| 摘要 |
PURPOSE:To apply a high preheating voltage to filaments by forming a preheating circuit, including control means for controlling inductance elements for increasing inductance while a discharge lamp is lighted. CONSTITUTION:A load circuit IV and a preheating circuit V are provided, and the first sides of transformers T4, T5 are connected in series to respective parts of the secondary output of a transformer T1, and switching means SW2, SW3 are connected to the respective secondary sides of the transformers T4, T5. In this case, when the switchs SW2, SW3 are turned on and a shortcircuit current is caused to flow to the secondary sides, then a magnetic flux of more than the core maximum magnetic flux density is applied to a core and the core is saturated and the transformers T4, T5 lose their functions. When the switchs SW2, SW3 are turned off, voltage lowering is caused by the transformers T4, T5 and a voltage lower than the secondary voltage of the transformer T is applied to filaments f1, f2. When preheating by application of a sufficient preheating voltage to filaments f1, f2 is needed, the switchs SW2, SW3 are turned on. A high preheating voltage is thus applied to filaments. |
