Principle of Li-ion battery protection circuit

Li-ion battery integrated protection circuit principle During the use of lithium-ion batteries, overcharge, over-discharge and over-current are important factors that affect the service life and performance of lithium-ion batteries. The lithium-ion battery integrated protection circuit effectively monitors and prevents damage to the lithium-ion battery through each protection unit circuit. Lithium-ion battery charge and discharge protection circuit. The lithium-ion battery protection circuit is composed of two field effect transistors and a control integrated circuit plus some resistance and capacitance elements. (1) Normal state In the normal state, both the CO terminal and the DO terminal of N1 output high voltage in the circuit, and the fets are in the conducting state, and the lithium-ion battery can be charged and discharged freely. Since the conduction resistance of the field effect transistor is very small, usually less than 30 meters, its conduction resistance has almost no effect on the circuit performance. In this state, the current consumption of the protection circuit is microampere, which is generally less than 7a. (2) The charging method required for overcharged lithium-ion batteries is constant current and constant voltage charging. The initial charging stage is constant current charging. As the charging process progresses, the charging voltage gradually increases to 4.2v (depending on the cathode material, some batteries have a constant voltage to 4.1v). During the charging of the lithium-ion battery, if the charger circuit is out of control, after 4.2v, the lithium-ion battery will continue to be charged with a constant current, and the voltage of the lithium-ion battery will continue to rise at this time. When the voltage of the lithium-ion battery is higher than 4.3v, the chemical side-use of the lithium-ion battery will be intensified, resulting in battery damage or safety problems. In the lithium-ion battery protection circuit, when the lithium-ion battery voltage tested by the control integrated circuit is 4.28V (the value is determined by the control IC, different integrated circuits have different values), the company will eventually convert the high potential to zero potential, so that VT2 is conducted to Turn off, cut off the charging circuit, the charger of the lithium ion battery cannot be charged, the charging protection effect. At this time, due to the body diode VD2 of VT2, the lithium-ion battery can discharge the external load through the diode. The control integrated circuit detects that the lithium-ion battery voltage exceeds 4.28v and there is a delay between sending the offVT2 signal. The delay time is determined by C3, and is usually set to about 1 to prevent interference from misjudgment of the protection. (3) Over-discharge state During the discharge process, the voltage of the lithium-ion battery will gradually decrease with the discharge process. When the voltage of the lithium-ion battery drops to 2.5v, its capacity has been completely exposed. If the lithium ion battery continues to be discharged, it will cause permanent damage to the lithium ion battery. During the discharging process of the lithium-ion battery, when the voltage of the lithium-ion battery tested by the control integrated circuit is lower than 2.3V, the value is determined by the control integrated circuit, and the integrated circuit has different values), it will be converted from a high potential to a zero potential, making VT1 Conduction to shutdown, cut off the discharge circuit, so that the lithium-ion battery can no longer be discharged under load, discharge protection effect. At this time, due to the presence of the VT1 body diode VD1, the charger can charge the lithium-ion battery through the diode. Since the voltage of the lithium-ion battery cannot be further reduced in the over-discharge protection state, the current consumption of the protection circuit is required to be minimized. At this time, the control integrated circuit will enter a low power consumption state, and the power consumption of the entire protection circuit will be less than 0.11a. There is also a delay between the control integrated circuit detecting that the voltage of the lithium-ion battery is lower than 2.3v and sending the offVT1 signal. The delay time is determined by C3, and is generally set to about 100ms to prevent interference from misjudging the protection. (4) Overcurrent status Due to the chemical nature of lithium-ion batteries, manufacturers limit their discharge rate to within 2 degrees Celsius. When the discharge rate of the lithium ion battery exceeds 2C, it will cause permanent damage or safety issues to the lithium ion battery. When the lithium-ion battery is discharged to the load normally, the discharge current will have a voltage drop across the series FET due to the conduction impedance of the FET. 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: Can drone batteries be taken on the subway?