Snubber Design for MOSFET over current protection switch HELP

Thread Starter


Joined Feb 7, 2018
Hi there,

I am currently trying to build a solid-state protection device SSPD and need to design a snubber for the MOSFET which is carrying out the fault interruption. I have built an overcurrent simulation in LTspice buy charging up a capacitor to 540Vdc and then creating a short circuit to discharge the cap which generates the fault current. I then use a voltage controlled switch which I have set to open when the fault current reaches 180 Amps (MOSFET tripping current) to provide the fault protection. But as expected I get a nasty voltage transient when the switch opens I have tried to design a RC snubber to prevent this spike using E=1/2CV^2=1/2Li^2 but can't seem to get the values right. If I'm honest I still haven't quite got my head around how the RC snubber works I assume the capacitor prevents the sudden change in voltage a absorbs the energy which it then dissipates into the resistor. Some advice on the correct process of designing this type of snubber would be very much appreciated. Also if there is an alternative method to prevent this voltage spike.

Thanks in advance