Simple reverse polarity protection

One of the circuits, which should be part of every device, which uses an external power supply is reverse polarity protection. Even expensive equipment can be damaged with a single mistake. There are several circuits, which can provide such protection. This circuit uses a P-channel MOSFET, for example IRF4905. This transistor has a resistance of 0.02Ω in the closed state and at a current of say 5A the loss on this circuit is 0.1V.

There is an input on the left side of the circuit, right output. With the correct polarity, the VGS voltage is high enough, to make the transistor trip, however, when the polarity is reversed, this voltage is low and the transistor does not conduct current. Diode D1 is a surge protector for a MOSFET transistor.

For higher currents, it is also possible to use a transistor with even smaller Rds in the closed state, for example IRFP9140. Different way reverse polarity protection described Ľubo OM6IN.