| 摘要 |
PURPOSE:To stop a high-frequency inverter instantly so as to prevent the generation of a high open voltage when a discharge lamp becomes to an opened condition, by comparing the detecting value of a detecting circuit to detect a no-load current of the discharge lamp with a standard value so as to regulate the oscillation frequency of an oscillation circuit. CONSTITUTION:A detecting circuit is composed of a current transformer T1, a diode bridge DB, resisters R4 and R5, and a capacitor C4. The output is compared with a standard voltage V2 in a comparator CP2. When a filament is cut off during a discharge lamp 5 is being lighted, or the lamp is removed for replacement, the current does not flow to a high-frequency inverter 2, thereby, the current detecting value by the current transformer T1 is equal to zero, and the - side of the comparator CP2 is made to the ground level being less than the standard voltage V2. As a result, the output of the comparator CP2 is opened, and an oscillator circuit IC1 stops the oscillation. Consequently, the oscillation of the inverter 2 is stopped to operate a no-load current detection, and the open voltage of the inverter 2 is prevented from being excessively large. |
