Self-oscillating contactless resonant converter with power transfer and current sensing integrated transformer

A contactless transformer with a shorted current sensing winding in the primary side is proposed to provide a passive current phase detection solution for a self-oscillating contactless resonant converter (SOCRC). It can detect the phase of the secondary current and feedback to the primary side rapidly and accurately regardless of the variable air gap. To guarantee the operation of the SOCRC, the influence of the coupling coefficient between the shorted current sensing winding and the secondary windings is analyzed in detail. Some experimental results on an 80W SOCRC are used to verify the analytical results of the proposed structure.