Reverse Voltage Protection for Chargers – Simple Yet Essential!
⚠️ The Problem :
Ever accidentally connected a charger’s input wires in reverse? It can instantly damage your charging circuit or the battery. Reverse voltage protection ensures that your charger survives wiring mistakes without a meltdown.
🛠️ The Solution :
The simplest method is using a Schottky diode in series with the positive input. For more efficiency and less voltage drop, use a P-channel MOSFET configured as a high-side switch. When voltage polarity is correct, the MOSFET turns on; if reversed, it stays off—protecting your circuit.
📦 Real-World Example :
A DIY Li-ion battery charger designed for a 12V input was accidentally connected to a 12V battery with reversed polarity. The result? A burnt PCB trace and dead IC. The fix: adding a P-channel MOSFET at the input—problem solved permanently.
📐 Quick Calculation :
If your charger draws 2A and you use a Schottky diode with a 0.4V drop, the power loss =
P = V × I = 0.4V × 2A = 0.8W
Switching to a low R<sub>DS(on)</sub> MOSFET with 50mΩ reduces loss to just
P = I² × R = 2² × 0.05 = 0.2W — 4x better!
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