Extended range DC-DC power converter circuit

A single-stage power converter has an input-to-output transfer characteristic with two portions, each having a different operational characteristic, with each portion being selected by changing ONLY the duty-cycle of the power switching devices. At low input voltage the converter operates as a Boost converter, while operating as a Buck converter for greater input voltages. This transfer characteristic is provided by a circuit wherein the primary winding center tap of a split-primary power transformer is coupled through an inductive element, with one of the pair of push-pull power switching devices connected to each primary winding end. Secondary winding rectification and filtering provides the power supply output in the Boost mode, and a portion of the power supply output in the Buck mode. The remainder of the Buck-mode output is supplied by the energy stored in the inductive element, preferably by use of a secondary winding on a transinductor (multiple-winding inductive) element having a primary winding providing the energy-storing inductance L.