optical couplers
TRANSCRIPT
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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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