I am building an Arduino shield and I want to protect it from reverse polarity. I would like to use a power mosfet for that instead of a big fat diode.
The circuit Max is 30V and 7 amps.

Is that possible with a mosfet?

Thanks

 

Is that possible with a mosfet?

Yes.
What's the minimum voltage?

 

The minimum would be about 9.3 volts. So, let's say 8 for a safety margin.

 

Okay.
Below is the LTspice sim of the circuit:
The output voltage (red trace) follows the input voltage (blue trace) for positive voltages, but blocks any negative voltage.
The circuit works because a MOSFET conducts equally well in either direction when biased ON.

The transistor can be any P-MOSFET with a 40V minimum voltage rating, and an on-resistance of <20mΩ, (so the MOSFET doesn't require a heatsink at 7A).
The 12V Zener, D1, is to keep Vgs below the transistor's max rating (usually 20V).

 

This is really excellent. Thank you so much crutschow !