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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I did look at the specs. This device could take 200A in the SOA. I did not think the generator would put out a transient spike that high, as it usually can do no more than 10A when loaded. I guess the transient spike did it in.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Why did you think you needed it anyway?
Let me speculate on that one. <speculate> I think it was your post in the "Schmidt trigger" thread
In "Schmidt trigger", Steve McConner wrote:
This is why I recommend a low-pass filter in the loop, to stop that kind of thing. A nice big capacitor strategically placed in the dump load unit wouldn't hurt either.
It immediately rang alarm bells for me, I could think of a place where it would be useful, and several where it wouldn't. Hence I posted straight after it
In "Schmidt trigger", Dr. Slack wrote:
You might like to elaborate for others' benefit what "strategically in" means.
In the absence of further information, it looks like Mr Smooth hit on one of the places where it wouldn't. </speculate>
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Well, if Dr. Smooth doesn't understand the implications of I=C*dV/dt, that's his problem, not mine. In any case, here is where I meant the capacitor to go:
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
The destruction of the IGBT was not smooth.
How is it that the IGBT/FET can handle such large currents going to the tank capacitor if mine, rated for 150A could not? Is it that the high frequency switching does not allow the current spike to get too high, while mine just opened and let it take in as much current as it could?
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
How is it that the IGBT/FET can handle such large currents going to the tank capacitor?
Ignore totally anything to do with induction heaters, put all confusing thoughts of those out of your head (ever heard of trying to run before you can walk). Just use I=C*dV/dt (a strong hint from Steve) to work out what current flows in your IGBT destroying arrangement, use a simulator by all means, and see whether that is in your SOA or not.
But to answer your question, the IGBT current drawn in the IH application is not as large as in your IGBT destroyer.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
At least nothing exploded.
I have the circuit working properly on a breadboard right now. It hits the trigger voltage, turns on the dump load, and after a slight delay turns off if the voltage falls sufficiently. I am getting ready to use a photoresist board to make the circuit board.
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driving an IGBT
