| 摘要 |
PURPOSE:To secure a bright, safe condition at the time of replacing a discharge lamp by controlling a high frequency oscillator circuit to detect and indicate the emission-less condition of one discharge lamp so that the lighting of each discharge lamp is continued. CONSTITUTION:A high frequency oscillator circuit 4, after a power source being turned on, oscillates at a preheating frequency to preheat filaments of discharge lamps l1, l2, and then lights each discharge lamp at a lighting frequency. If one of the discharge lamps becomes in an emission-less condition during the lighting, an oscillation circuit 4 is reset by an output of a detection circuit 2 of the lamp, each discharge lamp is put out, and then preheating and lighting are performed. Here, the number of detections of the emission-less condition is counted with a counter circuit 3. When the counted number exceeds a specified value, two lamp lighting condition is maintained. Thereafter, if both of the discharge lamps are lit under the condition of one lamp remaining without emission and one lamp goes out, the oscillation circuit 4 is switched to a one lamp frequency by an output of one lamp lighting detecting circuit 1. |
