self-protecting mosfets

Didn't someone once make an "indestructible" BJT in a TO-3 package that included lots of protection circuitry

I got some of these in to-220 pacs. (I can look up part numbers.. all from digikey.) I didn't use 'em. Some were a little slow, and they all had a bit of idle current (Drain to source) I assume to run the protection circuitry.

George H.

LM395. (to-220) Just don't hang a big inductor on the output. :^) Otherwise I like it. (spendy)

George H.

Den onsdag den 6. september 2017 kl. 19.53.34 UTC+2 skrev John Larkin:

we've used a lot of vnd7nv04 to switch solenoid valves and such, they seem to be available from all the usual places

We've started to use high side switching with an FPF270x instead

what was the load?

These fets usually specify some hundreds of mJ of unclamped flyback energy. That Zetex part is good for 550 mJ per shot (if you believe the data sheet) and zeners around 70 volts.

Cheap-ish.

I'll test some of those. Thanks.

Well, none. Power supply right across the fet. It's supposed to protect itself.

You could tack a current limiting transistor from emitter to base and a zener from collector to emitter across a 2N3055. But about the nicest thing you could say about the "poor man's" version is "it isn't fast"

My homemade SSR will have two of these fets back-to back, with a gate driver circuit (transformer and rectifier and filter) and some self-test stuff, in one square inch. 32 on a VME board.

Most interesting device, thanks! I can use these devices in my industry (pinball solenoid controls) just have to find ones that work closer to

John

OK all mine are from mouser. Mouser part numbers

I think the vnp part number was the best of the bunch. (also from Lasse)

George H

Oh the inductor as load was a student mistake. We sell an instrument with a heater and B-field coil both with banana plugs. Students plugged in the coil by mistake. A diode across the output fixes it.

(On my mind 'cause I had my second failure and sent out an email to all our users alerting them to the problem and fix.)

George H.

The vnp10n07 does 10A at 70 V. I think on digikey they are listed under thermal protection devices and not as FET's.

George h.

ST has quite a few 70V parts too

Den onsdag den 6. september 2017 kl. 21.34.06 UTC+2 skrev John Larkin:

I've done that with VNDs they just make a buzzing sounds as they go in and out of thermal shutdown from trying to limit current

I'm using the DRQ74 (15 uH) dual-winding inductor as the gate isolation transformer. It's rated for 200 volts between windings, so I connected it to a HV supply and cranked it up. At 2250V, it made sparks and went bip-bip about once a second. Seems fine now.

Den onsdag den 6. september 2017 kl. 21.46.28 UTC+2 skrev John Larkin:

how would an ADuM6132 (or ADuM6211 that has a channel for feedback too) compare on price/size?

Small size would be great, but the ADuM is big. And some of the fets work better with more gate drive voltage.

We'll probably do something like this:

which is cheap. Each SSR will take one square inch of PCB area, mainly for cooling, so it looks like we won't be squeezed on parts area. That transformer is 56 cents, and the diode and RC are a few cents more.

The ADuM6132 is $3 at 1K. And it's an insane power hog.