IGBTs are pretty fast
Tim Williams
http://webpages.charter.net/dawill/Images/Induction720.jpg
http://webpages.charter.net/dawill/Images/Induction721.jpg
Since there were no objections (..or encouragements..) to the proposed
arrangement, '719 is the bridge as I've reassembled it.
'720 is the output voltage and current waveform. Note this is at 120-130VDC
supply, and 29kHz or so (some amount before resonance around 21kHz).
I like these transistors more than the MOSFETs in that you can see the
discrete transistion as current passes through zero; the transistor won't
conduct backwards, so the reverse drop will always be that of the co-packed
FRED. Likewise, the forward bias is always a couple diode drops.
'721 is the rise and fall time of the output. 2.5V/ns is pretty good for
something this chunky.
On the left of this oscillograph, you can see a small dip, which I suspect
is miller capacitance. The gate fall respectively has a small blip on it as
it passes around zero. About 280ns after, Ic falls and Vc swings
completely in about 50ns.
When the FRED turns on, it clamps with about 10V of bounce that rings around
8MHz (t ~ 120ns), plus a lower harmonic. This sounds reasonable compared to
the published resonance frequency of the closest bypass caps of ~10MHz.
Any objections, comments, suggested measurements/conditions before I move on
to 200V supply?
Tim
--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Terry Given
- can you show a picture of the gate waveform, measured at the igbt?
- the output voltage waveform looks like it has a 100V spike on the
rising edge. can you zoom in on that?
- can u take a pic of your scope probe setup? that spike might not be
there....at these low voltages, use a coax scope probe tip adaptor, a
BNC socket an a short length of tightly twisted wire, soldered directly
across G-E or C-E.
- how far away is your gate drive setup? put it as close as possible
(creepage/clearance notwithstanding) to the IGBTs.
- your DC bus inductance is on the order of 500nH or so. if you get a
couple of pieces of double-sided Cu-clad PCB, and some 1mm nomex/lexan
you can make a DIY multi-layer PCB. just folding your existing assembly
flat would make a large difference.
how fast is your scope? whats its rise-time spec?
Cheers
Terry
Winfield Hill
>
>> I like these transistors more than the MOSFETs in that you can
>> transistor won't conduct backwards, so the reverse drop will
>> always be that of the co-packed FRED. Likewise, the forward
>> bias is always a couple diode drops.
That may be an attractive debugging tool, but it's far better to
have the reverse current flow through a conducting FET channel
than a diode with its reverse-recovery delay and snapoff after
shutoff. Unfortunately at high currents and voltages, MOSFETs
simply cannot keep pace with IGBTs in conductance capabilities.
That's why you will find them in this type of application.
--
Thanks,
- Win
Tim Williams
news:drp7b...@drn.newsguy.com...
> That may be an attractive debugging tool, but it's far better to
> have the reverse current flow through a conducting FET channel
> than a diode with its reverse-recovery delay and snapoff after
> shutoff.
As in junction charge stuff? Wouldn't that just subtract from the load
current, making it transition a little slower?
Saturation and diode voltages are both within +/-2V, even 1V around current
zero crossing. I see no harm in having a particularly slow recovery, as
long as it's fully recovered by the time it has to switch off.
> Unfortunately at high currents and voltages, MOSFETs
> simply cannot keep pace with IGBTs in conductance capabilities.
Yeah, so, when reverse-biased with a good 50A or so, there's going to be
diode conduction one way or the other, it doesn't really matter if there's
[reverse] current in the FET junction.
Which reminds me, if these IGBTs don't behave, I'm just going to buy a pair
of 600V FETs from Digikey (STW70NM60 looks pretty reasonable, and has low
enough Ron that I can even use my current desat circuit). So what if it'll
cost me three percentage points efficiency, it'll *work*...
Tim Williams
news:1138754474.466290@ftpsrv1...
> - can you show a picture of the gate waveform, measured at the igbt?
Sure.
http://webpages.charter.net/dawill/Images/IGBTWaveform4.jpg
5V/div vert, 2us/div horiz, waveform before gate resistors.
http://webpages.charter.net/dawill/Images/IGBTWaveform1.jpg
Ditto, waveform at gate.
Spikes are:
http://webpages.charter.net/dawill/Images/IGBTWaveform2.jpg
http://webpages.charter.net/dawill/Images/IGBTWaveform3.jpg
Same vertical; 200ns/div horiz. (at gate).
Note the spikes coincide with output voltage transitions, but are of the
wrong polarity with respect to voltage. (In #2, gate voltage is falling,
but the pulse starts negative whereas output is rising.) Thus I took a pic
of the emitter waveform, about 1mm from the package.
http://webpages.charter.net/dawill/Images/IGBTWaveform5.jpg
(Same phase, time and voltage scales as #1 and 4.)
Period is around 150ns for the pulse, i.e. 6.7MHz.
Incidentially, though the pulse appears on the transistor end of the gate
drive lines, the circuit side is clean. Alright, so I'll get some PCB and
solder up the drive circuitses...
> - the output voltage waveform looks like it has a 100V spike on the
> rising edge. can you zoom in on that?
That's from the current waveform. '721 is the output waveform zoomed,
showing about 20V overshoot.
> - can u take a pic of your scope probe setup? that spike might not be
> there....at these low voltages, use a coax scope probe tip adaptor, a
> BNC socket an a short length of tightly twisted wire, soldered directly
> across G-E or C-E.
The current transformer is a black ferrite toroid (probably high mu) with
quadfilar wound 26AWG totalling 280T (4 x 70T in series), and a 2.8 ohm load
resistor. Twisted pair leads back to the scope, with a few turns around a
ferrite bead for good luck. (I know, the CT is floating, and hanging on the
ground lead, so it shouldn't pick up much ground loop style hash that a
ferrite bead would be used for, but so what.)
The output waveform is measured with my 10x Tek probe clipped to the output
terminal at the DC side of the coupling capacitor.
> - how far away is your gate drive setup? put it as close as possible
> (creepage/clearance notwithstanding) to the IGBTs.
Not very healthy then... about 12". I do have twisted pair, which is a
Transmission Line(tm), though..
> - your DC bus inductance is on the order of 500nH or so.
How can that be? The 0.1 caps are an inch from any transistor, and all
together should be on the order of 100-200nH.
> if you get a
> couple of pieces of double-sided Cu-clad PCB, and some 1mm nomex/lexan
> you can make a DIY multi-layer PCB. just folding your existing assembly
> flat would make a large difference.
So the strips are flat with the heatsink y'mean?
> how fast is your scope? whats its rise-time spec?
SFA. The output waveform has no difference vs. vertical bandwidth
(switchable 20/100/200MHz). The oscillographs were taken at 100MHz. All
the same, it is spec'd at 1.8ns or so.
Terry Given
> "Terry Given" <my_...@ieee.org> wrote in message
> news:1138754474.466290@ftpsrv1...
>
>>- can you show a picture of the gate waveform, measured at the igbt?
>
>
> Sure.
