CONSTRUCTION OF UNTERRUPTIBLE
POWER SUPPLY
BY
NWAMBE CHUKWUNONSO .C.
REG. NO: EE/2005/124
DEPARTMENT OF ELECTRICAL/ELECTRONIC
ENGINERRING.
CARITAS UNIVERSITY
AMORJI NIKE
EMENE
ENUGU STATE.
PRESENTED IN PARTIAL FULFILMENT OF THE
REQUIREMENT FOR THE AWARD OF BACHELOR
OF ENGINEERING (B.ENG) DEGREE IN
ELECTICAL ELECTRONIC ENGINEERING.
AUGUST. 2010.
DEDICATION
This work is dedicated to God almighty, my beloved parents,
chief & Dr. mrs. S.N Nwambe. Without their help I wouldn’t realized
this work.
CERTIFICATION
This Project construction of ‘UNTERRUPTIBLE POWER
SUPPLY’ (UPS) was completed under the supervision and found
acceptable in partial fulfillment of the requirement for the award of
bachelor of Engineering (B.Eng) Degree in Electrical and Electronic
Engineering Caritas University Enugu.
Certified by:
………………….
Engr M. O Eze
(Project supervisor)
………………………
Date
Approved by:
…………………….
Prof G.C Ochiagha.
(H.O.D)
………………………
Date
ACKNOWLEDGEMENT
I wish to thank Almighty God who in his infinite mercy, granted
me the strength to do and complete this work, because it wasn’t easy.
Secondly, to my lecturers, My project supervisor Engr. Eze, My
H.O.D Prof. G.C Ochiagha, Engr. P.N Mba, Engr. Ejimofor, Engr.
Emeasoba, Engr Ochi, Engr. Nnaji, Engr. Ozoani, Engr. Mrs.
Otegburu and many others.
Once again am particularly grateful to my parents for their
encouragement till this stage of my life, many thanks also goes to
Engr. Boniface for teaching me circuitry connections.
However, am indebted to all the staff and teachers of faculty of
Engineering, Caritas University. My brothers Ejike, Chidi, my sisters
Chioma and Onyi should also be thanked for their supports and
encouragement.
Finally I wish to thank all my departmental staff for their help.
ABSTRACT
Uninterruptible power supplies (UPS) are used to provide power
when regular utility power is unavailable. Although they are
commonly used for providing power in remote locations or
emergencies, this is not because they are the same as auxiliary
power units, emergency power units or standby generators.
Unlike the aforementioned power sources, UPS provides an
immediate and continuous supply of power to a device, hence
protecting it from power interruption and allowing time for auxiliary or
emergency powers, to kick in equipment to be safely shut down or
utility power restored.
The major aim of this was to design a system which will be able to
convert battery voltage(12v) to 220v, which is equivalent to wall outlet
and secondly able to charge the battery.
The chapter one of this work, gives the over-view of UPS, it’s
importance, uses, and application and some of its special features
like its ability to correct frequency instability and many more.
Secondly, this work dealt with all components used in the
construction of the device, there working condition and uses. Some
basic abstract phenomenon were also treated like wave forms and
electronic switching.
The chapter three, basically dealt on all electrical measuring
instrument used in and on the device, how they are used, why and
where.
The fourth chapter explains how the components where assembled
into section and the sectional connection used to form the device.
The last chapter is a simple conclusion with honest recommendation.
TABLE OF CONTENT
CERTIFICATION -
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DEDICATION
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ACKNOWLEDGEMENT
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ABSTRACT
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TABLE OF CONTENT -
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CHAPTER ONE
1.1
INTRODUCTION
1.1
AIMS AND OBJECTIVES
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1.2
SCOPE OF THIS PROJECT
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1.3
AVAILABILITY OF DESIGN MATERIALS
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CHAPTER TWO
2.1
LITERATURE REVIEW
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2.1
WHAT IS A UPS? -
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2.2
WAVEFORMS
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2.2.1 SQUAREWAVE
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2.2.2 MODIFIED SINE WAVE
2.2.4 TRUE SNE WAVE -
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2.3
RESISTORS
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2.4
CAPACITORS
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1.4.1 CAPACITANCE
2.4.2 ELECTROLYTIC CAPACITOR
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2.4.3 PLASTIC FILM, CERAMIC NAD MONOLITHIC
CAPACTOR -
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DIODE
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2.5.1 MOUNTING A DIODE -
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2.5.2 CHARACTERISTICS CURVES OF A DIODE
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2.5.3 IDEAL DIODE
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2.5.4 LIGHT EMITTING DIODE
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2.5.5 DIODES AS RECTIFIERS
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2.5.5.1 HALF-WAVE RECTIFIER
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2.5.5.2 FULL-WAVE, CENTER-TAP RECTIFIE
2.5.6
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TRANSISTORS -
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2.6.1 TRANSISTOR AS A SWIRCH -
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2.6.2 MOSFETS -
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2.6.2.1 SUPER-HIGH INPUT IMPEDANCE -
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2.6.2.2. SETBACKS IN MOSFETS
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2.6.2.3 ITS FLEXIBILITY
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2.7.1 OPTO-COUPLER CHARACTERISTICS - -
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2.7.2 ITS INPUT -
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2.7.3 ITS OUTPUT
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2.6
2.7
FILTERS -
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2.7.4 ITS OPERATING MODE
2.8
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THE SG3524 INTEGRATED CIRCUIT
2.8.1 OPERATING PRINCIPLE OF SG3524
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CHAPTER THREE
3.0
METHODOLOGY
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3.1
ELECTRONIC WORKBENCH
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3.2
GALVANOMETER
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3.3
OSCILLOSCOPE -
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3.4
VOLTMETER
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3.5
AMPMETER
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3.6
WATTMETER
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3.7
MULTIMETERS -
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CHAPTER FOUR
4.0
DESIGN AND CONSTRUCTION METHODS
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4.1
COMPLETE CIRCUIT DIAGRAM OF A UPS
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4.2
STAGE BY STAGE DESIGN -
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4.2.2 DRIVER/SWITCHING SECTION
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4.2.3 THE OUTPUT SECTION
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4.2.4 THE CHANGEOVER SECTION
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4.2.5 THE LOW BATTERY CUT-OFF SECTION
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4.2.1 OSCILLATOR SECTION
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COMPONENT JUSTIFICATION
4.3.1 MOSFETS -
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4.3.2 SG3524 OSCILLATOR -
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4.3.3 OPTO-COUPLER -
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4.3.4 RESISTORS -
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4.4.1 TESTING AND SETTING THE INVERTER
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4.5
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4.4 TEST AND ANALYSIS
BILL OF ENGINEERING CONSTRUCTION
CHAPTER FIVE
5.0 CONCLUSION
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5.1 RECOMMENDATION
REFERENCES
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LIST OF FIGURES
Fig 1.
Offline/ standby diagram
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Fig 2.
A capacitor
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Fig 3.
Capacitors -
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Fig 4.
Circuit Symbol of a diode -
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Fig 5.
A Led
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Fig 6.
Half-wave rectifier
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Fig 7.
Half wave Rectifier
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Fig 8.
A full-wave centre tap rectifier
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Fig 9.
A Simple filter
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Fig 10.
Transistor as a Switch -
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Fig 11.
A Transistor as a Switch
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Fig 12.
A Mosfet
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Fig 13
Opto-Coupler’s Input
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Fig 14.
Inputs and output circuit of an opto-coupler - 32
Fig 15.
A Digram of a Voltmeter
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Fig 16.
Diagram of Amp meter -
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Fig 17
Diagram of a Wattmeter arrangement
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Fig 18
Oscillator Circuit -
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Fig 19
Pre-Driver Section
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Fig 20
Change over circuit of the UPS
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Fig 21
Low battery cut-off circuit
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CHAPTER ONE
1.10 INTRODUCTION
As blackouts roll through power-starved communities, the threat to
you and your computer is not the lack of electricity, but the change in
power. When the lights are off and you are about to start any
industrial or computer-based projects, all your efforts will be wasted.
Even when your system acts as a server, a sudden shutdown could
disrupt the processing of many others. You can make your work
immune to the intransigence of rolling blackouts and protect against
many other types of unexpected power disturbances. Your secret
weapon is the uninterruptible power supply or uninterruptible
power source. Commonly called the UPS, this devices is a cleaver
threefold package-a set of battery, an inverter that transforms the
low-voltage direct current of the batteries into the standard
alternating current equivalent to your wall outlet, and a battery
changer that assures that reserve power storage system (the
batteries) with interfaces to mach it to utility power and your
computer system. A UPS differs from an auxiliary emergency power
system or standby generator in that it will provide instantaneous or
near-instantaneous protection from input power interruptions by
means of one or more attached batteries and associated electronic
circuitry for low power users, and or by means of diesel generators
and flywheels for high power users. While not limited to protecting
any particular type of equipment, a UPS is typically used to protect
computers, data centers, telecommunication equipment or other
electrical equipment where an unexpected power disruption could
cause injuries, fatalities, serious business disruption and/or data loss.
UPS units range in size from units designed to protect a single
computer without a video monitor (around 200 VA rating) to large
units powering entire data centers, buildings, or even cities. The UPS
is designed to project against changes, specifically a temporary loss
of electrical supply.
This project focuses on conversion of AC to DC and from DC to AC
power inverters, which aim to efficiently transform a DC power
source to a high voltage AC source, similar to power that would be
available at an electrical wall outlet. Inverters are used for many
applications, as in situations where low voltage DC sources such as
batteries, solar panels or fuel cell must be converting electrical power
from a car battery to run a laptop, TV or cell phone.
DC and AC Current
In the world today there are currently two forms of electrical
transmission, Direct Current (DC) and Alternating Current (AC), each
with its own advantages and disadvantages. DC power is simply the
application of a steady constant voltage across a circuit resulting in a
constant current. A battery is the most common source of DC
transmission as current flows from one end of a circuit to the other.
Most digital circuitry today is run off of DC power as it carries the
ability to provide either a constant high or constant low voltage,
enabling digital logic to process code executions. Historically,
electricity was first commecially transmitted by Thomas Edison, and
was a DC power line. However, this electricity was low voltage, due
to the inability to step up DC voltage at the time, and thus it was not
capable of transmitting power over long distances.
V =IR
P=IV = I2R
As can be seen in the equations above, power loss can be derived
from the electrical current squared and the resistance of a
transmission line. When the voltage is increased, the current
decreases and concurrently the power loss decreases exponentially;
therefore high voltage transmission reduces power loss. For this
reasoning electricity was generated at power stations and delivered
to homes and businesses through AC power. Alternating current,
unlike DC, oscillates between two voltage values at a specified
frequency, and it’s ever changing current and voltage makes it easy
to step up or down the voltage. For high voltage and long distance
transmission situations, all that is needed to step up or down the
voltage of the transformer. Developed in 1886 by William Stanley Jr.,
the transformer made long distance electrical transmission using AC
power possible.
Electrical transmission has therefore been mainly based upon
AC power, supplying most Nigerian homes with a 220 volt AC source.
It should be noted that since 1954 there have been many high
voltage DC transmission systems implemented around the globe with
the advent of DC/DC converters, allowing the easy stepping up and
down of DC voltages. Like DC power, there exist many devices such
as power tools, radios and TV’s that run off of AC power.
It is therefore crucial that both forms of electricity transmission
exist; the world cannot be powered with one simple form. It then
becomes a vital matter for there to exist easy ways to transform DC
to AC power and vice versa in an efficient manner. Without this
ability people will be restricted to what electronic devices they use
depending on the electricity source available. Electrical AC/DC
converters and DC/AC inverters allow people this freedom in
transferring electrical power between the two.
Offline / standby
Inverters and Applications
Power inverters are devices which can convert electrical energy of DC
form into that of AC. They come in all shapes and sizes, from low
power functions such as powering a car radio to that of backing up a
building in case of power outage. Inverters can come in many
different varieties, differing in price, power, efficiency and purpose.
The purpose of a DC/AC power inverter is typically to take DC power
supplied by a battery, such as a 12 volt car battery, and transform it
into a 220 volt AC power source operating at 50Hz, emulating the
power available at an ordinary household electrical outlet. Power
inverters are used today for many tasks like powering appliances in a
car such as cell phones, radios and televisions. They also come in
handy for consumers who own camping vehicles, boats and at
construction sites where an electric grid may not be as accessible to
hook into. Inverters allow the user to provide AC power in areas
where only batteries can be made available, allowing portability and
freeing the user of long power cords. However, most UPS units are
also capable in varying degrees of correcting common utility power
problems like:
1.
Power failure: defined as a total loss of input voltage.
2.
Surge: defined as a momentary or sustained increase in the
mains voltage.
3.
Sag: defined as a momentary or sustained reduction in input
voltage.
4.
Spikes, defined as a brief high voltage excursion.
5.
Noise, defined as a high frequency transient or oscillation,
usually injected into the line by nearby equipment.
6.
Frequency instability: defined as temporary changes in the
mains frequency.
7.
Harmonic sinusoidal waveform distortion: defined as a
departure from the ideal expected on the line
Factors to consider when designing an inverter is
 The input voltage
 The output voltage
 The frequency of the oscillators
 The rating of the load to be powered by the inverter
 The ampere range of the charging unit
 The cost of the construction
 The relative importance of the inverter
 The ampere ranger of the charging unit
 The cost of the construction
 The relative importance of the inverter at that time specification
 D.C input voltage (12V-24V)
 A.C output voltage (220v-240v)
 Output frequency (50Hz-60Hz)
 Output power (450-550)
 Maximum power (550)
 Continuous output power (500)
 Overload shutdown
 Low voltage shutdown
1.11 AIMS AND OBJECTIVES
The objective of this project may be summarized as listed below
 To give a brief introduction on what UPS.
 To highlight the basic components used in the construction of a
UPS and their functions .
 To describe the way in which there are designed and
 Finally to highlight its application and relevance in the society
1.12 SCOPE OF THIS PROJECT
This project research encompasses the features of the variety of the
components used in the construction of a UPS, their limitations and
favourable working conditions, and the application of inverter in
different field.
1.13 AVAILABILITY OF DESIGN MATERIALS
Materials used in the construction of this UPS are readily available in
electronic stores across the country and are also very affordable
depending on the rating of the UPS to be constructed.
CHAPTER TWO
2.10 LITERATURE REVIEW
2.11 WHAT IS A UPS?
Uninterruptible power supply (UPS), also uninterruptible power
source is an electrical apparatus that provides emergency power to a
load when the input power source, typically the utility mains, fails. or
when the line voltage varies outside normal limits.
2.12 WAVEFORMS
Waveforms refers to the shape of the wave output of a given input
wave on a given circuitry design. But in UPS, there are three basic
waveforms produced by the solid state components they include
The square wave
 The sine wave
 The modified sine wave
2.12.1
SQUARE WAVE
Square waves are nothing like sine waves to electrical equipment,
however. The ratio between peak and average voltage is exactly one
because the peak and average voltage are exactly the same. At a
given voltage, square waves pack more power than sine waves which
is not necessarily good. The greater output of square wave can lead
to overheating of transformers. The major disadvantage of this nonsinusoidal wave form is its inability to power several appliances.
2.12.2
MODIFIED SINE WAVE
This represents a compromise between the low harmonics of a true
sine and a true sine wave. This can be gotten by altering the square
wave so that its peak-to-average ratio approaches that of sine waves,
which helps minimize overheating. One straightforward way of
achieving that goal is by shortening the duty cycle of the square
wave.
2.12.4 TRUE SINE WAVE
The modern UPS technology produces waveform that are better and
same with that of the power delivered. Harmonics are virtually
eliminated. This UPS design type provides smooth continues power
with low noise and no voltage spikes which could affect performance
or ultimately damage expensive electronic equipment.
2.13 RESISTORS
All conductor excepts super conductors offer resistance to electric
current. Providing a given amount of resistances required in a circuit.
It requires the use of various types of transistors which are available.
They usually consist of a rod of insulating ceramic coated with a
metal film, the film forms a spiral track running from one end of the
resistor to the other which makes contact with the terminal wires at
each end.
Resistor can also be made to a very high degree of precision but
precision resistors are usually unnecessary in many UPS designs.
Resistors are manufactured with a quoted degree of precision known
as tolerance.
For example if a resistor is marked with a normal value 33 with a
tolerance of 5%
Therefore, we can say that 5% of 33 equals
5/100 x 33 = 1.65
Therefore the tolerance =33+1.65.
Many resistors are so small that it would be difficult to print their
value and % tolerance on their body in digits. To overcome this, a
coding system based on bands of distinctive colors was developed to
assist in identification. Learning this color code is not as necessary as
it used to be (thanks to accurate, low cost digital millimeters). The
first thing to know is that in each decade of resistance i.e., from 10100ohm, 100-ikohm, 1k-10ohm, etc. There are only a finite number
of different nominal values allowed.
Fig 2.1 Cross section a resistor wit its various tolerances
2.14 CAPACITORS
A capacitor can simply be said to be a device consisting of two
conducting surface separated by layer of an insulating medium called
a dielectric. The conducting surface may be in the form of either
circular plates or be of spherical or cylindrical shape. The main
function or purpose of a capacitor is to store electrical energy by
means of electrostatic stress in the dielectric.
Fig 2.14 a capacitor
One plate is joined to the positive end of the supply and the other to
the negative end or can be said to be earthed. It has been
experimentally found that in the presence of an earthed plate B,
plate A is capable of withholding more charge when B is not there.
Therefore when such a capacitor is put across a battery, there is a
momentary flow of electron from A to B. as negative electrons are
withdrawn from it, it becomes positively charged and as these
electrons collect on B it becomes negatively charged.
2.14.1 CAPACITANCE
The property of a capacitor to store electricity is or may be known as
its capacitance. As for example we may measure the capacity of the
mass in kilograms of water required in raising its level by one meter.
Therefore the capacitance of a capacitor is defined as the amount of
charge required to cerate a unit p.d. between its plates. Suppose we
give Q coulomb of charge to one of the two plate of capacitor and if
a p.d of V volts is established between the two then it capacitance
can be given as
C= Q/V
Where C is the capacitance of the capacitor
Q is the charge
V is the potential difference across the plates
Hence, capacitance can be said to be the charge required per unit
potential difference.
