Applied Circuit Research On Lithium-ion Battery Series

In practice, the problems such as safety, equilibrium among batteries and high power dissipation of management system restrict the wide applications of Li-ion battery series. Therefore, how to resolve these factors by applying external circuit has become a growing interest.This paper mainly developed applied circuits for typical battery series with two, four and seven Li-ion battery in series, which were adopted in practical projects. And those developed applied circuits were demonstrated to be valid in experiments.On the safety property which is mostly important for two Li-ion batteries in series, the working principle of protection circuit was introduced in detail, especially, the selecting rules of protection IC chips and external components were discussed. Furthermore, the practical over-temperature protection circuit, discharge ending circuit and short-circuit protection circuit which can act in 5μs were designed to ensure the safety of Li-ion battery series.Besides the safety consideration for four Li-ion batteries in series, a circuit based on the corresponding relationship between the discharge energy and voltage was developed to detect the energy and working time of battery series. Also, combining with a time-delaying LED display circuit made it more practical. Further, heat dissipation and the ratio of energy transition of the power distributive circuit were calculated and analyzed.For seven Li-ion batteries in series, the protection circuit used for more than four batteries in series was also developed, which was simple and had low power dissipate with operating current less than 47μA. Furthermore, the output voltage stabilized by an automatic circuit controlled by the PWM signal. Moreover, the equilibration circuit for Li-ion battery series was developed based on comparing the maximum value of the single battery with the average value of the battery series. The availability of the designed equilibration circuit was proved in experiments.