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:
- 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.
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.
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.
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
-- Deep Fryer: a very philosophical monk. Website:
5V/div vert, 2us/div horiz, waveform before gate resistors.
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Ditto, waveform at gate. Spikes are:
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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.
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(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...
That's from the current waveform. '721 is the output waveform zoomed, showing about 20V overshoot.
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.
Not very healthy then... about 12". I do have twisted pair, which is a Transmission Line(tm), though..
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.
So the strips are flat with the heatsink y'mean?
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.
Tim
-- Deep Fryer: a very philosophical monk. Website:
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.
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 :)
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.
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.
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.
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.
Humm. Second hit on Google is quite attractive, but not quite an Application Note. :-))~
scope.
and one end connected to, say, earth.
I'll keep that in mind.
Yabbut, it's not a continuous loop- IGBT each side of the gate resistors, so the induced field would tend to bootstrap, no?
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.
Hell no ;-)
Tek 475.
Tim
-- Deep Fryer: a very philosophical monk. Website:
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.
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.
Alright, so I "at least squish[ed] the gate resistors in".
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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.
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.
It isn't.
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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
-- Deep Fryer: a very philosophical monk. Website:
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.
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 3µs.
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.
myself. And once the circuit operates correctly, re-build it on a piece
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.
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.
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
-- Deep Fryer: a very philosophical monk. Website:
how can you be sure? intermittent connections tend to work except when you are looking.
an open-circuit could do that :)
heres a clue - "something" shouldnt happen once the circuit works.
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.
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.
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.
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.
Er, so when I'm looking, they tend to be intermittent, thus, I would know about them?
Screwdrivers aren't part of the design equation, you're changing the conditions! ;-)
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.
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!
The circuit, before and after the faliure, tested fine. It was the bridge's fault, as near as I can tell.
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. ;)
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.
Tim
-- Deep Fryer: a very philosophical monk. Website:
what, too chicken to try it? why not, you seem to like your gatedrive construction....
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.
ignore the twisted pair. that inch or so just added a hundred nH or so to Zg.
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).
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.
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.
it does if you sit it on top of a ground plane.
I don't see PCB happening any
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.
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)
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?
Ya tell me about it... that's why my BK 3026 needs a fix... :-o
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).
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.
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.
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..
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.
Tim
-- Deep Fryer: a very philosophical monk. Website:
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.
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" :)
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.
I'd consider it blowing up to be a symptom.
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.
if done properly.
what, you think that POS proto-board isnt ugly?
besides, what self-respecting engineer trades functionality for aesthetics?
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 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.
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.
Weird...
Hmm...
Admit it -- it's better than some gnarly mess entangled through the air. ;-)
Doesn't have to be a trade. Look at the P-52, Spitfire, etc.
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
-- Deep Fryer: a very philosophical monk. Website:
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:
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.
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.
I've seen some masterpieces built that way :)
attempted facetiousness. all the truly great stuff looks cool too. stuff that looks dreadful usually is.
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?
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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:
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