By definition the unit of capacitance is coulomb/volt which is also
called farad.
There are different types of capacitors employed in circuitry design
depending on their need they include the green cap capacitor, the
MKT capacitor, the monolithic capacitor, the ceramic capacitor and
the electrolytic capacitor. In this project design I made used of green
cap and electrolytic capacitors.
2.14.2 ELECTROLYTIC CAPACITOR
Electrolytic capacitors take advantage of the ability of some metal
oxides to act as an excellent insulator (at low voltage) and also form
a dielectric material with a very high dielectric constant K. Most
common electrolytic capacitors use aluminum oxide as the dielectric,
but special -purpose and low leakage types generally use tantalum
oxide. The main shortcoming of electrolytic capacitors.
2.14.2 ELECTROLYTIC CAPACITOR
Electrolytic capacitors take advantage of the ability of some metal
oxides to act as an excellent insulator (at low voltage) and also form
a dielectric material with a very high dielectric constant K. Most
common electrolytic capacitors use aluminum oxide as the dielectric,
but special-purpose and low leakage types generally use tantalum
oxide. The main shortcoming of electrolytic capacitors is that the
insulating and dielectric properties of the metallic oxides are polarity
sensitive. So most electrolytic capacitors must be connected into
circuit so that voltage is always applied to them with the correct
polarity (which is marked on their body). The only exception is non
polarized or bipolar (BP) electrolytes, which are effectively two
electrolytes in series back-to-back. Because the oxide dielectric layer
in electrolytic capacitors is extremely thin, these capacitors are more
prone to breakdown at higher voltages. So all electrolytes are clearly
marked in terms of their safe maximum operating voltage. In most
ceases electrolytes also have their capacitance value shown directly
on the case as well.
The three most common types of aluminum electrolytic in current use
are the axial-lead or RT type, the radial-lead or RB type (for vertical
mounting on PC boards) and the chassis-mounting or RG type. There
is also a variation on the RB type called the RP, with a third lead for
orientation and added support.
The most common type of tantalum electrolytic in current use is the
solid or TAG tantalum type, where the tantalum oxide dielectric is
formed on the surface of a solid block of sintered tantalum granules.
These capacitors provide low leakage and very high capacitance in a
very small volume, but are limited to quite low voltage. Typically less
than 33V.
The figure represents the different types of
capacitors ;electrolytic capacitors, greencap,
monolithic,ceramic,MKT
Fig 2.14.2 Capacitors
2.14.3. PLASTIC
FILM,
CERAMIC
AND
MONOLITHIC
CAPACITORS
Most of these types have their nominal value either printed directly
on them or use the EIA coding system which is a bit like resistor color
coding, but in digits. The first two digits followed by a multiplier
showing the number of zeroes. With this code the value is generally
given in pico farads (pF), which you will need to divide by either one
million or one thousand (respectively) if you want the value in
microfarads (nF). Hence a capacitor marked 104 has a value of 10
with 4 zeroes after it, or 100,000pF which is the same as 100nf.
Similarly 681 means 68 with a single zero or 680pF. While 472 means
47 with two zeroes or 4700pF (which is the same as 4.7nF).
2.15 DIODE
It is two terminal device consisting of a P-N junction formed either in
Ge or Si crystal. Its circuit symbol is shown below.
Anode
cathode
Fig 2.15 Circuit Symbol of a diode
The P and N type regions are referred to as anode and cathode
respectively. An arrow head indicates the direction of current flow
when forward biased. It is the same direction in which hole(+) flow
takes place. Commercially available diodes usually have means to
indicate which lead is P and which lead is N. By standards, a mark on
terminal indicates that the terminal is the cathode.
The low current diode whose body is about 3mm long can carry a
forward current of about 100mA, have saturation current of 5 micro
ampere at room temperature (250C) and can withstand a reverse
voltage of 75V without breaking down. The medium current diodes
can pass a forward current of about 500mA and can withstand a
reverse voltage of 250v.the high current diodes or power diodes can
pass a forward of many amperes and can survive several hundred
volts of reverse voltage.
2.15.1 MOUNTING A DIODE
Usually low and medium current diodes are usually mounted by
soldering their leads to the connecting terminals. The heat generated
by this diode is small enough to be carried away by air convection
and conduction along the connecting leads. However high current
stud-mounted diode generate large amount of heat for which air
convection is totally inadequate. Therefore for cooling they need heat
sink made of metals such as copper or aluminum which are good
conductors of heat. The sink absorbs heat from the device and then
transfers it to the surrounding air by convention and radiation since it
has large surface area. A P-N junction diode is one way device
offering low resistance when forward biased and behaving almost as
an insulation when reverse biased hence such diodes are mostly used
as rectifiers.
