Protected MOSFETs

I was using the VND14NV04 to switch rectified AC 12V RMS (just the bridge, no filter cap). In a 100 channel lab device, there were 4 failures over 5 years. Interestingly, the failure mode has always been half-open. No data from purely DC applications, it was enough for me to send them to the trashcan.

I have good experience with the IPS161, although it is not exactly what you are asking, but IMHO close enough to mention it.

Best regards, Piotr

I was thinking about a protected-gate mosfet, which is pretty common these days. They basically have a roughly 40 volt symmetric zener from gate to source. That's nice.

I tried three of the claimed really protected mosfets, the ones with current and thermal limits. The ones that I tried were terrible. One didn't really protect itself. One oscillated horribly. Something else was nasty about the third.

They seem to power their protection circuits from the gate drive, which means that you wind up doing half the work.

If you find a good one, let us know.

Lately I've been putting some power parts on a PCB copper pour with a shutdown thermistor incorporated into the MAX809 powerup reset circuit. Seems to work.

You can do fun stuff around a MAX809.

We need a MAX809 sort of thing that has a temperature shutdown built in. May exist. Isolated tab would be good.

Zetex makes a SOT23 nickel RTD with isolation.

This is disturbing.

We have a few thousand of the NCV8402STT1G protected FET out and in use over the last couple of years. They are used as a uC interface to drive

Those are the ones I was talking about.

Not a bad idea. I usually use LM393s for that, but in situations where you need a POR anyway, dorking a MAX809 might be a win.

MIC280 looks nice--settable local plus remote temperature measurement and thermal alarm, SMBus. I've never used it. Seems to be the only game in town, but doesn't have an externally-accessible POR function.

Cheers

Phil Hobbs

sniptechnology.com:

which ones and what did you try? other than one type from Onsemi some 10 ye ars ago I've not heard of any issues

usually ~1mA gate drive and a series resistor how is that half the work?

Right, I tested a few of these for a simple heater (I was mostly interested in the thermal limit) and none of them were as robust as I wanted. Nothing like thermally protected bjt parts (lm317, lm395)

George H.