Brief analysis of the working principle of lithium battery protection circuit

Working principle of lithium battery protection circuit This circuit has the functions of overcharge maintenance, overdischarge maintenance, overcurrent maintenance and short circuit maintenance. The analysis of its working principle is as follows: 1 Normal state Under normal conditions, the CO and DO pins of N1 both output high voltage in the circuit, and the mosfet is in the conducting state. The battery can be charged and discharged freely, because the conduction impedance of the MOSFET is very small, generally less than 30 milliohms, so its conduction resistance has little effect on the function of the circuit. In this case, the current consumption of the maintenance circuit is Class A, which is generally less than 7kvA. 2 Overcharge maintenance Lithium battery, as a rechargeable battery, should be charged with constant current/constant voltage. Constant current charging is required at the initial stage of charging. During the charging process, the charging voltage will rise to 4.2v (according to different cathode materials, some batteries require a constant voltage value of 4.1v), and then change to constant voltage charging until the current becomes smaller and smaller. During the charging process, if the charger circuit is out of control, the battery voltage will continue to be charged with constant current after the battery voltage exceeds 4.2v. At this time, the battery voltage will continue to rise. When the battery charging voltage exceeds 4.3v, the chemical side reaction of the battery will be aggravated, resulting in battery damage or safety problems. In the battery maintenance circuit, when the control integrated circuit detects the battery voltage 4.28V (the selected value is the operation of the integrated circuit, different integrated circuits have different values), the company's pin goes from high voltage to zero voltage, V2 conducts to close , And then cut off the charging circuit, the charger can no longer charge the battery, charging maintenance effect. Now, thanks to V2's own diode VD2, the battery can use it to release the external load. There is also a delay time between the battery voltage 4.28v detected by the control IC and the closing of the V2 signal. The delay time is selected by C3, and is generally set to about 1 second to prevent misjudgment due to interference. Over-discharge maintenance In the process of discharging, the voltage of the battery will gradually decrease with the process of discharging. When the battery voltage drops to 2.5v, its capacity has been completely released. At this time, it is assumed that the battery will continue to discharge, which will constitute permanent damage to the battery. During the battery discharge process, when the control IC detects that the battery voltage is lower than 2.3V, the selected value is the operation of the integrated circuit, different integrated circuits have different values), the pin is made from high voltage zero voltage V1 from conduction to shutdown, and then Cut off the discharge circuit, the battery can no longer sustain the influence of the discharge load. Now due to V1's own body diode VD1, the charger can charge the battery through the diode. Since the battery voltage cannot be lowered in the case of over-discharge maintenance, the current consumption requirement of the maintenance circuit is very small. At this time, the control IC will enter a low power consumption state, and the power consumption of the entire maintenance circuit will be less than 0.11a. When the control IC detects that the battery voltage is lower than 2.3v and declares that the V1 signal is off, there is also a delay time. The delay time is selected by C3, and is generally set to about 100ms to prevent misjudgment due to interference. 4 Overcurrent maintenance Due to the chemical characteristics of lithium batteries, the battery manufacturer stipulates that the maximum discharge current of lithium batteries cannot exceed 2C (Cu003dbattery capacity/hour). When the battery discharges more than 2C, permanent damage or safety issues will occur. In the process of cell discharge under normal load, the discharge current after a series of two MOSFETs, due to MOSFET stimulation, impedance will attack the voltage at both ends, voltage Uu003dI*RDS*2, RDS is stimulated by a MOSFET, and the impedance is controlled by the IC. V-pin test voltage value, if the load is abnormal due to some reason, the loop current increases, when the ocean current is U>0.1V (the selected value is the operation of the integrated circuit, different ICs have different values), do The pin changes from high voltage to zero voltage to make V1 from on to off, and then cut off the discharge circuit, so that the current in the circuit is zero, which has the effect of maintaining the overcurrent. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: Where is the market for lithium titanate batteries?