Reverse Polarity Protection in Solar Inverters
🚨 The Problem :
In solar inverter systems, accidentally connecting the battery or solar panel with reversed polarity can damage MOSFETs, controllers, or the entire power stage. This mistake is common during installation or maintenance, especially in DIY setups.
🔧 The Solution :
To prevent damage, reverse polarity protection is essential. The simplest method is to place a Schottky diode in series, but it causes voltage drop and power loss. A smarter, efficient approach uses a P-channel MOSFET as a reverse polarity switch, allowing normal operation when polarity is correct and blocking current when reversed.
💡 Practical Example :
Let’s say you’re building a 24V solar inverter. Instead of risking damage from a misconnected battery, you can use a P-MOSFET with the source connected to the positive rail. If polarity is correct, the MOSFET conducts. If reversed, the MOSFET stays off, preventing current flow.
🧮 Sample Calculation :
Assume inverter current = 5A.
Choose a P-MOSFET with low R<sub>DS(on)</sub> (say 30mΩ):
Power loss = I² × R = 5² × 0.03 = 0.75W,
far lower than a diode’s voltage drop (e.g., 0.7V × 5A = 3.5W)!
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