JPS6472494A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To prevent any overinput to an inverter even if a discharge lamp is subjected to a half-wave discharge by installing a specified characteristic filter in a voltage detector in a feedback controller which preferably controls a load characteristic of the output variable inverter. CONSTITUTION:Switching frequency of an inverter 1 is controlled on the basis of load voltage and load current of a discharge lamp 2 by a voltage detector 31 and a current detector 32 each of a feedback controller 3, and thereby a load characteristic of the inverter 1 comes to constant voltage and constant current characteristics. In this detector 31, there is provided with a filter 4 whose output characteristic grows larger at the time of increment than at the time of decrement in inverter output frequency, and when the switching fre quency is decreased, a detected value of the detector 31 comes to a low value because an increase by a characteristic of the filter 4 is added to an output increase of the inverter and thereby an output voltage fails to keep the constant voltage. In consequence, even if the discharge lamp approximated to its life period is subjected to half-wave discharge, overinput into the inverter is prevented from occurring, thus parts forming the inverter are protected from breakdown.