After watching Afrotechmod's tutorial about reverse voltage protection, I wondered if I could incorporate it in a circuit I'm working on. Unlike the circuit in the video, mine's dual supply, and there's where things get lost on me.
Do I need to tie the MOSFET's gate to GND, or to the supposedly negative power rail? Is is even possible to do this with a single MOSFET, or do I need another one? If so, P-channel or N-channel?
simulate this circuit – Schematic created using CircuitLab
You need two polarity protection devices (two diodes, or two MOSFETs), because otherwise, if you invert the polarity, only one rail will be interrupted and the other rail (now reversed) could still damage the circuit making current flow in the reverse direction through the ground rail.
See for example this circuit.
Ground is only a definition. You could just put your ground symbol to -12V and call the upper rail 24V instead of +12V and its still the same circuit. So yes, the same method can be used for reverse voltage protection.
However in this case you will run into another problem. The reverse voltage protection is based on the fact that the Gate-Source voltage is either negative and the MOSFET is conducting or in reverse positive and the MOSFET is not conducting.
Your problem here is that the Gate-Source voltage difference is 24V. The MOSFET IRF9530 chosen by you has a maximum of +-20V (and most MOSFETS will not be higher).
Here you would need to add the following:
