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

In the front-end of two-stage voltage regulator modules in 48V-based data centers, a dc transformer (DCX) is required to convert the 48V bus to an intermediate voltage with a fixed buck ratio. In this paper, 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, 48V to 12V converter prototype is designed and tested. Experimental results well validate the concept with a 97.23% peak efficiency.