Patent ID: 7403401

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; an oscillator for generating triangular wave: a comparator for comparing output of said oscillator and a feedback signal formed in accordance with said detection current; and a logic circuit for receiving output of said oscillator and output of said comparator, and for generating a signal turning on/off each of said first, second, third and fourth semiconductor switches, wherein said logic circuit is adapted to: turn on said fourth switch when said triangular wave is at minimum level, to turn off said fourth switch when said triangular wave exceeds said feedback signal, and to turn off said, third switch when said triangular wave is at maximum level, during a first period when a triangular wave changes from its minimum to maximum level; turn on said second switch when said triangular wave is at minimum level, to turn off said second switch when said triangular wave exceeds said feedback signal, and to turn off said first switch when said triangular wave is at maximum level, during a second period following said first period, when a triangular wave changes from its minimum to maximum level turn on said first switch during a period between the time when said triangular wave of said first period has exceeded said feedback signal and when said triangular wave becomes maximum level; turn on said third switch during a, period between the time when said, triangular wave of said second period has exceeded said, feedback signal and when said triangular wave becomes maximum level; and repeat said first period and said second period alternately.