| 摘要 |
PURPOSE:To make it possible to adjust the luminance of a fluorescent lamp with a simple structure by lighting the fluorescent lamp periodically and controlling the ratio of the periods of light-on and light-off. CONSTITUTION:In an oscillation circuit 20A of a lighting apparatus 20 used for a back light for a liquid crystal display device, a variable resistor 21 for luminance adjusting is connected in parallel to a resistor 22 to divide voltage VCC of an electric power source, and by this, the variable resistor 21 is adjusted so as to variably control a base voltage of a transistor 23. Also, an emitter resistor 25 is formed in the transistor 23 and collector voltage is divided by resistor 27, 28 so as to apply the divided voltage to a transistor 29. Meanwhile, the transistor 29 is connected to the emitter resistor of the transistor 23 through a resistor 30 and at the same time connected to the base of the transistor 23 through a capacitor 31 and a resistor 32, and thus an output signal of the transistor 29 is returned to the transistor 23. As a result, by only adjusting the resistor 21, an oscillation output signal with variable duty ratio can be obtained and periodically lighting a fluorescent lamp is made possible. |
