The reason why lithium battery (rechargeable) needs to be protected depends on its own characteristics. Due to the material of lithium battery itself, it can't overcharge, over discharge, over current, short circuit and ultra-high temperature charge and discharge, so the lithium battery module will always have a delicate protection board and current fuse.

The protection function of lithium battery is usually completed by protection circuit board and current device (such as PTC). The power battery protection board is composed of electronic circuits, which can accurately monitor the battery voltage and charge and discharge at any time in the environment of - 40 ℃ to + 85 ℃. PTC can prevent serious battery damage in high temperature environment.

The function of power lithium battery protection board is to protect the battery, prevent the battery from overcharge, over discharge and large current damage, and balance the battery voltage after full charge. In order to protect the service life of the lithium battery pack, it is recommended that the battery charging voltage should not exceed 3.6V, that is, the protection voltage of the lithium battery protection board should not be higher than 3.6V. To keep the balance, the recommended voltage is 3.4v-3.5v, and the battery discharge protection voltage is usually 2.5V or higher. can.

When the battery is discharged through the external load, the battery voltage will drop slowly. At the same time, dw01 will monitor the battery voltage in real time through R1 resistor. When the battery voltage drops to about 2.3V, dw01 will consider that the battery voltage is in the over discharge voltage state. Please immediately disconnect the output voltage of one pin to make the voltage of one pin become 0V. Since there is no voltage on the fifth pin, the switch tube in 8205a has been closed.

At this time, the B - of the battery cell and the p - of the protection board are disconnected. That is, the discharge circuit of the battery cell is cut off, and the battery cell will stop discharging. The protection board is in over discharge state and has been maintained. After indirectly charging P and P - of lithium battery protection board with charging voltage, dw01 stops over discharge immediately after B - detects charging voltage, and outputs high voltage on pin 1 again to generate over voltage. -The discharge control tube is connected in 8205a, that is, the B - of the battery unit and the p - of the protection board are reconnected, and the battery is charged directly through the charger.

When the lithium battery is normally charged by the charger, with the increase of charging time, the voltage of the battery will be higher and higher. When the battery voltage rises to 4.4V, dw01 will consider that the battery voltage is in the overcharge voltage state, and it will immediately disconnect the output voltage of the third pin, so that the voltage of the third pin becomes 0V, and the switch tube is in the state of no voltage on the fourth pin, so 8205a is closed. At this time, the B - of the battery cell and the p - of the protection board are disconnected. That is, the charging circuit of the battery cell is cut off, and the battery cell will stop charging. The protection board is overcharged and has been maintained.