> http://webpages.charter.net/dawill/Images/IGBTWaveform4.jpg
> 5V/div vert, 2us/div horiz, waveform before gate resistors.
> http://webpages.charter.net/dawill/Images/IGBTWaveform1.jpg
> Ditto, waveform at gate.
> Spikes are:
> http://webpages.charter.net/dawill/Images/IGBTWaveform2.jpg
> http://webpages.charter.net/dawill/Images/IGBTWaveform3.jpg
> Same vertical; 200ns/div horiz. (at gate).
>
> Note the spikes coincide with output voltage transitions, but are of the
> wrong polarity with respect to voltage. (In #2, gate voltage is falling,
> but the pulse starts negative whereas output is rising.) Thus I took a pic
> of the emitter waveform, about 1mm from the package.
> http://webpages.charter.net/dawill/Images/IGBTWaveform5.jpg
> (Same phase, time and voltage scales as #1 and 4.)
> Period is around 150ns for the pulse, i.e. 6.7MHz.
>
then the pulse probably isnt "real" but it shows several important things:
- your probing technique is picking up stray fields (or perhaps even
oscillating by itself, but my guess is H). dont use a ground clip, take
it off and use a BNC tip adaptor (the scope probe should have come with
one, at least in theory), and a bnc with a short length of tightly
twisted wire. that ought to make a significant difference. a simple test
is to probe to your ground clip. If you see a spike, its the probe.
oh yeah, make sure the wire you use has suitable insulation voltage rating.
read Jim Williams LT AN47, and do what he says.
- there is obviously plenty of stray field to pick up - invariably its
due to the loops in your power circuitry. you cant do much about your
work coil (other than ensure the current is sinusoidal), but contain the
rest of your fields.
> Incidentially, though the pulse appears on the transistor end of the gate
> drive lines, the circuit side is clean. Alright, so I'll get some PCB and
> solder up the drive circuitses...
>
its well twisted, but still....with care it should work fine, but making
it work gets trickier as the gatedrive moves further away. and until it
works, it destroys IGBTs :)
>
>>- the output voltage waveform looks like it has a 100V spike on the
>>rising edge. can you zoom in on that?
>
>
> That's from the current waveform. '721 is the output waveform zoomed,
> showing about 20V overshoot.
>
>
>>- can u take a pic of your scope probe setup? that spike might not be
>>there....at these low voltages, use a coax scope probe tip adaptor, a
>>BNC socket an a short length of tightly twisted wire, soldered directly
>>across G-E or C-E.
>
>
> The current transformer is a black ferrite toroid (probably high mu) with
> quadfilar wound 26AWG totalling 280T (4 x 70T in series), and a 2.8 ohm load
> resistor. Twisted pair leads back to the scope, with a few turns around a
> ferrite bead for good luck. (I know, the CT is floating, and hanging on the
> ground lead, so it shouldn't pick up much ground loop style hash that a
> ferrite bead would be used for, but so what.)
I like to use coax terminated into 50R (I have some bnc thru
terminators, but a T and an end terminator are about 10x cheaper) at the
scope.
you can also place a faraday shield between the CT windings - suitably
insulated Cu pipe, extending a short way from either side of the toroid,
and one end connected to, say, earth.
>
> The output waveform is measured with my 10x Tek probe clipped to the output
> terminal at the DC side of the coupling capacitor.
>
>
>>- how far away is your gate drive setup? put it as close as possible
>>(creepage/clearance notwithstanding) to the IGBTs.
>
>
> Not very healthy then... about 12". I do have twisted pair, which is a
> Transmission Line(tm), though..
>
>
>>- your DC bus inductance is on the order of 500nH or so.
>
>
> How can that be? The 0.1 caps are an inch from any transistor, and all
> together should be on the order of 100-200nH.
>
WAG. but the loop looks to be about 1" square, so a perimeter of 4". if
we use 0.01" for the "wire" thickness,
L = 0.00508*4"*[ln(4*4"/.01")-2.853] = 100nH
OK, 200nH total :)
so using the same IGBTs and bus caps, you can halve the total inductance.
>
>>if you get a
>>couple of pieces of double-sided Cu-clad PCB, and some 1mm nomex/lexan
>>you can make a DIY multi-layer PCB. just folding your existing assembly
>>flat would make a large difference.
>
>
> So the strips are flat with the heatsink y'mean?
yes - they make parallel-plate transmission lines, which have very low
inductance - Uo*spacing/width
Ye Gods - look at the gate paralleling resistors. they form a great big
loop,which (like your scope probe) *will* pick up any and all stray H
field. remmeber the gate is just a cap, so a low Rg doesnt really help
much here - and besides the inductance of the loop (and Tx line) also
increases Zg, and the gate drive output impedance will also rise with
frequency (it looks inductive).
you have to be careful with your power paths, but *PARANOID* with gate
drives. I have had loops smaller than this cause fatal problems, and it
wouldnt surprise me if that is the case here.
>
>
>>how fast is your scope? whats its rise-time spec?
>
>
> SFA. The output waveform has no difference vs. vertical bandwidth
> (switchable 20/100/200MHz). The oscillographs were taken at 100MHz. All
> the same, it is spec'd at 1.8ns or so.
thats fast enough.
an HP 17xx?
>
> Tim
Cheers
Terry
Tim Williams
> a simple test
> is to probe to your ground clip. If you see a spike, its the probe.
Well, the probe works fine- it only picks up a couple hundred mV when
grounded as such. Little enough that I can ignore it on the 5V/div scale.
I'll admit a forehead-slapping-worthy moment: the above readings were taken
with the gate drive through a ferrite bead. I've had weird results in the
past so I have the scope grounded to the circuit, and the circuit and output
connected with the gate drive ground only.
That means any current appearing between the output and circuit grounds will
cause a voltage to appear across it. The gate drive itself is perfectly
fine and the world is happy -- but since the scope *probe* wasn't going
through the FB too, it got a nasty bounce!
I now have an 8" clip lead ferrying the signal through the FB and the
emitter shows a pulse of like 4V peak, 30ns wide. The gate OFF bias is more
than sufficient to cover this, at this current anyway.
> read Jim Williams LT AN47, and do what he says.
Humm. Second hit on Google is quite attractive, but not quite an
Application Note. :-))~
> I like to use coax terminated into 50R (I have some bnc thru
> terminators, but a T and an end terminator are about 10x cheaper) at the >
scope.
>
> you can also place a faraday shield between the CT windings - suitably
> insulated Cu pipe, extending a short way from either side of the toroid, >
and one end connected to, say, earth.
I'll keep that in mind.
> Ye Gods - look at the gate paralleling resistors. they form a great big
> loop,which (like your scope probe) *will* pick up any and all stray H
> field.
Yabbut, it's not a continuous loop- IGBT each side of the gate resistors, so
the induced field would tend to bootstrap, no?
> you have to be careful with your power paths, but *PARANOID* with gate
> drives. I have had loops smaller than this cause fatal problems, and it
> wouldnt surprise me if that is the case here.
