controlling the negative gate bias voltage of the Gate drive transformer

[prabhatkumar]

Hi there everyone,
I was wondering if there is a way to control the negative excursions of the gate voltage applied to the IGBTs. Since in most general circuits I see there is +15V, -7V gate bias voltage.
Do all IGBTS( smaller one's) do well with the +-15V excursions?.
I am actually planning to use SiC in a full bridge circuit( not a tesla coil, but a very similar power circuit). So I found online that most SiC gate drivers use a +15 -4V gate drive voltage. Hence I wanted to know if there is a circuit by which we can control the negative excursions of the gate drive voltage.
Thank you.

[davekni]

The thing that struck me is that I do not think there is neagtive gate voltage applied at the output of the gate drive transformer from the steve wards UD1.3b or later revisions. I maybe very well wrong here. Please correct me if I am wrong.

I'm curious how you came to this conclusion?
Transformer windings, both input and output, have no DC voltage.  (This is ignoring the small voltage that may be caused by winding resistance and any DC current.)  Thus all positive voltage is matched with equal negative voltage.  (Equal in volt-seconds, integral of voltage over time.  Not necessarily equal in peak voltage.)

[prabhatkumar]

Hi David,
Thanks again for the reply. I had understood my mistake after a while, but forgot to edit my question. The actual question goes like this:
Can small IGBTs handle the +-15V excursions. Since usually the commercial gate drivers employ a +15 and -7V bias to the gate. So is there a way in which I can make the negative excursion a bit less by adding few complimentary components?

[davekni]

Can small IGBTs handle the +-15V excursions. Since usually the commercial gate drivers employ a +15 and -7V bias to the gate.

Yes, small IGBTs are fine with +-15V, and fine with +-24V as you will get if running UD2.7 on 24Vdc.

+15 to -7V reduces gate charge and therefore power dissipation in driver circuitry compared to +-15V.  Also allows use of lower voltage IC technology which reduces driver chip cost.  For commercial applications those factors are significant.

Smaller IGBTs can be driven 0-15V as long as emitter lead and wiring inductance is minimized.  My DRSSTC uses 0-19V gate drive on all 40 TO247 IGBTs.  Gate drive is through a commercial isolated gate driver chip followed by a discrete buffer to handle 10 paralleled IGBTs for each switch.

[prabhatkumar]

Great, thanks for the help.