Essential Guidelines for Using Optocouplers in PCB Designs

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Are you trying to come up with one of your first PCB designs? You should seriously consider using an optocoupler.

These are useful components for regulating circuit connections. You can use them with infrared light, which enables you to activate circuits from long-distance is and doesn’t put the same kind of strain on circuit parts as rotary switches and other connectors.

What types of PCB applications are optocouplers is used in?

Many different PCB designs rely on optocouplers. Some examples are listed below:

  • Handling the input and output switching for microprocessors
  • Regulating AC and DC power controls
  • Processing communications on PCs
  • Isolating digital signals
  • Regulating power supplies that have been hampered by existing ground loops

You should be aware of the purposes of optocouplers and know whether they are appropriate for your project.

What is an optocoupler and what parts are used in it?

An optocoupler (which is also known as an optoisolator) is a switch that is activated by infrared light emitted by an LED to a phototransistor or any other device capable of detecting infrared. When this light is interrupted or blocked by some object the circuit is opened acting as an open switch.

Parts of an optocoupler

The optocoupler is composed of 2 main elements: an infrared LED and an element capable of detecting infrared light such as a phototransistor, a phototriac, MOSFET phototransistor, or a Fotodarlington.

How does an optocoupler work?

Despite being a somewhat complex device, the principles behind optocouplers are easy to understand. This is mainly because an optocoupler only has one transmitter and one receiver. The emitter is an infrared LED that sends a beam of light to the receiver, which is normally a phototransistor. When this device captures the signal, it acts as a closed switch, and when it is interrupted it acts as an open switch.

Types of optocouplers

There are currently many different types of optocouplers on the market. They can be distinguished by either their output or their type of use. Some of the most common types of optocouplers are listed below.

DIP encapsulation

This type of optocoupler is mainly used in electronic boards since its operation is based on activating and deactivating the circuit through the voltage. They are mainly used to isolate possible interferences between two stages operating at different voltages, such as the control stage with the power stage. Different versions are distinguished by their type of output.


A phototransistor is the most common of all and controls direct current in its output.


A Darlington array is added that has two transistors together, which results in a large current gain.


A phototriac is designed to control alternating current on its output.

Schmitt trigger

This interface has a binary output. This means its logical value is either 0 or 1.

AC input – transistor output

With this type of photocoupler interface, you can make a change from alternating current to direct current.

As a sensor

This type is used as an optical sensor as the transmitter and receiver are placed linearly and when the infrared light is emitted it bounces off a surface causing it to return to the receiver. When the receiver does not receive any signal, it means that there is no object nearby.

As an optical switch

This is practically the most popular type of photocouplers since it is used as an interface in logic circuits, usually used for the user to pass a card or some object with little thickness. When you pass the object the signal is interrupted and this causes a change of state which indicates that your logic circuit can act either to activate or deactivate anything, such as a motor, a lock, a simple led, and so on.

Understand the Principles of Optocouplers and Use them in Your PCB Designs Properly

There are many different benefits of optocouplers, which is one of the reasons they are frequently used in PCB designs. You need to know how to incorporate their designs properly, which means that it is important to study how they work and what their most common applications are.

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