Abstract: To address the problems of limited voltage regulation range, efficiency degradation, and even operational instability associated with conventional pulse frequency modulation (PFM) under high-step-down and light-load conditions for CLLLC resonant converters operating over a wide output voltage and load range, a hybrid pulse frequency modulation-extended phase shift modulation (PFM-EPSM) strategy was proposed. By establishing accurate gain and power models for EPSM, the coupling mechanism between power and phase-shift angles was revealed. A critical power switching logic based on soft-switching constraints was designed to achieve optimal switching between PFM and EPSM modes under different operating conditions, balancing efficiency and voltage regulation performance. Additionally, a sensorless synchronous rectification (SR) control method was proposed, which is applicable to both under-resonant and over-resonant states, ensuring reliable operation of SR switches across all operating conditions. Based on Gallium Nitride (GaN) devices, an experimental prototype with an input of 540 V, an output of 42~56 V, and a rated power of 3 kW was developed. Experimental results demonstrate that the proposed hybrid modulation strategy exhibits excellent dynamic response and steady-state regulation capability, while the synchronous rectification control operates accurately across the full voltage and power range, significantly improving the overall efficiency and adaptability of the converter to wide operating conditions.