A Boost PFC Stage Utilized as Half-Bridge Converter for High-Efficiency DC-DC Stage in Power Supply Unit

Abstract

The half-bridge (HB) LLC converter is one of the most attractive dc-dc converters for medium power supplies due to its soft switching capability. However, its conversion efficiency is considerably degraded in wide-link-voltage applications because of a small magnetizing inductance and wide switching frequency variation for a high voltage gain. In this paper, a boost power factor correction (PFC) stage, which can also play an important role during the hold-up time, is proposed for a high-efficiency HB LLC converter. In the proposed PFC stage, the boost PFC converter can be effectively utilized as a HB converter by replacing a boost diode and inductor with a synchronous switch and transformer, respectively. After the ac line is lost, the proposed PFC stage can operate as the HB converter and regulate the output voltage instead of the HB LLC converter. Thus, it enables the HB LLC converter to be designed with a large magnetizing inductance and narrow switching frequency variation. As a result, the proposed PFC stage can enhance the overall efficiency of the PSU by improving the efficiency of the HB LLC converter. To confirm the validity of this paper, a prototype with 180-264-Vrms ac line, 250-400-V link voltage, and 48 V/480 W output is tested.