4500 volt mosfet

snipped-for-privacy@highlandsniptechnology.com wrote in news: snipped-for-privacy@4ax.com:

Ya saw how far apart them thar legs are.

At those potentials everything would need to be potted.

Incorporate at full potential very carefully (planning and engineering).

That data sheet is a bit sneaky. The DC specs (fig 13 and 14) are nowhere near as impressive as the headline figures.

But, given that a lot of your designs are about making crazy-fast pulses, that might not matter.

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How about the venerable 6BQ5 ?? With 100V on the plate, it will pass over 150mA = 600 ohms Rpk on. Max plate V is speced at 1100V - it will easily take double that without breakdown.

Transconductance is about 12mA/V = well less than a MOSFET, but not bad thing with kV of output signal involved. Dissipation is 12W long term, 10 times that ( 150mA at 800V) for a few seconds without failure. That big lump of steel ( the plate ) takes some time to get red hot.

OTOH the MOSFET chip will fail in sub 1 mS if abused like that.

Tubes can actually arc over internally from extreme plate voltages without failure, particularly all glass types like the 6BQ5. AKA the EL84 to non Yanks .....

FYI:

I have a test rig here that uses a pair in P-P, 650V on the plates and 325V on the screens. Operated in Class AB. Outputs 60W of clean, sine wave power without distress.

...... Phil

At 40 volts/mil creepage, that fet is good for 8 KV or so. One could put a little slot in the board too. Or a dab of conformal coat around the pins.

I'd expect the silicon to break down before the pcb insulation does. I'll have to test one and see what actually happens. I have an old Spellman 30 KV supply that might still work.

But a tube costs less and, if picking a Russian one, is more available right now :-)

Just need the tube and a floating grid driver and a 4500 volt isolated filament transformer. All surface mount of course.

I just got some Ixys mega-dpak parts to play with, so they seem to be available. I'll crank up the old Spellman and blow some up.