Rectifier-Integrated Printed-Circuit-Board Winding Structure of Secondary-Side Center-Tapped Transformer for Suppressing Parasitic Resonance between Decoupling Capacitors

In many practical LLC DC-DC converters, the isolation transformer is commonly designed to have a secondary-side center-tapped configuration with one-turn secondary windings. Conventionally, the rectification circuit is installed outside the transformer. However, the recent LLC converters are designed to operate at increasingly high switching frequencies, which indispensably causes the proximity effect in the rectification circuit as well as the wire that connects this circuit to the transformer secondary windings, resulting in large copper loss generation outside the transformer. The previous paper addressed this problem by proposing a secondary winding structure integrating the rectification circuit, although this structure caused the parasitic resonance inside the rectification circuit and reduced the rectification efficiency. To prevent the reduction in the rectification efficiency, this paper proposes an improved winding structure based on the printed-circuit-board technology for suppressing parasitic resonance. The experiment revealed further improvement in the rectification efficiency compared to the previously-proposed structure, suggesting the effectiveness of the proposed winding structure.