What Are the Advantages and Disadvantages of Optocouplers?

An optocoupler, or optoisolator, is a device which can be used as an interface between two circuits that operate at different voltage levels. When an optocoupler is used to connect two circuits, the only contact between the input and output is a beam of light. As a result of this capability, optocouplers have many benefits, particularly for connecting two circuits without the passage of electricity. In this article we will discuss the various advantages and disadvantages of optocouplers and how they may best be applied to an electrical system.

On a basic level, optocouplers consist of an LED emitter in close proximity with a light-responsive phototransistor, all of which are encased in a shell with contact pins on either side. The phototransistor is made with a mix of semiconductive materials which only allow current to pass through them when subjected to light. As a result, when the circuit with the LED is activated, it will simultaneously start the flow of current in the circuit connected to the other side of the optocoupler. With this capability, an optocoupler can connect one circuit to another without needing to transfer any current. Many optocouplers have four pins so that there is an input and output for each circuit. However, many variations exist with a greater number of pins to accommodate more than two circuits.
 
The contactless connection is a key advantage of the optocoupler which allows it to work with circuits of different voltages. This design also adds an additional method of security which ensures that if one side of the connected circuits experiences a voltage spike, it will not harm the opposite side. Optocouplers also block noise from passing between the two connected circuits. This attribute is especially useful for the coupling between high-voltage, information-gathering circuits and low-voltage, digital logic circuits. Besides being useful for coupling several circuits in an assembly, optocouplers may also be used in a number of sensor applications to sense the presence of physical objects which break the beam of light. Lastly, optocouplers are beneficial because they are cheaper, more compact, more lightweight, and consume less power than other couplers.
 
One of the disadvantages of optocouplers is that they need external biasing voltage in order to operate. In addition, they have poor high-frequency response and are not capable of handling high current. Finally, it should be noted that optocouplers using phototransistors do not have as good a linear relationship between the changes in light input and output current as photodiode types. In conclusion, optocouplers are useful instruments for connecting two circuits with different voltages. However, they may not be well-suited in applications that subject them to high-frequency or high current.

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