How to protect OpAmp output?


I have an OpAmp which controlls the Gate of a MOSFET.
When the MOSFET dies, sometimes the voltage it's running on (50V) somehow gets to stand over the OpAmp's output which destroys it.

What's the best way to protect the OpAmp from the high voltages that get to stand over the output?

Will a zener do the trick?
Trigger transformer won't be easy to use here because It's a PWM controller so I need nice block waves.
Diode on the output? but won't this be bad for delivering good current to the Gate?
Any ideas?

gmoon5 years ago
Have you tried a current-limiting resistor between the Op amp and the gate?

Most MOSFETs have pretty high input impedance, and since they are "voltage in" devices, rather than "current in", a decent-sized gate resistor shouldn't hurt. Although Inductive spikes can be HUGE, way higher than the 50V supply...
iceng5 years ago
Did you not know that a mosfet has an intrinsic inverse high speed diode
as a "you understood" part of the fet structure ?

What are you driving ? If its a switched load, then using a proper gate driver is the way to go, if its a linear load, then you could isolate it with a fast opto-isolator

Show a circuit of your op-amp/gate connection.