| 摘要 |
PURPOSE: To enable lamp current to be controlled according to lamp voltage by providing a means for varying a lighting frequency according to the lamp voltage of a fluorescent lamp, and varying the lighting frequency so that when the lamp voltage is in a stable low state, lamp current flows by a smaller amount than under normal conditions. CONSTITUTION: A circuit consisting of a transistor 24 and a resistance 28 varies a current passed through a transistor (Tr) 24, depending on the differential voltage between the voltage VL at each end of a capacitor 23 and a voltage VR, thus controlling an oscillating frequency; i.e., a collector current IC flowing through the Tr 24 becomes IC=CVR-VL)/R28×hFE. Therefore, when the lamp voltage VLP of a fluorescent lamp 6 is great, the VL is also great, and the collector IC becomes smaller. When the lamp voltage VLP of the fluorescent lamp 6 is small, the VL is also small, the collector IC becomes greater, and the combined resistance of the R terminal becomes R=R27 //(VR/IC). Therefore, controlling the lamp current according to the lamp voltage EVLP is made possible. |