Would you suggest, uh, Idunno- twisted pair for each IGBT? Maybe twisted
pair off each, then tee them together after a ferrite bead, so as to allow
some common-mode squishiness? The emitters should be doing the same thing
so connecting lines together shouldn't be a problem ... but that says
nothing of differing turn-on/off speed between the two.
> an HP 17xx?
Hell no ;-)
Tek 475.
Terry Given
> "Terry Given" <my_...@ieee.org> wrote in message
> news:1138830756.148853@ftpsrv1...
>
>>a simple test
>>is to probe to your ground clip. If you see a spike, its the probe.
>
>
> Well, the probe works fine- it only picks up a couple hundred mV when
> grounded as such. Little enough that I can ignore it on the 5V/div scale.
>
> I'll admit a forehead-slapping-worthy moment: the above readings were taken
> with the gate drive through a ferrite bead. I've had weird results in the
> past so I have the scope grounded to the circuit, and the circuit and output
> connected with the gate drive ground only.
>
> That means any current appearing between the output and circuit grounds will
> cause a voltage to appear across it. The gate drive itself is perfectly
> fine and the world is happy -- but since the scope *probe* wasn't going
> through the FB too, it got a nasty bounce!
>
> I now have an 8" clip lead ferrying the signal through the FB and the
> emitter shows a pulse of like 4V peak, 30ns wide. The gate OFF bias is more
> than sufficient to cover this, at this current anyway.
>
>
>>read Jim Williams LT AN47, and do what he says.
>
http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1154,C1009,C1028,P1219,D4138
>
> Humm. Second hit on Google is quite attractive, but not quite an
> Application Note. :-))~
>
>
>>I like to use coax terminated into 50R (I have some bnc thru
>>terminators, but a T and an end terminator are about 10x cheaper) at the >
>
> scope.
>
>>you can also place a faraday shield between the CT windings - suitably
>>insulated Cu pipe, extending a short way from either side of the toroid, >
>
> and one end connected to, say, earth.
>
> I'll keep that in mind.
>
>
>>Ye Gods - look at the gate paralleling resistors. they form a great big
>>loop,which (like your scope probe) *will* pick up any and all stray H
>>field.
>
>
> Yabbut, it's not a continuous loop- IGBT each side of the gate resistors, so
> the induced field would tend to bootstrap, no?
yes it is. ignore the 2nd IGBT, consider a single gate circuit.
hopefully you have a 0V plane on your gatedrive PCB, so we can ignore
the loop at that end; similarly they are well twisted so we can ignore
the contribution of the dangly wires. but you then open up into a bloody
great (physical) loop with the gate resistor. At the very least, squish
it right down. Ideally, join the emitters of a pair of paralleled IGBTs
with a nice flat copper strip, with the gate drive 0V connecting to
this, and the gate lead and Rg's sitting on top of it - IOW a "ground
plane" around the IGBT gate connections/parts.
it doesnt matter how well twisted or ground-planed the rest of the
gatedrive is, this loop buggers it up.
Firstly, it will pick up any H field and convert it into a gate voltage.
Me and a buddy once spent 2 weeks tracking down such a loop-related
problem in a drive - if we powered up the DC bus just right, it would
turn all the IGBTs on, and blow up :) In the end a scalpel and a bit of
wire-wrap wire cured the problem.
Secondly, the inductance "softens" the gate drive response to an edge.
For Rg = 10R, 100nH has the same impedance at 16MHz - a rise time of
around 20-30ns. for negligible contribution, rise times need to be less
than 200-300ns, which they are NOT. So when some evil dV/dt happens (say
every edge), current flows into the gate, raising (or lowering) Vge....
Its pretty easy to mess with an IGBT's gate if its got a nice big loop.
Its a often lot easier to mess with the gatedrive circuitry itself, its
really just an amplifier, so you need to be absolutely certain H wont
cause you any problems. ground plane, ground plane, ground plane.
>
>
>>you have to be careful with your power paths, but *PARANOID* with gate
>>drives. I have had loops smaller than this cause fatal problems, and it
>>wouldnt surprise me if that is the case here.
>
>
> Would you suggest, uh, Idunno- twisted pair for each IGBT? Maybe twisted
> pair off each, then tee them together after a ferrite bead, so as to allow
> some common-mode squishiness? The emitters should be doing the same thing
> so connecting lines together shouldn't be a problem ... but that says
> nothing of differing turn-on/off speed between the two.
>
thats why you have separate Rg's.
the single twisted lead is fine, its what you do after the twisted lead
that is the problem.
can U show us a pic of the gatedrive PCB....
>
>>an HP 17xx?
>
>
> Hell no ;-)
>
> Tek 475.
I love my 7904 :)
>
> Tim
Cheers
Terry
Tim Williams
<snip>
> ... and the gate lead and Rg's sitting on top of it - IOW a "ground
> plane" around the IGBT gate connections/parts.
>
> it doesnt matter how well twisted or ground-planed the rest of the
> gatedrive is, this loop buggers it up.
Alright, so I "at least squish[ed] the gate resistors in".
http://webpages.charter.net/dawill/Images/IGBT3.jpg
There's a strip of cardboard there to try to ensure they don't short out.
The bottom left (high side) resistor runs across the transistor, placing it
closer to whatever loops are in the transistor, and the collector (B+ rail)
current waveform. This should at least be similar to the emitter current,
no? The alternative is to route it down and around, which opens up a 1/4"
loop, which is "bad".
The upper right (low side) transistor has the same problem and solution,
except there's only the transistor to "ground plane" it.
> Secondly, the inductance "softens" the gate drive response to an edge.
> For Rg = 10R, 100nH has the same impedance at 16MHz - a rise time of
> around 20-30ns. for negligible contribution, rise times need to be less
> than 200-300ns, which they are NOT. So when some evil dV/dt happens (say >
every edge), current flows into the gate, raising (or lowering) Vge....
Yabbut that's what the negative bias (-5V OFF state) is for, as I recall,
isn't it? (That and emitter L flyback.)
Current can fall at 50ns (IGBT t_off), but gate voltage falls in around
200ns. It easily passes the linear region in 50ns though.
> can U show us a pic of the gatedrive PCB....
It isn't.
http://webpages.charter.net/dawill/Images/GateDrive.jpg
It's all mounted on an aluminum backplane, but I don't see a ground for it.
Can always mount a screw for one, I suppose. The circuit seems to be
working fine at the moment.
Terry Given
ye gods
> It's all mounted on an aluminum backplane, but I don't see a ground for it.
> Can always mount a screw for one, I suppose. The circuit seems to be
> working fine at the moment.
>
> Tim
one single intermittent connection can destroy your IGBTs.
such breadboards are great for prototyping, I've made gatedrives on them
myself. And once the circuit operates correctly, re-build it on a piece
of copper-clad PCB. that way bits wont move, impedances are far more
controlled, stray inductance reduces (perhaps dramatically), and wires
wont fall off.
when it all works nicely, you can then build a little box around the
circuit using more Cu-clad PCB, and solder up all the edges. that helps
keep all the nasty fields out (and/or in), as well as clipped off leads etc.
also dont forget the dangers of small components (eg nuts, washers),
tools etc.
make sure all the HV stuff is well secured (eg screwed to a large
plank), with a shield overtop (1mm lexan is good stuff). that will help
prevent blowups, contain the carnage and reduce the shock hazard. If its
on the floor, dont slip and fall on the bus-bars while its live.
