I am using this solution to drive a large (huge) relay on a boat.
The system works well for months on end, but eventually the MOSFET (T2) dies suddenly.
I have modified the schematic to include the modification suggested by Jack Creasey and others (circled in RED, not part of original design), as well as a further explanation as to how the system is wired to battery ground to illustrate why the typical snubber diode may be inadequate (it dissipates back-EMF to battery ground through a 4-ohm wire).
Simulations suggest that with this cable resistance back-EMF may push LOCAL_GND down to -20 V with respect to BATTERY_GND, the controller would see 34 V and fry.
I am hoping to find suggestions on the correct way to protect the MOSFET in this situation.
I am not able to make modifications to anything outside of the gray box and no strong GND connection is available in this part of the system.
12VDC is the battery voltage and may vary depending on load, generator output, other loads switching, etc. Typically 11-14.4 volts.
The relay draws approximately 6 A from PULSE_OUT, but I have never had access to the actual relay to perform measurements on its inductance or behavior when switched on or off.
Because the relay is bistable and requires only a pulse to turn on, PULSE_TTL is driven with 200 ms pulses at 3.3 V. These pulses are typically very infrequent, but they can occur every 5 seconds worst case. Another identical circuit drives the turn off coil in a similar fashion.