| 摘要 |
PURPOSE:To minimize the voltage applied across the transistor of a constant-current element so as to prevent the diappearance of a display caused by an insufficient supply voltage even in a low-temperature state where a lamp voltage is boosted by proportionally controlling the voltage of a DC power source in accordance with the detecting output of the lamp voltage. CONSTITUTION:When a fluorescent discharge lamp 1 makes a minor discharge by means of a starting power source 4 and minor discharge resistance R1 after a filament 1f is preheated, a base current is made to flow to a transistor Q1 by the command signal of a display control section 11 and a DC voltage control section 9 operates so as to make the voltage of a resistance R6 coincident with a reference voltage Eref. As a result, an electric current is made to flow to the lamp 1 through a constant- current element 6 and a detected voltage is obtained at a voltage detecting section 7. When a lamp voltage by which the voltage of a capacitor C1 becomes higher than the reference voltage Eref is produced thereafter, the control section 9 operates so as to make the voltage of the resistance R6 to correspond to the reference voltage Eref. Therefore, the output voltage of the control section 9 is controlled proportionally to the lamp voltage and, when the lamp voltage becomes higher, the output voltage is also boosted. |
