High-Efficiency Single-Stage LLC Resonant Converter for Wide-Input-Voltage Range

In this paper, a new single-stage half-bridge (HB) resonant <inline-formula><tex-math notation="LaTeX">$LLC$ </tex-math></inline-formula> converter additionally employing one resonant capacitor and two relays with one package is proposed, compared with a single-stage HB <inline-formula><tex-math notation="LaTeX">$LLC$</tex-math></inline-formula> converter. Moreover, a center-tapped transformer is replaced with a coupled transformer. Since the proposed converter changes the turns ratio of the coupled transformer using a relay according to low- or high-input-voltage range, it can decrease the range of its needed voltage gain. It means that the proposed converter can be designed with large transformer magnetizing inductance compared with the conventional single-stage HB <inline-formula> <tex-math notation="LaTeX">$LLC$</tex-math></inline-formula> converter. As a result, the primary conduction and turn-off losses are reduced. Moreover, in low input voltage range, it has smaller total primary wire resistance of the transformer due to parallel connection of the coupled transformer, which decreases its conduction loss. In addition, additionally employed small-sized components can be inserted to the conventional system. To confirm the operation, features, and validity of the proposed converter, universal input with low line and high line and 16.5 V/60 W output laboratory prototype targeting laptop adapters with wide-input-voltage range is built and tested.