| 摘要 |
PURPOSE:To suppress the power loss of a semiconductor switch element, loosen the temperature rise, and improve the safety by detecting the emissionless state generated at the life terminal stage of a discharge lamp, shortening the excitation period of the semiconductor switch, and opening a thermal protector at the abnormal temperature rise of the semiconductor switch element. CONSTITUTION:A voltage divider is provided between the collector and the emitter or a transistor Q1, the voltage with a large peak value at the emissionless state of a discharge lamp (1) is detected by a Zener diode ZD2, a capacitor C5 is charged via this Zener diode ZD2, and a transistor Q5 is turned on. When the transistor by is turned on, it becomes the same state as that a dimmer switch Sd is turned on, and the reference voltage VK is set to a low value. The time until the voltage VC3 of a capacitor C3 reaches the reference voltage VK is shortened, and the on-period T1 of the transistor Q1 at the emissionless state is shortened. The output current is suppressed, the temperature rise of the transistor Q1 is loosened to maintain the oscillation, and a thermal protector TP is operated before the main transistor Q1 is finally broken by the temperature rise. |
