| 摘要 |
PURPOSE:To detect the lighting of one lamp and the half-wave discharge state at the terminal period of life of another lamp by setting the threshold voltage to the voltage between the output voltage of the voltage detecting circuit when multiple discharge lamps are normal and the output voltage of the voltage detecting circuit when one of them is in the half-wave discharge state. CONSTITUTION:The threshold voltage E of a voltage judging circuit 7 is set to E1<E<E3, where E1 is the voltage across the smoothing capacitor 65 of a voltage detecting circuit 6 when both discharge lamps L1, L2 are normal, and E3 is the voltage across the capacitor 65 of the circuit 6 when one of them is in the half-wave discharge state. When both lamps L1, L2 are normal, the output of a comparator 71 is a low level, a transistor TR73 is off, an inverter circuit 4 is operated normally, the lamps L1, L2 are lit. When one of the lamps L1, L2 is removed or in the half-wave discharge state, the output of the comparator 71 becomes a high level, the control electrode and reference potential electrode of the switching element 42 of the circuit 4 are short-circuited, the oscillation of the circuit is stopped, and the lamps L1, L2 are turned off. The state of lamps can be thereby detected easily. |
