All Things You Need to Know about PCM of Lithium Battery

Lithium battery can be seen everywhere. There are two main components of the finished lithium battery, the lithium battery cell and PCM.

So, what is PCM? Maybe you have no idea about it.

Read on and make your own mind up

What is PCM?

PCM, Protection Circuit Module, it is a circuit board that welds electronic components on an empty PCB or an empty FPC board and achieves a certain electrical function after combination.

Structure of PCM:

Secure IC+ MOS switches+ Micro-volume and micro-resistance+ other assistant components

Why does a Lithium Battery Need PCM?

The reason why rechargeable lithium batteries need protection is determined by their own characteristics.

Since the material of the lithium battery itself determines that it cannot be overcharged, over-discharged, over-current, short-circuited, ultra-high temperature and ultra-low temperature charging and discharging.

The lithium battery pack needs a protection board to protect it to prevent the battery pack from overcharging, over-discharging and other abnormalities.

Functions of PCM

  • Overcharge protection→ If the battery is charging abnormally (Fault, error, incorrect charging).It may be charged to more than 4.2V. In this case, the PCM action turns off the charging
  • Over-discharge protection→ Excessive battery discharge will make electrical equipment (telephone, personal computer). Errors and failures occur, in this case, the PCM takes action. Turn off over-discharge and protect the battery from discharging and maintain a certain voltage.
  • Overcurrent protection →Abnormally high current in the battery will cause errors and failures in small electrical equipment. In this case, the PCM acts and turns off the over-current
  • Short circuit protection→ It protects the battery from external short circuits (coins, keys, etc.).

Types of PCM

According to the control method, PCM is devided into 2 parts:

Hardware board: The protection parameters of the circuit are set in advance inside the IC, and the protection parameters cannot be changed externally.


  1. stable performance
  2. low price


  1. the parameters can only be seated one-to-one.

Software board: The protection parameters of the intelligent protection chip can be set and programmed by the host computer on the circuit board to reach the final desired protection parameters.


  1. Wide application, it is versatile and scalable: communication protocols, Bluetooth, mobile phone APPS, GPS positioning


  1. Expensive prize
  2. slightly complicatedsoftware operation

According to the way of use, PCM are also devided into two parts:

Common port board: The protection board has the same way of charging and discharging ports.

Advantage: it is easy to use with the same port for charging and discharging

Disadvantage: the number of charging and discharging MOS is as large and the cost is high, and the heat generated by the charging MOS tube during discharge is twice as high as that of the port plate.

Separate board: different charge and discharge ports.


  • For small charging currents, fewer MOS tubes can be used to decrease cost.
  • There is no need to generate heat through the charging MOS tube when discharging.


  • You need to pay attention to distinguishing between the charging cable and the discharging cable when wiring;
  • if you use the discharging port for charging, the charging protection board will not protect and may cause the battery to be overcharged.

How to choose PCM?

When you choose your PCM, the following things you should pay attention to:
1.Types of battery: Ternary battery, Lithium iron battery or Lithium titanium battery
2.Number of battery series: (determine series and parallel, choose PCM according to series)
3.Common port or separate port: depends on your battery. The common port the load and charge port are together. The split port has a charge port and a battery port. Remember: the common port can play a role as separate port, but separate port can’t.
4.Charging termination voltage: (number of series* battery charging termination voltage)
5.Discharge termination voltage: (number of series* battery discharge termination voltage)
6.Charging current: (the limit current of the PCM when charging, the charging time can be 5-8 hours, which should be greater than the charger current, otherwise it will be overprotected)
7.Discharge current: (the limit current of the PCM when discharging, the greater the current, the more expensive the price)
8.Battery balancing function: ( If the PCM has balancing function, it will be market. Almost are passive balancing, it is cheap.)
9.Communication Function
10.Heating plate control function: (be sure to consult the seller in the northern regions, especially in cold weather areas
11.The self-dischargeof the PCM: (generally 20-100 micro-amps) Pay attention to the conversion: 1 A=1,000mA=1000,000µA
12.Water resistance: (the price of the battery is much higher than that of the PCM)
13.Size (length*width*height): After determining all things, the most optimistic PCM will in your mind.

What’s the difference between a BMS and PCM?

BMS(Battery Management System): A system with many functions to protect the whole battery pack


Monitoring all parameters like current, voltage, temperature and etc.
Dividing these collected information into different parts like overcharge current, discharging and Charging in high temperature and etc.
Storing these information and then provide to user.
PCM: Protection Circuit Module
Some functions are the same with BMS, however, PCM can not realize all functions like BMS.
Function: Protecting Li-ion battery pack charging and discharging process mainly

Detect the over-voltage, under-voltage, over-current, short-circuit, and over-temperature status of every single cell in the battery pack to ultimately protect and extend the battery’s life