N-channel mosfet turn constantly on after a while

Question

Hi;
N-channel mosfet (Q4) work fine for couple of time and suddenly turn on constantly.
I changed Q4 multiple of times and each time it work for couple of time and suddenly turn on constantly.
the output of mosfet is connected to a 2.5 amper 12 volt car windshield washer pump and the reason of C11 and R33 is because of water pump noise that cause microcontroller to dont work normal.
What could be the reason of this problem ?

Andy aka · Answer

You need to prevent back emfs from the washer motor destroying your MOSFET when it deactivates. The normal method is a "reverse" diode in parallel with the motor such as this (equally needed for a BJT as a MOSFET): -

This suggestion is made assuming that the motor is never operated in reverse - if it is then a slightly different arrangement is needed.

N-channel mosfet turn constantly on after a while

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