A high efficiency PFM half-bridge converter utilizing a half-bridge LLC converter under light load conditions

Till now, the various types of the half-bridge (HB) converters with output inductor have been developed, and they exhibit a good performance in medium power applications such as the server power supplies and personal computer (PC) power supplies requiring the hold-up time conditions and high output current. However, they have common problems such as high snubber loss and switch turn-off losses 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 at light load conditions in this paper. Since the proposed converter operates like the HB LLC converter by turning on additional switch at light load conditions, the snubber loss and switch turn-off losses can be minimized. Therefore, the proposed converter can achieve a high efficiency at light load conditions. To confirm the operation, validity, and features of the proposed converter, a 330-400V input and 12V/400W output laboratory prototype is built and tested.