Battery Charger and Discharger Using USB Power Supply

This DIY circuit operates using a standard USB power supply to manage both charging and discharging tasks for up to four 1.2V rechargeable batteries simultaneously. The system uses a USB connector to receive incoming DC power, which is then routed through the circuit board. To regulate voltages accurately, a TL431 shunt regulator (IC1) works alongside an LM324 quadruple op-amp (IC2) to monitor and control current paths. For the discharge function, four 30-ohm 1W power resistors (R1-R4) act as resistive loads to bleed energy safely out of the batteries. Four 1N4007 diodes (D1-D4) are included to prevent reverse current flow, protecting the power supply and sensitive components from accidental back-feeding. A preset variable resistor (VR1) allows fine-tuning of the circuit's threshold levels. Finally, an array of nine LEDs (LED1-LED9) provides visual status indicators for operational states like power-on, charging, and discharging, while four small 2.5V 200mA bulbs serve as additional indicators or load components during testing.