RE: IGBT BSM75GB170DN2 ...

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Steve Conner" <steve.conner-at-optosci-dot-com> 

 >Will the IGBT or its gate be destroyed if the gate resistance in my circuit
 >is less than 3 ohms ?

I can't see any reason why this would happen. The DRSSTC guys seem to
regularly use gate resistors of less than 3 ohms, in fact some builders seem
to use no gate resistor at all! The IGBTs don't seem to suffer any ill
effects.

The main reason for a gate resistor seems to be to deliberately slow the
switching speed of the device. This is sometimes needed with IGBT bricks in
hard-switching applications. If the device is driven at its full speed the
high di/dt can cause dangerous oscillations in the package stray
inductances. This should not be an issue in a resonant circuit like a DRSSTC
(as I is small at the switching times) so you can aim for the fastest
switching speed possible. Of course if your coil is not tuned properly the
IGBTs will be hard switching to some extent and you lose this advantage.

Another use of the gate resistor is to damp out ringing caused by stray
inductance in the gate driver circuit. Too much ringing can cause high
voltage peaks that may damage the gate insulation.

I used no gate resistors in my OLTC work when driving 600A Powerex bricks,
as I found the resistance of the circuit itself was enough to damp the
ringing, and I wanted the fastest turn-on time possible. I think I was
delivering about 20-30A of peak current to the gate.

Steve C.