Cheers
Terry
Tim Williams
> ye gods
Sounding just a little stark there Terry...
> one single intermittent connection can destroy your IGBTs.
Well, it hasn't yet, and I've had a few instances, so I don't know what to
say...
I have, evidently, blown (open, not shorted) the PNP gate drive/follower
transistor (which is still only a 2N4403, not the ZTX I purchased for the
purpose). This results in a slow, constant turn-off time, since the current
mirror is in effect through what's left of the Vbe (I guess the collector
blew in this case). And, of course, the desat shoots, turning off at least
one half of the bridge within 3盜.
I have had one instance where something happened to the gate and it stayed
high, resulting in the power transformer groaning *as if the bridge had
shorted*. In reality, the battleship sized transistors were just owning it.
;-)
Not very healthy... but if it happened with the old wiring I would probably
be down another $40. The tighter bridge wiring works much better.
> such breadboards are great for prototyping, I've made gatedrives on them >
myself. And once the circuit operates correctly, re-build it on a piece
> of copper-clad PCB. that way bits wont move, impedances are far more
> controlled, stray inductance reduces (perhaps dramatically), and wires
> wont fall off.
Inductance, sure, but I'm still not seeing how the breadboard is going to
screw things up. Honestly, I've used longer air runs between components
when messing around with the output of my 1ns pulse generator, and the
pulses still plink around well enough (20% rule in effect) whatever I have
hooked up.
> when it all works nicely, you can then build a little box around the
> circuit using more Cu-clad PCB, and solder up all the edges. that helps
> keep all the nasty fields out (and/or in), as well as clipped off leads
> etc.
Hmm... fields...(yeah, "hummmm indeed", ha! ha ha!). Well the thing is,
it's pretty much as bad as it's going to get, *as is*. But I'm not getting
any trouble, even with the induction coil less than a foot away. So if I
pack it up on a PCB, I'll have less to worry about, which means...I'll have
nothing to worry about?
All the spurious signals occur on edges, and the gate drive and all circuits
already know what they are doing on the edges, plus I have power supply
bypasses scattered about, so I don't really worry about it.
> make sure all the HV stuff is well secured (eg screwed to a large
> plank), with a shield overtop (1mm lexan is good stuff). that will help
> prevent blowups, contain the carnage and reduce the shock hazard. If its
> on the floor, dont slip and fall on the bus-bars while its live.
That's not a bad idea. I almost peed my pants last time I had some MOSFETs
go off like shotguns.
The strange thing is, though, the last about 20 transistors I've
burned...didn't. Fuckers won't even tell me who died!
I guess that means I'm getting good at this solid state thing, but I'd much
rather they just ooze the smoke so I don't have to lift and probe each damn
lead to find the dead one(s)...
Terry Given
> "Terry Given" <my_...@ieee.org> wrote in message
> news:1139357225.272181@ftpsrv1...
>
>>ye gods
>
>
> Sounding just a little stark there Terry...
>
>
>>one single intermittent connection can destroy your IGBTs.
>
>
> Well, it hasn't yet, and I've had a few instances, so I don't know what to
> say...
how can you be sure? intermittent connections tend to work except when
you are looking.
>
> I have, evidently, blown (open, not shorted) the PNP gate drive/follower
> transistor (which is still only a 2N4403, not the ZTX I purchased for the
> purpose). This results in a slow, constant turn-off time, since the current
> mirror is in effect through what's left of the Vbe (I guess the collector
> blew in this case). And, of course, the desat shoots, turning off at least
> one half of the bridge within 3盜.
>
an open-circuit could do that :)
> I have had one instance where something happened to the gate and it stayed
> high, resulting in the power transformer groaning *as if the bridge had
> shorted*. In reality, the battleship sized transistors were just owning it.
> ;-)
heres a clue - "something" shouldnt happen once the circuit works.
>
> Not very healthy... but if it happened with the old wiring I would probably
> be down another $40. The tighter bridge wiring works much better.
>
>
>>such breadboards are great for prototyping, I've made gatedrives on them >
>
> myself. And once the circuit operates correctly, re-build it on a piece
>
>>of copper-clad PCB. that way bits wont move, impedances are far more
>>controlled, stray inductance reduces (perhaps dramatically), and wires
>>wont fall off.
>
>
> Inductance, sure, but I'm still not seeing how the breadboard is going to
> screw things up. Honestly, I've used longer air runs between components
> when messing around with the output of my 1ns pulse generator, and the
> pulses still plink around well enough (20% rule in effect) whatever I have
> hooked up.
>
try running the bridge at full power, then bashing the side of your
gatedrive mockup with the handle of a large screwdriver. wear safety
goggles.
the interconnects in prototype boards start out as cheap and nasty.
Unlike fine wine, they do not improve with age. A diode-like
interconnect once cost me, another engineer and a tech 3 days once - we
narrowed the fault down to a resistive divider that didnt work linearly.
replacing the protoboard fixed the problem; the old one got Widlarised.
inductance causes three problems:
firstly, the loops radiate H fields, making EMC compliance harder.
Secondly, they pick up H fields, and can convert them to gatedrive signals.
Thirdly they increase the output impedance of your gatedriver - trace
the loop from gate thru Rg, npn or pnp (turn-on or turn-off loops),
supply rail, cap, 0V, emitter - the loop is in series with the gate.
>
>>when it all works nicely, you can then build a little box around the
>>circuit using more Cu-clad PCB, and solder up all the edges. that helps
>>keep all the nasty fields out (and/or in), as well as clipped off leads
>>etc.
>
>
> Hmm... fields...(yeah, "hummmm indeed", ha! ha ha!). Well the thing is,
> it's pretty much as bad as it's going to get, *as is*. But I'm not getting
> any trouble, even with the induction coil less than a foot away. So if I
> pack it up on a PCB, I'll have less to worry about, which means...I'll have
> nothing to worry about?
>
didnt your IGBT bridge blow up? doesnt that count as "trouble" ?!
now I've seen the gatedrive construction, I'd list mechanical problems
at the top of the "why my igbts died" list.
> All the spurious signals occur on edges, and the gate drive and all circuits
> already know what they are doing on the edges, plus I have power supply
> bypasses scattered about, so I don't really worry about it.
solve the mechanical issues first. while you do that, you might as well
build it on a ground plane - it will take no longer than soldering
together a rats nest, while minimising susceptibility to stray fields.
>
>
>>make sure all the HV stuff is well secured (eg screwed to a large
>>plank), with a shield overtop (1mm lexan is good stuff). that will help
>>prevent blowups, contain the carnage and reduce the shock hazard. If its
>>on the floor, dont slip and fall on the bus-bars while its live.
>
>
> That's not a bad idea. I almost peed my pants last time I had some MOSFETs
> go off like shotguns.
