Patent ID: 8077482

Claim:
A DC-DC converter of a forward type comprising: a direct-current power supply; a first condenser; a first semiconductor switch element provided with an antiparallel diode; a second semiconductor switch element provided with an antiparallel diode; a first diode; a transformer provided with a first coil, a second coil and a third coil; a rectification circuit; and a smoothing circuit, wherein the direct-current power supply and the first condenser are connected in series, wherein the first semiconductor switch element and the second semiconductor switch element are connected in such a manner that the antiparallel diode of the first semiconductor switch element and the antiparallel diode of the second semiconductor switch element face a same direction, wherein a terminal of the first condenser that is not connected to the direct-current power supply and a terminal of the second semiconductor switch element that is not connected to the first semiconductor switch element are connected with each other, wherein a terminal of the direct-current power supply that is not connected to the first condenser and a terminal of the first semiconductor switch element that is not connected to the second semiconductor switch element are connected with each other, wherein the first coil of the transformer is connected between a connection point of the direct-current power supply and the first condenser and a connection point of the first semiconductor switch element and the second semiconductor switch element, wherein among a pair of terminals of the second coil of the transformer, one terminal of a same polarity as a terminal of the first coil that is connected to the direct-current power supply is connected to a connection point of the first condenser and the second seminconductor switch element through the first diode, and other terminal is connected to the connection point of the direct-power supply and the first condenser, wherein the third coil of the transformer is connected to the smoothing circuit through the rectification circuit, wherein a direction of the first diode is set in such a manner that energy can be transferred to the first condenser from the second coil of the transformer when the first semiconductor switch element is in a conduction state, and wherein the rectification circuit applied a voltage of same polarity to the smoothing circuit in both case where the first semiconductor switch element is in a conduction state and the second semiconductor switch element is in a conduction state.