RE: OL-DRSSTC 7 - It's Alive!

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Original poster: "Jason Judd" <JJudd@xxxxxxxxxxxxxxxx>

Hi Terry,

> Were you using gate drive resistors and all??  The IRG4PG50WD
> can take 750 amps!!  But if the gate voltage is being driven
> high by "shoot through" (Miller capacitance from drain to
> gate is driving the gate voltage too high and blowing out
> that gate capacitor), they will blow real fast...  Maybe
> clamp the gates and slow the dV/dT...

I tried gate resistors from 0 to 50 Ohms and used 25V TVS between gate
and emitter. I have used the IRG4PF50WD IGBTs up to 550 amps in an OLTC
and take your word that they will do 750 amps. What I was trying to say
before is that I don't think they can hard switch currents of that
level. My problem only seemed to occur when I was hard switching current
much over 200 amps (peak 320 amps)which is what was happening due to
driver delays and the 130Khz operating freq.

The gate spikes I was seeing were going negative for about 50 ns, but I
never saw them exceed the gate voltage rating. Could those fast spikes
tear the gate apart without exceeding the voltage rating ?

Maybe I should set up a test rig and try to prove either way if hard
switching 200+ amps = smoke. That still may leave doubt as to the exact
mechanism of failure thgouh.

Jason.

>
> I don't know for sure, but your problem sounds like it needs
> TVS right across the gates and gate drive resistors to slow
> the switching down a little...
>
> Cheers,
>
>          Terry