A magnetic integration half-turn planar transformer for LLC resonant DC-DC converters

This paper presents a new half-turn planar transformer with integrated leakage inductance for LLC resonant DC-DC converters. A simple EILP32 ferrite core is adopted in the proposed transformer. The primary side windings are placed at both the center and side legs of the ferrite core. By adjusting the distribution of the windings on the center and side legs, the leakage inductance of the transformer can be changed. In order to balance the core loss and the copper loss, the turn number of the secondary side winding is designed to 0.5. Two configurations of secondary winding and circuit structure are given and compared. The characteristics of the proposed transformer are simulated using Maxwell and Simplorer. Finally, a 380V / 12V, 500 kHz, 750W LLC converter was built to evaluate the performance of the proposed transformer. The converter can reach 12V stable output when the input voltage range is from 360V to 400V, and realize the highest efficiency of 97 % at half load condition.