| 摘要 |
PURPOSE:To take measures suitable for the respective conditions by providing a means to detect an abnormal condition from a current of a switching element, and a control circuit equipped with a frequency change and control means of an electric discharge lamp filament preheating and lighting, its change-over means and its abnormality judging means. CONSTITUTION:When the filament of an electric discharge lamp l is preheated, an inverter is caused to work with the first frequency, and when the electric discharge lamp l is lit up, a control circuit 1 which causes the inverter to work by changing to the second frequency lower than the first frequency is provided. The electric discharge lamp l is preheated by operating the inverter with the first frequency for a fixed time after a power source is on through the control circuit 1, and then, the lamp l is lit up by changing to the second frequency. A resistance R1 is inserted between the emitter of a transistor Q1 and the earth for the control circuit 1 to detect an abnormal condition (emitterless or no-load) judging from voltages at both the ends. When an abnormality occurs during the lamp is lit up, the control circuit 1 continues operation of the inverter with the first frequency and if normality is taken back, it will be continued as it is, and when another abnormality is successively detected, the inverter is stopped. |
