Is protection zener necessary for SMPS with high side FET drive?

Hello,
Is the ringed zener diode always essential in all SMPS high side FET drives?
(to prevent overvoltaging the FET gate to source voltage)

Schematic and ltspice simulation provided.

Adding diode capacitance to a gate may not be a great a solution. But it is necessary to stay within Absolute Max limits of 20V. So why not try something else like replace D22 with a suitable power rating Zener?

Keep in mind you have a thermal runaway condition with high ambient temperature raising RdsOn significantly. If you can compare the body diode forward voltage with a reference diode, you may be able to sense the thermal junction temp. to prevent catastrophic failure. with a safety shutdown circuit.

The greatest danger is probably at initial sudden power up of the high voltage dc input supply rail.
Gate drain capacitance can be enough to pop the gate insulation if the gate is initially left floating.

Whatever drives the gate may clamp the gate voltage, or it may not, and you cannot rely on the gate driver circuit being initially fully powered up before high dc voltage hits the drain.

Sometimes a gate source resistor is used, sometimes a zener, and sometimes the design of the driver itself clamps the gate to the driver supply and its usually large bypass capacitor.

In this circuit, I see nothing besides the zener capable of protecting the gate, so removing it may not be a good idea, unless you can protect the gate some other way.

So why not try something else like replace D22 with a suitable power rating Zener?

Click to expand...

Thanks, D22 is the DC restoration diode. It is , I believe, too far away from the gate of the fet to be useful as a zener. As you said, the fet gate needs protection.

The greatest danger is probably at initial sudden power up of the high voltage dc input supply rail.
Gate drain capacitance can be enough to pop the gate insulation if the gate is initially left floating.

Click to expand...

Thanks, this is , I believe a great point.

I also think that there needs to be an ultra fast diode connected from gate to source of the FET. (Cathode to gate) This protects the FET from overly negative gate-to-source voltage. Zeners, I believe, do not respond quickly enough in forward bias to be able to fulfill this diode function, so the extra ultra fast diode is needed, as in the schematic attached to this post. (LTspice sim also attached). Do you agree?