A PROJECT REPORT ON FORCED COMMUTATION TECHNIQUES USING ARDUINO “SUBMITTED IN PARTIAL FULFILLMENT REQUIREMENTS FOR THE AWARD OF THE DEGREE OF” ELECTRICAL AND ELECTRONICS ENGINEERING Submitted by BANOTH SUDHAKAR-(11245A0209) UNDER THE ESTEEMED GUIDANCE OF B.VASANTH REDDY, M.TECH (Assistant Professor) DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING AND TECHNOLOGY Hyderabad, Andhra Pradesh 2013-2014
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A PROJECT REPORT
ON
FORCED COMMUTATION TECHNIQUES USING
ARDUINO
“SUBMITTED IN PARTIAL FULFILLMENT REQUIREMENTS FOR
THE AWARD OF THE DEGREE OF”
ELECTRICAL AND ELECTRONICS ENGINEERING
Submitted by
BANOTH SUDHAKAR-(11245A0209)
UNDER THE ESTEEMED GUIDANCE OF
B.VASANTH REDDY, M.TECH (Assistant Professor)
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING
AND TECHNOLOGY
Hyderabad, Andhra Pradesh
2013-2014
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING
AND TECHNOLOGY
Hyderabad, Andhra Pradesh
CERTIFICATE
This is to certify the major project entitled FORCED COMMUTATION USING ARDUINO that
is being submitted by B.SUDHAKAR in the partial fulfillment for the award of the Degree of Bachelor of
Technology in Electrical and Electronics Engineering in the Jawaharlal Nehru Technological University is
a record of bona-fide work carried out by them under my guidance and supervision. The results embodied
in this project report have not been submitted to any other University or Institute for the award of any
Graduation degree.
Under the Guidance of H.O.D
B.VASANTH REDDY, M.TECH Dr.M.CHAKRAVARTHY
(Assistant professor)
External Examiner
GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING
AND TECHNOLOGY
Hyderabad, Andhra Pradesh
DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING
Batch No.B13
K.VINAY KUMAR (10241A0292)
N.VIJAY KUMAR (10241A02A3)
P.SIVAIAH (10241A02A5)
B.SUDHAKAR (11245A0209)
Under the Guidance of
B.VASANTH REDDY
M.TECH (NIT), (Assistant professor)
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING
AND TECHNOLOGY
Hyderabad, Andhra Pradesh
2013-2014
ACKNOWLEDGEMENT
This is to place on record my appreciation and deep gratitude to the persons without whose support
this project would never see the light of day. I have immense pleasure in expressing my thanks and deep sense of gratitude to my guide Mr.
B.Vasanth reddy, Assistant Professor, Department of Electrical and Electronics Engineering, G.R.I.E.T for his guidance throughout this project.
I wish to express my profound sense of gratitude to Mr. P. S. Raju, Director, and G.R.I.E.T for his guidance, encouragement, and for all facilities to complete this project.
I also express my sincere thanks to Dr. M. Chakravarthy, Head of the Department, G.R.I.E.T and
for extending their help. Finally I express my sincere gratitude to Mr. E. Venkateshvarulu, Associate Professor, Professor,
Department of Electrical and Electronics Engineering, G.R.I.E.T and all the members of the faculty and my friends who contributed their valuable advice and helped to complete the project successfully.
BY
BANOTH SUDHAKAR
ABSTRACT
This project mainly focus on various forced commutation techniques used in various DC to DC
converters operating at high voltages, thyristors based inverters. The name forced commutation means
turning off of the device by applying reverse voltage across device and making current through device zero
using auxiliary devices, capacitors and inductors.
These techniques are used only for DC supply operated converters which does not have natural current
zero. In order to control output voltage of converter to desired level converter switches are on and off by
forced commutation. The various forced commutation techniques used in choppers and inverters are self
commutation or load commutation (class A), resonant commutation or current commutation (class B),
complimentary commutation (class C), impulse or voltage commutation (Class D).
