An Improved Synchronous Rectification LLC Resonant Converter for Hold-Up Time Operation

An innovative improved synchronous rectification LLC (ISR LLC) resonant converter is proposed for applications that demand extended hold-up time, such as data center power supplies. The design greatly simplifies the hold up operation circuit by integrating only one switch into the conventional synchronous rectification LLC converter. Utilizing a fixed-frequency phase shift control strategy, the converter achieves an enhanced voltage gain, which in turn, substantially prolongs the hold-up time. Compared with the traditional pulse frequency modulation LLC resonant converter, a larger magnetizing inductance can be employed, effectively diminishing the system's conduction losses and elevating conversion efficiency. The topology, operation principle, voltage gain characteristics, and design considerations of the converter will be elaborately introduced. The prototype converter with 200–400 V input and 48 V/500 W output is presented to validate its effectiveness.