| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide an illuminance sensor which is prevented from malfunctioning due to disturbance light. SOLUTION: This sensor is equipped with a photodiode D, a converting- amplifying part 10 equipped with a first variable resistor R1 and amplifying a converted voltage by a desired amplification factor, a comparison part 20 for comparing an amplified voltage Vin from the amplifying part 10 with a reference voltage Vref, a switching part 11 for switching the value of the voltage Vin corresponding to the brightness of outside light to another value, according to an output voltage signal Vout fed back from the comparison part 20, and a second variable resistor R7 having resistance varying in conjunction with the variable resistor R1. In switching the value of the amplified voltage Vout, the switching part 11 switches it to a value which corresponds to the resistance value of the resistor R7. Even when the amplification factor of the amplifying part 10 is set appropriately so as to cause the comparison part to control the opening/closing of an external triac Q in dim outside light conditions, a disturbance light tolerance L is kept at or above a prescribed quantity by the selection part 10 and malfunctions due to fluctuations in external light and due to disturbance light can be prevented.</p> |
