Principle and Working of Opto Coupler

Opto Coupler

Opto coupler is a solid state component in which light emitter the light path and light detector are all enclosed within the component and cannot be altered externally. Usually infrared emitting diode (IRED) can be used as a light emitter. Photo transistor can be used as a light detector.

Principle:

Here is one way transistor of electrical signal from LED (IRED) to photo transistor without any electrical connection between the input and output circuitry.
The degree foe solation between input and output depends on the kind of material used in the light path and on the distance between the light emitter and signal light detector. If the distance between emitter and detector is greater, then the isolation is better but current transfer ratio of detector to emitter current is lower.

Working:

The fig shows the symbol of Opto coupler. The coupler may be operated as a switch in which cause both the LED and photo transistor are normally OFF. A pulse of current through the LED (IRED) causes the transistor to be switched ON for the duration of the pulse. Operation as a linear coupler is also possible by setting up a bias current in the LED. The signal is then capacitively coupled to the LED and causes it’s to increase or decrease. Thus the photo transistor receives a light signal which increases and decreases, linearly around the constant bias level.

                                                                                               Opto Coupler

Parts:

1.       Anode

2.       Cathode

3.       Collector

4.       emitter