmission line
ratio needs to be at HF. It looks like a capacitor at middle frequencies,
and a resistor (of one value or the other) at the asymptotes. In this case,
100:1 into 50 ohms is 5k, and 5k/10 is 500, so the distributed resistors are
500 ish.
Failure to observe the correct design process results in heavily ringing
waveforms (the coax is shorted by caps at either end, so resonates like an
inductor), and in mistakes, like having to solder your resistors in
after-the-fact in a layout that wasn't made to fit them. :-)
Tim
--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com
"Tim Williams" <tiw...@seventransistorlabs.com> wrote in message
news:o8egdp$65c$1...@dont-email.me...
https://www.seventransistorlabs.com/Images/HighVoltageBridge2.jpg
No visible damage, but the three high side are ~shorted.
Just a show of the last version: 10pF Miller caps, which kicked dV/dt up to
17k/us or thereabouts (that's 100ns at 1.7kV).
Tried 220 ohm damper resistors in series with the 10p's, but that wasn't
actually helpful/useful (actually, may've been harmful? no idea). (The
ringing was something else.)
Ferrite beads (type #31) on the gates, and then bigger ones on the gate
drive pairs (emphasis on the middle ones, because, guess why!), fixed the
100-400MHz screaming pretty nicely, as confirmed by near-field loop
"sniffer".
I realized early on, my conspicuous lack of high voltage, wideband probes...
well, that won't do.
So....I know!
https://www.seventransistorlabs.com/Images/HighVoltageProbe.jpg
10 x 1M 0805, in parallel with (20p + 487), and then 110k || (varicap +
49.9) at the bottom. Requires 1 meter coax and 15pF || 1M scope.
Probe circuits are traditionally drawn with "speed up caps" across the
divider resistors, and nothing else, but that's dumb. It's an impedance
equalizer, going from ~megs at DC, down to whatever the transmission line
ratio needs to be at HF. It looks like a capacitor at middle frequencies,
and a resistor (of one value or the other) at the asymptotes. In this case,
100:1 into 50 ohms is 5k, and 5k/10 is 500, so the distributed resistors are
500 ish.
Failure to observe the correct design process results in heavily ringing
waveforms (the coax is shorted by caps at either end, so resonates like an
inductor), and in mistakes, like having to solder your resistors in
after-the-fact in a layout that wasn't made to fit them. :-)
Tim
--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com
news:o8egdp$65c$1...@dont-email.me...
John Larkin
Feb 21, 2017, 11:49:10 PM2/21/17
to
Krytron!
https://dl.dropboxusercontent.com/u/53724080/Tubes/Kry_Danger.jpg
--
John Larkin Highland Technology, Inc
Tim Williams
Feb 22, 2017, 12:05:28 AM2/22/17
to
"John Larkin" <jjla...@highlandtechnology.com> wrote in message
news:md5qac1s0ekk8j5vi...@4ax.com...
> They seem to have good lifetimes. You can't fire an avalanche stack at
> a very high rate!
You maybe. I've blasted a 2N3904 at 100kHz. :)
> a very high rate!
And I said with current. This is in the spec sheet too: you don't get too
many peak kilowatts, before the life curve goes from "she'll outlive me" to
"you have one second of run time, better make it important".
> There is a Zetex appnote about using them in series and parallel. The
> cool thing about a series stack is that a small pulse, TTL class, can
> trigger the bottom one, and the whole stack zippers.
you have the problem of current. Any transmission line you hang on the
output is going to be hundreds of ohms, and after a few kV, you get into
transistor-popping currents, no problem.
And then the problem spirals geometrically out of control.
To make something like IEC 61000-4-4 EFT, you need about a hundred of the
poor things, in series-parallel. Such an innocent noise signal -- but it's
brutally spiky.
> The Zetex parts are designed to avalanche. They are made in Russia,
> probably on an ancient diffusion line. They have really low Fts, like
> 40 MHz, which good avalanche transistors seem to.
ancient diffusion lines (or maybe some epitaxy too).
