The Problem :

Reverse polarity on a 24V power rail—often caused by wiring mistakes—can instantly damage sensors, controllers, and other connected devices. Unlike 5V systems, 24V rails carry more energy, so the risk is higher.

The Solution :

To protect your circuit, add a reverse voltage protection circuit using either a Schottky diode or a P-channel MOSFET in series with the input. Diodes are simpler but cause a small voltage drop. For better efficiency, a P-MOSFET configured in a “high-side switch” gives low loss and fast response.

Practical Example :

Say you’re powering an industrial sensor module with a 24V SMPS. If the power lines are reversed during maintenance, the internal logic ICs could burn out. But with a P-MOSFET like the IRF9540, you can automatically block the current when polarity is reversed.

Sample Calculation :

If your circuit draws 1A, a diode with a 0.6V drop causes:

Power loss = V × I = 0.6V × 1A = 0.6W.

A MOSFET with 50mΩ Rds(on) only loses:

P = I² × R = 1² × 0.05 = 0.05W, making it far more efficient.

Product Suggestions :

MOSFET

Schottky Diode

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