| 摘要 |
PURPOSE:To make uniform the brightness of a filament by a method wherein a voltage waveform smoothing means such as an inductor is provided so that the rise of voltage in a phase control element such as a thyristor may be rendered gentle near the conducting angle. CONSTITUTION:An AC voltage 6 is phase-controlled by a thyristor-type control circuit 8. The controlled output is stepped down by a matching transformer 9 to a voltage level demanded by a filament 4. The output of the matching transformer 9 is applied to the filament 4 via an inductor 10. The inductor 10 is connected in series across the matching transformer 9 and filament 4, which suppresses the otherwise sharp rise in the thyristor-controlled voltage to the level of that in the inputted AC frequency. As the result, the thyristor- controlled output is equipped with a voltage change rate roughly similar to that of an AC output after conduction. It is so set by adjusting a voltage divider 7 that the conducting angle of a thyristor controlling the current to the filament 4 may always be smaller than the total angle. |