>
> The strange thing is, though, the last about 20 transistors I've
> burned...didn't. Fuckers won't even tell me who died!
>
> I guess that means I'm getting good at this solid state thing, but I'd much
> rather they just ooze the smoke so I don't have to lift and probe each damn
> lead to find the dead one(s)...
>
> Tim
its cheaper to not break them in the first place.
power electronics is more about how you do things than what you do. the
circuitry is often the easy part.
Cheers
Terry
Tim Williams
> how can you be sure? intermittent connections tend to work except when
> you are looking.
Er, so when I'm looking, they tend to be intermittent, thus, I would know
about them?
> try running the bridge at full power, then bashing the side of your
> gatedrive mockup with the handle of a large screwdriver. wear safety
> goggles.
Screwdrivers aren't part of the design equation, you're changing the
conditions! ;-)
> inductance causes three problems:
>
> firstly, the loops radiate H fields, making EMC compliance harder.
>
> Secondly, they pick up H fields, and can convert them to gatedrive
> signals.
Yabbut, moot point as the loops aren't particularly wide and the only signal
they recieve is, at most, in the milivolt range -- a pulse could cause a
comparator to switch early, but only when it's about to switch anyway.
> Thirdly they increase the output impedance of your gatedriver - trace
> the loop from gate thru Rg, npn or pnp (turn-on or turn-off loops),
> supply rail, cap, 0V, emitter - the loop is in series with the gate.
I have 0.1uF ceramics at the transistors, so the output loop on the board is
under an inch diameter. There's more before the lead turns to twisted pair!
> didnt your IGBT bridge blow up? doesnt that count as "trouble" ?!
The circuit, before and after the faliure, tested fine. It was the bridge's
fault, as near as I can tell.
> now I've seen the gatedrive construction, I'd list mechanical problems
> at the top of the "why my igbts died" list.
Afraid I have to disagree on this one. Heh, the IGBTs blew too fast for any
mechanical fault to have a reasonable propability to show up. ;)
> solve the mechanical issues first. while you do that, you might as well
> build it on a ground plane - it will take no longer than soldering
> together a rats nest, while minimising susceptibility to stray fields.
As in those RF lashups? Uhh...no.
For GHz circuits I would take the time and tediousness for it, but for
pete's sake Terry my edges are two and a half orders of magnitude slower,
and even as nearby as things are, the inverse square law is with me on stray
fields.
I can do point-to-point wiring on perfboard, or a step up from that, the
perfboard RS sells that has individual copper pads. This doesn't lend
itself to ground plane technique very easily. I don't see PCB happening any
time soon since I don't have PCB design software, resist, etchant, or any
reasonable way whatsoever to drill the holes lined up properly.
Terry Given
> "Terry Given" <my_...@ieee.org> wrote in message
> news:1139430680.684090@ftpsrv1...
>
>>how can you be sure? intermittent connections tend to work except when
>>you are looking.
not
>
>
> Er, so when I'm looking, they tend to be intermittent, thus, I would know
> about them?
>
>
>>try running the bridge at full power, then bashing the side of your
>>gatedrive mockup with the handle of a large screwdriver. wear safety
>>goggles.
>
>
> Screwdrivers aren't part of the design equation, you're changing the
> conditions! ;-)
what, too chicken to try it? why not, you seem to like your gatedrive
construction....
>
>
>>inductance causes three problems:
>>
>>firstly, the loops radiate H fields, making EMC compliance harder.
>>
>>Secondly, they pick up H fields, and can convert them to gatedrive
>>signals.
>
>
> Yabbut, moot point as the loops aren't particularly wide and the only signal
> they recieve is, at most, in the milivolt range -- a pulse could cause a
> comparator to switch early, but only when it's about to switch anyway.
>
how do you know that?
it is often quite easy to cause gatedrivers to switch several times on
any given edge. that can be a great way of making switching losses much
higher than you expected. I have tracked down several such problems in
the past, that exhibited themselves as "random' failures during soak
testing.
after enough time spent tracking down these sorts of faults, one learns
to avoid them in the first place.
>
>>Thirdly they increase the output impedance of your gatedriver - trace
>>the loop from gate thru Rg, npn or pnp (turn-on or turn-off loops),
>>supply rail, cap, 0V, emitter - the loop is in series with the gate.
>
>
> I have 0.1uF ceramics at the transistors, so the output loop on the board is
> under an inch diameter. There's more before the lead turns to twisted pair!
>
ignore the twisted pair. that inch or so just added a hundred nH or so
to Zg.
>
>>didnt your IGBT bridge blow up? doesnt that count as "trouble" ?!
>
>
> The circuit, before and after the faliure, tested fine. It was the bridge's
> fault, as near as I can tell.
>
you blew up the igbts without breaking the gatedrivers? thats a good
trick, normally the collector shorts across to the gate, and trashes the
gatedrive output stage (or more).
>
>>now I've seen the gatedrive construction, I'd list mechanical problems
>>at the top of the "why my igbts died" list.
>
>
> Afraid I have to disagree on this one. Heh, the IGBTs blew too fast for any
> mechanical fault to have a reasonable propability to show up. ;)
>
you obviously dont understand my point.
one single intermittent connection in a gatedrive/igbt assembly can
*destroy* the power electronics. your construction technique (OK, I was
going to say "hairy-assed mess") is just *begging* for such an event to
occur. Hell, it may have done so already (and IMO probably has).
whats worse, once you fix everything, the intermittent connection might
not be obvious.
the only practical solution is to build the damn thing properly.
plus murphys law applies directly here.
>
>>solve the mechanical issues first. while you do that, you might as well
>>build it on a ground plane - it will take no longer than soldering
>>together a rats nest, while minimising susceptibility to stray fields.
>
>
> As in those RF lashups? Uhh...no.
>
> For GHz circuits I would take the time and tediousness for it, but for
> pete's sake Terry my edges are two and a half orders of magnitude slower,
> and even as nearby as things are, the inverse square law is with me on stray
> fields.
fancy pushing on some of the proto-board wires while its running? no?
why not?
AFAT inverse square law goes, look at the impedances too - if its a nice
high-Z circuit node, it might not need much to push it around. and with
enough wiring inductance, even a low-Z node can look high-Z to a nice
fast edge.
hell, once 50fF of capacitance buggered up a perfectly good circuit I'd
designed. yep, 0.05pF. 5V square wave with 10ns edges, 50fF to the -ve
input of an opamp, with Z = 10k or so.
thats a moot point though - if you need to improve the mechanical
construction, you might as well do it in as "RF" a manner as possible.
why not think about it from a risk management perspective? them IGBTs
aint cheap, it should behoove one to try not to break them.
>
> I can do point-to-point wiring on perfboard, or a step up from that, the
> perfboard RS sells that has individual copper pads. This doesn't lend
> itself to ground plane technique very easily.
it does if you sit it on top of a ground plane.
I don't see PCB happening any
> time soon since I don't have PCB design software, resist, etchant, or any
> reasonable way whatsoever to drill the holes lined up properly.
