Putting P-channel MOSFET reverse polarity protection into existing circuit for over voltage protection


Joined Jun 19, 2012
That's not the best circuit.

The trigger threshold is going to vary all over the place, the trigger voltage of the triac gate is temperature-dependent.
Considering that the 5V is divided down to the trigger voltage, this amplifies the temperature effects- making it even worse.
The MOSFET gate voltage is going to be only about 3.6 volts due to the GREEN Led circuit - this is going to make the RDS-ON higher than you want.

Google "over-voltage crowbar" circuits- this is how it's normally done.