Reverse polarity—accidentally connecting your power supply the wrong way—is a common mistake that can instantly destroy your robotic circuits. Whether you’re powering a microcontroller, motor driver, or sensor module, one misstep can mean starting over. But there’s a simple fix: reverse polarity protection.
The Problem: Wrong Polarity = Dead Circuit
In robotics, we often deal with swappable batteries or external power adapters. If positive and negative wires are reversed, unprotected components like ICs or MOSFETs can burn out immediately.
The Solution: Use a Diode or P-Channel MOSFET
A Schottky diode or P-channel MOSFET in the power input path will block reverse current. While a diode is simple, it drops some voltage. A MOSFET offers higher efficiency with minimal loss.
Real-World Example
Imagine a DIY line-following robot powered by a 12V battery. To protect the motor controller:
Add a P-channel MOSFET (e.g., IRF9540) on the positive input line.
Connect gate to ground through a 10kΩ resistor. When polarity is correct, it turns on. If reversed, it blocks current.
Simple Efficiency Check
Diode voltage drop (e.g., 0.4V) at 1A = 0.4W loss
MOSFET Rds(on) = 0.05Ω → Power loss = I²R = 1² × 0.05 = 0.05W — a huge improvement!
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