A Novel Resonant Topology for Battery Charger Application

For battery charger application, a wide switching frequency range is required for LLC resonant converter, which brings difficulties to magnetic components and driver circuit design, and the system efficiency would be degraded. To narrow the switching frequency range, in this paper, a novel topology based on the LLC and LCL-T resonant tanks is proposed. During the constant current (CC) charge mode, the proposed converter is operating with LCL-T resonant tank, which provides constant charging current; during the constant voltage (CV) charge mode, the structure of the proposed converter is modified to a traditional LLC resonant converter, and it is operating at the series resonant frequency to perform as a constant voltage source. Due to the high accuracy of these resonant tanks, the required operating switching frequency range can be significantly reduced. Operation principles and design considerations for the proposed converter are presented. Finally, experimental results are provided.