Re: IGBTs are pretty fast

"Terry Given" <my_name@xxxxxxxx> wrote in message
news:1139452184.934258@xxxxxxxxxx
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.

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms


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