In this project forced commutation is obtained by turning on and off of main and auxiliary thyristors by
generating gating pulses using software coding in Arduino UNO. This pulses are generated based on
switching times of devices in order obtain desired output voltages.
i
CONTENTS
Abstract i
Contents ii
List of figures iii
Tables iv
Legends v
Abbreviation and acronyms vi
Result vii
Date sheet of devices viii
ii
CHAPTER-1
COMPONENTS OF CIRCUIT
1.1. Introduction 1
1.2. Resistance 3
1.3. Inductor 4
1.4. Capacitor 5
1.5. thyristor
1.5.1. Introduction 8
1.5.2. thyristor symbol and operation 9
1.5.3. Triggering characteristics 11
1.5.4. Latch and hold characteristics 12
1.5.5. Switching characteristics 12
CHAPTER-2
DC POWER SUPPLY DESIGN
2.1 Introduction 16
2.2 Circuit component 16
2.2.1 Voltage regulator 17
2.2.2 Transformer 18
2.2.3 Diode 19
2.2.4 Bridge rectifier 22
CHAPTER-3
TRIGGERING CIRCUIT DESIGN
3.1 Introduction 24
iii
3.2 opto -isolator 24
3.3 photo diode opto-isolator 25
3.4 photo transistor opto-isolator 27
3.5 silicon controlled rectifier (SCR) 28
CHAPTER-4
ARDUINO
4.1 Introduction 31
4.2 digital arduino 31
4.3 analog arduino 32
4.4 output signals 33
4.5 input signals 34
4.6 Serial setup 36
CHAPTER-5
COMMUTATION TECHNIQUES
5.1 Introduction 38
5.2 line commutation 38
5.3 forced commutation 40
5.3.1 Voltage commutation 40
5.3.2 Current commutation 42
5.3.3 Load commutation 42
CHAPTER-6
CONCLUSION AND FUTURE WORK
6.1 Conclusion 49
6.2 Future work 49
iv
6.3 Reference 49
LIST OF FIGURES
CHAPTER-1
Fig no. Name of figure page no
1.1 Resistance symbol. 1
1.2 Inductor symbol. 3
1.3 Capacitor symbol and circuit diagram. 4
1.4 Representation of capacitor symbol. 5
1.5 Representation of diode symbol and schematic diagram. 8
1.6 Characteristics of diode in forward and reverse bias. 9
1.7 Silicon controlled rectifier. 11
1.8 SCR Triggering characteristics. 12
1.9 Switching characteristics of SCR. 12
CHAPTER-2
2.1 Voltage regulator with filtering capacitor. 17
2.2 Voltage regulator symbol and pin configuration. 17
2.3 Two winding Transformer. 18
2.4 Representation of diode symbol and schematic diagram. 20
2.5 Characteristics of forward and reverse bias. 21
2.6 Operating during negative half cycle. 22
2.7 DC power supply design circuit diagram. 23
v
CHAPTER-3
3.1 An opto- isolator. 24
3.2 Photo diode opto- isolator. 25
3.3 Opto-isolator. 27
3.4 Basic operating principle of a thyristor. 28
CHAPTER-4
4.1 Arduino 31
CHAPTER-5
5.1 Voltage commutation DC-DC chopper and most 40
Significant waveforms
5.2 A current commutated DC-DC chopper and 42
Most significant waveforms
5.3 Load commutation circuit 43
5.4 Output waveforms of load commutation 44
LIST OF TABLES
1. TYN612 data sheet regulator
2. 7824 date sheet regulator
vi
LEGENDS
µH - Micro Hendry
µc - Micro coulomb
R - Resistance
Ω - Ohms
VBO - Forward break over voltage
VBR - Reverse break over voltage
trr - Reverse recovery voltage
tq - circuit turn off time
β1 - Base current time1
β2 - Base current time 2
NP - Primary turn of a transformer
Ns - Secondary turns of a transformer
Ix - Internal current
Vm - Peak inverse voltage
RθJC - Thermal Resistance Junction-Cases (TO-220)
TSTG - Storage Temperature Range
TOPR - Operating temperature range
RθJA - Thermal Resistance Junction-Air (TO-220)
ITSM - Non-repetitive surge peak on-state current
IT (RMS) - RMS on-state current
VDRM - Repetitive peak off-state voltages
Vcc - common collector voltage
vii
Abbreviation and acronyms
SCR - Silicon controlled rectifier
PWM - Pulse Width Modulation
DC - Direct current
AC - Alternating current
R - Resistor
C - Capacitor
L - Inductor
1
Chapter-1
COMPONENTS OF CIRCUIT
1.1. INTRODUCTION:
Basic components in forced commutation techniques for voltage commutation, current commutation
and load commutation techniques are.
