Reverse Polarity Protector

A series diode is often
used as a means of protecting equipment from accidental power supply
reversal, particularly in battery-powered equipment. Due to forward
voltage losses, this is sometimes impractical. One solution is to use an
enhancement mode P-channel power Mosfet (Q1) in series with the
positive supply rail. A device with low drain-source “on” resistance can
be selected to minimise voltage losses, which in turn extends battery
life and reduces heat dissipation.

Circuit diagram:

Reverse Polarity Protector Circuit

Reverse Polarity Protector Circuit Diagram

Zener diode ZD1 must be included to protect against excessive
gate-source voltage, while a 100kΩ resistor limits zener fault current. A
second 100kΩ resistor across the output ensures that the gate doesn’t
float when the input is disconnected. A series fuse and bidirectional
transient voltage suppressor (TVS1) could be included to provide
over-voltage protection, if desired. If common input & output
grounds are unimportant, then a version of this circuit employing an
N-channel power Mosfet in series with the negative (0V) rail could also
be employed.

Author: Bruce Griffiths – Copyright: Silicon Chip Electronics

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