Patent ID: 7272022

Claim:
A dc-ac converter, comprising: a dc power supply; a transformer having a primary side and at least one secondary side; a switch circuit having a first and a second semiconductor switches connected in series with each other via said primary side to allow a primary current from said dc power supply to flow through said primary side in a first direction, and a third and a fourth semiconductor switches connected in series with each other via said primary side to allow a primary current from said dc power supply to flow through said primary side in a second direction; a current detection circuit for detecting a detection current associated with the current through a load connected to said secondary side; and a logic circuit for generating and outputting a first switch signal for switching on/off said first semiconductor switch, a second switch signal for switching on/off said second semiconductor switch, a third switch signal for switching on/off said third semiconductor switch, and a fourth switch signal for switching on/off said fourth semiconductor switch, according to a feedback signal formed on the basis of said detection current, said logic circuit configured to: establish alternately a first current path for allowing current to flow in said first direction by simultaneously switching on said first and second switches and a second current path for allowing current to flow in said second direction by simultaneously switching on said third and fourth switches; establish first simultaneous OFF periods during which said first and fourth switches are simultaneously switched off and second simultaneous OFF periods during which said third and second switches are simultaneously switched off; and generate said first through fourth switch signals at the timing of changing the direction of said primary current between said first and second directions when the level of said primary current is zero.