The battery protection board is mainly an integrated circuit board that protects rechargeable batteries (generally referred to as lithium batteries). The reason why lithium batteries (rechargeable) need protection is because the material of the lithium battery itself determines that it cannot be overcharged, over-discharged, over-current, short-circuited, and charged and discharged at ultra-high temperature. Therefore, the lithium battery always has a protective plate and a A current fuse appears. The following figure shows the battery board protection circuit. PTC: Positive temperature coefficient thermistor; NTC: Negative temperature coefficient thermistor. When the ambient temperature increases, its resistance value decreases. Use electrical equipment or charging equipment to respond in time, control internal interruption and stop charging and discharging; U1 is Circuit protection chip, U2 is two MOSFET switches connected in reverse. Under normal conditions, both CO and DO of the battery board U1 output high voltage, and both MOSFETs are on, and the battery can be charged and discharged freely.

Overcharge protection: When U1 detects that the battery voltage reaches the overcharge protection threshold, the CO pin outputs a low level, the MOS tube switch 2 turns from on to off, the charging circuit is turned off, and the charger can no longer charge the battery. Overcharge protection.

Over-discharge protection: During the battery discharge process, when U1 detects that the battery voltage is lower than the over-discharge protection threshold, the DO pin changes from high to low, and MOS tube switch 1 is turned off, so that the battery can no longer be discharged; over-discharge In the protection state, the battery voltage can no longer be lowered, and the current of the protection circuit is required to be very small, and the control circuit enters low power consumption. 

Overcurrent protection: Under normal circumstances, the battery discharges the load, and the current passes through two MOS tube switches connected in series. The VM pin detects that the voltage drop voltage of the two MOS tubes is U. If the load causes U abnormal for some reason, the loop current will increase. When U is greater than a certain value, the DO pin will change from a high voltage to a low voltage, and the MOS tube switch 1 will be turned off, so that the discharge loop current will be zero and the over Current protection.