Lithium battery due to the relationship of materials, decided that the lithium battery can not be overcharged, overdischarged, overcurrent, while short circuit and charging and discharging at ultra-high temperature will also cause great risk, so the lithium battery is usually equipped with a protection board used at the same time.
The design function of the lithium battery protection board contains the following points.
1、Overcharge detection voltage
2、Over-charge voltage release
3、Over-discharge detection voltage
4、Over-discharge release voltage
5、Over-current 1 detection voltage
6、Over-current 2 detection voltage
7、Load short circuit detection voltage
8、Charger detection voltage
9、Usual working current consumption
10、Over discharge consumption current
Lithium battery protection board overhaul principle
1、Normal state
In the normal state of the circuit N1 "CO" and "DO" pin output high voltage, the two MOSFETs are in a state of conduction, the battery can be charged and discharged freely, due to the MOSFET on impedance is very small, usually less than 30 milliohm, so its on resistance on the performance of the circuit is very small. The current consumption of the protection circuit in this state is μA level, usually less than 7 μA.
2、Overcharge protection
If the charger circuit loses control, it will cause the battery voltage to exceed 4.2V and then continue to charge at constant current, at which time the battery voltage will continue to rise, and when the battery voltage is charged to more than 4.3V, the chemical side reactions of the battery will intensify, which will lead to battery damage or safety problems.
When the lithium battery pack with protection board is overcharged, the control IC detects that the battery voltage reaches 4.28V (determined by the control IC), the "CO" pin will change from high voltage to zero voltage, so that V2 will turn off from on to off, thus cutting off the charging circuit, so that the charger can no longer charge the battery and play the role of overcharge protection. role.
3、Short circuit protection
Lithium battery in the discharge, when the circuit current is large to a certain value (the value is determined by the control IC), the control IC is judged to be a load short circuit, its "DO" pin will quickly change from high voltage to zero voltage, so that V1 from on to off, cut off the discharge circuit, to play the role of short circuit protection. The delay time of short-circuit protection is extremely short, usually less than 7 microseconds. Its working principle is similar to the overcurrent protection, but the judgment method is different, the protection delay time is also different.
4、Overcurrent protection
Lithium battery discharge process, the discharge current in series through the 2 MOSFETs, due to the MOSFET on impedance, will generate a voltage at both ends, the voltage value U = I * RDS * 2, RDS for a single MOSFET on impedance, the control IC "V-" pin on the voltage value to detect If the load is abnormal for some reason, so that the circuit current increases, when the circuit current to a certain value (the value is determined by the control IC), the "DO" pin will be changed from high voltage to zero voltage, so that V1 from conduction to turn off, thus cutting off the discharge circuit, so that the circuit current is zero, to play a role in over-current protection.
5、Over-discharge protection
Lithium battery in the process of discharge, when the voltage drops to 2.5V, indicating that the capacity has been completely discharged, at this time, if the battery continues to discharge, will cause permanent damage to the battery. In the lithium battery with protection board discharge, when the control IC detects that the battery voltage is lower than the set value (determined by the control IC), the "DO" pin will be changed from high voltage to zero voltage, so that V1 from on to off, thus cutting off the discharge circuit, so that the battery can no longer discharge to the load, to play a role in over-discharge protection.
Welcome to visit our company website: www.manlybattery.com. If you have any interests in batteries, please feel free to contact us: info@manlybattery.com
