| Li-ion and Li-polymer battery are being widely used. The charger with safe, reliable, fast and high efficiency is important for the performance and application of the battery. In this thesis, the chemic structure, performance and charging scheme of Li-ion and Li-polymer battery are studied. And based on the effect of charging process and method to battery's performance, some problems in the period of charging are raised and as a solution a DC/DC charger IC for single Li-ion or Li-polymer battery is designed.Following the operational principle of the Li-ion battery fast-charging and the existing charging approaches, the trickle pre-charge mode and constant temperature charging mode are added based on the CC/CV mode, i.e. pre-charge the battery using trickle current at the initial of charging cycle to fix and protect the over-discharged battery. After which, the battery will be charged by large constant current to allow the fast charging. Finally, the constant voltage charging is adopted to guarantee the battery was charged to its full capacity. Under the condition that the temperature has raised to a certain threshold at the constant current charging stage, the over temperature circuit is performing and it provides a compensation current which switches the system to constant temperature charging mode with the intention of protecting the IC. Besides, the battery under and over temperature protection module, battery status detection module, and power status detection module are also added in the system to allow the intelligent control of the charging process. The charging current and period can be programmed by user to provide friendly interface. In order to enhance its efficiency, the cooperation capability between IC and current limited adapter has been reinforced in this circuit to overcome the problem of low efficiency of the linear charger. In actual applications, the efficiency is same as the conventional linear charger when the IC is powered by constant voltage source and is similar to pulse or switch charger when current limited source is used for power supply.In this thesis, the composition and chemical principle of the Li-ion battery are presented firstly, which is followed by its characteristic and common charging approaches introduction. Finally, the whole system is discussed where actual circuit design and realization are emphasized. The HSPICE simulation results indicate that the charging current is up to 2A and the precision of termination voltage is very high with the error only around 10-3. The efficiency is approximate 68% when the IC is powered by fix voltage source and up to 95% when the IC is powered by current limited source. |
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