One of the circuits that should be part of every device that uses an external power supply is protection against polarity reversal. Even an expensive device can be damaged by a single mistake. There are several districts that can provide such protection. This circuit uses MOSFET s kanálom P, napríklad IRF4905. This transistor has a resistance of 0.02Ω in the switched state, and with a current of say 5A, the loss in this circuit is 0.1V.
On the left side of the circuit is the input, on the right is the output. With the correct polarity, the voltage VGS is large enough to turn the transistor on, but when the polarity is reversed, this voltage is low and the transistor does not conduct current. Diode D1 is an overvoltage protection for the MOSFET transistor.
For larger current, it is also possible to use a transistor with an even smaller Rds in the on state, for example the IRFP9140.