Patent ID: 6791286
Filing Date: 2004-09-14
Classification: H05B,Y02B,Y10S

Abstract:
A lighting circuit for an HID lamp in which a DC voltage supplied to a full-bridge type inverter having four switching elements is converted into an AC rectangular wave voltage at a predetermined frequency and applied to the HID lamp, comprising a control section fordetecting a value of a current flowing in the HID lamp, calculating a resistance value in a positive direction and a resistance value in a negative direction of the HID lamp corresponding to the direction of the polarity of the AC rectangular wave voltage based thereon, setting the duty ratio between the positive direction and the negative direction of the AC rectangular waveform voltage so as to be in an inverse proportion with the magnitude for each of the resistance values, and outputting a polarity control signal that switches each of the switching elements at a predetermined timing such that the voltage value is kept at a ground potential for a predetermined period of time when the direction of the AC rectangular waveform voltage is inverted.