JPS6489185A - Lighting device for discharge lamp - Google Patents

Abstract

PURPOSE:To detect the terminal stage of the life and reduce the uncomfortable feeling by repeatedly controlling the output of the lighting circuit of a discharge lamp to the dim state in response to the half-wave discharge detection output of the discharge lamp when the discharge lamp is fully lit and continuously controlling it at the dim state after a fixed time. CONSTITUTION:When a discharge lamp 3 is half-wave-discharged at the terminal stage of its life, the detection current through a serial circuit 13 is increased, and the comparator 15 of a detecting means 4 generates an output. A multivibrator 16 is thereby operated, a transistor(TR) 18 is repeatedly controlled, and the output of the lighting circuit 2 of the discharge lamp 3 is changed to the dim or full lighting state. The lighting state of the discharge lamp 3 is changed to the full lighting state or dim state accordingly, thus an abnormality of the discharge lamp 3 can be reported. After a fixed time, the operation of the vibrator 16 is stopped in response to the count output of a counter 17, a TR 19 is invariably turned on, and a dimming element 2 is invariably inserted in series to the discharge lamp 3. The flicker lighting of the discharge lamp 3 is temporary, and the uncomfortable feeling can be reduced.