Abnormality detecting circuit for discharge lamp with delayed interruption for undervoltage

摘要

A lighting circuit for a discharge lamp comprises abnormality detection means for detecting an input voltage and/or an input current to be input to a lighting circuit from a power supply and stopping power supply to a discharge lamp when detecting an abnormality in the value of the input voltage and/or the value of the input current. First and second reference values or reference ranges for comparison (the first reference value or reference range is smaller than the second reference value or reference range) are set for the input voltage and/or the input current. When the state where the value of the input voltage and/or the value of the input current is equal to or smaller than the first reference value or the first reference range continues for a predetermined time or longer, the abnormality detection means stops power supply to the discharge lamp. When the state where the value of the input voltage and/or the value of the input current is equal to or greater than the second reference value or the second reference range continues for a predetermined time or longer, the abnormality detection means permits power supply to the discharge lamp.