Reduction of leakage inductance and AC resistance of planar transformers by optimising the current distribution

Planar transformers (PTs) are becoming increasingly popular in high-power density, high-frequency SMPS in recent years due to their unique advantages including low profile structures and excellent thermal properties. This study focuses on detailed investigation of the effects of coil current distribution within each winding layer on leakage inductance and AC resistance of a PT, and an analytical derivation based on variational method is given. Then the optimal current distribution is proposed and verified through 3D finite element analysis simulation and physical experiments. The results show that the leakage inductance and AC resistance can be reduced further by optimising the current distribution. Accordingly, a practical implementation method is proposed to control the current distribution within a winding layer by adjusting the widths of conductors.