Design considerations for a high efficiency 3 kW LLC resonant DC/DC transformer

In this paper, the design principles, procedures and considerations for a 3 kW high efficiency LLC resonant DC/DC transformer is presented. The efficiency-oriented design procedure involves analytical methods for calculating converter RMS current on both primary side and secondary side, transformer winding AC loss and MOSFET switching loss. These methods are reviewed in this paper. The resonant inductor is integrated with the transformer. Implementation issues that arise due to integration of the resonant inductor and the transformer are analyzed with special attention given to modeling of voltage ringing on the secondary side MOSFETs. Finally, a converter prototype is built, which achieves 98.24% efficiency at nominal load. The design concepts and models are verified by the prototype.