Re: Series connection of Mosfets/IGBTs

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

Original poster: "Rajesh Seenivasan" <rajeshkvs-at-hotmail-dot-com>
>Dear forum members,
>
>I have seen parallel connection of MOSFETs to increase the load current
>capability.
>Anybody in this forum tried series connection of MOSFETs/IGBTs and increase
>the supply voltage to greater than 2KV ?


It's possible, but requires a *considerable* deal of care to equalize the 
stack voltages during both slow and fast fault conditions.  It's far easier 
and more reliable to just use the higher voltage silicon.  The Mitsubishi 
4.5kV silicon is fine for up to 3kV working voltage, and the Infineon 6.5kV 
silicon works reliably up to 4kV+.  Mitsubishi has also just announced a 
6.5kV process, with beta samples now on the street.  At work last week we 
received a 6.5kV, 24-die package for evaluation, that should be suitable 
for 6kA pulsed service.
When higher output voltages are needed, historically the preferred method 
is to use pulse xfmrs or fractional-turn xfmrs to combine multiple IGBT 
drive circuits in series.