A transformer includes a core with a surface, a primary winding with two or more primary winding turns wrapped about the core, and a secondary winding with one and only one secondary winding turn extending about the core. The one and only one secondary winding turn is interleaved among the two or more primary winding turns on the surface of the core to limit magnetic flux leakage along the primary winding and the secondary winding. Power converters and power conversion methods are also described.