Patent ID: 7095632

Claim:
A dc-ac converter, comprising: a dc power supply; a transformer having a primary winding and at least one secondary winding; a switch circuit having a first and a second semiconductor switches connected in series via said primary winding, said first and second switches capable of flowing a current in a first direction from said dc power supply to said primary winding, and a third and fourth semiconductor switches connected in series via said primary winding, said third and fourth switches capable of flowing a current in a second direction from said dc power supply to said primary winding; a current detection circuit for detecting a detection current that flows through a load connected to said secondary winding; a triangular signal generation circuit for generating a triangular signal train for pulse-width modulation (PWM); a PWM circuit for generating a PWM signal upon comparison of a feedback signal based on said detection current received from said current detection circuit with said triangular signal train; and a logic circuit for outputting, based on said PWM signals, switch signals that include 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, wherein said logic circuit is configured to alternately establish a first current path for allowing a current to flow in said first direction by simultaneously switching on said first and second switches and a second current path for allowing a current to flow in said second direction by simultaneously switching on said third and fourth switches, and establish a first simultaneous OFF period during which said first and fourth switches are simultaneously switched off and a second simultaneous OFF period during which said third and second switches are simultaneously switched off, and switch the direction of said current flowing through said primary winding from one direction to the other when the magnitude of said current is zero.