| 摘要 |
PURPOSE:To stably retain a lighting state even when power voltage is decreased down to below discharge voltage for an electric discharge lamp by increasing a preheating frequency on detecting a decrease in voltage and by activating thermionic emission from the electric discharge lamp. CONSTITUTION:A voltage decrease detecting circuit 31 is operated when DC output voltage VDC from an AC/DC inverting circuit 8 is decreased to around discharge voltage for an electric discharge lamp 9. A resistor R32 is connected in parallel with a resistor R26b on a preheating timer circuit 26 to decrease charging voltage for a capacitor C26. A transistor Tr26 on the circuit 26 is, therefore, lead to an off state to set collector voltage to VDC, resulting in sending operating instructions 26S to a preheating frequency switching circuit 24, and increasing the entire light-lighting frequency of a modulated light controlling circuit 20S to preheating frequency. Thus flickering due to a decrease in voltage or troubles due to lights-off are eliminated to stably retain lighting by switching an oscillating frequency to the preheating frequency through the preheating timer circuit on decreasing power voltage and by activating thermoelectron emission from an electric discharge lamp. |
