Relutance-Controlled Arbitrary Non-Integer Turns Ratio Planar Transformer for DCX with High-Current Applications

Owning to its high efficiency characteristic, resonant converter is designed to operate at resonant frequency as a DC transformer (DCX), where the transformer turns ratio is designed based on the nominal input and output voltages. However, limited by the number of printed circuit board(PCB) layers and turns, it is difficult for planar transformer to achieve non-integer turns ratio. The common solutions include fractionalturn transformer and matrix transformer, but neither method can achieve non-integer turns ratio without increasing the number of turns. This paper proposes a reluctance-controlled arbitrary noninteger turns ratio planar transformer structure. The proposed structure splits the center column, and primary windings are wound on two columns and connected in series. By adjusting reluctance ratio of two columns, the proposed method can achieve arbitrary non-integer turns ratio in fewer turns. Finally, a 30 V/12 V 120 W LLC converter is built. Compared with the traditional solution, the total number of turns is reduced from 9 to 6, winding loss and total transformer loss are reduced by 1.2 W and 51.8%, respectively.