High-Efficiency High-Power-Density LLC Converter with Copper Foil Parallel Interleaved Winding Planar Transformer in High-Output Current Applications

In high-output current applications, printed circuit board (PCB) planar transformers face problems of huge winding loss and limited winding current-carrying capacity. The design of secondary-parallel multiple interleaved copper foil planar transformer is proposed. To diminish DC resistance, the secondary side of the transformer is connected in parallel with three copper foil layers. The primary and secondary windings are interleaved to achieve lower AC resistance. In order to further reduce the terminal loss, the primary side of the transformer adopts the structure of direct connection in the air to reduce the number of the PCB connectors and redundant power loops. A 1.5-kW GaN LLC prototype is built with 650 kHz resonant frequency. The LLC power density is 524 W/in3 and the efficiency is up to 98% with 28 V/53.5 A output at full load.