This paper introduces a novel topology of LLC resonant converter employing a transformer with an adjustable number of active turns to achieve a wide voltage gain, making it well-suited for battery charger applications with constant-current/constant-voltage (CC/CV) charging and large input voltage variations. Unlike conventional approaches that require additional bidirectional switches, the proposed converter integrates these functions with the inverter switches, resulting in a simpler and more compact circuit structure. Operating at the resonant frequency minimizes circulating current, ensures stable operation across a wide load range, and allows optimal sizing of passive components, while fixed-frequency PWM simplifies control. Furthermore, zero-voltage switching (ZVS) of the inverter and zero-current switching (ZCS) of the rectifier are achieved, improving efficiency and reliability. Preliminary analysis and simulation results validate the effectiveness of the proposed topology. Final paper will present a 4 kW prototype (200–500 V in, 600–800 V out) with experimental results to validate the proposed converter’s performance.
