Universal‐Input Single‐Stage Bridgeless Dual‐Boost‐LLC AC‐DC Converter With Reduced Bus Voltage and Improved Efficiency

This paper proposes a single‐stage bridgeless dual‐boost‐LLC AC‐DC converter that integrates a dual‐boost bridgeless power factor correction (PFC) stage with a full‐bridge LLC resonant stage. The proposed topology addresses the limitations of existing soft‐switched single‐stage approaches, such as high and widely varying intermediate bus voltage and narrow input range, by employing a hybrid pulse‐frequency modulation/pulse‐width modulation (PFM/PWM) strategy with output voltage feedback. This proposed control enables universal 85‐ to 265‐V input operation while restricting the bus voltage to a narrowed range of 300–475 V. An optimized parameter design procedure based on the power‐balance principle is introduced to maintain discontinuous conduction mode (DCM) operation and natural high power factor correction across the entire input range. A 300‐W prototype with 12‐V/25‐A output was built and tested. Experimental results verify soft switching of all shared switches, a peak efficiency of 93.6%, and a power factor above 0.98 throughout the universal input range.