Why do lithium batteries need protection circuit board??

Because the lithium battery is overcharged, over-discharged, or short-circuited, the battery may be scrapped. The protection board is used for this protection. If you can ensure that the battery is overcharged, over-discharged, or short-circuited during use, you don’t need the protection board. . During the use of lithium batteries, every time they are overcharged, over-discharged, or short-circuited, the battery life will be reduced. In severe cases, the battery will be scrapped directly! If there is no lithium battery protection board, directly short-circuit the lithium battery and overcharge it will cause the battery to bulge. In severe cases, it will leak, depressurize, explode or catch fire.

The protection board is to ensure safety and the lithium battery is not considered to be overcharged or overdischarged, because the previous lithium-ion battery overcharge and overdischarge will cause the battery to be damaged or explode or catch fire. Therefore, when the lithium-ion battery is introduced The protection board also came into being. Recently, with the emergence of lithium iron phosphate batteries, it is said that lithium iron phosphate batteries are not afraid of overcharging or overdischarging. Therefore, there has been a theory that it can be done without a protection board, but so far There is no battery manufacturer that publicly declares that it does not use the protection circuit. The protection board is the bodyguard, and the protection board is to ensure the safety of the lithium battery.

The function of the lithium battery protection board is mainly to protect the cells of the rechargeable battery, maintain the safety and stability of the battery during the charging and discharging process, and play an important role in the performance of the entire battery circuit system.

1. Overcharge protection function: The overcharge protection function means that when a certain voltage (hereinafter referred to as overcharge detection voltage) is reached, it is forbidden to continue charging by the charger. That is, the MOS tube that controls overcharge is turned off to stop charging.

2. Over-discharge protection function: The over-discharge protection function stops discharging the load when the voltage of the lithium battery becomes low. The MOS tube that controls the over-discharge enters the off state, and it is prohibited from discharging. This process is just the opposite of the action during overcharge detection.

3. Over-current protection function: The over-current protection function stops discharging the load when a large current is consumed. The purpose of this function is to protect the battery and the MOS tube to ensure the safety of the lithium battery under working conditions. After the over-current detection, the battery will return to the normal state after being separated from the load, and can be recharged or discharged.

Principle of Lithium Battery Protection Board

When the lithium battery protection board is normal, Vdd is high, Vss and VM are low, DO and CO are high. When any parameter of Vdd, Vss, VM is changed, the power of DO or CO is Ping will change.

1. Overcharge detection voltage: Under normal conditions, Vdd gradually increases to the voltage between VDD and VSS when the CO terminal changes from high level to low level.

2. Overcharge release voltage: In the charging state, Vdd gradually decreases to the voltage between VDD and VSS when the CO terminal changes from low level to high level.

3. Overdischarge detection voltage: Under normal conditions, Vdd gradually decreases to the voltage between VDD and VSS when the DO terminal changes from high level to low level.

4. Overdischarge release voltage: In the overdischarge state, Vdd gradually rises to the voltage between VDD and VSS when the DO terminal changes from low level to high level.

5. Overcurrent 1 detection voltage: In the normal state, VM gradually rises to the voltage between VM and VSS when DO changes from high level to low level.