Light and dark sensor and clock with light and dark sensor

摘要

PROBLEM TO BE SOLVED: To provide a clock with a light and darkness sensor which can detect light and darkness with high accuracy and requires only low power consumption even when an interval to detect light and darkness is short.;SOLUTION: A photodiode 21a outputs current corresponding to ambient brightness. An NPN type transistor 21d changes on the basis of output current of the photodiode 21a, and causes current to flow from an output node N1. When a switch 21f is turned on, a PNP type transistor 21e becomes a current source to cause current to flow to the output node N1. The transistor 21e and a transistor d change the voltage of the output node N1 in accordance with ambient brightness.;COPYRIGHT: (C)2007,JPO&INPIT