dumb!

Sorry, I mistyped. Yes, Source to gate. Or ground in your case.

Maybe a 12V zener source to gate?

It will be completely pinched off at -8V or so, so the channel leakage current of 100nA or whatever will flow through the zener to ground/gate.

End result is that more voltage appears across the switch than the transistor.

Best regards, Spehro Pefhany

I already looked at the datasheet.

I still can't see what the circuit is supposed to do, and the description of what the board is supposed to do is pretty vague to start with, which doesn't help.

So back to Q2, there's a switching device in series with a pushbuton switch, with the gate wired to ground.

Why?

Vague ?>:-}

Depletion mode FET, so, when pushbutton is activated, it's a current-limited source rather than just a switch? ...Jim Thompson

Ah- that works for me.

But the off gate-to-source voltage was not limited. I think that's what the "dumb" was all about... not real clear. ...Jim Thompson