High efficiency soft-switched step-up dc-dc converter with hybrid mode LLC+C resonant tank

To improve the efficiency performance for the dc-dc converter used in extra wide input range applications, a novel resonant converter with a combinatorial LLC+C tank is proposed in this paper. The proposed resonant tank has a hybrid operational mode, which can operates as LLC resonant tank for high line input or as LLCC resonant tank for the low line input, realized by the topology shift through the control of a cost-effective shifting switch. By being carefully designed and with the ZVS+ZCS soft switching feature, the proposed converter can accommodate the extra wide input range applications without sacrificing the overall efficiency. The details for the design procedure are presented, small signal compatibility is discussed, and the control strategy for topology shifting is also stated. A prototype with 100V-400V input voltage range, 24V/10A output power rating was built to verify the validity and applicability of this proposed converter. A comparison with a single topology LLC converter with the same specifications was also made to show the superiority of the proposed converter when applied for the extra wide input range applications.