Fixing conmutation for high voltage switching with power MOSFET
Analysis

Capacitor specifications are not given, so a typical part,
e.g. 1&nbsp;mF @600&nbsp;V ESR=92 [mΩ] @ 10&nbsp;kHz 20°C, using this capacitor, Kemet ALC70(1)102FP600.

FET RdsOn= 270 mΩ, so out of 270 mΩ + 92 mΩ total, the FET will draw 75% of the power and energy.

The capacitor Ec = 1/2 CV² = 1/2 * 0.001 F * 400² V = 80 J, so the capacitor ESR will dissipate 25% of 80 or 20 J while charging up to 80J for a total transfer of 100J . So the FET must transfer and dissipate 75% of 100 J or 75 J.

The worst-case FET safe operating area (SOA) must be observed.



Yet, the FET can only handle about 900 mJ at 92&nbsp;µs, but with RdsON*C = 270 mΩ * C = 270&nbsp;µs, the SOA curve points to about 500 mJ vs. a requirement to transfer to dissipate 75&nbsp;J.

So a much bigger FET is needed with a lower RdsOn in the 10 mΩ range, I suspect. I doubt if the supply or capacitor can handle a steady diet of these pulses, so it is back to the drawing board. The term "instantly" needs to be specified and relaxed with a current limiter.

The short circuit current on the capacitor is about 4000 amperes at 400&nbsp;V.

"Houston, I think we have a problem"

Actual simulation below  (not with an ideal Voltage source the Battery supplies a peak of 441 MW with a 362 ps time constant. ( ideal battery is not possible)









simulate this circuit &ndash; Schematic created using CircuitLab

This is Houston.  We think we have a solution.