MOSFET varieties

Reverse supply polarity and use a depletion NFET. (You’re basically asking for a depletion PFET, but nobody makes them. )

Cheers

Phil Hobbs

Many thanks, Phil.

A p-channel JFET would do that.

Supertex makes some great depletion-mode NFETS, and someone else has equivalents. They make nice constant-current loads and current limiters.

What are you trying to do?

Supertex is now a Microchip company.

Thanks, John, but I don't want to start another lengthy thread here which would no doubt happen if I explained - and everyone chipping in a different idea so I end up losing track. So - no comment! :)

Well, OK. I like to post problems here to brainstorm possibilities. Even silly ideas help me think about possibilities.

But one can get lost-in-space too. Confusion is good, but not forever.

Depletion fets are great fun. I like to discharge power supply caps with a depletion fet and an LED. It discharges linearly and winks out at 2 or 3 volts.

Not sure I have *any* depletion mode FETs 'in stock' here. I have hundreds of E-mode ones. Never ceases to amaze me how despite having tens of thousands of parts, the design always seems to call for something I don't have. Even if it's something - as in this case - that I designed myself!

BTW I discover that there are 1700V SiC JFETs, such as the Qorvo UF3N170400B7S.

Cheers

Phil Hobbs

I used some 1200 volt Cree SiC fets in my Pockels Cell driver. They are a niusance to drive, +18 and -12 on the gate. Had to use GaN fets to drive that.

Silicon drives GaN drives SiC.

That is truly impressive. I'll have to look the price up now, just out of curiosity.

Ixys, now Littlefuse, makes a 4700 volt mosfet. It's about $100.

Wow! I am just so out of touch with what's available today. Fortunately, since I'm not a designer, I can afford to be. :)