Protection board over-discharge protection control principle: Take DW01 with MOS tube 8205A as an example. When the battery cell is discharged through an external load, the voltage of the battery cell will slowly decrease.
At the same time, DW01 will monitor the battery cell voltage in real time through the R1 resistor. When the battery cell voltage drops to about 2.5V, DW01 will think that the battery cell voltage is in an over-discharge voltage state, and immediately disconnect the output voltage of pin 1, so that the voltage of pin 1 becomes 0V.
The switch tube in 8205A is closed because there is no voltage on pin 5. At this time, the B- of the battery cell and the P- of the protection board are in a disconnected state. That is, the discharge circuit of the battery cell is cut off, and the battery cell will stop discharging. The protection board is in an over-discharge state and remains so.
After the charging voltage is indirectly applied to P and P- of the protection board, DW01 stops the over-discharge state immediately after detecting the charging voltage through B-, and outputs a high voltage at pin 1 again, turning on the over-discharge control tube in 8205A, that is, B- of the battery cell and P- of the protection board are reconnected, and the battery cell is charged directly through the charger.