| 摘要 |
PURPOSE:To prevent erroneous detection by detecting the lamp service life terminal stage from a logical product of a H signal outputted from a preheating timer or a light dimmer signal a certain time later and a H detecting signal of the voltage across a lamp. CONSTITUTION:When a switching element 6 or 7 of an inverter circuit 5 is started, the element is switched automatically at a prescribed oscillation frequency by alternate input from a base coil 4b. Input electric power is controlled by a control element 2, and light dimming is carried out on a lamp 12 at the light dimming ratio according to a light dimming signal S1. High voltage of the lamp gives a detecting signal S2 of an H signal to one input terminal of AND gates 18. When this is a high voltage pulse when the lamp is started and light dimming is carried out, the light dimming signal is inputted to the gates 18 through a preheating timer and a delay circuit 17, but output S4 is not generated from the gates 18. When it is the high voltage except when the lamp is started or the light dimming is carried out, both two input of the gates 18 becomes H, and H output can be obtained, and a lamp service life terminal stage signal S4 is issued, and a latch circuit 19 opens a switch SW1, and cuts off DC electric power supply 1. |
