Design and Optimization of Fractional-Turn Transformer With Low Core Loss and Profile

In data center applications where most power supplies are in light-load operation, hence optimizing light-load efficiency is immensely crucial. In this article, a fractional-turn planar transformer with an elliptical core is proposed, which reduces the eddy loss of the core and improves the light-load efficiency. This structure also reduces the magnetic core profile and improves the power density. Magnetic loss theory, winding configuration and core optimization were analyzed in detail. Finally, a detailed optimization process about transformer is carried out based on finite-element analysis, and two 1 MHz 380 V–12 V 720 W LLC converters are designed based on the conventional fractional-turn transformer and the proposed fractional-turn transformer, respectively.