2.15.2 CHARACTERISTICS CURVES OF A DIODE
When the diode is forward biased and the applied voltage is
increased from zero, hardly any current flows through the device in
the beginning. It is so because the internal base voltage Vb whose
value is 0.7v for silicon and 0.3v for germanium. As soon as Vb is
neutralized, current through the diode increases rapidly with
increasing applied battery voltage. It is found that as little a voltage
as 1.0V produces a forward current of about 50mA. A burnout is
most likely to occur if the forward voltage is increased beyond a
certain safe limit.
2.15.3
IDEAL DIODE
There is no such thing as an ideal diode or a perfect diode. The
existence of such a diode is visualized simply as an aid in analyzing
the diode circuits.
An ideal diode may be defined as a two terminal device which
conducts with zero resistance when forward biased and appears as
an infinite resistance when reverse-biased. In other words, such a
device acts as a short-circuit in the forward direction and as an open
circuit in the reverse direction. Some type of dioxide use in the
design of inverter are the zener diodes and light sensible diodes
commonly known as LEDS.
2.15.4
LIGHT EMITTING DIODE
As the name implies it a forward biased P-N junction which emits
visible light when energized. As discussed earlier charge carrier
recombination takes place when electron from the N-side cross the
junction and recombine with the holes on the P-side now the
electrons are in the higher conduction band on the N-side. whereas
holes are in the power valence band on the P-side. During
recombination, some of the energy difference is given up in the from
of heat and light. But for Si and Ge junctions, greater percentage of
this energy is given up in the form of heat so the amount emitted as
light is insignificant.
There are two categories of LEDS which are the surface-emitting and
the edge-emitting LEDS.
The surface emitting LEDS emits light in a direction perpendicular to
the PN-junction plane. While the edge-emitting LEDS emit light in a
direction parallel to the PN junction plane.
Fig 2.15.4
a led
The forward voltage across a LED is considerably greater than that of
a silicon PN junction diode. Typically, the maximum forward voltage
for LED is between 1.2V and 3.2V depending on the device. Reverse
breakdown voltage for an LED is of the order of 3V to 10V. The LED
emits light in response to a sufficient forward current. Therefore it
can be said that the amount of power translated onto light onto light
is directly proportional to the forward current.
2.15.5 DIODES AS RECTIFIERS
Diodes can be connected in appalled to increase the current rating.
When this is done, small-value resistors are placed in series with
each diode in the set to equalize the current burden among the
diodes. Each resistor should have a voltage drop of about IV.
Fig 2.15.5 half-wave rectifier
2.15.5.1 HALF-WAVE RECTIFIER
In a half-wave rectifier circuit, the average output voltage is
approximately 45 percent of the rms ac input voltage, but the PIV
across the diode can be as much as2.8 times the rms ac input
voltage. It is a good idea to use diodes whose PIV ratings are at least
1.5 times the maximum expected PIV, therefore, with a half-wave
supply, the diodes should be rated for at least 4.2 times the rms ac
input voltage. Half-wave rectification has some shortcomings. First,
the output is difficult to smoothen-out because the waveform is so
irregular. Second, the output voltage tends to drop when the supply
is connected to a load (this can be countered to some extent by
means of a good voltage regulator). Third, half-wave rectification
puts a disproportionate strain on the power transformer and the
diodes. Half-wave rectification is useful in supplies that so not have
to deliver much current, or that do not need to be well regulated.
The main advantage of using a half- wave circuit in these situations
is that it costs a little less than full wave or bridge circuits.
Fig 2.15.5.1 Half Wave Rectifier
2.15.5.2 FULWAVE, CENTER-TAP RECTIFIER
A much better scheme for changing ac to dc is to both halves of the
ac cycle. Suppose you want to convert an ac wave to dc with positive
polarity, then you can allow the positive half of the ac cycle to pass
unchanged, and flip the negative portion of the wave upside-down,
making it positive instead. This is the principle behind full-wave
rectification. One common full-wave circuit uses a transformer with a
centre-tapped secondary, the centre tap, a wire coming out of the
exact middle of the secondary winding, is connected to common
ground. This produces out-of-phase waves at the ends of the
winding. These two waves can be individually at the ends of the
winding. These two waves can be individually half-wave rectified,
cutting off the negative half of the cycle. Because that wave are 180
degrees (half a cycle) out of phase, the output of the circuit has
positive pulses for both halves of the cycle. In this circuit has positive
pulses for both halves of the cycle. In this rectifier circuit, the
average dc output voltage is about 90 percent of the rms ac input
voltage. The PIV across the diodes can be as much as 2.8 times the
rms input voltage. Therefore, the diodes should have a PIV rating of
at least 4.2 times the rms ac input. The full –wave, center-tap
rectifier is kinder to the transformer and diodes than a half-wave
circuit. Furthermore, if a load is applied to the output of the full-wave
circuit, the voltage will drop much less than it would with a half-wave
supply because the output has more substance.
