The lithium ion/polymer batteries will be damaged or its
cycle life will be shortened if it's over charged or over discharged.
Protection Circuit Module is used to protect lithium ion/polymer batteries from over-charging,
over-discharge, overcurrent, short circuit.
1. The Necessities of Protective Circuit
Module and its protection functions
The Lithium ion/polymer battery will expand, leakage or explosion if it's over charged
or over discharged. The protective circuit module is designed to avoid
this happen when the battery or the charger has problem, or incorrect
usage caused the battery failure etc.
• Overcharge voltage protection
• Over discharge voltage protection
• Over-current protection
• Short circuit protection
• Battery high temperature protection
• Battery's internal pressure increase protection
2. Protection Components of Lithium
IC + MOSFET: Prevent overcharge voltage, overdischarge voltage, and
• Current Fuse: Prevent overcharge voltage
• Thermal Fuse: Prevent overcharge voltage,
overcurrent,and too high temperature of the battery.
• PTC: Prevent too high temperature of the
battery and overcurrent. Bimetal Prevent temperature
increase in the batteries and overcurrent.
• Safety vent: Prevent overcharge voltage,
too high pressure inside the battery, and too high temperature of the
• Fusing resistor: Prevent overcharge voltage
3. Electrical Diagram
to positive terminal of cell
B-: Connect to negative terminal of cell
V+: Positive power supply input for charger
V-: Negative power supply input for charger
4. The Installation of the Protective Circuit Module
The protective circuit module is installed integrated with the battery
pack and it should be installed in battery shell. When the charger or
related instruments occur problems, the protective circuit can protect
the batteries perfectly.
Lithium ion/polymer battery must use "Constant Current
/ Constant Voltage (CC/CV)" charging method. First the battery is
charged till it reaches limited voltage 4.2V by using a set constant current
and then charged with this constant voltage till the current is below
2mA. It requires high precise charging circuit and protective circuit
to control the charge.
This battery is not suitable for big current
discharge, big current discharge will shorten the discharging time. It
will cause high internal temperature of battery and decrease capacity.
Over current discharge will damage the battery.