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Li-ion Charger - How it works

The Li-Ion Charger and Li-Ion Charger with Protection are compact modules designed to safely charge single-cell lithium-ion (3.7V nominal) batteries. They incorporate efficient charge management ICs that follow the standard CC/CV (Constant Current / Constant Voltage) algorithm.

Li-Ion Charger
Li-Ion Charger
Li-Ion Charger with Protection
Li-Ion Charger with Protection

How Charging Works​

1. Constant Current (CC) Phase​

When the battery is deeply discharged, the charger supplies a constant current (up to 500mA depending on the module) to the battery while monitoring its voltage. This rapidly charges the battery from 3.0V to approximately 4.2V.

2. Constant Voltage (CV) Phase​

Once the battery voltage reaches 4.2V, the charger switches to constant voltage mode. The charging current gradually decreases while maintaining the 4.2V level. Charging ends when the current drops below a preset threshold (usually about 10% of the initial current).

Charging Process Steps​

  1. Battery Detection – The IC detects the battery and checks its voltage level.
  2. Preconditioning – If the battery voltage is very low, the charger applies a gentle current to revive it.
  3. CC Phase – The charger delivers full current until approximately 4.2V is reached.
  4. CV Phase – Voltage is held steady while the current drops gradually.
  5. Charge Complete – When the current drops low enough, charging stops, as indicated by the status LED.

Charger with Protection​

The version with protection includes a battery protection circuit, which prevents:

  • Over-discharge – Stops discharging below approximately 2.5V.
  • Overcharge – Cuts off charging above approximately 4.25V.
  • Short circuit – Immediately disconnects the output.
  • Overcurrent – Limits the maximum current draw.

This makes it suitable for standalone battery packs where no additional BMS is used.

⚠️
For older Li-ion charger with protection boards, connect the TEMP pin to GND to initiate charging. The onboard CHRG LED will indicate the charging status.

TP4056 Charging IC​

The TP4056 is a linear charger designed for single-cell lithium-ion batteries. It includes an internal PMOSFET, thermal regulation, and current monitoring.

TP4056 IC
TP4056 Linear Li-ion Charger Controller

Key features:​

  • Constant-current / constant-voltage operation
  • 1% charging accuracy
  • Built-in protection for overvoltage and undervoltage
  • LED charge and full indicators

DW01 + FS8205A Protection Circuit​

The Li-ion Charger with Protection includes the DW01A battery protection IC and FS8205A dual MOSFET to guard against overcharge, overdischarge, and short circuits.

DW01 + FS8205A
DW01 and FS8205A on protected charger

Additional Protection Features:​

  • Overcharge protection at 4.28V
  • Overdischarge cutoff at 2.4V
  • Short-circuit and overcurrent protection
  • Automatically resumes operation when safe

Status LEDs​

  • Red LED – Charging
  • Green LED – Charge complete
charging
Red LED - Charging status

Input Power Sources​

These modules can be powered from:

  • USB-C port
  • Header pins (5V in)

Make sure the input is at least 5V for proper operation. The output is typically 4.2V max when charging and follows the battery voltage when discharging.