Reverse Polarity Protection for UPS – A Must for DIY Builders
⚠️The Problem :
When working with uninterruptible power supplies (UPS), especially in custom or DIY builds, reverse polarity is a silent killer. Accidentally connecting the battery terminals in reverse can instantly damage MOSFETs, controllers, and other sensitive components.
✅The Solution :
Implement reverse polarity protection using a P-channel MOSFET or a Schottky diode. A MOSFET-based solution is more efficient because it introduces minimal voltage drop, unlike diodes which waste power and generate heat.
🛠️ Practical Example :
Imagine you’re prototyping a 24V UPS for a solar-powered IoT gateway. If someone connects the battery backwards, you risk blowing out the entire system. By placing a P-MOSFET in the power path (source to battery positive, drain to system input), the body diode blocks reverse flow. When polarity is correct, the gate is pulled low to turn the MOSFET on—simple and effective!
🔢 Sample Calculation :
Say your load current is 5A and your MOSFET has an Rds(on) of 0.04Ω:
Power loss = I² × R = 25 × 0.04 = 1W
A good heatsink ensures safe operation.
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