OPTO-COUPLER=
Also known as Opto-Isolator.
As
name suggests it is a light activated and a combined transducer used in special
application. It produces an electrical isolation between input and output to
separate two circuits from each other. It has two internal transducers, both are
photo transducer.
1. LED
2. Photodiode
LED converts electric current into light.
Opto-coupler converts or senses light and generates electric
signal.
But, first
we need to know what are LED and Opto-coupler…..
1.LED=
LED
is la light source which uses semiconductors and electroluminescence to create
light. There are two kinds of light of light emitting diodes. LED and
OLED. The LED is different than EL lamp
in that it uses small semiconductor crystals with reflectors and other parts to
make the light brighter and focused into single point. The OLED is very similar
to the EL lamp.
Currently the LED is popular
due to its efficiency and many believe it is a new technology. Led is around
for over 50 years.
///Advantages///
1. Energy efficient source of light for short distances.
2. Durable and shockproof
3. used in many circuits
///Disadvantages///
1. Thin copper connections cracks in PCB.
2. may be unreliable in outside application.
3. Semiconductors are sensitive to being damaged by heat.
2.Photo-diode =
A Photo-diode is a semiconductor device that converts light into an
electric current. The current is generated when photons are absorbed by the
photodiode. Photodiodes may contain optical filters, built in lenses, and may
have large or small surface area. It is a two terminal electronics device
which, when exposed to light the current starts flowing I the diode. It is
operated in reverse bias only.
///Advantages///
1.
The reverse current is low in the tens of
microampere.
2.
The rise and fall times in case of photodiodes
is very small making it suitable for high speed counting and switching
applications.
///Disadvantages///
1.
It has lower light sensitivity than cadmium
sulphide.
///Applications///
1.
Used for detection of visible as well as
invisible light rays
2.
In communication system
3.
Character recognition techniques and IR remote
control circuits.
Lets see Working, Advantages and Disadvantages of Opto-Coupler.
WORKING OF OPTO-COUPLER=
When input voltage
is given to an opto-coupler it conducts LED and emits light. The light falls on
its Photo-diode and it produces the output current. It means that if the input
signal is varying in amplitude then the light is fluctuating, due to
opto-coupling its output is also varying in step with current. The opto-coupler
couples input to output or an input signal of one circuit without any physical
contact and by means of emitter and light sensor just like a transmitter and a
receiver hence known as opto-coupler.
///Advantages///
1.
Better frequency response
2.
Linear
3.
Less noisy
4.
Highly sensitive to light
///Disadvantages///
1.
Small active area
2.
Require amplification at low temp.
3.
Temp. dependent characteristics
USES=
1.
In tachometer.
