Re: IGBT gate drive experiences-Reply II

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

Original poster: "David Sharpe by way of Terry Fritz <teslalist-at-qwest-dot-net>" <sccr4us-at-erols-dot-com>

Hi Marco

Another comment concerning CCPS Rev. B ...

Tesla list wrote:

 > Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" 
<Marco.Denicolai-at-tellabs-dot-com>
 >
 > Hello all,
 >
 > During this year 2002 I have been modifying the Thor switching power
 > supply (CCPS), attempting to improve its reliability.
 > A significative part of the modifications are related to the gate drive
 > of its IGBT full-bridge. As I found myself with quite many saved
 > oscilloscope snapshots, I decided to write down about my measurements.
 > The result is a pretty long (and boring) chronicle, but maybe some of
 > you can find something interesting in there.
 >
 > I refer to the upgraded power supply as "CCPS rev. B". You can find the
 > above mentioned paper, together with schematics and PCB Gerber files at
 >
 > http://www.iki.fi/dncmrc/
 >

I admire your determination to resolve the issue of EMI/RFI induced failures
in your PS.  One thing I noticed is you have no snubbing network (C, R+C,
or R+C+D) across IGBT's or associated half-bridge totem poles.  Maybe
by bypassing HF transients around devices, your miller capacitance transfer
into relatively high impedance drive circuits will be less of an 
issue.  I'm waving
my hands with much conjecture here...  I do know in induction heating,
bypass capacitors (foil PP, direct mount to CE of IGBT) are used, value
is a guess but typical I've seen is in the 1-10nF range.  I have some URL's
that I can locate and e-mail to list from EUPEC, and several other vendors
concerning snubber design based on operational frequency, applied voltage
and currents etc.  Circuit stray inductances and the havoc it can raise are
also 'cussed and discussed, particularly in high current, high voltage, high
frequency applications.  100nH don't sound like much, but a 10kA/usec
dI/dt can lead to some very catastrophic avalanche conditions (Ref:
earlier posting from Greg Leyh at SLAC with current crowding failures
in IGBT's at extreme pulse power applications).  The other point is the
loop area between your filter capacitor and the IGBT totem pole must be
as small as possible, the loop area and induced currents can generate
horrible ringups, this is why multilayer stripline busbar technology is used
in high power applications.

This circuitry is nearly identical to IR21531D half bridge circuit I'm building
for a SSTC / IH driver so that's why your work is of much interest at this end.

Best Regards and Happy New Year!

Dave Sharpe, TCBOR
Chesterfield, VA. USA