In this paper, an automatic frequency shifting technique is developed for achieving output voltage regulation of LLC series resonant converter (LLC-SRC). Furthermore, the operating modes and dc characteristics are discussed for designing the steady state operating point. Finally, an LLC-SRC, rated about 90 W with operating frequency range from 92 KHz to 102 KHz is provided to verify the control strategy. As theoretical analysis, the proposed system gives a satisfactory result within the overall load range. This technique is very promising in resonant converter applications