A High Efficiency LLC Resonant Converter with Wide Ranged Output Voltage Using Adaptive Turn Ratio Scheme for a Li-Ion Battery Charger

In this paper, a LLC resonant converter battery charger using adaptive turn ratio scheme is proposed to achieve high efficiency and wide ranged output voltage. In the proposed scheme, the high frequency transformer of the LLC converter has an adaptively changed turn ratio by the auxiliary control circuitry. As a result, the optimal converter design with a large magnetizing inductance is easily achieved to minimize the conduction and the turn-off losses, while providing widely regulated voltage gain capability to charge a Li-ion battery properly. The operational principle and the optimal design considerations of the proposed converter are illustrated in detail. Finally, several simulation results verify the effectiveness of the proposed a LLC resonant converter battery charger.