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What is an Optocoupler? Its Advantages, Disadvantages & Applications

The optocoupler circuits are used in various electronic projects. In this, we discuss the basics of Optocoupler, Types, Advantages, Disadvantages& Applications in detail

What is Optocoupler?

Optocouplers are electronic components that use light to transfer electrical signals between two isolated circuits They prevent high voltages from affecting the circuit receiving the signal.  They are made up of an LED and a phototransistor and come in a variety of packages. We’ll use a simple optocoupler with one LED and one phototransistor in this circuit today. The input circuit receives an incoming signal, whether it’s AC or DC, and uses it to turn on the LED.

Optocouplers come in four different configurations, each having the same infrared LED but a different photosensitive component. In DC circuits, photo-transistor and photo-Darlington are commonly utilized, whereas photo-SCR and photo-TRIAC are commonly employed to control AC circuits. The transistor in a photo-transistor optocoupler could be PNP or NPN. The Darlington transistor consists of two transistors, one of which controls the base of the other. The Darlington transistor is a high-gain transistor.

Benefits of an Optocoupler

  • Remove electrical noise from signals
  • Isolate low-voltage devices from high-voltage circuits. The device is able to avoid disruptions from voltage surges (ex: from radio frequency transmissions, lightning strikes, and spikes in a power supply)
  • Allow the usage of small digital signals to control larger AC voltage

Structure of Optocoupler:

An optocoupler is made up of two electrically isolated circuits. The first circuit has an infrared emitting diode, whereas the second circuit contains an infrared sensor device, such as a photodiode, phototransistor, photo TRAIC, or photo SCR. Glass, air, or translucent plastic can be used to fill the space between the two circuits. The light is emitted by the LED, and it is received and amplified by the phototransistor. The anode and cathode of the LED are the first and second pins, whereas the emitter and collector of the phototransistor are the third and fourth pins.

Working of Optocoupler:

First, the current is applied to the optocoupler, which causes the LED to generate infrared light proportional to the current flowing through it. When light strikes the photosensor, it conducts a current and turns on. The IR beam is switched off when the current running through the LED is disrupted, forcing the photosensor to stop conducting. The photosensor is the output circuit that detects light, and the output is either AC or DC depending on the type of output circuit.

The output of an electrically isolated circuit is controlled by adjusting the circuit’s input, which is the basic operating concept of an optocoupler. A voltage source provides input to the Infrared LED, and the intensity of the voltage source can be varied by altering the input voltage. The light emitted has a specific wavelength. This light is detected by the photodetector, which turns light energy into photocurrent. The generated output current is then amplified. The output current is proportional to the amount of light that strikes the device.

Advantages of Optocoupler:

  • Compact and less weight
  • Low cost
  • Works very fast
  • Less noise
  • The optocoupler works well on either AC or DC high-voltage signals.
  • It is also used in a number of sensor applications to sense the presence of physical objects.
  • The lifetime of optocouplers can exceed several decades.
  • It offers a very good response at lower frequencies.
  • No contact bounce, no interference caused by arcs, wear the circuitry.
  • It consumes less power.
  • It has a high switching frequency due to short switch-on and switch-off times.

Disadvantages of Optocoupler:

  • Optocouplers are not capable to handle high current
  • Optocoupler needs external biasing voltage for its operation.
  • The High-frequency response is poor.
  • Optocouplers using phototransistors do not have such as good a linear relationship between the changes in light input and output current as photodiode types

Applications of Optocoupler:

  • Used for ground isolation
  • Used in high voltage monitoring circuits
  • Used in lighting control circuits
  • Used in dimmer circuits

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