HIGH-FREQUENCY DISCHARGE LAMP LIGHTING DEVICE

PURPOSE:To eliminate an unpleasant feeling in a preventive operation and to improve the condition only by replacing the lamp with a normal lamp, by carrying out a protective operation of an inverter circuit from an abnormal condition of a lamp at the final phase of the service life only by separating a circuit in which the lamp current to be a load flows from the inverter circuit, instead of stopping the oscillation. CONSTITUTION:When a lamp 22 is in the normal condition, transistors 6 and 7 for oscillation are turned on and off alternatively to start the oscillation, and a voltage is generated from an oscillation transformer 4. And at the same time, when the charging voltage of a capacitor 30 exceeds the threshold value of a Zener diode 28, a transistor 23 is turned on, and the lamp 22 is made in the lighting condition through a relay 24. When the lamp 22 reaches the end of its service life in such a condition, the lamp voltage is increased by a half-wave discharge and it exceeds the threshold value of a Zener diode 19, and thereby, a thyristor 32 is made in the ON condition, a transistor 31 is also in the ON condition, and the potential of the capacitor 30 is lowered to the earthing voltage. As a result, the Zener diode 28 and the transistor 23 are also turned off to open the relay 24, and the voltage of the transformer 4 is cut off from the lamp 22.