Where: 1 is a single lithium-ion battery; 2 is the overvoltage shunt discharge branch resistance; 3. Switch device for shunt discharge branch control; 4 is overcurrent detection protection resistance; 5 is the omitted lithium-ion battery protection chip and circuit connection part; 6 is a single lithium-ion battery protection chip (generally including charge control pin CO, discharge control pin DO, discharge overcurrent and short circuit detection pin VM, battery positive end VDD, battery negative end VSS, etc.); 7. The charging overvoltage protection signal is isolated by optocoupler and forms a parallel relationship to drive the MOS tube gate for charging control in the main circuit; 8. The discharge undervoltage, overcurrent and short circuit protection signals are isolated by optical coupling to form a series relationship to drive the MOS tube gate for discharge control in the main circuit; 9 is the charging control switch device; 10 is the discharge control switch device; 11 is the control circuit; 12 main circuit; 13 is the shunt discharge branch. The number of protection chips for a single lithium-ion battery is determined according to the number of lithium-ion battery packs and used in series to protect the charging and discharging, overcurrent and short-circuit states of the corresponding single lithium-ion battery respectively. In this system, the on-off of the shunt discharge branch switch device is controlled by the protection chip at the same time of charging protection to realize balanced charging. This method is different from the traditional method to realize balanced charging at the charger end, and reduces the cost of designing and applying Li-ion battery pack charger.

Charging circuit

When the lithium-ion battery pack is charged, the positive and negative electrodes of the external power supply are respectively connected to the positive and negative ends of the battery pack BAT+ and BAT-. The charging current flows through the positive electrode of the battery pack BAT+, a single lithium-ion battery 1~N in the battery pack, the discharge control switch device, the charging control switch device, and the negative electrode of the battery pack BAT-.

In the control circuit part of the system, the charging overvoltage protection control signal of a single lithium-ion battery protection chip is isolated by the optocoupler and output in parallel, and the gate voltage is supplied to the conducting of the charging switch device in the main circuit. If one or several lithium-ion batteries first enter the overvoltage protection state in the charging process, the overvoltage protection signal will control the shunt discharge branch of a single lithium-ion battery connected in parallel at both ends of the positive and negative poles, and the corresponding single lithium-ion battery connected in series will be disconnected from the charging circuit at the same time.

Main circuit and shunt discharge branch

When a lithium-ion battery pack is charged in series, the influence of single battery capacity difference is ignored, and the battery with smaller internal resistance is charged first. At this time, the corresponding overvoltage protection signal controls the switch device of the shunt discharge branch to close, and a shunt resistor is connected in parallel at both ends of the galvanic cell. According to the PNGV equivalent circuit model of the battery, the shunt branch resistance is equivalent to the load of a single lithium-ion battery charged first, and the battery is discharged through it to maintain the terminal voltage of the battery in a very small range near the full state. Assuming that the first lithium-ion battery is charged first and enters the overvoltage protection state, the current flow direction in the main circuit and the shunt discharge branch is shown in Fig.3. When all single batteries charging into the overvoltage protection, all of the single section lithium-ion battery voltage size within the error range completely equal, each section protection chip charging protection control signals are less, cannot give priority to supply grid bias circuit of charging control switching devices, shut off, the primary loop disconnect, namely the realization of equalizing charge, the charging process is complete.