Working principle of lithium battery charger

A lithium-ion battery charger is a device that converts alternating current (AC) to direct current (DC) to charge lithium-ion batteries. Its core principle is to achieve safe and efficient charging of the battery through rectification, filtering, and voltage regulation circuits. The specific working principle is as follows:

1. Rectification and Filtering: First, the AC power is converted into pulsating DC power by a rectifier bridge. Then, the waveform is smoothed by a filter circuit composed of capacitors and inductors to reduce ripple.

2. Voltage Regulation and Constant Current: Chargers typically use PWM (Pulse Width Modulation) technology to control the output voltage and current. Initially, it charges quickly in constant current mode (e.g., 0.5C-1C current). Once the voltage reaches a set value (e.g., 4.2V/cell), it switches to constant voltage mode to prevent overcharging.

3. Protection Mechanisms: These include overvoltage, overcurrent, short circuit, and temperature protection (monitored by an NTC thermistor) to ensure battery safety. Some high-end chargers also have a balancing function to balance the voltage of multiple cells.

4. Communication Protocol: Smart chargers communicate with the battery's BMS (Battery Management System) via I²C or SMBus to adjust parameters in real time.