The market of electronic products such as mobile phones and portable devices grows rapidly while the demand of lithium battery for fast charge, long duration, and long life cycle increases significantly as well. There are several charge methods for lithium battery, such as constant current (CC)/constant voltage (CV) charge [1], pulse charge [2] and reflex charge [3], etc. In general, a flyback converter has been widely adopted as the front-end converter of battery charger due to its low-cost, wide power range, and galvanic isolation between input and output stage. The battery charge controller with flyback converter has been developed in digital control with opto-coupler feedback [4]–[6]. The conventional flyback converter with CC or CV applications always requires two sensed ADC channels for regulating [7]–[9]. An improved control method is proposed in this study to achieve CC/CV by only one ADC channel. This study presents a battery charge mechanism with a flyback converter and associated trickle charge method for the temperature compensation. The PSR is adopted for switching the charge modes within trickle current (TC), constant current (CC) and constant voltage (CV). The TC charging method is used to avoid the rapid increase in the temperature of the battery which is based on the characteristics of the internal resistance of the battery [10]. The proposed system circuit contains two stages in topology. The first stage is a front-end flyback converter which operates in DC-DC discontinuous current mode (DCM) by using PSR to sense the output voltage from auxiliary winding. It is adopted to replace the opto-coupler for avoiding temperature limitation for operations and reducing cost. The software Powersim is used to simulate the proposed flyback converter and PSR method. The second stage is the digital feedback loop, which processes the controlled signal by a digital processor (DSP) TMS320F2812. The experimental results were compared with general CC/CV method. The results show favorable performance of the propose charging method.
