4N25 is a widely used optocoupler / optoisolator / is the photocoupler. It is produced in 6 pin dip package and SMD package. The device consists of one IR LED and a phototransistor / Detector that detects the light coming from one IR LED. Since 4N25 is also connected to the base pin of the detector transistor to pin 6 of the body, the user can control the transistor with two inputs, one from the IR LED light connected to pin1 and pin2, the other controlling the transistor with its base.
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