| Protection
Circuit Module(PCM) For Lithium Rechargeable Battery
The lithium rechargeable batteries (Li-ion/Li-Po)
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 battery from over-charging, over-discharge, overcurrent,
short circuit.
1. The Necessities of Protective
Circuit Module and its protection functions
The Lithium 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
rechargeable Batteries
• Protection
IC + MOSFET: Prevent overcharge voltage, overdischarge voltage,
and overcurrent.
• Current Fuse: Prevent overcharge voltage
and overcurrent.
• 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 battery.
• Fusing resistor: Prevent overcharge
voltage and overcurrent.
3. Electrical Diagram

B+: Connect
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.
Charging/Discharging
Lithium rechargeable 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.
Lithium rechargeable 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.

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