A guy wants me to make a device that will switch a relay on and off (will provide a ground), but the relay will be external to my system. How can I protect the FET or BJT (havn't decided which I'm going to use yet, though it won't really matter to the design)? The relay will switch on for 10 seconds, and off for 5 seconds so long as the car is turned on and the AC is on. Are BJT's as sensitive to those high voltage spikes as FETs?
The relay is the one for driving an AC system in a car, I don't know if it has a built in flyback diode or not. I suppose I could just put the diode at the drain/collector to 12v of the car, no reason it has to be right next to the coil...