What are the working processes of the lithium battery protection board

With the widespread use of electric vehicles, the lithium battery industry has also seen unprecedented development, and the lithium battery protection board exists as the core component of the lithium battery. It is the protector of the lithium battery and has overcharge protection and overcharge protection. Main protection functions such as discharge protection, overcurrent protection, and short circuit. Since the role of lithium battery protection board is so great, it is urgent for us as consumers to master the basic knowledge of lithium battery protection board.

1. How to activate the protection board: When the protection board P+ and P- are not output in the protection state, you can short-circuit B- and P- to activate the protection board. At this time, Dout and Cout will be low Level (the two ports of the protection IC are high level protection, low level is normal) state opens two MOS switches.

2. Charging: P+ and P- are respectively connected to the positive and negative poles of the charger, and the charging current passes through two MOSs to charge the cells. At this time, the VDD and VSS of the IC are both the power supply terminal and the cell voltage detection terminal (via R1). As the charging progresses, the cell voltage gradually increases. When it reaches the protection IC threshold voltage (usually 4.30V, usually referred to as the overcharge protection voltage), Cout will output a high level and turn off the corresponding MOS. The charging circuit is also disconnected. After the overcharge protection, the cell voltage will drop. When it drops to the IC threshold voltage (usually 4.10V, usually called the overcharge protection recovery voltage), Cout returns to a low level and opens the MOS switch.

3. Discharge: Similarly, when the battery is discharged, the VDD and VSS of the IC will also detect the cell voltage. When the cell voltage drops to the IC threshold voltage (usually 2.40V, usually called over When the protection voltage is discharged), Dout will output a high level immediately and the corresponding MOS will be turned off, and the discharge circuit will be disconnected. After the over-discharge protection, the cell voltage will rise. When it rises to the IC threshold voltage (usually 3.00V, usually called the over-discharge protection recovery voltage), Dout returns to a low-level state and opens the MOS switch.

Four. Over-current, short-circuit: When the main circuit current is large during the discharge process (refer to the design parameters of the protection board for specific details), there is also internal resistance due to MOS saturation and conduction , So when the current flows between B- and P-, there will be a voltage drop across the MOS. V- and VSS (through R2) of the protection IC will detect the voltage across the MOS at any time. When the voltage rises to the IC protection threshold (generally When it is 0.15V, which is called the discharge overcurrent detection voltage), Dout will immediately output a high level and the corresponding MOS will be turned off, and the discharge circuit will be disconnected. Seeing this, some students have probably realized that if you choose MOS with low turn-on internal resistance or IC with high discharge overcurrent detection voltage, can you get a large output current? The answer is yes, but the power of the selected MOS and the capacity of the battery must also be considered!

V. The role of NTC (T port): When the battery is working, there is no overcharging, overdischarging or overcurrent, short circuit, etc., but because the working time is too long, the battery temperature rises (For example, we usually use our mobile phones to talk on the phone) very quickly. The NTC resistor is close to the battery cell to monitor the temperature of the battery cell. As the temperature rises, the NTC resistance value gradually decreases. The consumer CPU notices this change. When the resistance value drops to the set value of the CPU, the CPU sends a shutdown command to stop the battery. Powering it, only maintains a small standby current, to achieve the purpose of protecting the battery.

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