A High-Efficiency PFM Half-Bridge Converter Utilizing a Half-Bridge LLC Converter Under Light Load Conditions

Recently, the various types of the half-bridge (HB) converters with the output inductor have been developed, and they exhibit a good performance in medium power applications such as the server power supplies and personal computer power supplies requiring high output current. However, they have common problems such as the primary and secondary switch turn-off losses and snubber loss in the secondary side caused by the output inductor, which degrades light load efficiency. To relieve these limitations of the conventional HB converters, a new HB converter, which employs one additional switch and capacitor in the secondary side, is proposed for a high efficiency under light load conditions in this paper. Since the proposed converter operates like the HB LLC converter with below operation by turning on additional switch under light load conditions, the switch turn-off losses and snubber loss can be minimized, and the zero-voltage switching (ZVS) capability can be improved. Consequently, the proposed converter can achieve a high efficiency under light load conditions. To confirm the operation, features, and validity of the proposed converter, a 330-400 V input and 12 V/300 W output laboratory prototype is built and tested.