Resistor
Inductor
Capacitor
Diode
Thyristor
1.2 RESISTOR:
A resistor is a passive two-terminal electrical component that implements electrical resistance as a
circuit element. Resistors act to reduce current flow, and, at the same time, act to lower voltage levels
within circuits. Resistors may have fixed resistances or variable resistances, such as those found
in thermistors, varistors, trimmers, photoresistors and potentiometers.
Figure 1.1: Resistance symbol
The current through a resistor is in direct proportion to the voltage across the resistor's terminals. This
relationship is represented by Ohm's law:
Where I is the current through the conductor in units of amperes, V is the potential difference
measured across the conductor in units of volts, and R is the resistance of the conductor in units
of ohms (symbol :).
2
The ratio of the voltage applied across a resistor's terminals to the intensity of current in the circuit is called
its resistance, and this can be assumed to be a constant (independent of the voltage) for ordinary resistors
working within their ratings.
Resistors are common elements of electrical networks and electronic circuits and are ubiquitous
in electronic equipment. Practical resistors can be composed of various compounds and films, as well
as resistance wires (wire made of a high-resistivity alloy, such as nickel-chrome). Resistors are also
implemented within integrated circuits, particularly analog devices, and can also be integrated
into hybrid and printed circuits.
The electrical functionality of a resistor is specified by its resistance: common commercial resistors
are manufactured over a range of more than nine orders of magnitude. When specifying that resistance in
an electronic design, the required precision of the resistance may require attention to the manufacturing
tolerance of the chosen resistor, according to its specific application.
The temperature coefficient of the resistance may also be of concern in some precision applications.
Practical resistors are also specified as having a maximum power rating which must exceed the anticipated
power dissipation of that resistor in a particular circuit: this is mainly of concern in power electronics
applications. Resistors with higher power ratings are physically larger and may require heat sinks. In a
high-voltage circuit, attention must sometimes be paid to the rated maximum working voltage of the
resistor. While there is no minimum working voltage for a given resistor, failure to account for a resistor's
maximum rating may cause the resistor to incinerate when current is run through it.
Practical resistors have a series inductance and a small parallel capacitance; these specifications can
be important in high-frequency applications. In allow-noise amplifier or pre-amp, the noise characteristics
of a resistor may be an issue. The unwanted inductance, excess noise, and temperature coefficient are
mainly dependent on the technology used in manufacturing the resistor. They are not normally specified
individually for a particular family of resistors manufactured using a particular technology. A family of
discrete resistors is also characterized according to its form factor, that is, the size of the device and the
position of its leads (or terminals) which is relevant in the practical manufacturing of circuits using them.
3
1.2. INDUCTOR:
An inductor, also called a coil or reactor, is a passive two-terminal electrical
component which resists changes in electric current passing through it. It consists of a conductor such as a
wire, usually wound into a coil. When a current flows through it, energy is stored temporarily in a magnetic
field in the coil. When the current flowing through an inductor changes, the time-varying magnetic field
induces a voltage in the conductor, according to Faraday‟s law of electromagnetic induction, which
opposes the change in current that created it.
Figure 1.2: inductor symbol
An inductor is characterized by its inductance, the ratio of the voltage to the rate of change of current,
which has units of henries (H). Inductors have values that typically range from 1 µH (10-6H) to 1 H. Many
inductors have a magnetic core made of iron or ferrite inside the coil, which serves to increase the magnetic
field and thus the inductance. Along with capacitors and resistors, inductors are one of the three
passive linear circuit elements that make up electric circuits. Inductors are widely used in alternating
current (AC) electronic equipment, particularly in radio equipment. They are used to block the flow of AC
current while allowing DC to pass; inductors designed for this purpose are called chokes. They are also
used in electronic filters to separate signals of different frequencies, and in combination with capacitors to
make tuned circuits, used to tune radio and TV receivers.
4
1.3. CAPACITOR:
A capacitor (originally known as a condenser) is a passive two-terminal electrical component used to
store energy electro statically in an electric field. The forms of practical capacitors vary widely, but all
contain at least two electrical conductors (plates) separated by a dielectric (i.e., insulator). The conductors
can be thin films of metal, aluminum foil or disks, etc. The 'none conducting' dielectric acts to increase the
capacitor's charge capacity. A dielectric can be glass, ceramic, plastic film, air, paper, mica, etc. Capacitors
are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, a
capacitor does not dissipate energy. Instead, a capacitor stores energy in the form of an electrostatic
field between its plates
.
