To achieve high efficiency and high power density, the transformer structure of a fractional-turn winding can reduce core volume and conduction loss on the secondary-side winding. The optimized transformer design also enables the turn ratio of the fractional-turn to achieve normal coupling of primary and secondary sides without generating flux imbalance.

This project has proposed winding methods to achieve a fractional-turn secondary-side winding that balances the flux of the transformer. Given that the number of turns and considering core loss, copper loss, and power density, an optimized core size was determined based on the core parameters equation. Simulation was used to verify the proposed structure and confirm that its flux was balanced.

LLC converters are frequently used as isolated converters in server power supplies. To increase power density in a limit volume, we need to focus on high efficiency and high power density when designing converters. To reduce secondary-side winding loss, a quarter-turn planar transformer was proposed to minimize winding loss and the volume of the transformer.