| 摘要 |
PROBLEM TO BE SOLVED: To realize a large voltage amplitude change amount and high speed response by providing a transistor for controlling an amount of emission of an emission element in response to an incident light amount to a phototransistor. SOLUTION: Light from LED 2 is reflected or transmitted on or into an object to be inspected, and made incident on a phototransistor 1. The phototransistor 1 changes collector current by the change of an incident light amount, and the intensity of irradiated light is detected. LED 2 is an emission element in which an emission amount changes by a flowing current amount. A bipolar transistor 3 controls the emission amount of LED 2 in response to the incident light amount to the phototransistor 1. In other words, the emission amount of LED 2 is increased and decreased so as to cancel the change of the reflectance or transmittance of an object to be inspected. As a result, frequency characteristics are good, large output of a voltage amplitude change amount and low output resistance not receiving the influence of noise can be obtained, and the irregularity of the phototransistor 1 and the conversion efficiency of the emission element is reduced.
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