| 摘要 |
PURPOSE:To prevent excessive current flow through the filaments of a discharge lamp by detecting the current flow through the filaments of the discharge lamp to restrain short-circuit current to less than a preset value. CONSTITUTION:A current detecting resistance R3 for detecting current flow through the filaments 4a, 4b of the discharge lamp 4 is connected between the emitter and ground of a transistor Q2. A converter transformer T1 which has a drive coil S1 having each filament 4a, 4b of the discharge lamp 4 connected to its secondary side and which has the control coil S2 of a switching element Q1, and a lighting circuit 6 and the like for shortcircuiting according to the timing of transmitting electricity to the discharge lamp 4 are provided, and the current flow through the filaments 4a, 4b of the discharge lamp 4 is detected and a short-circuit current is restrained during preheating to less than a preset value. Thereby excessive current flow through the filaments 4a, 4b is prevented and proper preheating is enabled regardless of the output of the converter transformer T1. |
