PC817 pin 4 Optocoupleur phototransistor

How to use PC817 IC

Using the PC817 IC is pretty much straight forward, we just have to connect the anode pin of the IR LED (pin 1) to the logic input which has to be isolated and the cathode (pin 2) of the IR led to the ground. Then Pull high the collector pin of the transistor using a resistor (here I have used 1K) and connect the collector pin to the output of your desired logic circuit. The Emitter (pin 4) is grounded.Note: The ground line of the IR LED (pin 2) and the ground line of the transistor (pin 4) will not be connected together. This is where the isolation occurs.Now, when the Logic input is low the IR LED will not conduct and hence the transistor will also be in off state. Hence the Logic output will remain high, this high voltage can be set anywhere up-to 30V (Collector-Emitter Voltage) here I have used +5V. There pull-up resistor 1K acts as a load resistor.But when the Logic input is made high, this high voltage should be a minimum of 1.25V (Diode Forward voltage) the IR LED conducts and so the photo-transistor is also turned on. This will short the collector and emitter and hence the Logic Output voltage will become zero. This way the logic input will be reflected at the logic output and still provides and isolation between the two. The complete working can also be understood form the GIF file above.