Figure 1.3: capacitor symbol and circuit diagram
When there is a potential difference across the conductors (e.g., when a capacitor is attached across a
battery), an electric field develops across the dielectric, causing positive charge (+Q) to collect on one plate
and negative charge (-Q) to collect on the other plate. If a battery has been attached to a capacitor for a
sufficient amount of time, no current can flow through the capacitor. However, if an accelerating or
alternating voltage is applied across the leads of the capacitor, a displacement current can flow.
An ideal capacitor is characterized by a single constant value for its capacitance. Capacitance is
expressed as the ratio of the electric charge (Q) on each conductor to the potential difference (V) between
them. The SI unit of capacitance is the farad (F), which is equal to one coulomb per volt (1 C/V). Typical
capacitance values range from about 1 pF (10−12 F) to about 1 mF (10−3 F).
The capacitance is greater when there is a narrower separation between conductors and when the
conductors have a larger surface area. In practice, the dielectric between the plates passes a small amount
5
of leakage current and also has an electric field strength limit, known as the breakdown voltage. The
conductors and leads introduce an undesired inductance and resistance
.
Figure 1.4: representation of capacitor symbol
Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating
current to pass. In analog filter networks, they smooth the output of power supplies. In resonant
circuits they tune radio to particular frequencies. In electric power transmission systems they stabilize
voltage and power flow.
1.4. DIODE:
A diode is the simplest sort of semiconductor device. Broadly speaking, a semiconductor is a material
with a varying ability to conduct electrical current. Most semiconductors are made of a poor conductor that
has had impurities added to it. The process of adding impurities is called doping.
In the case of LEDs, the conductor material is typically aluminum-gallium-arsenide (AlGaAs). In
pure aluminum-gallium-arsenide, all of the atoms bond perfectly to their neighbors, leaving no free
electrons (negatively charged particles) to conduct electric current. In doped material, additional atoms
change the balance, either adding free electrons or creating holes where electrons can go. Either of these
alterations makes the material more conductive.
6
Figure 1.5: representation of diode symbol and schematic diagram
A semiconductor with extra electrons is called N-type material, since it has extra negatively charged
particles. In N-type material, free electrons move from a negatively charged area to a positively charged
area.
A semiconductor with extra holes is called P-type material, since it effectively has extra positively
charged particles. Electrons can jump from hole to hole, moving from a negatively charged area to a
positively charged area. As a result, the holes themselves appear to move from a positively charged area to
a negatively charged area.
A diode consists of a section of N-type material bonded to a section of P-type material, with electrodes
on each end. This arrangement conducts electricity in only one direction. When no voltage is applied to the
diode, electrons from the N-type material fill holes from the P-type material along the junction between the
layers, forming a depletion zone. In a depletion zone, the semiconductor material is returned to its original
insulating state -- all of the holes are filled, so there are no free electrons or empty spaces for electrons, and
charge can't flow.
7
1.6 Characteristic of diode in forward and reverse bias
To get rid of the depletion zone, you have to get electrons moving from the N-type area to the P-type
area and holes moving in the reverse direction. To do this, you connect the N-type side of the diode to the
negative end of a circuit and the P-type side to the positive end. The free electrons in the N-type material
are repelled by the negative electrode and drawn to the positive electrode. The holes in the P-type material
move the other way. When the voltage difference between the electrodes is high enough, the electrons in
the depletion zone are boosted out of their holes and begin moving freely again. The depletion zone
disappears, and charge moves across the diode.
If you try to run current the other way, with the P-type side connected to the negative end of the circuit
and the N-type side connected to the positive end, current will not flow. The negative electrons in the N-
type material are attracted to the positive electrode. The positive holes in the P-type material are attracted
to the negative electrode. No current flows across the junction because the holes and the electrons are each
moving in the wrong direction. The depletion zone increases.
