A Switching-based Fast Battery Charger by Continuously Compensating Built-In Resistance Effect

Abstract

Recently, as the increment of functions in mobile devices, the long using time is continuously demanded by the market. Li-ion battery is widely used in mobile devices due to the advantages such as high energy density, high voltage level, and so on. Because the battery capacity has been continuously increased to prolong the using time, the high efficient charger is widely studied to reduce charging time in these days. The method that increases the charging current is normally used to reduce charging time, but it is limited to increase the charging current because it brings some problems such as degradation of battery life, heating, and so on. By these reasons, the charging methods that reduce the charging time effectively with high efficiency become very important issue in the most recent charger. This thesis proposes a switching-based charger which supports constant current-constant voltage (CC-CV) charging method. The proposed charger reduces the charging time by compensating the voltage difference due to the built-in resistance in the battery pack. The proposed charging method uses the ripple characteristics of the switching-based charger, and can calculate the built-in resistance from the ratio of the amplitude of voltage ripple in battery to the amplitude of current ripple in inductor. From the result, the proposed charger reduces the charging time using the compensated reference voltage which determines the transition point from CC mode to CV mode. The charger is designed to support the input voltage range from 4.5 V to 5.5 V, operating frequency of 500 KHz, and maximum charging current of 2 A. The simulation result shows that the proposed charger is suitable for mobile devices.