Commonly used equalization charging technologies include constant shunt resistor equalization charging, on-off shunt resistor equalization charging, average battery voltage equalization charging, switched capacitor equalization charging, buck converter equalization charging, and inductive equalization charging. When groups of lithium batteries are charged in series, each battery should be balanced and charged, otherwise the performance and life of the entire battery will be affected during use. The existing single-cell lithium battery protection chip does not include the balanced charging control function, and the multi-cell lithium battery protection chip equalization charging control function needs an external CPU; through serial communication with the protection chip (such as I2C bus), the The complexity and design difficulty of the protection circuit, the efficiency and reliability of the system are reduced, and the power consumption is increased.
In this paper, the power lithium battery is used in groups. The lithium batteries of each section require the protection of charging over voltage, discharge under voltage, over current and short circuit. In the charging process, the problem of equalizing the charging of the whole battery should be realized. Lithium battery protection chip Design of a battery protection board with balanced charging function for protecting any series of lithium batteries in series. The simulation results and industrial production application prove that the protection board has perfect protection function, stable operation, high cost performance, and the balanced charging error is less than 50mV.
1 Lithium battery pack protection board balanced charging principle structure
The block diagram of the lithium battery pack protection board with balanced charging capability designed by a single-cell lithium battery protection chip is shown in Figure 1.
Figure 1 Block diagram of lithium battery pack protection board
Among them: 1 is a single-cell lithium-ion battery; 2 is a charging over-voltage shunt discharge branch resistor; 3 is a shunt discharge branch control switching device; 4 is an overcurrent detection protection resistor; 5 is an omitted lithium battery protection chip and circuit Connection part; 6 is a single-cell lithium battery protection chip (generally including charging control pin CO, discharge control pin DO, discharge overcurrent and short-circuit detection pin VM, battery positive terminal VDD, battery negative terminal VSS, etc.); The charging overvoltage protection signal is isolated by the optocoupler to form a parallel relationship driving the gate of the MOS transistor for charging control in the main circuit; 8 is a discharge undervoltage, overcurrent, short circuit protection signal is isolated by the optocoupler to form a series relationship driving the main circuit discharge Control MOS tube gate; 9 is charge control switching device; 10 is discharge control switching device; 11 is control circuit; 12 is main circuit; 13 is shunt discharge branch. The number of single-cell lithium battery protection chips is determined according to the number of lithium battery cells, and is used in series to protect the charge, discharge, overcurrent and short circuit conditions of the corresponding single-cell lithium battery. The system realizes balanced charging by controlling the on/off of the shunt discharge branch switching device while protecting the chip. This scheme is different from the traditional method of achieving balanced charging at the charger end, and reduces the design of the lithium battery pack charger. The cost of the application.
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