| 摘要 |
PURPOSE:To quicken rising of lamp output in a photographic copying machine having manual exposure adjusting function by keeping the lamp current above a fixed value by an automatic exposure adjusting device only at the time of starting. CONSTITUTION:The value of voltage applied from a power source 31 to an exposure lamp 2 is known by rectifying voltage applied to a dummy-load circuit 33 which is equivalent to the lamp 2 by a waveform shaping circuit 34. A trigger pulse generating circuit 41 controls a thyristor 32 so that the sum of this and the value obtained by detecting reflected light from an original by a light detecting circuit 38 become equal to output of a reference voltage generating circuit 39, and lamp output is automatically adjusted to correspond to the density of the original. It is also possible to make manual adjusting by changing a switch 36 to a contact (b). However, as rising up is slow and amount of light is unstable if lamp current is small when lighting up of the lamp is started, the switch is kept to a contact (a) of automatic adjusting side during specified time determined by a timer. |