>
> Tim
I dont do those things either, I build circuits on top of a piece of
copper-clad board. some chips end up upside down, others dont. go read
the two books edited by Jim Williams, and/or some of the analog devices
& linear tech app notes on how to build a decent prototype.
with a bit of practice, its no slower than using proto-boards.
Peroration:
there are a wide variety of problems that can, and do, beset power
electronics. physical construction is usually at the top of the list (my
circuit looks OK, why does it blow up) - both from an EMC and a
reliability perspective.
If you deliberately avoid the really dumb mistakes (a wire fell off, a
clipped lead got into the hardware, I forgot to fasten the IGBT to the
heatsink, giant loops everywhere, DIY thru-plated pcbs etc) that leaves
you free to focus on the real problems.
Cheers
Terry
Tim Williams
> > Screwdrivers aren't part of the design equation, you're changing the
> > conditions! ;-)
>
> what, too chicken to try it? why not, you seem to like your gatedrive
> construction....
Hum...
LOL. I should take a picture of... no heck, take a video, of me dropping a
screwdriver on the circuit, with the scope watching gate drive outputs and
watching what happens.
Probably end up something like shorted power supply, or the signal just
stops, or something. If I were to do this, I'd be more worried about the
voltage regulators letting out smoke than anything else... simply because
nothing else is designed to push as much current.
Oh- FYI, the breadboard itself is actually in pretty good condition. Nice
and stout springs, not even any melted holes! (yet)
> > a pulse could cause a
> > comparator to switch early, but only when it's about to switch anyway.
>
> how do you know that?
It would've done it by now? Idunno.
How could I prove it either way? Lesse, I could use an air core coil say
10" dia. for the series matching inductor, and wave the board through it.
That should induce a pretty sick current in anything of note, eh?
> you blew up the igbts without breaking the gatedrivers? thats a good
> trick, normally the collector shorts across to the gate
Ya tell me about it... that's why my BK 3026 needs a fix... :-o
> you obviously dont understand my point.
No I understand your concern, I just don't really see it happening in near
probability (I can see you worried about once-in-a-decade events, like
dropping a screwdriver on something ordinarily sealed in a chassis, but to
me that's a freak accident and I certainly don't mind the down time fixing
the circuit, sans expensive transistors of course).
> fancy pushing on some of the proto-board wires while its running? no?
> why not?
Eh? I don't get you. Of course I push on wires, being a low voltage
circuit I often twiddle wires and resistors and capacitors while live. As
long as the high and low power sections are seperate I can develop then
test, in that order. If there were scratchy contacts, I would've tracked
them down by now.
> why not think about it from a risk management perspective? them IGBTs
> aint cheap, it should behoove one to try not to break them.
Well, yeah...but that doesn't change the measured fact that the gate drive
works (in lieu of catastrophic mechanical climate change, so to speak ;),
and pretty reasonably for an LM393 and five 2N440x transistors. I have
fault protection, albeit rudimentary (local desat would be better, but I
would have to have three-way communication to shut down high side, low side
drive and oscillator sections when either drive poops, plus reset them all).
The only question remaining is mechanical rigidity (perhaps I didn't
articulate this, but obviously this breadboard isn't permanent, it will be
soldered some day -- when the circuit becomes *set in stone* mind you) and
RFI concerns, which I have so far seen few symptoms of.
> > I can do point-to-point wiring on perfboard, or a step up from that, the
> > perfboard RS sells that has individual copper pads. This doesn't lend
> > itself to ground plane technique very easily.
>
> it does if you sit it on top of a ground plane.
Pointy underside bits with voltage don't really like flat conductors. I
don't know what kind of an insulator you would recommend there, besides
distance, which in that case I would call it shielding (like those tin cans
on various TV and monitor boards) more than a ground plane.
Speaking of shielding, the whole thing (if possible) will be inside a mild
steel box or two, which should control coil EMI and switching noise
reasonably. Plus a line filter..
> I dont do those things either, I build circuits on top of a piece of
> copper-clad board. some chips end up upside down, others dont. go read
> the two books edited by Jim Williams, and/or some of the analog devices
> & linear tech app notes on how to build a decent prototype.
>
> with a bit of practice, its no slower than using proto-boards.
BUT IT'S SOOOO FUCKING UGLY!
Alright, let me put it this way. If plane practice is better...
...Why does everything I take apart have printed circuit boards?
Production aside.
I'm not trying to attack your point of view, that's absurd- you're literally
in the business. I'm trying to apply your view to my situation is all.
Terry Given
> "Terry Given" <my_...@ieee.org> wrote in message
> news:1139452184.934258@ftpsrv1...
>
>>>Screwdrivers aren't part of the design equation, you're changing the
>>>conditions! ;-)
>>
>>what, too chicken to try it? why not, you seem to like your gatedrive
>>construction....
>
>
> Hum...
>
> LOL. I should take a picture of... no heck, take a video, of me dropping a
> screwdriver on the circuit, with the scope watching gate drive outputs and
> watching what happens.
>
> Probably end up something like shorted power supply, or the signal just
> stops, or something. If I were to do this, I'd be more worried about the
> voltage regulators letting out smoke than anything else... simply because
> nothing else is designed to push as much current.
>
> Oh- FYI, the breadboard itself is actually in pretty good condition. Nice
> and stout springs, not even any melted holes! (yet)
>
>
>>>a pulse could cause a
>>>comparator to switch early, but only when it's about to switch anyway.
>>
>>how do you know that?
>
>
> It would've done it by now? Idunno.
QED
>
> How could I prove it either way? Lesse, I could use an air core coil say
> 10" dia. for the series matching inductor, and wave the board through it.
>
> That should induce a pretty sick current in anything of note, eh?
>
you raise a very good point - just how do you "know" that this is
happening. self-interference can be devilishly hard to measure. The only
sure-fire way I have found is with making changes and observing problems
disappear; reverse the change, watch the problem come back. repeat until
convinced.
then examine the root cause of the problem, and resolve never to do it
again.
>
>>you blew up the igbts without breaking the gatedrivers? thats a good
>>trick, normally the collector shorts across to the gate
>
>
> Ya tell me about it... that's why my BK 3026 needs a fix... :-o
>
>
>>you obviously dont understand my point.
>
>
> No I understand your concern, I just don't really see it happening in near
> probability (I can see you worried about once-in-a-decade events, like
> dropping a screwdriver on something ordinarily sealed in a chassis, but to
> me that's a freak accident and I certainly don't mind the down time fixing
> the circuit, sans expensive transistors of course).
