| 摘要 |
An output of a load voltage detector is read by an A/D converter, and a reference value Is and a switching frequency are decided by a microcomputer. In order that the decided switching frequency can be achieved, a SET signal is inputted from a switching frequency counting unit to a drive controller, and a switching element is turned on. When a current flowing through the switching element, which is detected by a resistor, exceeds the reference value Is of a reference arithmetic unit, a RESET signal is inputted from a current detector to the drive controller, and the switching element is turned off. Thereafter, the reference value Is and the switching frequency are set so that the switching element can be turned on at the next time at timing when a regenerative current of a diode turns to substantial zero. As described above, the switching frequency is controlled in response to a state of a discharge lamp while controlling the switching element to turn on at the timing when the regenerative current turns to substantial zero without bringing up a cost increase of a discharge lamp lighting device.
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