Overview: I have an electric quad that I have heavily modified. The motor will need to be replaced every now and then because I am driving a 48 volt motor with a 72 volt supply that can give extremely high currents (6 12V motorcycle batteries) . This is no problem as I dont mind getting a new motor periodically. I am looking to exploit the limits of this small vehicle!

Gate driving Problem: I am using a microcontroller to drive a Gate Driver to drive a MOSFET that powers a DC motor (with Flyback Diode IDW75E60). There are two power supplies; one to power the motor (72V) and the other one powers the control circuitry (including Gate Driver) (12V). MOSFET Gate is pulled to ground with a 5W 220ohm resistor (probably too low/unnecessary resistance). Everything shares a common "star" ground.

Every time I try to test this circuit I notice 3 things happen: (1) The circuit seems fine initially at very low throttle before the motor even start to turn (I can hear the 500HZ PWM signal hum). (2) When throttle is increased slightly more to rotate the motor, the Gate Driver]1 BLOWS UP! (3) The MOSFETs are then ruined as Gate and Drain are shorted. As well as Source and Drain.

I have a large toggle switch to shut off the circuit in an emergency. The switch connects the Source on the MOSFET to Ground (turning it off breaks the motor circuit mechanically and reliably in an emergency event).

Instinctive Solution?: Add a Diode between Source and Drain on the MOSFET? Increase PWM frequency? Reduce the Gate-Source resistor to 10K. Add a 220ohm resistor between the Gate Driver output and MOSFET? All the above?