In
Out
Fig 2.15.5.2 a full-wave centre tap rectifier
2.15.6 FILTERS
Electronic equipment does not respond smoothly to the pulsating dc
that comes straight from a rectifier. The ripple in the waveform must
be smoothed out, so that pure, battery-like dc is supplied. The
simplest filter is one or more large-value capacitors, connected in
parallel with the rectifier output. Electrolytic capacitors are almost
always used. They are polarized; They must be hooked up in the
right direction. Typical values range in the hundreds or thousands of
microfarads. The more current drawn, the more capacitance is
needed for good filtering. This is because the load resistance
decreases as the current increases. The lower the load resistance,
the faster the filter capacitors will discharge. Larger capacitances hold
charge for a longer time with a given load.
Filter capacitors work by trying to keep the dc voltage at its peak
level. This is easier to do with the output of a full-wave rectifier as
compared with a half-wave circuit. The remaining waveform bumps
are the ripple. With a half-wave rectifier, this ripple has the same
frequency as the ac, or 60Hz. With a full-wave supply, the ripple is
120Hz that is double the supply frequency. The capacitor gets
recharged twice as often with a full-wave rectifier, as compared with
a half-wave rectifier. This is why the ripple is less severe, for a given
capacitance with full-wave circuits.
Fig 2.15.6 a simple filter
2.16 TRANSISTORS
A transistor is an electric component that has a base, emitter and
collector. In the UPS circuit layout, the transistor is used to generate
oscillation signal, amplification of signal and to switch on/off various
circuits.
2.16.1 TRANSISTOR AS A SWITCH
Switching is a very important process in the UPS. Inverter and other
electronic devices use common bipolar transistors and MOSFETs for
the switching operation. The job of a switch is to keep the flow of
current in a circuit in on or off condition. Mechanical switches are
very slow and they have sparking problems, this can be eliminated by
using electronic switches in a circuit.
When an electronic device such as common bipolar transistor or
MOSFET is used to switch on/off flow of current in a circuit that
device is said to be working as an electronic switch. Because of the
switching speed and other advantages mentioned above, the use of
electronic switching is increasing day by day. Let us see how a
transistor is used as a switch. When the base of the NPN transistor
receives enough biasing it switches on. This results in a current flow
from its collector to the emitter terminal.
Fig 2.16.1 Transistor as a switch
When the base biasing is removed, the transistor switches off and
the current flow stops. So by charging the base, the transistor can be
made to work as a switch. A figure presentation shown can be used
to understand this better. In this figure a lamp RL is used as load at
the collector of transistor TI. As shown in the figure A, when the
switch SI at base at base of TI is in off position transistor does not
receive base biasing.
This keeps the TI is off condition and the current will not flow from
collector. This keeps the bulb at the collector in off position. When
the switch SI is turned on, the base of TI receives enough biasing
and the TI switches on.
Fig 2.16.1 a transistor as a switch
Advantages of Electronic Switch
 Electronic switches are small in size and weight, compared to the
mechanical switch.
 Electronic switch does not have any moving parts; this eliminates
the problem of sparking etc.
 Electronic switch does not produce any sound/noise during
operation.
2.16.2 MOSFETS
The acronym MOSFET (pronounced “Moss-fet”) stands for metal
oxide-semiconductor
field-effect
transistor.
A
simplified
cross-
sectional drawing of an N-channel MOSFET, along with the schematic
symbol, is shown in fig. 216.2. The N-channel device is diffused into
a substrate of P-type semiconductor material. The P-channel device is
diffused into a subtract of N-type material.
Fig 2.15.2 A MOSFET
2.16.2.1 SUPER-HIGH INPUT IMPEDANCE
When the MOSFET was first developed, it was called an insulated-
gate FET or IGFET. This is perhaps more descriptive of the device
than the currently accepted name. The gate electrode is actually
insulated, by a thin layer of dielectric, from the channel. As a result,
the input impedance is even higher than that of a JFET; the gate-tosource resistance of a typical MOSFET is comparable to that of a
capacitor. This means that a MOSFET draws essentially no current,
and therefore no power, from the signal source. Some MOSFETs
have input resistance exceeding a trillion (10^12) ohms.
