| 摘要 |
A lamp voltage detecting section detects the lamp voltage of the high-pressure discharge lamp and transmits it to a current calculating section. A lamp current detecting section detects the lamp current of the high-pressure discharge lamp and transmits it to a differential amplification circuit. A target power value to be supplied to the high-pressure discharge lamp is input to the current calculating section from a target setting device. The current calculating section divides the target power value by the lamp voltage detected by the lamp voltage detecting section to calculate a target current value, and transmits the target current value to the differential amplification circuit. A control section controls the chopping operation of a semiconductor switch so as to make the target current value approximate to the lamp current value. A capacitor of a timer circuit is charged with a current correlating with the target power value simultaneously with the operation of the target power setting device, and discharging is executed when the high-pressure discharge lamp is turned off. When the operation is started, the target power setting device sets the target power value on the basis of the charging voltage of the capacitor, and allows the target power value to be varied in response to the duration of operations.
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