That at least leaves some HOTs useful for SRD, as you've found.
Tim Williams
Feb 22, 2017, 12:06:09 AM2/22/17
to
"John Larkin" <jjla...@highlandtechnology.com> wrote in message
news:2v5qactcbg6qhmcqf...@4ax.com...
Much shorter lifetime -- though, in their intended use, a slightly bigger
bang. ;D
Clifford Heath
Feb 22, 2017, 1:24:02 AM2/22/17
to
On 22/02/17 16:05, Tim Williams wrote:
> "John Larkin" <jjla...@highlandtechnology.com> wrote in message
> news:md5qac1s0ekk8j5vi...@4ax.com...
>> They seem to have good lifetimes. You can't fire an avalanche stack at
>> a very high rate!
>
> You maybe. I've blasted a 2N3904 at 100kHz. :)
Find that appnote Tim. They'll avalanche 60A/20ns for >10E11 cycles.
> "John Larkin" <jjla...@highlandtechnology.com> wrote in message
> news:md5qac1s0ekk8j5vi...@4ax.com...
>> They seem to have good lifetimes. You can't fire an avalanche stack at
>> a very high rate!
>
> You maybe. I've blasted a 2N3904 at 100kHz. :)
See e.g.
<http://datasheet.octopart.com/FMMT415TD-Zetex-datasheet-8374939.pdf>
Clifford Heath.
mrda...@gmail.com
Feb 22, 2017, 1:35:22 AM2/22/17
to
On Tuesday, February 21, 2017 at 7:53:43 PM UTC-8, Tim Williams wrote:
> <mrda...@gmail.com> wrote in message
> news:21c519f7-9b06-4b72...@googlegroups.com...
> > Nice! Did you draw this with Autodesk's Inventor?
> >
>
> GAH! Choke!
>
> No, Altium. The real deal. ;-)
>
> (You might recognize some shapes and default colors from Win's drawings as
> well; he uses an old copy of Protel, IIRC. The ground symbols haven't
> changed a pixel!)
>
> Tim
>
Oh, nice! I'll have to check Altium out. :)
> <mrda...@gmail.com> wrote in message
> news:21c519f7-9b06-4b72...@googlegroups.com...
> > Nice! Did you draw this with Autodesk's Inventor?
> >
>
> GAH! Choke!
>
> No, Altium. The real deal. ;-)
>
> (You might recognize some shapes and default colors from Win's drawings as
> well; he uses an old copy of Protel, IIRC. The ground symbols haven't
> changed a pixel!)
>
> Tim
>
Your schematic looked a bit Inventorish. I took an AutoCAD class at the junior college last year, and the prof also made us use Inventor a few times. I found it a bit cumbersome, and I just preferred AutoCAD.
Thanks,
Michael
Tim Williams
Feb 22, 2017, 4:10:01 AM2/22/17
to
"Clifford Heath" <no....@please.net> wrote in message
news:58ad2e7b$0$32564$b1db1813$19ac...@news.astraweb.com...
width -- returning to the 61000-4-4 example, the nominal pulse width is
50ns, but that's only to the 50% level of an exponential decay. Diodes Inc.
defines pulse width as half-cycle sinusoid,
https://www.diodes.com/diodes-part-files/DJ/FMMT417/Application%20Notes/201342.pdf
so the equivalent duration would probably be even longer (100ns?).
That simple hyperbola seems to suggest a deeper truth: that the conductive
channel has constant voltage drop, and the delivered energy needs to be
limited to a constant.
Let's see. If the curve is an exponential decay, with a half-life of 50ns,
then the time constant is 72ns, and the total area under the curve, divided
by the amplitude, is simply the time constant. So it's more than 50ns, but
less than 100 at least, not quite as bad as I had been thinking.
There is quite a large disparity between the "no failure" and modest-life
curves. For this curve, it's about 16A vs. 60A.
Which would be switching impedances of 19 ohms, and 5 ohms respectively,
which is pretty damn low! And, a stack of ten gets you 3kV into 50 ohms --
supplying up to 10 hours of continuous EFT duty!
Not as bad as I remember calculating before.
Still, if you need long life, the point about parallel strings stands --
that's a ~4x reduction in load current, so you need a four strings of ten to
switch it.
news:58ad2e7b$0$32564$b1db1813$19ac...@news.astraweb.com...
> Find that appnote Tim. They'll avalanche 60A/20ns for >10E11 cycles.
> See e.g.
> <http://datasheet.octopart.com/FMMT415TD-Zetex-datasheet-8374939.pdf>
>
2N3904 likely isn't as robust, but also, notice how much it drops with pulse
> See e.g.
> <http://datasheet.octopart.com/FMMT415TD-Zetex-datasheet-8374939.pdf>
>
width -- returning to the 61000-4-4 example, the nominal pulse width is
50ns, but that's only to the 50% level of an exponential decay. Diodes Inc.
defines pulse width as half-cycle sinusoid,
https://www.diodes.com/diodes-part-files/DJ/FMMT417/Application%20Notes/201342.pdf
so the equivalent duration would probably be even longer (100ns?).
That simple hyperbola seems to suggest a deeper truth: that the conductive
channel has constant voltage drop, and the delivered energy needs to be
limited to a constant.
Let's see. If the curve is an exponential decay, with a half-life of 50ns,
then the time constant is 72ns, and the total area under the curve, divided
by the amplitude, is simply the time constant. So it's more than 50ns, but
less than 100 at least, not quite as bad as I had been thinking.
There is quite a large disparity between the "no failure" and modest-life
curves. For this curve, it's about 16A vs. 60A.
Which would be switching impedances of 19 ohms, and 5 ohms respectively,
which is pretty damn low! And, a stack of ten gets you 3kV into 50 ohms --
supplying up to 10 hours of continuous EFT duty!
Not as bad as I remember calculating before.
Still, if you need long life, the point about parallel strings stands --
that's a ~4x reduction in load current, so you need a four strings of ten to
switch it.
Winfield Hill
Feb 22, 2017, 7:59:11 AM2/22/17
to
Tim Williams wrote...
However my PCB engineer, Chuck Fisk, who
retired a few years ago, stayed with Protel.
Re: colors, I'm constantly honing my choice.
I dislike Altium's default ground symbol,
but haven't figured out how to change it.
--
Thanks,
- Win
>
> (You might recognize some shapes and default
> colors from Win's drawings as well; he uses
> an old copy of Protel, IIRC. The ground
> symbols haven't changed a pixel!)
No, I use the latest rev of Altium Designer.
> (You might recognize some shapes and default
> colors from Win's drawings as well; he uses
> an old copy of Protel, IIRC. The ground
> symbols haven't changed a pixel!)
However my PCB engineer, Chuck Fisk, who
retired a few years ago, stayed with Protel.
Re: colors, I'm constantly honing my choice.
I dislike Altium's default ground symbol,
but haven't figured out how to change it.
--
Thanks,
- Win
Winfield Hill
Feb 22, 2017, 8:07:52 AM2/22/17
to
Tim Williams wrote...
is going off, can create a damaging rail-rail
shoot-through. The shoot-through name refers to
fast hidden high-current spikes. High di/dt means
high V = L di/dt voltage spikes, blow out gates.
--
Thanks,
- Win
>
>Aaaand...it's dead. Oh well, fun while it lasted. :^)
>
>https://www.seventransistorlabs.com/Images/HighVoltageBridge2.jpg
Remember my advice:
>Aaaand...it's dead. Oh well, fun while it lasted. :^)
>
>https://www.seventransistorlabs.com/Images/HighVoltageBridge2.jpg
"You should have two sets of drivers and gate
transformers, one each for high and low sides.
