What is Optocoupler,Working, Types & Applications

Hello readers welcome to the new post. Here we will learn What is Optocoupler. The optocoupler is a semiconductor device that converts an electrical single into two isolated circuits. The optocoupler comes with two parts LED that releases infrared light and photosensitive devices that sense light from LED. These two parts are confined in a black box having pins. The input circuit get the incoming signal that can be AC or DC and uses for on LED.

Table of Contents

What is an Optocoupler

An optocoupler also known as an optoisolator is a semiconductor device that helps signal to shift between two distinct circuits.

There are two parts off of optocoupler first one is LED which releases infrared light and 2nd one is photosensitive which senses light for LED

These two parts are configured in boards. and photo sensor is an output circuit that senses light and based on the type of output circuit, the output will be AC or DC.

The current source is connected at the input of the optocoupler as a result LED releases infrared light in direct proportional to the current that passes through devices.

If light collides with the photosensor’s current work and then switches on. If the curent passing through the LED is stopped or interrupted, the IR beam is cut off, resulting in the photosensor stopping operating.

There are 4 types of optocouplers the difference is the use of photosensitive devices. Phototransistor and phot Darlington are used for DC circuits and photo SCR and photo TRIAC are used for controlling AC circuits.

In photo-transistors, optocoupler transistors can be PNP or NPN. Darlington transistor is 2 transistor pair, one used to control 2nd transistor base terminals. The Darlington transistor comes with a high-value gain

The working principle of an Optocoupler

The input impedance of the photocoupler is a small value that is about some hundred ohms and the impedance of the interference source is high which is 105 to 106 ohms. Based on the voltage division rule, if the amplitude of interference voltage is high spurious voltage given to the input of the photocoupler is small and can produce a small value of current, that is suppressed since there is not enough value to make the dipole light

The photocoupler of the input circuit and output circuit do not have an electrical connection and the other is not common ground, distributed capacitance is also less, and insulation resistance is of high value. So not easy to feed the noise from one side of the circuit to the photocoupler to the other side, affecting the production of interference signals from common impedance coupling.

Different Types of Optocoupler

Photo-Transistor Optocoupler

Here you can see the inner structure of the phototransistor optocoupler. The transistor used can be either PNP or NPN. Phototransistors of two types based on output pins. In the above photo, there is extra pins that innerly connected to the base of the transistor. Pin 6 is used for controlling the sensitivity of this module

Pin is used to connect with ground or negative through the use of a high-value resistor. here false triggering due to noise or electrical transients can regulated.

Before connection of the phototransistor optocoupler must know the transistor rating. PC816, PC817, LTV817, and K847PH are a mostly used photo-transistor-based optocouplers. .

Photo-Darlington Transistor Optocoupler

here you can see that there are two types of symbolic representations inner structure of photo Darlington according to Optocouler.

Darlington Transistor is a 2 transistor pair combination of one transistor control 2nd transistor base. here Darlington transistor offers high gain value. Normally LED releases infrared light and regulates base of the transistor pair.

This opto coupler is also employed for DC circuits based on part of isolation. The 6th pin is connected to the base of the transistor used for controlling transistor sensitivity.

Common examples of photo-Darlington based optocoupler are 4N32, 4N33, H21B1, H21B2, H21B3

Photo-TRIAC Optocoupler

here you can see a photo of the inner structure of TRIAC based opto coupler. TRIAC is used for AC-based circuits or switching processes. LED can be controlled with the use of DC and TRIAC used for controlling AC. Optocoupler offers good isolation also. The photo triac-based opto couplers are IL420, 4N35 etc are examples of TRIAC-based optocouplers.

Photo-SCR based Optocoupler

SCR or silicon-controlled rectifier also called thyristor. Here you can see a photo SCR-based opto coupler. That is like other opto coupler LED releases infrared. The SCR is controlled through the intensity of the LED.

Photor SCR opto couplers are used in AC circuits. Common example are MOC3071, IL400, MOC3072 etc.

Advantages of Optocoupler

it is small in size and less weight so can easily be managed.
it is low price component and easily operated
An optocoupler is best for AC and DC high-voltage signals.
It is also used for detecting the existence of objects for different sensor uses.
They also have longer working life about many decades.
It comes with a good response for lower frequencies.
it does not have contact bounce no circuit wear and uses less energy.
It comes with a high switching frequency due to short switch-on and switch-off times,

Disadvantages of Optocoupler

They do not have features to handle high current values.
They needed external biasing voltage to operate.
High-frequency response is not enough.
Phototransistors-based optocouplers do not have the same linear features for variation in light input and output current as photo diode-based types.

Applications of optocouplers

Photocouplers are used to make different logic circuits as anti-interface operation and isolation working of photocouplers is good compared to transistor and logic circuit make.
Switching circuits it used to provide separation between the control circuit and sitch that is not easy to get for the normal electronic switch.
it is also used in bistable output circuits since light-emitting diodes are connected in series in two tube emitter circuits. That solves output and load isolation ground issues.
Linear photocoupler is used for linear circuits having high linearity and good galvanic isolation properties.

Faqs

What is opto couplers explain its working principle?

The optocoupler isolated output and input circuits and operated like a switch connecting two isolated circuits on boards. If current not flowing in LED phototransistor devices also stop working and get off.

What is the most popular optocoupler?

PC817 is a famous optocoupler used in electronics. It is a standard circuit having a phototransistor and infrared LED diode that separates two parts of the circuit and avoids transmission of undesired noise and ground loops.

What is the primary purpose of an optocoupler?

The main use of an optocoupler is a galvanic separation between circuits. The use of transformed is high cost and done with AC circuits. For safety uses operating mains connected from low voltage electronics parts.

What are other names for optocoupler?

An optocoupler also called an opto-isolator, photocoupler, or optical isolator used to transfer signals between two isolated circuits with the use of light.

Is an optocoupler a relay?

Optocpuler relay is used to isolate control signal and load. These compact DIN rail configured relays come with load voltatge about 250 VAC/48VDA, and current ratings are about ten amperes. MOSFET, transistor, or TRIAC output options are used.

Is an optocoupler active or passive?

organic optocouplers are polymer-based electronic passive optical components mix and split transmission data from polymeric optical fibers.

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What is an Optocoupler

The working principle of an Optocoupler