Operating circuit for electric discharge lamp

Claim 1

Operating circuit for an electric discharge lamp comprising: first DC operating means for supplying a DC output voltage higher than a rated lamp voltage to said electric discharge lamp to start the electric discharge lamp and for making the electric discharge lamp operative by a current smaller than a rated lamp current; second DC operating means, connected in parallel to said first DC operating means, for making said electric discharge lamp operative by a voltage near the rated lamp voltage and by a current near the rated lamp current; third DC operating means, connected in parallel to said first and second DC operating means, for making the electric discharge lamp operative by a current larger than said rated lamp current when the electric discharge lamp has a lamp voltage lower than the rated lamp voltage; switching means for detecting the predetermined electrical characteristic of the electric discharge lamp after the electric discharge lamp has started, and for cutting off said first DC operating means from the electric discharge lamp; first reverse current preventing means, connected in series to said second DC operating means, for preventing the current from reversely flowing from said first DC operating means to said second DC operating means; and second reverse current preventing means, connected in series to said third DC operating means, for preventing the currents from reversely flowing from said first and second DC operating means to said third DC operating means.