I would like to add a reverse polarity protection circuit to protect my circuit from reverse polarity.
I tried to use following circuit at this link
With NMOS FET, I have a little problem. If the voltage is too low the FET isn't turning on and the current flow through the internal diode. But I think the diode isn't in a good direction. If the voltage is high enough e.g. >3V, the MOSFET is turning on and current flow through the MOSFET.