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Power battery protection board common features
Overcharge voltage protection: to prevent the charge voltage is higher than the battery voltage limit caused by battery failure, causing security incidents
Over-voltage protection: to prevent the battery depth of discharge, to avoid shortening the battery life or cause safety incidents
Overcurrent protection: limits the size of the current through the protection board and the battery
Short circuit protection: to avoid short circuit caused by a safety accident
Temperature control switch: to protect the battery and the protection board temperature is too high to create security risks.
Power battery protection board principle
Power battery protection board has two core components: a protection IC, which is a reliable comparator to obtain reliable protection parameters; the other is the MOSFET string in the main charge and discharge circuit to play high-speed switch, the implementation of protection action.
1, the following describes the protection IC pin function: VDD is the IC power positive, VSS is the power supply negative, V- is the overcurrent / short circuit detection, Dout is the discharge protection executive, Cout is the charge protection implementation.
P +, P - are the positive and negative electrodes of the protection board output, respectively; T is the temperature resistance (NTC) port, generally need to use the MCU with the electrical With the generation of protection action, will be introduced later, the port is sometimes marked as ID, that is, identify the port, then the figure on the R3 is generally a fixed resistance of the resistance, let the CPU of the appliance to determine whether the specified battery.
Protection board work process:
1, the activation of the protection board: When the protection board P +, P- no output is in a protected state, you can short circuit B-, P- to activate the protection board, then, Dout, Cout will be low (protection IC two Port is high level protection, low level normal) state to open two MOS switches. The following are the same as the "
2, charging: P +, P- were connected to the positive and negative charger, charging current through the two MOS on the battery charge. At this time, the IC's VDD, VSS is the power supply side, but also the battery voltage detection side (by R1). As the charge progresses, the cell voltage rises gradually, and when it rises to the protection IC threshold voltage (typically 4.30V, commonly referred to as overcharge protection voltage), Cout then outputs a high level that will correspond to that MOS turn- The charging circuit is also disconnected. Overcharge protection, the battery voltage will drop, when the drop to the IC threshold voltage (usually 4.10V, usually referred to as overcharge protection recovery voltage), Cout to restore the low state to open the MOS switch.
3, the discharge: Similarly, the battery discharge, the IC's VDD, VSS will be the battery voltage detection, when the battery voltage drops to the IC threshold voltage (usually 2.40V, commonly known as over-release protection voltage), Dout Then the output high will correspond to the MOS turn off, the discharge circuit is disconnected. Overdischarge protection, the battery voltage will rise, when the rise to the IC threshold voltage (usually 3.00V, usually referred to as over-release protection recovery voltage), Dout to restore the low state to open the MOS switch.
4, MOS saturation conduction there is internal resistance, so the current flows through the B-, P- at both ends of the MOS will produce a voltage drop, protect the IC's V- and VSS (after R2) 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 immediately output high will correspond to the MOS turn off, the discharge circuit is disconnected. See here, probably some students have realized that if the use of low internal resistance of the MOS or discharge overcurrent detection voltage IC, you can get a large output current, but also consider the choice of MOS power and batteries capacity.
5, NTC (T port) role: When the battery work, there has been no charge, over discharge or overcurrent, short circuit, etc., but because the working time is too long, resulting in cell temperature rise (such as normal we use the phone Talk on the phone) soon. And NTC resistance close to the cell to monitor the cell temperature, with the temperature rise NTC resistance gradually decreased, with the appliance CPU found this change, when the resistance dropped to the CPU set value, CPU issued a shutdown command, let the battery stop Its power supply, only to maintain a small standby current, to protect the battery.
