| 摘要 |
PURPOSE:To enlarge light adjustment range and miniaturize and lighten the device stated in the title by providing a comparing circuit for comparing the detection result of a secondary current detecting circuit to a reference value so as to control the firing angle of a phase control circuit, and making the reference value of the comparing circuit variable. CONSTITUTION:A secondary current detecting circuit 18 for detecting a secondary current from both ends of an advanced phase condensor 14, a comparing circuit 20 to which the detection output of the detecting circuit 18 is input, and a phase control circuit 24 having a bidirectional thylister 22 are provided. The phase control circuit 24 is connected in series to a discharge lamp 16 to control the phase of a secondary current, and the comparing circuit 20 compares the detection result of a secondary current detecting circuit 18 to a reference value, and controls the firing angle of the phase control circuit 24 according to the result of comparison. The reference value of the comparing circuit 20 is variable. The firing angle of the phase control circuit 24 is varied by varying the reference value of the comparing circuit 20 as desired, so that light adjustment range is enlarged and also that the lighting device is miniaturized and lightened. |