8
1.5. Thyristor:
1.5.1. Introduction
Thyristors can take many forms, but they have certain things in common. All of them are solid state
switches which act as open circuits capable of withstanding the rated voltage until triggered. When they are
triggered, thyristors become low−impedance current paths and remain in that condition until the current
either stops or drops below a minimum value called the holding level. Once a thyristor has been triggered,
the trigger current can be removed without turning off the device.
Silicon controlled rectifiers (SCRs) and triacs are both members of the thyristor family. SCRs are
unidirectional devices where triacs are bidirectional. An SCR is designed to switch load current in one
direction, while a triac is designed to conduct load current in either direction.
Structurally, all thyristors consist of several alternating layers of opposite P and N silicon, with the
exact structure varying with the particular kind of device. The load is applied across the multiple junctions
and the trigger current is injected at one of them. The trigger current allows the load current to flow
through the device, setting up a regenerative action which keeps the current flowing even after the trigger is
removed.
These characteristics make thyristors extremely useful in control applications. Compared to a
mechanical switch, a thyristor has a very long service life and very fast turn on and turn off times. Because
of their fast reaction times, regenerative action and low resistance once triggered, thyristors are useful as
power controllers and transient overvoltage protectors, as well as simply turning devices on and off.
Thyristors are used in motor controls, incandescent lights, home appliances, cameras, office equipment,
A Voltage regulator is designed to automatically maintain a constant voltage level. A voltage
regulator may be a simple "feed-forward" design or may include negative feedback control loops. It may
use an electromechanical mechanism, or electronic components. Depending on the design, it may be
used to regulate one or more AC or DC voltages.
Figure 2.1: voltage regulator with filtering capacitors
A simple voltage regulator can be made from a resistor in series with a diode. Due to the
logarithmic shape of diode V-I curves, the voltage across the diode changes only slightly due to changes in
current drawn or changes in the input. When precise voltage control and efficiency are not important, this
design may work fine.
Figure 2.2: voltage regulator symbol and pin configuration
18
Feedback voltage regulators operate by comparing the actual output voltage to some fixed reference
voltage. Any difference is amplified and used to control the regulation element in such a way as to reduce
the voltage error. This forms a negative feedback control loop increasing the open- loop gain tends to
increase regulation accuracy but reduce stability (avoidance of oscillation, or ringing during step changes).
There will also be a trade-off between stability and the speed of the response to changes.
If the output voltage is too low (perhaps due to input voltage reducing or load current increasing),
the regulation element is commanded, up to a point, to produce a higher output voltage–by dropping less of
the input voltage, or to draw input current for longer periods if the output voltage is too high, the regulation
element will normally be commanded to produce a lower voltage.
However, many regulators have over-current protection so that they will entirely stop sourcing
current (or limit the current in some way) if the output current is too high, and some regulators may also
shut down if the input voltage is outside a given range.
2.2.2. TRANSFORMER:
A transformer is an electrical device that transfers energy between two circuits
through electromagnetic induction. A transformer may be used as a safe and efficient voltage converter to
change the AC voltage at its input to a higher or lower voltage at its output. Other uses include current
conversion, isolation with or without changing voltage and impedance conversion.
Figure 2.3: two winding transformer
19
A transformer most commonly consists of two windings of wire that are wound around a common
core to provide tight electromagnetic coupling between the windings. The core material is often a
laminated iron core. The coil that receives the electrical input energy is referred to as the primary winding,
while the output coil is called the secondary winding.
An alternating electric current flowing through the primary winding (coil) of a transformer generates
a varying electromagnetic field in its surroundings which causes a varying magnetic flux in the core of the
transformer. The varying electromagnetic field in the vicinity of the secondary winding induces an
electromotive force in the secondary winding, which appears a voltage across the output terminals. If a load
impedance is connected across the secondary winding, a current flows through the secondary winding
drawing power from the primary winding and its power source.
A transformer cannot operate with direct current; although, when it is connected to a DC source, a
transformer typically produces a short output pulse as the current rises
2.2.3. DIODE:
A diode is the simplest sort of semiconductor device. Broadly speaking, a semiconductor is a material
with a varying ability to conduct electrical current. Most semiconductors are made of a poor conductor that
has had impurities added to it. The process of adding impurities is called doping.
In the case of LEDs, the conductor material is typically aluminum-gallium-arsenide (AlGaAs). In
pure aluminum-gallium-arsenide, all of the atoms bond perfectly to their neighbors, leaving no free
electrons (negatively charged particles) to conduct electric current. In doped material, additional atoms
change the balance, either adding free electrons or creating holes where electrons can go. Either of these
alterations makes the material more conductive.
