Abstract: A DC-DC converter for supplying stabilized DC power to a load comprises a transformer, a switch, first and second capacitors, a control circuit, and a rectifying and smoothing circuit. The transformer has a primary winding, a secondary winding and a tertiary winding. The primary winding of the transformer is connected in series to the switch. The secondary winding of the transformer is connected to the rectifying and smoothing circuit, and the tertiary winding is connected to a control terminal of the switch so as to drive the switch by positive feedback voltage. The first and second capacitors repeat charge and discharge periodically. When voltage of the first capacitor attains to the threshold voltage of the switch, the switch is converted from the OFF state into the ON state. When voltage of the second capacitor attains to the prescribed value, the control circuit converts the switch from the ON state into the OFF state. Circuit parts of the DC-DC converter is small in number.