Lumina
Newbie level 4
I am trying to protect a FET from an Ldi/dt voltage spike and would really appreciate any advice. I am trying to protect in the event of a short circuited load. When I short out the load ie. connect Lead A to Lead B in the diagram below the FET blows, not from over current but over voltage. The leads are about 2 foot long 16 AWG. The supply is current limited at 25 Amps. i have some 1500 watt bidirectional TVS diodes with a clamping voltage of 55 Volts.( It's an 80 volt FET ) When I put 1 TVS across the output of the FET the TVS went up in smoke when I created the short. I tried putting 3 TVS in parallel and that worked at a 50% duty cycle however as I tried adjusting the duty cycle they failed. Is it just a matter of adding a higher power TVS. Should I try a thyristor based crowbar instead? The FET will see probably 8 Amps max when working. The 25 Amp supply will be shared across other channels. Should I put a PTC in line as well so that once the over voltage is clamped the PTC will go after some time? As you can tell I am a newbie when it comes to FET protection. Thanks for any advice.