| 摘要 |
PURPOSE:To reduce a flickering of a lamp by providing a lamp voltage detecting device to generate the output when the voltage of a discharge lamp exceeds a specific value, and making the first and the second operation periods of a control circuit variable to reduce the first and the second operation periods when the output of the lamp voltage detecting device is generated. CONSTITUTION:While a discharge lamp DL1 is being lighted, a lamp voltage detecting circuit Y detects the lamp voltage VDL and when the value exceeds a specific value, it generates an output, and adds the output to a control circuit X2. The first and the second operation periods of the control circuit 12 are reduced consequently. When a voltage variation to increase the equivalent conductance and to reduce the voltage VDL from the former half to the latter half in the first and the second operation periods respectively resulting from the fact that the voltage VDL exceeds the specific value by the functions of the detecting circuit Y and the control circuit X2, the first and the second operation periods are reduced. As a result, the variation width of the equivalent conductance is reduced, and the variation width of the voltage VDL is also reduced. A flickering of the discharge lamp DL1 when the voltage VDL is increased can be reduced consequently. |
