Methods for Reverse Power Protection:

1)     Series Diode

This is the cheapest and simplest method but it is only good if the board can accept large series voltage drops(0.7V) and the operating currents are low (<100 mA). It may also increase power consumption by an unacceptable amount.

Strengths

·       Low-cost, simple solution: <$1

·       Fast blocking, resettable

·       Potential for very high breakdown (up to 1000 V+)

Limitations

·       The cost benefit is quickly minimized as operating currents go up. At higher currents, the increased power consumption ultimately requires a larger, more expensive IC with a more thermally conductive package and heat-sinking structure. 

·       The voltage drop and power consumption associated with this method typically rule out implementation in all but a few applications.

2)     Series Schottky

The Series Schottky method is similar to the Series Diode method, but with less voltage drop and lower associated power consumption. It is a good choice if the design can accept large series voltage drops (0.3-0.6 V) and the operating voltages remain fairly low (<200 mA).

Strengths

·       Low cost, simple design-in: <$1

·       Very good blocking, Resettable

·       High breakdown (up to 200 V+)

Limitations

Reduced voltage drop allows for lower thermal management requirements relative to a traditional PN diode. This may allow for smaller, less expensive packages, but power consumption and the drop in operating voltage still need to be considered.

3)     Series MOSFET

A MOSFET is the best choice for low voltage drops and power losses but it can be more expensive and more complicated than other solutions. MOSFETs can be set up in series with the power supply so that its gate to source voltage (VGS) is enough to turn it on during normal operation. When the power is connected in reverse polarity the VGS will be too low to turn on the MOSFET and the power will be disconnected from the board. A MOSFET with a very low drain to source resistance can be used which means that the voltage drop and power losses during normal operation would be much less than using a diode. It is better to use a PMOS because it cuts off the positive rails which can be safer in some situations. Notice that the PMOS is connected “backwards” with the drain to the power supply and the source to the load.

Things to consider when choosing PMOS and setting up circuit:

·       Drain to Source resistance – A lower drain to source resistance would mean a lower voltage drop and less power losses. e.g.               300mOhm @ 7.2A, 10V

·       Drain to Source Voltage – The drain to source voltage needs to be higher than the circuit voltage. e.g., ±20V

·       Drain Current – This should be larger than the drain current. e.g., 12A (Tc)

·       Zener Diode Voltage – Choose a Zener diode that is less than the gate to source voltage of the MOSFET

·       Resistance Value - The resistor value needs to be chosen in a way that it should not be high enough to not overheat the Zener, but low enough to provide adequate Zener bias current and to discharge the Gate rapidly if the supply voltage is suddenly reversed.

Strengths

·       Low (user-defined) series resistance and voltage drop

·       Resettable blocking function

Limitations

·       Complexity of implementation

·       More expensive than other solutions: <$3

https://components101.com/articles/design-guide-pmos-mosfet-for-reverse-voltage-polarity-protection

http://www.geofex.com/Article_Folders/mosswitch/mosswitch.htm