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In universal-line ac/dc converters that require power factor correction (PFC), maintaining a high efficiency across the entire line and load ranges poses a major challenge. Typically, a boost PFC front end exhibits 1%-3% lower efficiency at 100-V line compared to that at 230-V line. It is shown in this paper that a buck PFC front end with an output voltage in the 80-V range can maintain a high efficiency across the entire line and load ranges. A thorough analysis of the buck PFC converter operation and performance along with design optimization guidelines are presented. Experimental results obtained on a 90-W notebook adapter are provided. A loss analysis based on SIMPLIS and PSPICE simulations is also included. Major factors that contribute to the improved efficiency of the buck PFC versus the boost PFC are briefly explained.