Optical Couplers

8/2/2019 Optical Couplers

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GROUP MEMBERS: BUSHRA MUBEEN 10ES03

MAHEEN ARSHAD 10ES250

RAAZIA ABID 10ES07

SHAHIDA PERVEEN 10ES04

KHIZRA RAHMANI 10ES06


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SUBJECT :

ELECTRONIC DEVICES AND CIRCUITS

TOPIC OF PRESENTATION:

OPTICAL COUPLERS

ASSIGNED BY:

ENGINEER USMAN ALI KHAN


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Overview Introduction of optical couplers

Construction

Optical couplers basics Types of detectors

Types of optical couplers

Specifications of optical couplers

Applications


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DEFINITON OF OPTICAL COUPLERS

In optical coupler, also called optical isolator, is an

electronic component that transfers an electrical signal or

voltage from one circuit to another by utilizing the light ,

while electrically isolating the two circuits from each other.


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CONSTRUCTION


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Why we use optical couplers? Generally, machine-controlling equipment generates

induced noise which may cause malfunctions. This

unwanted noise in input signals can be isolated by meansof optical couplers.

The main purpose of optical isolator is to prevent thehigh voltage or rapidly changing voltages on one side of the

circuit from damaging component or distortingtransmission on the other side.


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Physical appearance

It is enclosed in thesingle package.

It has a appearance ofintegrated circuit(IC)

or transistor.


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Optical couplers basics The optical couplers is a component that contain two

element required for an optical isolator.

1. Light Emitter

2. Light Detector

Light Emitter

Lie in input side Convert electrical signal into light

Typically light emitter is LED.


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Light Detector

Detect light coming from emitter.

Convert back into electrical signal.

It is usually used photodiode, phototransistor, photo

Darlington ,LASCR etc.

PHOTODIODE PFOTOTRANSISTOR PDOTODARLINGTON


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SPECTRAL RESPONSE OF SILICON Since silicon has a response to light (spectral response) that peaks at

infrared wavelengths (between 800 and 950 nanometers).

silicon devices are preferred as the photo detector section.

Matching the infrared LED to the silicon chip provides a maximumtransfer of the desired electrical signal.


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TYPES OF DETECTOR OF OPTOISOLATORThe input circuit of an optical coupler is typically an LED but the

output can take several forms. There are many types of detectors

used in optical couplers. Few are discussed here.

1- Photodiode optical isolators

2- photo transistor optical isolators

3- Darlington Transistor coupler

4- LASCR optical isolators

5- phototriac optical coupler


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Photodiode Optical isolators:

It has a LED at input side and photodiode on outputside.


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Phototransistor Optical isolators:

When the input voltage forward biases the lighttransmitted to the phototransistor turns it on producingcurrent through the external load.


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Darlington transistor coupler: It is used when increased output current capability is

needed beyond that provided by the phototransistoroutput.


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LASCR output coupler: This device can be used in applications where a low level input voltage is

required to attain a high voltage for the purpose of activating some type ofelectromechanical device.


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Photo triacs optical coupler It contain LED optically coupled to output phototriacs.

Phototriacs contain light sensitive ICs act as a trigger

device.


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Types of optical couplers

There are two types of optical couplers:

1. Slotted optical couplers

2. Reflective optical couplers


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1. Slotted optical couplers: Slot is molded into package between LED and

phototransistor.

An air gap between its section.

Light can blocked by placing opaque object in slot.


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Application of slotted optical

couplersIt is used in following :

End-of-tape detection

Limit switching

Liquid level detection

Punch card reader


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2.Reflective optical couplers LED and photo sensor are optically screened.

The object sited short distance outside, in line with LEDand sensor.


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Application of reflective optical

couplersIt is used in following:

Tape position detection. Smoke or fog detection

speed measurement


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Specification of the optical couplers:

Isolation voltage

Current transfer ratio

LED Trigger current

Transfer gain

Soldering temperature

Isolation Resistance

Isolation capacitance


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APPLICATION OF SLOTTED OPTOCOUPLER

The slotted opticalcoupler is available withphoto transistor and

photo Darlington photodetectors

The package normallyhas an air gap between

its two sectionsmeasuring about one-eighth of an inch inwidth.


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The infrared light beam that

links the two sections of an opto

coupler can be broken by the

mechanical insertion of any thin

object As the infrared light beam is

interrupted, pulses are generated

at the output of the coupler.

rotational speed of the disk can

be measured, and motor speed

control can be achieved.


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Applications:As Solid state Relay.

As a switching time reducer

Noise reduction.

Modem-telephone connections.


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Modem-telephone connections:Two optical couplers are employed

for upstream signals anddownstream signals.

Allows computer to be connectedto a telephone line without risk ofdamage from electricaltransients(surges or spikes).

Modem using optical isolatorprovides superior protectionagainst surges as compared withmodems having surge suppressers.


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Solid state Relay: SSR(solid state relay)is a circuit that uses a dc input voltage to pass or

block an ac signal.

When the dc input has the polarity shown(below),the waveform at theinput (ac1) is coupled to the ac output(ac2)and thus to the load.

As long as the dc potential remains , ac signal will be coupled to loadand if dc source is removed output goes open circuit and ac signal isblocked from the load.


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As a switching time reducer: Output being taken from the collectorbase diode. In this mode of

operation, the emitter is left open, the load resistor is connectedbetween the base and ground. collector is tied to the positive voltage

supply . Using the coupler in this way reduces the switching timefrom 2 to 3 ms to 100 ns.


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Noise Reduction: an electrical shield in the optical path between

LED and photodiode reduces noise transmissionmaking optical coupler useful in signaltransmission in high-induced noise environments.


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Further Advantages:1

Provides different grounds for input and output sections.Loading(output)doesnt affect the input section

2

Fastest way of transferring data. Small interfacing devices are used for large voltages.

3 .they are not affected by electromagnetic fields as light is

composed of photons.

4

small sized.

light weight.


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Date post:	06-Apr-2018
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Optical Couplers

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