Design functions and requirements of lithium battery protection board (BMS)

Lithium batteries cannot be overcharged, over-discharged, or over-current due to materials. At the same time, short-circuit and charging and discharging at ultra-high temperatures will also cause great risks. Therefore, lithium batteries are usually equipped with a protection board and used at the same time. The design functions of the lithium battery protection board include the following points: 1. Overcharge detection voltage 2. Overcharge release voltage 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, Current consumption during normal operation 10, Overdischarge current consumption Lithium battery protection board maintenance principle 1. Normal state in the normal state of the circuit in the N1' Both CO' and'DO' pins output high voltage, both MOSFETs are in the on state, and the battery can be charged and discharged freely. Since the on-resistance of the MOSFET is very small, usually less than 30 milliohms, its on-resistance There is little impact on the performance of the circuit. In this state, the current consumption of the protection circuit is μA, usually less than 7 μA. 2. If the overcharge protection charger circuit loses 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 voltage is charged to more than 4.3V, the battery will have chemical side reactions. Will be exacerbated, causing battery damage or safety issues. When the lithium battery pack with a protection board is overcharged, when the control IC detects that the battery voltage reaches 4.28V (determined by the control IC), its'CO' pin will change from high voltage to zero voltage, making V2 turn from on to Shut off, thereby cutting off the charging circuit, so that the charger can no longer charge the battery, play a role in overcharge protection. 3. Short circuit protection When the lithium battery is discharged, when the loop current reaches a certain value (the value is determined by the control IC), the control IC judges that the load is short-circuited, and its'DO' pin will quickly change from high voltage to zero voltage , Turn V1 from on to off, cut off the discharge circuit, and play a role in short-circuit protection. The delay time of short circuit protection is extremely short, usually less than 7 microseconds. Its working principle is similar to that of over-current protection, but the judgment method is different, and the protection delay time is also different. 4. During the discharge process of overcurrent protection lithium battery, when the discharge current passes through 2 MOSFETs connected in series, a voltage will be generated at both ends of the MOSFET due to the on-resistance of the MOSFET. The voltage value Uu003dI*RDS*2, RDS It is the on-resistance of a single MOSFET. The'V-' pin on the control IC detects the voltage value. If the load is abnormal for some reason, the loop current will increase. When the loop current reaches a certain value (the value is controlled by the When IC decides), its'DO' pin will change from high voltage to zero voltage, turning V1 from on to off, thereby cutting off the discharge circuit, making the current in the circuit zero, and playing the role of overcurrent protection. 5. Over-discharge protection When the voltage drops to 2.5V during the discharge process of the lithium battery, it indicates that the capacity has been completely discharged. If the battery continues to discharge at this time, it will cause permanent damage to the battery. When the lithium battery with the protection board is discharged, when the control IC detects that the battery voltage is lower than the set value (determined by the control IC), its'DO' pin will change from high voltage to zero voltage, making V1 change from on to Shut off, thereby cutting off the discharge circuit, so that the battery can no longer discharge the load, play a role in over-discharge protection. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete.