| 摘要 |
PROBLEM TO BE SOLVED: To simplify detecting circuit constitution and reduce circuit loss by commonly using detecting resistance for detecting high frequency current flowing in a discharge lamp, controlling a consumption power so as to become a reference value, and detecting the abnormality of the lamp. SOLUTION: High frequency voltage produced in a detecting resistance R6 is leveled with an integrating circuit IN, and inputted as a consumption power detecting value in an inverting input terminal of an error amplifying IC 3. Reference voltage determined by resistances R9, R10 is inputted in a non- inverting input terminal of the IC 3, and as a result, the oscillating frequency of an IV control IC 2 is controlled so that the consumption power detecting value is made equal to the reference voltage, the power consumed in the discharge lamp is held in a setting value. In the case of non-lighting in the last stage of the life of the lamp or by the failure of the lamp, resonance high voltage is applied to the discharge lamp LA by the LC series resonance of a ballast choke T and a starting capacitor C6, but if the lamp is not lit, peak voltage exceeding a threshold value of an abnormality detecting terminal appears in the resistance R6, and oscillation stops. |
