| 摘要 |
PURPOSE:To obtain a liquid crystal display back light device which has a lamp current below a specific value and long life by varying the current when a lamp voltage varies at the time of the startup or during the illumination of a lamp so that the voltage becomes constant. CONSTITUTION:The lamp 1 is a hot-cathode type fluorescent lamp having a filament which is, for example, 2600mm in overall length and 7mm in internal diameter and has thermionic emission property. This 1 is made to illuminate at high frequency without using a preheating current to the filament by using a lighting circuit 2, and a lamp voltage detection part 3 and a lamp current control part 4 are combined with this circuit 2. The lamp voltage is set to 100V and the lamp current is varied between 10 and 50mA so that the lamp voltage reaches 100V. The lamp current values during the illumination, but the lamp is made to illuminate while the lamp current is held below 40mA on the average. Consequently, no sputtering is caused and oxides at the periphery of a bright point are not contaminated, so the thermionic emissivity is held excellent. |
