RE: Series connection of Mosfets/IGBTs

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

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

Original poster: Greg Leyh <lod-at-pacbell-dot-net>

 >At work last week we
 >received a 6.5kV, 24-die package for evaluation, that should be suitable
 >for 6kA pulsed service.

Mmmmm nice :9

Greg, if anyone knows the answer to this question, it's gotta be you: How
much voltage can I hit the IGBTs in my OLTC with? The datasheet rating is
1.2kV. I'm running them at 850V at the moment but I'm hungry for more power,
and the "voltage" knob on my power supply still has a way left to go. Is
there anything I need to worry about as I start scraping the datasheet max
voltage, apart from the obvious problem of not having much headroom for
transients?

Technical data:
2x Powerex CM600HA-24H (1.2kV 600A) IGBT blocks connected in parallel
Primary current: 2500A peak per block, 66kHz (estimated)
On-time: 60uS approx (4 cycles of oscillation)
Gate voltage: 25V

My control circuit works well enough that the IGBTs are never hard-switched.
They are fully on well before the primary current reaches its first peak,
and soft turned-off at a current zero near the first notch.

Also, the chances of the IGBTs ever seeing a true "short-circuit" fault like
the ones described in your paper are nil, since the primary current is
limited by design to a value I know they can stand, and the power supply
"follow through" current is negligible.

Finally, is it safe to break down the IGBTs with a small current (eg 10mA)
so I can measure what their breakdown voltage actually is? I guess these
things vary in manufacture, so I'm hoping mine might actually be more than
1.2kV.

Your thoughts on the matter much appreciated

Steve Conner
Power Electronics MisApplications Engineer
scopeboy-dot-com