>
sooner or later, it will happen with your gatedrive - it may have
already, there isnt really any way of telling.
heres a wee tale - it involves a gatedrive design for a 20-drive product
range. we never tested it with the biggest IGBT, and it lacked a bit of
grunt. the poor gatedrive increased losses enough that the drive would
die after 2 hours on soak test, so we didnt release the larger drives,
and went back to the drawing board. time was short, so when we got a
proto pcb laid out, our CEO went and ordered 1500, rather than the 10 we
would have got. Sure enough, there was one mistake - 2 pins of a
comparator were swapped. So we lifted a leg on a SOIC8, added a few
dangly wires and off we went.
except the damn drive blew up after a couple hours on soak.
re-build
re-test
re-sounding bang.
re-peat, with teeth a-gnashing
eventually we tracked the problem down - an intermittent connection
*within* the LM393. a heat gun could make the gate drive turn itself off
and on - the pin concerned was the reference voltage against which the
isolated gatedrive signal was compared. looks like we damaged the bond
wire bending the leg. perhaps 10 times in a row (over a period of
several days) using new chips each time. Hmm.
so we re-did the layout, the circuit worked perfectly, and has never
been changed since then (although about 50,000 drives have been made, so
300,000 copies of that circuit).
a few weeks later, the CEO lambasted my manager for "wasting so much
money on prototype pcbs" :)
>
>>fancy pushing on some of the proto-board wires while its running? no?
>>why not?
>
>
> Eh? I don't get you. Of course I push on wires, being a low voltage
> circuit I often twiddle wires and resistors and capacitors while live. As
> long as the high and low power sections are seperate I can develop then
> test, in that order. If there were scratchy contacts, I would've tracked
> them down by now.
>
I've learned to stay the hell away when its running, and fiddle with
nothing. I also bite people who approach carrying cups of coffee etc.
>
>>why not think about it from a risk management perspective? them IGBTs
>>aint cheap, it should behoove one to try not to break them.
>
>
> Well, yeah...but that doesn't change the measured fact that the gate drive
> works (in lieu of catastrophic mechanical climate change, so to speak ;),
> and pretty reasonably for an LM393 and five 2N440x transistors. I have
> fault protection, albeit rudimentary (local desat would be better, but I
> would have to have three-way communication to shut down high side, low side
> drive and oscillator sections when either drive poops, plus reset them all).
> The only question remaining is mechanical rigidity (perhaps I didn't
> articulate this, but obviously this breadboard isn't permanent, it will be
> soldered some day -- when the circuit becomes *set in stone* mind you) and
> RFI concerns, which I have so far seen few symptoms of.
>
I'd consider it blowing up to be a symptom.
>
>>>I can do point-to-point wiring on perfboard, or a step up from that, the
>>>perfboard RS sells that has individual copper pads. This doesn't lend
>>>itself to ground plane technique very easily.
>>
>>it does if you sit it on top of a ground plane.
>
>
> Pointy underside bits with voltage don't really like flat conductors. I
> don't know what kind of an insulator you would recommend there, besides
> distance, which in that case I would call it shielding (like those tin cans
> on various TV and monitor boards) more than a ground plane.
sidecutters, and flip the PCB over so the Cu side faces away from the rest.
its easier if you just learn how to assemble circuits on top of Cu-clad
PCB. google manhattan method, there is a nice PDF and some truly lovely
examples to look at.
>
> Speaking of shielding, the whole thing (if possible) will be inside a mild
> steel box or two, which should control coil EMI and switching noise
> reasonably. Plus a line filter..
>
if done properly.
>
>>I dont do those things either, I build circuits on top of a piece of
>>copper-clad board. some chips end up upside down, others dont. go read
>>the two books edited by Jim Williams, and/or some of the analog devices
>>& linear tech app notes on how to build a decent prototype.
>>
>>with a bit of practice, its no slower than using proto-boards.
>
>
> BUT IT'S SOOOO FUCKING UGLY!
what, you think that POS proto-board isnt ugly?
besides, what self-respecting engineer trades functionality for aesthetics?
>
> Alright, let me put it this way. If plane practice is better...
> ...Why does everything I take apart have printed circuit boards?
> Production aside.
several reasons. Firstly, most of what you dismember isnt a whopping
great piece of power electronics. pull a few of them apart....
PCBs can have ground planes too.
most consumer gear is incredibly cost-competitive (HTF does one make a
DVD player that retails for NZ$48 ?!), which is why they use the
cheapest, nastiest PCBs known to man (single-sided phenolic paper, with
many machine-inserted links). and a team of engineers to ensure the damn
thing passes EMI (but only just, thats enough)
a lot of consumer gear just doesnt work very well. its not uncommon to
buy things that dont work at all, and nobody is suprised when mall-wart
stuff falls to bits....
power electronics is nasty stuff, and is what generates the EMI that
designers must work around.
also, if you know exactly what you are doing, ground planes are not
mandatory. its just that they make life SO EASY....
>
> I'm not trying to attack your point of view, that's absurd- you're literally
> in the business. I'm trying to apply your view to my situation is all.
>
> Tim
I make quite a nice living out of fixing other peoples EMI problems,
usually by using a decent ground plane.
one particular job, the PCB was large and a frightening mess. missed EMC
by miles, and product regularly went bonkers. the solution: turn the
artwork from a 2-layer PCB into a 4-layer PCB. Assign mid1 as 0V, mid2
as +5V. delete all 0V & 5V traces on top and bottom layers. Voila,
product now passes. perhaps 2hrs of work. the build volume was very low,
so it was cheaper to add $20 to the PCB cost and spend almost no NRE.
Cheers
Terry
Tim Williams
> you raise a very good point - just how do you "know" that this is
> happening. self-interference can be devilishly hard to measure. The only
> sure-fire way I have found is with making changes and observing problems
> disappear; reverse the change, watch the problem come back. repeat until
> convinced.
>
> then examine the root cause of the problem, and resolve never to do it
> again.
Yeah, Occam's razor, change one bit at a time and all that...
I think I'm going to put a few turns in series with Lmatch and wave it over
the board, see what starts freaking out. Should be able to find quirky bits
pretty easily and relatively non-destructively.
> eventually we tracked the problem down - an intermittent connection
> *within* the LM393. a heat gun could make the gate drive turn itself off
> and on - the pin concerned was the reference voltage against which the
> isolated gatedrive signal was compared. looks like we damaged the bond
> wire bending the leg. perhaps 10 times in a row (over a period of
> several days) using new chips each time. Hmm.
Weird...
> its easier if you just learn how to assemble circuits on top of Cu-clad
> PCB. google manhattan method, there is a nice PDF and some truly lovely
> examples to look at.
Hmm...
> > BUT IT'S SOOOO FUCKING UGLY!
>
> what, you think that POS proto-board isnt ugly?
Admit it -- it's better than some gnarly mess entangled through the air. ;-)
> besides, what self-respecting engineer trades functionality for
> aesthetics?
Doesn't have to be a trade. Look at the P-52, Spitfire, etc.
> a lot of consumer gear just doesnt work very well. its not uncommon to
> buy things that dont work at all, and nobody is suprised when mall-wart
> stuff falls to bits....
No doubt there, but what of 1980s monitors? The kind that are 19" or more
and have BNC connectors for video? I've taken apart a few. Those were the
days when they *cared* to put in perforated aluminum shielding.
Terry Given
> "Terry Given" <my_...@ieee.org> wrote in message
> news:1139467811.483429@ftpsrv1...
>
>>you raise a very good point - just how do you "know" that this is
>>happening. self-interference can be devilishly hard to measure. The only
>>sure-fire way I have found is with making changes and observing problems
>>disappear; reverse the change, watch the problem come back. repeat until
>>convinced.
