| 摘要 |
PURPOSE:To prevent the occurrence of chattering even though the ambient luminance varies at a level near the working luminance, by giving the hysteresis characteristics to a comparator and at the same time varying the threshold luminance of the comparator. CONSTITUTION:The output Vs of a photoelectric converting circuit 3 is supplied to a comparator 4 to which the reference voltage Vr equivalent to the threshold luminance is applied. A load 6 is turned on and off by the output To of the comparator 4. While the output Vs is also supplied to an auxiliary comparator 7 to which the reference voltage V'r equivalent to the threshold luminance is applied. The voltage V'r is set at a value of the level to which the ambient luminance does not change. When the output To is produced, the output T'o of the comparator 7 is supplied to the load 6 via an output circuit 5. In such a way, the hysteresis characteristics are given to a comparator and at the same time the threshold luminance is variable. Thus the occurrence of chattering is prevented even though the ambient luminance has a change at a level near the working luminance. |
