| 摘要 |
PURPOSE:To ensure impression of a start voltage without excession or shortage in preheating by specifying the ratio of the cold resistance of filament electrodes to the dynamic resistance at the time of preheating, and impressing the start voltage between the filament electrodes under specified conditions. CONSTITUTION:The cold resistance of each filament electrode 31 shall be R0 ohm while the dynamic resistance during preheating be R ohm. The value of dynamic resistance R is sensed by a sensing device 5 and calculated by a calculator circuit 6. The ratio R/R0 is calculated by a calculator circuit 7, and the start voltage is impressed between electrodes 31 when the condition 4.0<=R/R0<=5.5 is met, and a discharge lamp 3 is lit up. Variation of R/R0 during preheating is calculated by the calculator circuit 7 and compared with the desired value under abovementioned specific conditions set on a comparator circuit 9. When the rate of change in the R/R0 is in decremental tendency, the preheating power for the electrode 31 is increased, and when in incremental tendency the preheating power is decreased. This eliminates wasteful exhaustion of the electrode 31. and certain lighting-up is provided. |
