Abstract: A DC-DC converter for converting a primary DC voltage to a secondary DC voltage comprises a transformer with a primary winding and a secondary winding each wound on a ferromagnetic core, a primary DC voltage power source, a plurality of switching transistors connected between said DC voltage power source and the primary winding of the transformer, means for controlling the status (ON or OFF) of the transistors so that an alternate current or an intermittent current in the predetermined direction flows from the DC power source to the primary winding of the transformer, a rectify/smoothing circuit connected between the secondary winding of the transformer and a load, and said primary winding of the transformer having a center tap which is connected to one end of the DC voltage power source through a capacitor.