>>
>>then examine the root cause of the problem, and resolve never to do it
>>again.
>
>
> Yeah, Occam's razor, change one bit at a time and all that...
>
> I think I'm going to put a few turns in series with Lmatch and wave it over
> the board, see what starts freaking out. Should be able to find quirky bits
> pretty easily and relatively non-destructively.
I've done that sort of thing quite a few times (40W ham transmitters
sitting next to drives, that sort of thing) in the past. and invariably
the problems are:
mechanical - interconnects, soldering, damaged smt parts, swarf, tools,
hardware etc. IOW self-inflicted.
electrical - H and E fields, stray inductance and capacitance are what
separates simulations from reality.
these "EMI" problems can be further divided as:
source
path
victim
any and all of which can be modified to solve the problem.
stopping the noise at the source is best - control your fields. for H,
keep loops small, use parallel-plate transmission-line construction,
"ground" planes etc. E needs electrostatic shielding, and a ground plane
is a good start.
sometimes the path can be altered - eg orienting magnetics at right
angles, placing a sensitive circuit well away from a noisy one etc.
the victim usually needs to be "hardened" with power electronics, as it
tends to sit in very close proximity to the source. ground planes solve
a lot of the problems, but keeping impedances low is usually a good idea
to reduce the effects of capacitive coupling to, say, power devices,
busbars etc.
if you read a few books on EMI, and fix a few problems, you pretty soon
see how the physical construction of circuitry is so important.
simulation tools are good enough that gross circuit problems can be
sorted out before building actual hardware. The circuit effects of stray
L and C are dead easy to simulate. its instructive to play "what if"
with spice, and sprinkle L's and C's at various points in a circuit.
>
>
>>eventually we tracked the problem down - an intermittent connection
>>*within* the LM393. a heat gun could make the gate drive turn itself off
>>and on - the pin concerned was the reference voltage against which the
>>isolated gatedrive signal was compared. looks like we damaged the bond
>>wire bending the leg. perhaps 10 times in a row (over a period of
>>several days) using new chips each time. Hmm.
>
>
> Weird...
not as weird as an MLC capacitor exploding when charged to half its
rated voltage. because it was hand-soldered, develop thermal stress
cracks and failed within a week.
>
>
>>its easier if you just learn how to assemble circuits on top of Cu-clad
>>PCB. google manhattan method, there is a nice PDF and some truly lovely
>>examples to look at.
>
>
> Hmm...
>
>
>>>BUT IT'S SOOOO FUCKING UGLY!
>>
>>what, you think that POS proto-board isnt ugly?
>
>
> Admit it -- it's better than some gnarly mess entangled through the air. ;-)
>
I've seen some masterpieces built that way :)
>
>>besides, what self-respecting engineer trades functionality for
>>aesthetics?
>
>
> Doesn't have to be a trade. Look at the P-52, Spitfire, etc.
attempted facetiousness. all the truly great stuff looks cool too. stuff
that looks dreadful usually is.
>
>
>>a lot of consumer gear just doesnt work very well. its not uncommon to
>>buy things that dont work at all, and nobody is suprised when mall-wart
>>stuff falls to bits....
>
>
> No doubt there, but what of 1980s monitors? The kind that are 19" or more
> and have BNC connectors for video? I've taken apart a few. Those were the
> days when they *cared* to put in perforated aluminum shielding.
>
> Tim
Cheers
Terry
Tim Williams
them and positioned over the heatsink. Aside from the arrangement of the
buss strips and the yet-ungrounded heatsink, this should work pretty
reasonable huh?
http://webpages.charter.net/dawill/Images/Induction724.jpg
The biggest gate loops are basically the transistors themselves. All
external loops are under 1/4" the best I can tell.
The gate drives alone test well: estimated output impedance 1 ohm, 500mA+
source/sink capacity, 0.65us low-side propagation delay, 0.8ns high-side
(the coupling transformer adds 150ns); output edge fall time 360ns (RC
slope), rise time 140ns.
I need to tweak the UVLO circuit, and the desat is untested (obviously,
since I haven't tried the drives with the output circuit yet).
Tim
--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
"Terry Given" <my_...@ieee.org> wrote in message
news:1139532960.209787@ftpsrv1...
> I've done that sort of thing quite a few times (40W ham transmitters
> sitting next to drives, that sort of thing) in the past. and invariably
> the problems are:
>
> mechanical - interconnects, soldering, damaged smt parts, swarf, tools,
> hardware etc. IOW self-inflicted.
>
> electrical - H and E fields, stray inductance and capacitance are what
> separates simulations from reality.
>
> these "EMI" problems can be further divided as:
>
> source
> path
> victim
>
> any and all of which can be modified to solve the problem.
...
Terry Given
> Soldered the gate drives the last few days, taped a piece of cardboard under
> them and positioned over the heatsink. Aside from the arrangement of the
> buss strips and the yet-ungrounded heatsink, this should work pretty
> reasonable huh?
>
> http://webpages.charter.net/dawill/Images/Induction724.jpg
>
> The biggest gate loops are basically the transistors themselves. All
> external loops are under 1/4" the best I can tell.
>
> The gate drives alone test well: estimated output impedance 1 ohm, 500mA+
> source/sink capacity, 0.65us low-side propagation delay, 0.8ns high-side
> (the coupling transformer adds 150ns); output edge fall time 360ns (RC
> slope), rise time 140ns.
>
> I need to tweak the UVLO circuit, and the desat is untested (obviously,
> since I haven't tried the drives with the output circuit yet).
>
> Tim
Hi Tim,
that looks great. does it go?
Cheers
Terry
Tim Williams
> that looks great. does it go?
Yeah, powered it up, looks to work pretty good. No complaints about kicking
it up to 200V? How about the full 320VDC? How about the full 50A? ;-)
Terry Given
> "Terry Given" <my_...@ieee.org> wrote in message
> news:1140156561.127966@ftpsrv1...
>
>>that looks great. does it go?
>
>
> Yeah, powered it up, looks to work pretty good. No complaints about kicking
> it up to 200V? How about the full 320VDC? How about the full 50A? ;-)
>
> Tim
See :)
A guy I worked with once did a somewhat silly thing. His sidekick had
spent 6 months developing a monstrous (almost 2'x2'), wire-wrapped
vector controller for driving an induction motor. it was wired into a
2.2kW drive in the test lab, in a rather ungainly manner. S came in on
the weekend, saw it was all hooked up and thought he'd give it a whirl.
Alas in a moment of clumsiness he knocked some wires off the bench which
got caught in the spinning shaft of the test set, which proceeded to rip
the controller of the bench and tear most of the wires off. oops.
then there was the girl who dropped a scope probe into a 70kW drive, and
shorted the national grd thru our 1yr old HP33xxx AWG. *BANG*
the awg was basically a single 4-layer PCB, with earth running thru the
middle of the PCB. it had a 5mm thick 50mm round delaminated portion
where the earth track vaporised, and cost us IIRC $500 less than a new
instrument to repair it.
Cheers
Terry