In this way, an incoming signal from the input circuit is coupled to the output circuit. Thus a changing voltage is generated across the collector-emitter terminal of the transistor. This means that the low-intensity light emitted by the LED will cause a low-level current to flow through the phototransistor. As the LED glows due to this current, hence, when current will be low so as the light intensity of LED.Īs we have already discussed earlier the intensity of emitted light by the LED will be equal to the corresponding current flowing through the phototransistor. An input resistance placed at the beginning of the circuit will decrease the amount of current flowing through the LED if its value is increased. The current flowing through the phototransistor is directly proportional to the supplied input voltage. This emitted light when falls on a phototransistor cause a current to flow through the same. As we can see in the below-shown circuit diagram, when a high voltage appears across the input side of the Optocoupler, a current start to flow through the LED.ĭue to this current LED will emit light. Working Of an OptocouplerĪn Optocoupler is a combination of LED and a Photo-diode packed in a single package. A single phototransistor is used at the output stage of a simple isolating optocoupler. The base terminal of the phototransistor is externally available. A resistance is connected at the beginning of the circuit which is used to limit the current and the other resistance is connected between the supply voltage and the collector terminal.īefore proceeding further let’s see the pin description of an optocoupler: The LED is kept on the input side and the light-sensitive material is placed on the output side. The infrared LED and the device that are light sensitive is packed in a single package. Let’s have a look at the basic diagram of an Optocoupler: The semiconductor photosensitive device can be a photodiode, phototransistor, a Darlington pair, SCR or TRIAC. Construction of an OptocouplerĪn optocoupler mainly consists of an infrared LED and a photosensitive device that detects the emitted infrared beam. Optical couplers can be used to work on both ac and dc high voltages.
Isolated circuits are the circuits which do not have a common conductor in between them and proper isolation is maintained.Īs we are already aware of the fact that the information signal highly contains noise and additional distortions in it which can be beyond the tolerance limit of the logic circuit at the output end during transmission. Till now we have talked about an isolated circuit but one should know the meaning of it before going into any further aspect.
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