RE: OLTC Update - Primary circuit resistance.

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Marco.Denicolai-at-tellabs-dot-com>

Hi Terry,

> -----Original Message-----
> From: tesla-at-pupman-dot-com [mailto:tesla-at-pupman-dot-com]
> Sent: 19. elokuuta 2002 21:22
> To: tesla-at-pupman-dot-com
> Subject: Re: OLTC Update - Primary circuit resistance.
> 
> 
> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> 
> Marco mentions that I am running the gates at pretty high 
> voltage (18V).
> IGBTs like these usually "break" at about 50 volts on the 
> gate.  No problem
> nearing the 20 volt spec there.  

If you are really using the IRG4PF50WD, check carefully its datasheet.
Its Vge max value is truly +/- 20V, not 50V.

> nice.  Shoot through from the Ccg capacitance is a concern 
> and that is why
> I have 100 ohm gate resistors to slow the turn on way down 
> compared to what
> it "could" be.  

Another thing. You have the 20V TVS on the driver side of the gate 
resistor, to protect the driver, I suppose.
If your IGBT fails, it will go short and you'll get the 500V (or 
whatever) right onto the gate. So this is a good strategy indeed.
But more bucks are lost if you damage the IGBT. To protect the IGBT from 
transients, I suggest you to put another TVS (or a 16V zener) *directly* 
from gate to emitter. Otherwise the 100 ohm in series will make its 
effect null.

Best Regards