What are the working principles of the power battery protection board

With the continuous development of the electric industry, it has also brought a new future to the power battery industry. As the core component of the power battery, the power battery protection board has attracted people's attention and is the escort sail for the safety of the power battery. What are the working principles of the power battery protection board? Today, the Chinese Chuangfa will learn with everyone, and the power battery protection board has two core components: a protection IC, which uses an accurate comparator to obtain reliable protection parameters, and the MOSFET is stringed in the main charging and discharging circuit. Act as a high-speed switch and perform protection actions. The circuit schematic diagram is as follows:

1. The following describes the function of protecting IC pins: VDD is the positive pole of the IC power supply, VSS is the negative pole of the power supply, and V- is the over-current/short-circuit detection terminal , Dout is the discharge protection execution end, and Cout is the charge protection execution end.

2. Description of the port of the protection board: B+ and B- are the positive and negative terminals of the battery cell respectively; P+ and P- are the positive and negative poles of the output of the protection board respectively; T is the temperature resistance (NTC) port, Generally, it needs to cooperate with the MCU of the electrical appliance to produce a protection action. As we will introduce later, this port is sometimes marked as ID, which means the identification port. At this time, R3 in the figure is generally a fixed resistance resistor, allowing the CPU of the electrical appliance Identify whether it is a designated battery.

3. The working process of the protection board: 　　

1. The method of activating the protection board: When the protection board P+ and P- are not in the protection state, you can short-circuit B- and P- Activate the protection board. At this time, both Dout and Cout will be in the low level (the two ports of the protection IC are high level protection, and the low level is normal). Turn on the 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 immediately and the corresponding MOS will be turned off. The charging circuit is also disconnected. After 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 state 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 immediately outputs a high level and the corresponding MOS is turned off, and the discharge circuit is 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.

　4, MOS saturation conduction also has internal resistance, so when the current flows between B- and P-, a voltage drop will occur at both ends of the MOS to protect the V- and VSS of the IC (through R2) It will detect the voltage across the MOS at any time. When the voltage rises to the IC protection threshold (usually 0.15V, called the discharge overcurrent detection voltage), Dout will immediately output a high level to turn off the corresponding MOS, and the discharge circuit will be disconnected. Seeing this, probably some students have realized that if you choose MOS with low turn-on internal resistance or IC with high discharge overcurrent detection voltage, you can get a large output current, but you must also consider the power of the selected MOS and the battery core. capacity.

5. The role of NTC (T port): When the battery is working, there is no overcharge, overdischarge or overcurrent, short circuit, etc., but because the working time is too long, the cell 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 CPU setting value, 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.