So I have a need to protect a few gate from over voltage conditions with a clamping diode.
I want to clamp the gate directly to the source. So it can never exceed to the zener voltage.

I tried to put this in the sim but for some reason I am not seeing any clamping action.

Any ideas?

All I see at the gate is the input sign wave. I am expecting to see the gate clamp at the zener voltage with is 10V

 

Do fat gates consume large amounts of junk food?
No clamping action, because. at 18V(pk) on the gate, there is 10V across the zener and 8V across R2?
Are you aware that a zener adds a capacitative load to the gate?

 

hi Mike,
The MOSFET is a Source follower, what do you expect the Source voltage to be when a positive drive over voltage is applied to the Gate.?
E

 

Try it with the load on the drain.

Or connect the Zener to ground instead of across the gate.

 

Sorry I drew it wrong
Here is what I meant it to be
Also, sorry about the typo, not enough coffee I guess

 

hi Mike,
Please post your LTS asc file.
E

 

It seems to work now in this simplified model. My real model of my real circuit still doesn't work. I need to examine it a bit more I think. hmmm

 

As I mentioned, the zener looks like a capacitor and will discharge the gate very slowly, if at all. Could a pulldown resistor in parallel with the zener hurt you?

 

As I mentioned, the zener looks like a capacitor and will discharge the gate very slowly, if at all. Could a pulldown resistor in parallel with the zener hurt you?

Thank you, that is very interesting, I did not know that. I saw that effect in the sim the other day. It almost looked like the FET was latching on it was interesting

 

So I have a need to protect a few gate from over voltage conditions with a clamping diode.

Why do you think you need to do that? You control the maximum gate voltage when you design a circuit.

BTW, what is a "fat gate"?