A Switched-Capacitor and Series-Resonant Hybrid MHz DCX in Data Center Applications

In the front-end of two-stage voltage regulator modules in 48 V-based data centers, a dc transformer (DCX) is required to convert the 48 V bus to an intermediate voltage with a fixed buck ratio. In this article, we present a novel switched-capacitor and series-resonant hybrid DCX specifically for this application. The proposed DCX combines a 2:1 resonant switched-capacitor cell with a series-resonant converter, enabling a conversion ratio of 4 n: 1 with an n: 1 transformer. It demonstrates excellent soft-charging and soft-switching performances, effectively mitigating the switching loss. Furthermore, zero-voltage switching does not rely on the transformer's magnetizing current. Therefore, the magnetizing inductance can be optimized to improve the efficiency and to facilitate a simplified magnetic design. Theoretical analysis, design considerations, and topology comparison are provided to showcase the advantages of the proposed topology. A 1 MHz, 300 W-rated, 48 V to 12 V converter prototype is designed and tested. Experimental results well validate the concept with a 97.23% peak efficiency.