I am reading about reverse voltage protection and I have found this circuit with its explanation but I do not understand why the capacitor C8 improves the behavior of the circuit when there is a rapid change in input voltage polarity.In adition, Is it really worth adding R2 and C8?

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  • \$\begingroup\$ Note that if a 25v-gate MOSFET were used (assuming nothing over 25v would ever be applied) then the zener and cap would be unnecessary. \$\endgroup\$ – rdtsc Aug 23 '19 at 12:22

R2 and the zener are there to protect the MOSFET gate from the input voltage exceeding the gate voltage rating. Even a momentary transient can permanently damage the thin gate oxide layer.

The capacitor is there to ensure the MOSFET switches rapidly and does not linger partially on dissipating excessive power. Otherwise the gate charge has to be supplied through the resistor, and the Miller effect results in a relatively long turn-on time especially for a large low-Rds(on) MOSFET.


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