A mathematical guideline for designing an AC-DC LLC converter with PFC

Although LLC topology has been applied to AC-DC power supplies as a Power Factor Correction (PFC) converter in the literature, there is no publications present intuitive equations that simplify LLC designing in order to meet the PFC gain requirements. In this paper, a mathematical design guideline is derived for LLC PFC converter applications, proving that by carefully designing the resonant tank gain at parallel resonant frequency at the peak AC voltage higher than 1, its gain will meet the PFC requirement for other AC voltages and result in a successful single-stage PFC design with power factor over 0.99. The guideline is extended to offline wide input and output voltage LLC PFC applications. A 240-Watt prototype of a single-stage LLC LED driver with PFC has been built to verify the feasibility of the proposed design guideline.