A wide output voltage LLC Series Resonant Converter with hybrid mode control method

It's difficult for LLC-Series Resonant Converter (LLC-SRC) to achieve a wide range of output voltage for a certain input voltage. Traditional solution to this problem is employing dummy load or burst control mode. Dummy load brings down the efficiency and burst control mode gives rise to a ripple of output voltage. To solve this problem, a PFM and phase-shift hybrid control strategy for full-bridge LLC resonant converter is introduced in this paper to generate output voltage from low voltage to high voltage regardless of the load condition. The selection consideration of phase-shift frequency is introduced. And detail analysis of operating conditions for phase-shift control mode and PFM mode is presented. Based on the proposed control strategy, an experimental prototype with 100V input, 150-550V output is provided. It achieves 88%-96% efficiency in full-load condition (4.6A) with 150V-550V output voltages, and above 90% efficiency in 550V output voltage with 5% - 100% load current.