This document proposes an interleaved boundary conduction mode power factor correction buck converter that maintains high efficiency across all load and line conditions. It uses an adaptive master-slave interleaving method to keep the two parallel buck converters 180 degrees out of phase during transients. This halves the input current ripple while doubling the ripple frequency, allowing for a smaller line filter. Experimental results from a 300W prototype with 80V output show efficiencies above 96% down to 20% load and above 94% even at 10% load, across the full universal line range. The input current harmonics also meet IEC61000-3-2 class D standards.