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Series Mosfet Drive for High Voltage

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FxDev:
Hello everyone,

I want to design 2000V high voltage switch for pulse generator.
It will run around 50~100kHz and duty will be variable (%1 to %50). 3300V switches are not cheap and not good for high frequency. Current will be around 3~5A.

So I want to try series mosfet drive, 2 series 1700V SiC is very good for me. I found some schematics, I simulate it but I wonder do you have some suggestion for me?

Some techniques:






jbb:
Hmm

Those are both cascade options… with some benefits and trade offs.

This is reminding me of a paper I saw years ago. I think the author used a stack of SiC JFETs connected much like your first figure, and a small (like 40V) Si MOSFET to control the source of the bottom JFET.

On topology:
You’ll need a diode for the return side. Not sure if a useful 3300V SiC diode will be available.
How about moving to something like a Neutral Point Clamped (NPC) converter (see https://www.vincotech.com/products/by-topology/more-about-npc.html) which effectively splits the job into two half bridges? Could help with control too; you move from a 2 level (0, 2kV) to a 3-level (0, 1kV, 2kV) output which means the volt second product your inductor is filtering is halved, and therefore the required inductor value is halved.

FxDev:
Hello again,

JFET looks good but 1700-2000V JFET is hard to find.

I want to use same topology on Flyback Converter too. So I have to use mosfet in series :)

Marco:
Voltage sharing isn't perfect, if the bottom MOSFET goes too fast you will get some avalanche.

Those designs are a bit old in the tooth, supercascodes are the new hotness. They tend to have avalanche diodes, so if something avalanches it's at least not the SIC FETs.

UF3N170400B7S seems relatively affordable and available ... for the moment ...

oz2cpu:
IGBT ??

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