Then you can create an adjustable deadtime."
Switching one side on at the same time the other
transformers, one each for high and low sides.
Then you can create an adjustable deadtime."
is going off, can create a damaging rail-rail
shoot-through. The shoot-through name refers to
fast hidden high-current spikes. High di/dt means
high V = L di/dt voltage spikes, blow out gates.
--
Thanks,
- Win
John Larkin
Feb 22, 2017, 3:19:02 PM2/22/17
to
pulses that were some fraction of the supply voltage, half maybe. The
Zetex things really turn on basically saturate, when they fire.
--
John Larkin Highland Technology, Inc
dagmarg...@yahoo.com
Feb 22, 2017, 4:43:42 PM2/22/17
to
https://www.diodes.com/diodes-part-files/DJ/FMMT415/Application%20Notes/201342.pdf
Cheers,
James Arthur
whit3rd
Feb 22, 2017, 4:49:01 PM2/22/17
to
On Wednesday, February 22, 2017 at 5:07:52 AM UTC-8, Winfield Hill wrote:
> Tim Williams wrote...
> >
> >Aaaand...it's dead. Oh well, fun while it lasted. :^)
> Tim Williams wrote...
> >
> >Aaaand...it's dead. Oh well, fun while it lasted. :^)
> Switching one side on at the same time the other
> is going off, can create a damaging rail-rail
> shoot-through. The shoot-through name refers to
> fast hidden high-current spikes. High di/dt means
> high V = L di/dt voltage spikes, blow out gates.
High enough di/dt will also blow up wires.
> is going off, can create a damaging rail-rail
> shoot-through. The shoot-through name refers to
> fast hidden high-current spikes. High di/dt means
> high V = L di/dt voltage spikes, blow out gates.
I've seen metal-case transistors lose internal wiring that way.
Tim Williams
Feb 23, 2017, 12:43:28 AM2/23/17
to
"John Larkin" <jjlark...@highlandtechnology.com> wrote in message
news:desracla2tdbn14t5...@4ax.com...
> Avalanching old 2nXXXX parts, like in the old Tek samplers, gave
> pulses that were some fraction of the supply voltage, half maybe. The
> Zetex things really turn on basically saturate, when they fire.
My experience with 2N3904 is it's about 10 ohms "on", which squares more or
> pulses that were some fraction of the supply voltage, half maybe. The
> Zetex things really turn on basically saturate, when they fire.
less with typical data on RC and RE. Given that those parameters will be a
bit lower due to the huge charge injection.
Recovery time is about 5-10us.
Tim Williams
Feb 23, 2017, 12:55:31 AM2/23/17
to
"Winfield Hill" <hi...@rowland.harvard.edu> wrote in message
news:o8k1u...@drn.newsguy.com...
> No, I use the latest rev of Altium Designer.
> However my PCB engineer, Chuck Fisk, who
> retired a few years ago, stayed with Protel.
> Re: colors, I'm constantly honing my choice.
> I dislike Altium's default ground symbol,
> but haven't figured out how to change it.
Put your vote in:
> However my PCB engineer, Chuck Fisk, who
> retired a few years ago, stayed with Protel.
> Re: colors, I'm constantly honing my choice.
> I dislike Altium's default ground symbol,
> but haven't figured out how to change it.
https://bugcrunch.live.altium.com/#Idea/2728
If it gets enough votes, they'll implement it. Maybe. Next decade...
I like the default colors well enough, but the libraries are horribly ugly.
So I've got my libraries with everything drawn the way I like.
