Application of Magnetic Composite Materials in Windings to Reduce Alternating Current Resistance in Leakage Transformers

LLC resonant dc–dc converters are high-efficiency converters capable of low-loss switching. Leakage transformers that combine resonant inductors and transformers are effective for the miniaturization of LLC resonant dc–dc converters. However, they exhibit a substantial leakage magnetic flux due to low coupling between the primary and secondary windings, and they exhibit high alternating current (ac) resistance due to the leakage magnetic flux acting on the windings. Thus, this study proposes an approach to reduce the ac resistance of leakage transformers by inducing a leakage flux through the application of magnetic composite materials to the windings. Magnetic field simulation and fabrication of transformers are used to clarify the effect of the loading position of a magnetic composite material on the ac resistance of leakage transformers. The ac resistance at 1 MHz was reduced by 33% from 743 to 501
$\text{m}\Omega $
by loading the magnetic composite material at the appropriate position in the winding.