| 摘要 |
PURPOSE:To detect the final phase of the service life of a discharge lamp in a simple structure, by detecting the quantity of electricity according to the lamp voltage of a discharge lamp in only the power feeding direction of a DC current, and controlling an electron stabilizing means so as to carry out a protective operation. CONSTITUTION:A discharge lamp 1 is lighted by a high-frequency output in which DC currents are superposed by a DC superposing means B. As a result, a filament to be at the anode side to a DC component is liable to receive a damage by the impact of electrons compared to the other side filament, and is deteriorated rapidly. And, at the final phase of the service life, a half-wave discharge is generated from the filament at the anode side to the other side, and the lamp voltage in this direction is raised. Such a phenomenon is detected by a detecting means C, and according to this output, a control circuit 23 converts the switching cycle of a transistor 7, so as to throttle or stop the high-frequency output. Since a filament liable to be deteriorated is specified, a detecting circuit of the quaitity of electricity can be simplified. |