I've taken to making discretes shaded light blue, and ICs yellow, using
descriptive symbols or pinouts where possible. (So TL431 is a yellow blob
with a zenery symbol inside, suggesting its dual nature of transistorishness
and ICness.)
https://www.seventransistorlabs.com/Images/Altium_Parts.png
https://www.seventransistorlabs.com/Images/Altium_LEDs.png
https://www.seventransistorlabs.com/Images/AltiumIndTap.png
Here's a very discrete schematic...
https://www.seventransistorlabs.com/Images/TubeCCS2.png
I also rather like making shiny 3D models, though it's a pretty bad way to
create them. I tend not to put in quite this much detail, unless I'm doing
it on my own time.
https://www.seventransistorlabs.com/Images/AltiumPRQ.png
Tim Williams
Feb 23, 2017, 1:13:09 AM2/23/17
to
"Winfield Hill" <hi...@rowland.harvard.edu> wrote in message
news:o8k2e...@drn.newsguy.com...
> Remember my advice:
> "You should have two sets of drivers and gate
> transformers, one each for high and low sides.
> Then you can create an adjustable deadtime."
>
> Switching one side on at the same time the other
> is going off, can create a damaging rail-rail
> shoot-through. The shoot-through name refers to
> fast hidden high-current spikes. High di/dt means
> high V = L di/dt voltage spikes, blow out gates.
Like I said, the dead time is huge -- it's driven with a short pulse, then
> "You should have two sets of drivers and gate
> transformers, one each for high and low sides.
> Then you can create an adjustable deadtime."
>
> Switching one side on at the same time the other
> is going off, can create a damaging rail-rail
> shoot-through. The shoot-through name refers to
> fast hidden high-current spikes. High di/dt means
> high V = L di/dt voltage spikes, blow out gates.
zero, then an opposite pulse, then zero. There's no opportunity for
shoot-through. It also helps that the off-side gets reverse bias at the
same time, increasing the noise margin even further!
Still, because of dV/dt, and because of common mode coupling in the
transformer, it might be the problem. Dunno. (But if that's the case, then
splitting the transformer would actually make it worse, because of the lack
of reverse bias. Hmm.)
Measuring the actual gate waveforms, accurately, is unlikely to succeed, so
it's hard to do more than speculate...
Tim Williams
Feb 23, 2017, 1:14:20 AM2/23/17
to
"whit3rd" <whi...@gmail.com> wrote in message
news:14e29d28-92c6-47af...@googlegroups.com...
(Exploding bridgewire, and slapper: supposedly these are used to ignite the
charge. The limited availability of JL's krytron seems to corroborate this
well enough, as do other available documents.)
news:14e29d28-92c6-47af...@googlegroups.com...
> High enough di/dt will also blow up wires.
> I've seen metal-case transistors lose internal wiring that way.
I've seen nuclear bombs lose internal wiring that way. :^)
> I've seen metal-case transistors lose internal wiring that way.
(Exploding bridgewire, and slapper: supposedly these are used to ignite the
charge. The limited availability of JL's krytron seems to corroborate this
well enough, as do other available documents.)
Tim Williams
Feb 27, 2017, 7:01:35 AM2/27/17
to
"John Larkin" <jjla...@highlandtechnology.com> wrote in message
news:md5qac1s0ekk8j5vi...@4ax.com...
> They seem to have good lifetimes. You can't fire an avalanche stack at
> a very high rate!
>
> There is a Zetex appnote about using them in series and parallel. The
> cool thing about a series stack is that a small pulse, TTL class, can
> trigger the bottom one, and the whole stack zippers.
Incidentally, I picked up some of the cheaper (not quite) alternative,
> a very high rate!
>
> There is a Zetex appnote about using them in series and parallel. The
> cool thing about a series stack is that a small pulse, TTL class, can
> trigger the bottom one, and the whole stack zippers.
FZT857. Rated for 350V, but this one actually snaps beyond 550V!
Seems to avalanche consistently, though appears to have 11.3 ohms ESR when
"on".
Output waveform is interesting, and I don't think it's due to circuit
parasitics (I've got a big fat 1.5nF silver mica on there, so it's not
without stray L).
Circuit is: +HV -- 100k charging resistor -- 1.5nF to GND -- FZT857 (C to
E) -- 50 ohm BNC (terminated). There's 2.2k B-E to make it click.
