The following is the power control part of the circuit I use in my car to control the wing mirror folding motors, the idea is that the whole circuit can power itself off after its done its job to prevent even minimum battery drain. (full circuit here)
The power goes through the P-channel power MOSFET and there's an N-channel signal MOSFET to drive the power MOSFET's gate low. The signal MOSFET's gate has a pull-down resistor to keep it off and may be driven on either from a 5V arduino signal or a 12V car signal, through diodes.
The N-channel MOSFET is failing every few days or weeks. I have tried using a 2n7000 small signal MOSFET and I have also tried the way overkill RFP50N06 power MOSFET in its place but both eventually failed. In both cases I believe I have stayed well within the maximum absolute ratings from their specs.
This is my first direct use of MOSFETs but as far as I've checked a MOSFET will burn mostly if the gate is kept on at a voltage below the Gate-Source Threshold voltage because part of the Drain-Source current dissipates at the MOSFET. In this case the threshold voltages are 2-4V and the gate is driven at 5V to 12V minus the diode's voltage drop, so it should be fine. In any case the Drain-Source current should be so small it shouldn't even matter.
What else could be the problem?
(I have also once tried a BJT NPN transistor in this place and I was surprised it didn't work, haven't investigated further)
