1. Lithium-ion battery protection board
When the cell voltage is between 2.5V and 4.3V, pins 1 and 3 of DW01 output a high level (equal to the supply voltage), while pin 2 outputs 0V. At this time, the voltages at pins 1 and 3 of DW01 are applied to pins 5 and 4 of the 8205A, respectively. Since the gate (G) terminal of the 8205A is connected to the voltage from DW01, both electronic switches within the 8205A are in a conducting state, meaning both electronic switches are in the open state. At this time, the negative terminal of the cell is effectively directly connected to the P- terminal of the protection board, and the protection board outputs voltage.
2. Over-discharge protection control principle of the protection board
When the battery cell discharges through an external load, its voltage gradually decreases. Simultaneously, the DW01 internally monitors the cell voltage in real time via resistor R1. When the cell voltage drops to approximately 2.3V, the DW01 interprets this as an over-discharge voltage condition and immediately disconnects the output voltage at pin 1, making the pin 1 voltage 0V. The switching transistor inside the 8205A then shuts off due to the lack of voltage at pin 5. At this point, the battery cell's B- pin is disconnected from the protection board's P- pin.
The lithium-ion battery protection board is in an over-discharge state and remains so. Once the charging voltage is connected between P and P- of the protection board, DW01 detects the charging voltage via B- and immediately stops the over-discharge state, outputting a high voltage at pin 1 again. This turns on the over-discharge control transistor in the 8205A, meaning that B- of the battery cell is reconnected to P- of the protection board, and the battery cell is directly charged by the charger.
3. Overcharge protection board
When the battery is charging normally through the charger, the cell voltage will increase with charging time. When the cell voltage reaches 4.4V, DW01 will consider the cell voltage to be in an overcharge state and immediately disconnect the output voltage at pin 3, making the voltage at pin 3 0V. The switching transistor in the 8205A will turn off because there is no voltage at pin 4. At this time, the connection between the cell's B- pin and the protection board's P- pin is broken. That is, the cell's charging circuit is cut off, and the cell will stop charging. The protection board remains in an overcharge state.
Once the discharge load is connected between P and P- of the protection board, although the overcharge control switch is closed, the positive direction of its internal diode is the same as the direction of the discharge circuit, so the discharge circuit can discharge. When the cell voltage is lower than 4.3V, DW01 stops the overcharge protection state and outputs a high voltage at pin 3, turning on the overcharge control switch in 8205A. That is, B- of the cell is reconnected to P- of the protection board, and the cell can perform normal charging and discharging again.