Rise time is 6ns, up to a plateau at 420V for 14ns. (Vce starts at 580V
before breakdown, so the transistor is dropping a lot of voltage and current
during this time.) Time constant is 92ns, suggesting 61.3 ohm loop
resistance, 50 of which is the termination, so the transistor appears to
account for about 11 ohms.
Recovery (recombination) time about 30us. Varies with size of the pulse
(i.e., size of capacitor).
...
Oh, scratch that... it seems I broke it. It's still avalanching, but now
it's doing it at 440V. I wonder if the plateau is not so much a "buildup"
phase, but a "she can't take anymore o' dis, captain" phase, that causes
damage. (Can semiconductors run out charges to free, so the current
saturates?)
I'm sure a large part of the cost, of the FMMT417s, is just aging. Remember
back in the days when the manufacturers had huge racks of toobs glowing
away? Yeah, like that...
Michael A. Terrell
Feb 27, 2017, 8:14:45 AM2/27/17
to
John Larkin wrote:
> On 21 Feb 2017 11:47:50 -0800, Winfield Hill
> <hi...@rowland.harvard.edu> wrote:
>
>> Tim Williams wrote...
format. Download them for free!
--
Never piss off an Engineer!
They don't get mad.
They don't get even.
They go for over unity! ;-)
> On 21 Feb 2017 11:47:50 -0800, Winfield Hill
> <hi...@rowland.harvard.edu> wrote:
>
>> Tim Williams wrote...
>>>
>>> Circuit, for posterity:
>>> https://www.seventransistorlabs.com/Images/High%20Voltage%20Bridge.pdf
>>
>>> Circuit, for posterity:
>>> https://www.seventransistorlabs.com/Images/High%20Voltage%20Bridge.pdf
>>
>> You should have two sets of drivers and gate
>> transformers, one each for high and low sides.
>> Then you can create an adjustable deadtime.
>>
>> transformers, one each for high and low sides.
>> Then you can create an adjustable deadtime.
>>
>> Another attractive idea: pos/neg pulsing to
>> turn a set of MOSFETs on or off, with the gate
>> capacitance storing the state. Combine fast
>> on/off times with low switching frequencies.
>
>> turn a set of MOSFETs on or off, with the gate
>> capacitance storing the state. Combine fast
>> on/off times with low switching frequencies.
>
> The old RadLab radar pulsers were cool. They used the stored energy in
> a transmission line to make rectangular pulses, with a single switch.
> I've made some very pretty pulses with a coax line and avalanche
> transistors: very small and simple circuit. I'm thinking one could
> merge the pulse storage line with the step-up-transformer function.
>
> a transmission line to make rectangular pulses, with a single switch.
> I've made some very pretty pulses with a coax line and avalanche
> transistors: very small and simple circuit. I'm thinking one could
> merge the pulse storage line with the step-up-transformer function.
>
> I asked about the RadLab books in a technical bookstore near the MIT
> campus. They'd never heard of them.
http://www.nj7p.org/Manuals/Radio_books.php Has all of the books in PDF
> campus. They'd never heard of them.
format. Download them for free!
--
Never piss off an Engineer!
They don't get mad.
They don't get even.
They go for over unity! ;-)
Steve Wilson
Mar 21, 2017, 1:47:11 AM3/21/17
to
>> I asked about the RadLab books in a technical bookstore near the MIT
>> campus. They'd never heard of them.
>
>> campus. They'd never heard of them.
>
> Yes, out of print. I bought the complete set from
> a guy at Flea at MIT, and gave them to the Institute.
> One book specializes in high-power radar pulses.
The entire series is available here in text searchable pdf's
> a guy at Flea at MIT, and gave them to the Institute.
> One book specializes in high-power radar pulses.
https://www.febo.com/pages/docs/RadLab/
Many of the photos are not very good.
0 new messages