I'm designing a MOSFET (FQP30N06L) circuit to drive a (50V, 3.4ohm) pinball solenoid controlled by a PWM pin on an Arduino DUE:
simulate this circuit – Schematic created using CircuitLab
The MOSFET gate and solenoid are tied to the terminal block to make external alterations easier. My concern is that, while altering the circuit I will forget to ground myself, and fry the MOSFET. My understanding is that when MOSFETs fail for this reason, they often become shorts which would fry the solenoid coil very quickly.
My question is, what can I do in-circuit between the terminal block and the MOSFET to protect the MOSFET from ESD?
Best Answer
If the gate is truly connected to a terminal block, it is vulnerable and needs to be protected. A series resistor and TVS diode would be my first stop at protecting it.
simulate this circuit – Schematic created using CircuitLab
A cap in parallel with the TVS will help slow the ESD event down, if you can afford the added capacitance on the gate, and give the TVS a little more time to turn on. Make sure the traces are short as possible and the TVS has a solid ground connection. A regular Zener diode is just too slow for ESD protection. It's better than nothing, but at that point, your primary means of protection will be the MOSFET's internal clamp, if it has one.