DC-AC converter, controller IC therefor, and electronic apparatus utilizing such DC-AC converter

A DC-AC converter, comprising:

• a transformer having a primary winding and at least one secondary winding;
• a first capacitor and a first semiconductor switch connected in series via said primary winding for allowing current to flow from a DC power source through said primary winding in a first direction;
• a second semiconductor switch and a second capacitor connected in series via said primary winding for allowing current to flow from said DC power source through said primary winding in a second direction;
• a current detection circuit for detecting the current that flows through a load connected to said secondary winding to thereby generate a current detection signal;
• a triangular wave signal generation circuit for generating a triangular wave signal;
• a PWM control signal generation circuit for generating a PWM control signal by comparing said triangular wave signal with an error signal generated on the basis of said current detection signal;
• an intermittent-operation control circuit adapted to
• set said error signal to a substantially zero level during OFF periods of the intermittent operation,
• gradually increase the error signal upon a transition from an OFF state to an ON state;
• and
• gradually decrease the error signal upon a transition from an ON state to an OFF state, and
• a logic circuit that operates on the basis of said PWM control signal to generate
• a first switch signal for turning on said first semiconductor switch and
• a second switch signal for turning on said second semiconductor switch in such a way that
• a simultaneously OFF period is established during which said first and second switches are simultaneously turned off, and
• the direction of the current flowing through said primary winding is changed from one direction to the other when the magnitude of said current is zero.

A control IC for supplying AC power to a load connected to a secondary winding of a transformer by driving a switch circuit that includes:

• a first and a second semiconductor switches connected in series via said primary winding of said transformer to cause current to flow from a DC power source through said primary winding in a first direction;
• and a third and a fourth semiconductor switches connected in series via said primary winding to cause current to flow from said DC power source through said primary winding in a second direction, said control IC comprising:
• a triangular wave signal generation circuit for generating a triangular wave signal;
• a PWM control signal generation circuit for generating a PWM control signal by comparing said triangular wave signal with an error signal formed on the basis of a current detection signal for the current flowing through said load;
• an intermittent-operation control circuit adapted to
• set said error signal to a substantially zero level during an OFF period of said intermittent operation,
• gradually increase said error signal upon transition from an OFF state to an ON state, and
• gradually decrease said error signal upon transition from an ON state to an OFF state;
• and
• a switch signal generation logic circuit that operates on the basis of said PWM control signal to generate a first, a second, a third, and a fourth switch signals for respectively turning on said first, second, third, and fourth semiconductor switches, in such a way that a first simultaneously OFF period is established during which said first and fourth switches are simultaneously turned off and a second simultaneously OFF period is established during which said third and second switches are simultaneously turned off, and that the direction of the current flowing through said primary winding is switched from one direction to the other when the magnitude of the current is zero.

A controller IC for supplying AC power to a load connected to a secondary winding of a transformer by driving a switch circuit that includes:

• a first capacitor and a first semiconductor switch connected in series via said primary winding of said transformer to cause current to flow current from a DC power source through said primary winding in a first direction;
• and a second semiconductor switch and a second capacitor connected in series via said primary winding to cause current to flow from said DC power source through said primary winding in a second direction, said control IC comprising:
• a triangular wave signal generation circuit for generating a triangular wave signal;
• a PWM control signal generation circuit for generating a PWM control signal by comparing said triangular wave signal with an error signal formed on the basis of a current detection signal for the current flowing through said load;
• an intermittent-operation control circuit adapted to
• set said error signal to a substantially zero level during an OFF period of the intermittent operation,
• gradually increase said error signal upon transition from an OFF state to an ON state, and
• gradually decrease said error signal upon transition from an ON state to an OFF state;
• and
• a switch signal generation logic circuit that operates on the basis of said PWM control signal to generate a first switch signal for turning on said first semiconductor switch and a second switch signal for turning on said second semiconductor switch in such a way that a simultaneously OFF period is established during which said first and second switches are simultaneously turned off and that the direction of the current flowing through said primary winding is switched from one direction to the other when the magnitude of said current is zero.