In one of my recent builds it was necessary to come up with a circuit that would sense if the inputs were hooked up reverse polarity. I came up with this circuit:
I have tested this circuit to 100 volts DC on its Test Input terminals. If the Test Inputs are under normal polarity the output is LOW and if the Test Inputs are under reverse polarity the Output is HIGH. Unfortunately the Test Inputs will not sense a reversed polarity below 3.5 Volts. While these limitations were not a problem for my build I am curious if there are other better circuits to test polarity than what I cooked up here. Also if you see problems with the circuit above any critique would be appreciated. R1 limits the forward current through LED1 which acts like a zener and keeps the voltage Gate to Drain from exceeding breakdown limits. D1 is reverse biased under proper polarity. R2 keeps the P CH MOSFET off until there is a Negative Voltage applied at the gate by a reversed Test Input polarity.
Thanks John
