Patent ID: 8063569

Claim:
A discharge tube power supply apparatus comprising a DC conversion circuit for converting AC power of an AC power source into DC power and an AC conversion circuit for converting the converted DC power into AC power and supplying the converted AC power to a discharge tube the AC conversion circuit including: a main transformer having a primary winding arranged on an AC power source side and a secondary winding arranged on a discharge tube side, the primary and secondary windings electrically insulating the AC power source side and the discharge tube side from each other; a drive unit arranged on the AC power source side; a plurality of switching elements arranged on the AC power source side and driven by the drive unit, to pass a current through the primary winding of the main transformer based on the DC power; a control unit arranged on the discharge tube side, configured to generate at least a pair of rectangular-wave signals those are used for conducting PWM control on the current passing through the discharge tube and have the same pulse width with a duty ratio of less than 50% and a phase difference of about 180 degrees; and one or more signal transfer insulated elements configured to send the pair of rectangular-wave signals from the control unit to the drive unit, wherein the drive unit drives the plurality of switching elements according to the pair of rectangular-wave signals from the one or more signal transfer insulated elements, so that positive-negative symmetrical AC power is supplied from the secondary winding of the main transformer to the discharge tube, wherein as an abnormality at the discharge tube or at any location on the discharge tube side from the secondary winding of the main transformer occurs, the control unit stops sending the rectangular-wave signals to the drive unit, to thereby stop power supply to the discharge tube.