Secondary winding configurations and methods particularly applicable for toroid transformers are described for winding secondary windings over the indexed primary winding and toroidal core. The secondary winding is formed in the configuration of a multifilar winding of a plurality of coplanar parallel filaments with a first elongate strip of electrically insulating material bonded to the filaments on one side and a second elongate strip of electrically insulating material bonded to the filaments on the other side and to the first elongate strip. The resulting electrically insulated multifilar strap winding contains the filaments in substantially parallel coplanar relationship. The multifilar strap winding is wound around the toroidal core in substantially equally spaced turns. The strap winding maintains the filaments substantially in equally spaced relationship relative to each other over irregular surfaces and compound curvature of the toroidal core without crossover. Mutual inductance between the secondary winding of the invention and the primary winding is optimized while leakage inductance is minimized. The disclosure is applicable for high frequency switching transformers used in the power supplies of microprocessors and computer accessories where losses and spikes from leakage reactance must be minimized.