Recently, many high efficiency and high power density dc-dc power modules have been proposed for the distributed power system of the server and telecommunication applications. Among these power modules, a conventional phase shift full bridge (PSFB) converter is one of the popular topology for medium or high power applications, which has desirable features such as the zero voltage switching (ZVS) operation and high efficiency. However, conventional PSFB converters have two serious disadvantages that the ZVS range of the lagging leg is very narrow and the freewheeling current consumes high circulating energy.
As a solution to the narrow ZVS ranges, a new PSFB converter with series-connected two transformers (SCTT) is proposed. The proposed converter shows wide ZVS ranges and no output inductor is needed since each transformer individually act as an inductor or a transformer during different times of the switching cycle. In addition, to cope with the high circulating energy, a new method based on the PSFB converter with SCTT, which is a capacitor is added in the primary side of the based converter, is proposed. The new method makes the turn ratio of the transformers increase as well. Therefore, the efficiency of the proposed converter is more increased. And it will be shown the proposed converter can be used for an ac-dc application with power factor correction (PFC).
The operational principle, large signal modeling, and design equations are presented. Experimental results demonstrate that the proposed converter can achieve a significant improvement in the efficiency for 100 W (5 V, 20 A) telecommunication on-board power supply.
The proposed converter is suitable for the server and telecommunication equipment using 48 V bus voltage and requiring the high efficiency and high power density.