piranha skrev:
Very nice Finn!
I had two questions.
1. What gate voltage are you guys running these days? I think the
Powerex bricks are "rated" at 15V but I was just wondering if you
still over drive and by how much.
2. You say there are no gate resistors. Is there a story behind
that? I would worry about the high dI/dT damaging the gates due to
very high gate currents (max Ig) during switching. But maybe the
gate driver is not enough to hurt the big CM600s. Of course,
switching noise is not a problem with good zero crossing and then
snubbers have no use.
Terry
Thanks,
Gate voltage is -10V +20V and the gate driver is a n/p channel totem
pole driver, which has very low shoot through.
At some point in the development phase, I got obsessed with creating a
totem pole without the usual intermediate resistor, to diminish the
inherent shoot trough of the combination.
The anti shoot through network on the gates of the N/P pair creates a
controlled current output of 10A, so the gate voltage swooshes up in
200nS.
http://www.hammertone.com/temp/totempole.jpg
The 2 diodes closest to the gates *really* are 10V zeners, but the cad
package didn´t have them in surface mount, so.....
It is pretty slick: You cannot see the Miller threshold as is usually
visible on gate voltage scope traces.
In comparison, the CM600 datasheet assumes a 2.1ohm gate resistor,
which would result in a 15 amp charging current given +-15V drive.
I did this to demonstrate that it *could be done* with the predikter,
without creating overshoot problems.
Do you think I am on safe ground with this?
Cheers, Finn Hammer
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