1,
lithium battery protection board composition
The general lithium battery protection board is composed of a control IC, a MOS tube, a resistance capacitor, and a FUSE, as shown in the following figure
1, overcharge protection principle
When the battery is charged, the current (direction shown by the arrow) flows into the positive electrode of the battery pack and flows out of the negative electrode through FUSE. The two MOS tubes at the bottom are both on.
When charging, the control IC X1 will always monitor the voltage between the 5th pin VDD and the 6th pin VSS. When this voltage is greater than or equal to the overcharge cut-off voltage and meets the delay time of the overcharge voltage, X1 will turn off the MOS tube Q2 by controlling the 3rd pin. After Q2 is turned off, the charging loop is cut off (Q2's body diode D2 is also reversed cut-off). At this point, the battery can only discharge.
Overcharge protection release conditions (meet one) :
1) The voltage at both ends of the cell drops to the overcharge recovery voltage of the protection IC.
2) Load discharge at the output end of the battery pack until the voltage is less than the overcharge protection voltage
2. Over-discharge protection
When the load is discharged at both ends of the battery pack, the current (the direction shown by the arrow) is opposite to the charge, as shown in the figure below.
When discharging, the control IC X1 will also always monitor the voltage between the 5th pin VDD and the 6th pin VSS, when this voltage is less than or equal to the overdischarge cutoff voltage and reaches the delay time of the overdischarge voltage, the control IC X1 will turn off Q1 through the 1st pin, Q1 is turned off after the discharge loop is cut off (Q1's body diode D1 is reverse cutoff), this time, Batteries can only be recharged.
Release conditions of over-discharge protection:
Remove the load, charge the battery pack, and when the voltage between VM-VDD reaches the overshoot recovery voltage value, the control IC X1 will turn the MOS tube Q1 back on.