20
Figure 2.4: representation of diode symbol and schematic diagram
A semiconductor with extra electrons is called N-type material, since it has extra negatively charged
particles. In N-type material, free electrons move from a negatively charged area to a positively charged
area.
A semiconductor with extra holes is called P-type material, since it effectively has extra positively
charged particles. Electrons can jump from hole to hole, moving from a negatively charged area to a
positively charged area. As a result, the holes themselves appear to move from a positively charged area to
a negatively charged area.
A diode consists of a section of N-type material bonded to a section of P-type material, with electrodes
on each end. This arrangement conducts electricity in only one direction. When no voltage is applied to the
diode, electrons from the N-type material fill holes from the P-type material along the junction between the
layers, forming a depletion zone. In a depletion zone, the semiconductor material is returned to its original
insulating state -- all of the holes are filled, so there are no free electrons or empty spaces for electrons, and
charge can't flow.
21
2.5. Characteristic of diode in forward and reverse bias To get rid of the depletion zone, you have to get electrons moving from the N-type area to the P-
type area and holes moving in the reverse direction. To do this, you connect the N-type side of the diode to
the negative end of a circuit and the P-type side to the positive end. The free electrons in the N-type
material are repelled by the negative electrode and drawn to the positive electrode. The holes in the P-type
material move the other way. When the voltage difference between the electrodes is high enough, the
electrons in the depletion zone are boosted out of their holes and begin moving freely again. The depletion
zone disappears, and charge moves across the diode.
If you try to run current the other way, with the P-type side connected to the negative end of the
circuit and the N-type side connected to the positive end, current will not flow. The negative electrons in
the N-type material are attracted to the positive electrode. The positive holes in the P-type material are
attracted to the negative electrode. No current flows across the junction because the holes and the electrons
are each moving in the wrong direction. The depletion zone increases.
22
2.2.4: bridge rectifier
During the positive half cycle both D3 and D1 are forward biased. At the same time, both D2 and
D4 are reverse biased. Note the direction of current flow through the load. During the negative half cycle
D2 and D4 are forward biased and D1 and D3 are reverse biased. Again note that current through the load
is in the same direction although the secondary winding polarity has reversed.
2.6. Operation during negative half cycle Peak Inverse Voltage:
In order to understand the Peak Inverse Voltage across each diode, look at figure below. It is a
simplified version of figure showing the circuit conditions during the positive half cycle. The load and
ground connections are removed because we are concerned with the diode conditions only. In this circuit,
diodes D1and D3 are forward biased and act like closed switches. They can be replaced with wires. Diodes
D2 and D4 are reverse biased and act like open switches.
The circuit of redrawn below. We can see that both diodes are reversing biased, in parallel, and
directly across the secondary winding. The peak inverse voltage is therefore equal to Vm.
23
Fig 2.7. Dc power supply design circuit diagram
Therefore,
Peak inverse voltage = Vm
24
Chapter-3
TRIGGERING CIRCUIT DESIGN
1.1 Introduction:
The following components are required to trigger a thyristor. They are:
Opto-isolator
5 volts dc supply
Arduino
Current limiting resistor
1.2 OPTO-ISOLATOR:
Figure 3.1 an opto-isolator
In electronics, an opto-isolator, also called an optocoupler, photocoupler, or optical isolator,
is a component that transfers electrical signals between two isolated circuits by using light.Opto- isolators
prevent high voltages from affecting the system receiving the signal. Commercially available opto- isolators
withstand input-to-output voltages up to 10 kV and voltage transients with speeds up to 10 kV/μs.
A common type of opto- isolator consists of an LED and a phototransistor in the same opaque
package. Other types of source-sensor combinations include LED-photodiode, LED-LASCR, and lamp-
photo resistor pairs. Usually opto-isolators transfer digital (on-off) signals, but some techniques allow them
to be used with analog signals.
History:
The value of optically coupling a solid state light emitter to a semiconductor detector for the purpose
of electrical isolation was recognized in 1963 by Akmenkalns, et al. (US patent 3,417,249). Photo resistor-
based opto- isolators were introduced in 1968. They are the slowest, but also the most linear isolators and