Asymmetrical secondary structure of LLC series resonant DC/DC converter for multi-output applications

This study proposes a new multi-output LLC series resonant topology, which has asymmetrical structures for the main and the auxiliary outputs. The novel topology is devoted to use as multi-output power conversion system. The topology is a good candidate for multi-output applications with limited light loads. According to the output power level, different structures of the secondary outputs can be flexibly adapted. All the switches of this topology operate under the condition of zero voltage switch (ZVS) or zero current switch (ZCS). Therefore it is suitable to high frequency and high power density applications. The asymmetrical operation principle between the main output and the auxiliary outputs is analysed. ZVS and ZCS operations are explained in detail. Moreover the key parameter design considerations are presented. The theoretical analysis was verified both by simulation and experiment results. Finally, a prototype, with 310 V input, 48 V@1-2 A main output, and 24 V@0-0.5 A auxiliary output, was built and tested to validate the analysis done. The experimental results do match the theoretical analysis very well. The efficiency of the prototype under nominal input and full load reached 93%.