Reverse Current Protection in Chargers – Simple, Smart & Safe
When designing or using battery chargers—especially for lithium or lead-acid batteries—reverse current protection is essential. Without it, energy from the battery can flow back into the charger once the power supply is off, risking heat buildup, circuit damage, or battery drain. Fortunately, adding protection is easy, even for beginners.
⚠️ The Problem: Reverse Current Can Damage Your Charger
Many chargers lack internal blocking, especially in DIY or budget modules. When the power goes off, the connected battery may push current backward into the charger circuit, possibly damaging sensitive components or triggering fire hazards.
✅ The Solution: Use a Diode or Ideal MOSFET
Simple fix: Place a Schottky diode in series with the charger output. It blocks reverse flow while maintaining low voltage drop.
Advanced fix: Use a P-channel MOSFET configured as an ideal diode—this offers higher efficiency with near-zero voltage drop.
🔧 Practical Example
Charging a 12V lead-acid battery with a DC adapter? Insert a 5A Schottky diode in series. It blocks reverse current when the adapter is unplugged.
📏 Sample Calculation
Power loss in Schottky = I × Vf
For 2A and Vf = 0.4V:
P = 2 × 0.4 = 0.8W – manageable with a heat sink.
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