Analysis of working principles of several battery circuits -Lithium - Ion Battery Equipment
The circuit has the functions of overcharge protection, overdischarge protection, overcurrent protection and short circuit protection. Its working principle is broken down as follows:
normal status
In the normal state, the "CO" and "DO" pins of N1 in the circuit both output high voltage, the two MOSFETs are in the conduction state, and the battery can be charged and discharged freely, because the conduction resistance of the MOSFET is very small, usually less than 30 milliohms, so its on-resistance has little effect on the performance of the circuit. 7|In this state, the consumption current of the protection circuit is μA level, usually less than 7μA.
overcharge protection
The charging method required by lithium-ion batteries is constant current/constant voltage. In the initial stage of charging, it is charged with constant current. With the charging process, the voltage will rise to 4.2V (according to the different positive electrode materials, some batteries require a constant voltage value of 4.1V. ), switch to constant voltage charging until the current becomes smaller and smaller. When the battery is being charged, if the charger circuit is out of control, the battery voltage will continue to charge at a constant current after exceeding 4.2V. At this time, the battery voltage will continue to rise. When the battery voltage is charged to more than 4.3V, the battery’s chemical Side effects will intensify, causing damage to the battery or safety issues.(Lithium - Ion Battery Equipment)
In a battery with a protection circuit, when the control IC detects that the battery voltage reaches 4.28V (this value is determined by the control IC, and different ICs have different values), its "CO" pin will change from high voltage to zero voltage, Make V2 turn from on to off, thus cutting off the charging circuit, so that the charger can no longer charge the battery, and it plays the purpose of overcharging protection. At this time, due to the existence of the body diode VD2 of V2, the battery can discharge the external load through this diode.
There is still a delay time between when the control IC tests that the battery voltage exceeds 4.28V and sends a signal to shut down V2, the length of the delay time is determined by C3, usually set to about 1 second to prevent errors judge.
Over discharge protection
When the battery discharges the external load, its voltage will gradually decrease with the discharge process. When the battery voltage drops to 2.5V, its capacity has been completely discharged. At this time, if the battery is continuously discharged to the load, it will cause battery damage. permanent damage.
During the battery discharge process, when the control IC detects that the battery voltage is lower than 2.3V (this value is determined by the control IC, and different ICs have different values), its "DO" pin will change from high voltage to zero voltage, making V1 Turning from on to off, thus cutting off the discharge circuit, so that the battery can no longer discharge the load, and it serves the purpose of over-discharge protection. At this time, due to the existence of the body diode VD1 of V1, the charger can charge the battery through this diode.
Since the battery voltage cannot be lowered in the over-discharge protection state, the current consumption of the protection circuit is required to be extremely small. At this time, the control IC will enter a low power consumption state, and the power consumption of the entire protection circuit will be less than 0.1μA.
There is also a delay time between when the control IC tests that the battery voltage is lower than 2.3V and sends a signal to shut down V1. The length of the delay time is determined by C3, usually set to about 100 milliseconds to prevent errors judge. 4. Overcurrent protection
Due to the chemical characteristics of lithium-ion batteries, battery manufacturers stipulate that the maximum discharge current cannot exceed 2C (C=battery capacity/hour). When the battery is discharged with a current exceeding 2C, it will cause permanent damage to the battery or safety problems.
During the normal discharge process of the battery to the load, when the discharge current passes through two MOSFETs in series, a voltage will be generated at both ends of the MOSFET due to the on-resistance of the MOSFET. The voltage value U=I*RDS*2, RDS is a single MOSFET on-resistance, control the "V-" pin on the IC to test the voltage value, if the load is abnormal for some reason, the loop current will increase, when the loop current is so large that U>0.1V (the value is determined by When the control IC decides that different ICs have different values), its "DO" pin will change from high voltage to zero voltage.
normal status
In the normal state, the "CO" and "DO" pins of N1 in the circuit both output high voltage, the two MOSFETs are in the conduction state, and the battery can be charged and discharged freely, because the conduction resistance of the MOSFET is very small, usually less than 30 milliohms, so its on-resistance has little effect on the performance of the circuit. 7|In this state, the consumption current of the protection circuit is μA level, usually less than 7μA.
overcharge protection
The charging method required by lithium-ion batteries is constant current/constant voltage. In the initial stage of charging, it is charged with constant current. With the charging process, the voltage will rise to 4.2V (according to the different positive electrode materials, some batteries require a constant voltage value of 4.1V. ), switch to constant voltage charging until the current becomes smaller and smaller. When the battery is being charged, if the charger circuit is out of control, the battery voltage will continue to charge at a constant current after exceeding 4.2V. At this time, the battery voltage will continue to rise. When the battery voltage is charged to more than 4.3V, the battery’s chemical Side effects will intensify, causing damage to the battery or safety issues.(Lithium - Ion Battery Equipment)
In a battery with a protection circuit, when the control IC detects that the battery voltage reaches 4.28V (this value is determined by the control IC, and different ICs have different values), its "CO" pin will change from high voltage to zero voltage, Make V2 turn from on to off, thus cutting off the charging circuit, so that the charger can no longer charge the battery, and it plays the purpose of overcharging protection. At this time, due to the existence of the body diode VD2 of V2, the battery can discharge the external load through this diode.
There is still a delay time between when the control IC tests that the battery voltage exceeds 4.28V and sends a signal to shut down V2, the length of the delay time is determined by C3, usually set to about 1 second to prevent errors judge.
Over discharge protection
When the battery discharges the external load, its voltage will gradually decrease with the discharge process. When the battery voltage drops to 2.5V, its capacity has been completely discharged. At this time, if the battery is continuously discharged to the load, it will cause battery damage. permanent damage.
During the battery discharge process, when the control IC detects that the battery voltage is lower than 2.3V (this value is determined by the control IC, and different ICs have different values), its "DO" pin will change from high voltage to zero voltage, making V1 Turning from on to off, thus cutting off the discharge circuit, so that the battery can no longer discharge the load, and it serves the purpose of over-discharge protection. At this time, due to the existence of the body diode VD1 of V1, the charger can charge the battery through this diode.
Since the battery voltage cannot be lowered in the over-discharge protection state, the current consumption of the protection circuit is required to be extremely small. At this time, the control IC will enter a low power consumption state, and the power consumption of the entire protection circuit will be less than 0.1μA.
There is also a delay time between when the control IC tests that the battery voltage is lower than 2.3V and sends a signal to shut down V1. The length of the delay time is determined by C3, usually set to about 100 milliseconds to prevent errors judge. 4. Overcurrent protection
Due to the chemical characteristics of lithium-ion batteries, battery manufacturers stipulate that the maximum discharge current cannot exceed 2C (C=battery capacity/hour). When the battery is discharged with a current exceeding 2C, it will cause permanent damage to the battery or safety problems.
During the normal discharge process of the battery to the load, when the discharge current passes through two MOSFETs in series, a voltage will be generated at both ends of the MOSFET due to the on-resistance of the MOSFET. The voltage value U=I*RDS*2, RDS is a single MOSFET on-resistance, control the "V-" pin on the IC to test the voltage value, if the load is abnormal for some reason, the loop current will increase, when the loop current is so large that U>0.1V (the value is determined by When the control IC decides that different ICs have different values), its "DO" pin will change from high voltage to zero voltage.
