Reverse Polarity Voltage Protection Using P-MOSFET


Could you please help me understand why in a reverse polarity circuit with P channel MOSFET Source of the MOSFET is connected to the LOAD and DRAIN to the power supply?
I understand the concept of a body diode in the MOSFET, but still I do not quite understand is there any reason why not connect SOURCE to the power supply and DRAIN to the load?
Let's neglect Zener diode and R1 in shown circuit.
enter image description here

Best Answer

If you understand the body diode then you should see that if you apply significant negative voltage to the input the body diode needs to block or it will pass the incorrect polarity to the output, probably destroying the circuitry it is connected to.

In normal operation (positive input) the body diode is shunted by the Rds(on) channel resistance of the MOSFET. In blocking operation (negative input) both the body diode and MOSFET channel block.