Protection and control principle of over discharge protection of protection board: take dw01 with MOS tube 8205a as an example, when the electric core discharges through the external load, the voltage of the electric core will slowly reduce, and at the same time, dw01 will monitor the voltage of the electric core through R1 resistance in real time, When the core voltage drops to about 2.5V, dw01 will consider that the core voltage has been in the state of over discharge voltage, and then immediately disconnect the output voltage of the first pin, so that the voltage of the first pin becomes 0V, and the switch tube in 8205a will be closed due to no voltage at the fifth pin. At this time, the b-of the electric core is disconnected from the p-of the protection plate. That is to say, the discharge circuit of the electric core is cut off, and the electric core will stop discharging. The protection board is in over discharge state and keeps it. When the P and p-of the protection board are indirectly charged, dw01 will stop the over discharge state immediately after b-detects the charging voltage, and output the high voltage at the first pin again, so that the over discharge control tube in 8205a is connected, that is, the b-of the core and p-of the protection board are connected again, and the core is charged directly by the charger.