2.16.2.2 SETBACKS IN MOSFETS
The trouble with MOSFETs is that they can be easily damaged by
static electric discharges. When building or servicing circuits
containing MOS devices, technicians must use special equipment to
ensure that their hands do not carry static charges that might ruin
the components. If a static discharge occurs through the dielectric of
a MOS device, the component will be destroyed permanently. Warm
and humid climates do not offer protection against the hazard.
2.16.2.3 ITS FLEXIBILITY
In actual circuits, an N-channel JFET can sometimes be replaced
directly with an N-channel MOSFET; P-channel device can be similarly
interchanged. But the characteristic curves for MOSFETs are not the
same as those for JFETs. The main difference is that the junction in a
MOSFET is not a P-N junction. Therefore, forward breakover cannot
occur. An EG of more than 0.6V can be applied to an N-channel
MOSFET, or an EG more negative than 0.6V to a P-channel device,
without current leakage. The device will work positive gate biased as
well as with negative gate bias. A P-channel MOSFET behaves in a
similar way, being usable with either positive or negative EG.
2.16 OPTO-COUPLER
The optical coupler is a venerable device that offers the design
engineer new freedoms in designing circuits and system. Problems
such as ground loop isolation, common mode noise rejection, power
supply transformations, and many more problems can be solved or
simplified with the use of an optical coupler. Operation based on the
principle of detecting emitted light. The input to the coupler is
connected to a light emitter and the output is a photo detector, the
two elements being separated by a transparent insulator and housed
in a light-excluding package. There are many types of optical
couplers; for example, the light source could be an incandescent
lamp or a light emitting diode (LED). Also, the detector could be
photovoltaic cell, photoconductive cell, photodiode, phototransistor,
or a light–sanative SCR. By various combinations of emitters and
detectors, a number of different types of optical couplers could be
assembled. Once an emitter and detector have been assembled as a
coupler, the optical portion is permanently established so that device
use is only electronic in nature. This eliminates the need for the
circuit designer to have knowledge of optics. However, for effective
application, he must know something of the electrical characteristics,
capabilities, and limitations of the emitter and detector.
2.17.1 OPTO-COUPLER CHARACTERISTICS
The 4N35 is an optical coupler consisting of a gallium arsenide
(GaAs)
LED
and
a
silicon
characteristics
are
given
in
phototransistor.
the
following
The
coupler’s
sequence:
LED
characteristics, phototransistor characteristics, coupled characteristic,
and switching characteristics.
2.17.2 ITS INPUT
For most applications the basic LED parameters IF and VF are all that
are needed to define the input. Figure below shows these forward
characteristics, providing the necessary information to design the LED
device circuit. Most circuit applications will require a current limiting
resistor in series with the LED input. The circuit shown below is a
typical drive circuit.
Fig 2.17.2 OPTO-COUPLER’S INPUT
2.17.3
ITS OUTPUT
The output of the coupler is the phototransistor. The basic
parameters of interest are the collector current IC and collector
emitter voltage, VCE. The diagram below shows the circuit layout of
the opto-coupler.
Fig 2.17.3 Inputs and output circuit of an opto coupler
2.17.4 ITS OPERATING MODE
The two basic modes of operation are pulsed and linear. In the
pulsed mode of operation, the LED will be switched on or off. The
output will also be pulses either in phase or 1800 out of phase if the
collector is used and in phase if the emitter is used for the output. In
the linear mode of operation, the input is biased at dc operating point
and then the input is changed about this dc point. The output signal
will have an ac and dc component in the signal.
2.18 THE SG3524 INTEGRATED CIRCUIT
The SG2524 and SG3524 incorporate all the functions required in the
construction of regulating power supply, inverter, or switching
regulator on a single chip. They also can be used as the control
element for high-power-output applications. They also can be used
as the control element for high-power-output applications. The
SG2524 and SG3524 were designed for switching regulators of either
polarity, transformer-coupled dc-to-dc converters, transformer less
voltage doublers, and polarity convert applications employing fixed48
frequency, pulse-width-modulation (PWM) techniques. The
complementary output allows either single-ended or push-pull
application. Each device includes an on-chip regulator, error
amplifier, programmable oscillator, pulse-steering flip-flop; two
uncommitted pass transistors, a high-again comparator, and currentlimiting and shut circuitry. The SG2524 is characterized for operation
from - 250c to 850c and the SG3524 is characterized for operation
from 00C to 700C
2.18.1 OPERATING PRINCIPLE OF SG3524
The SG2524 is a fixed-frequency Pulse-width-modulation voltage
regulator control circuit. The regulator operates at a fixed regulator
control circuit. The regulator operates at a fixed frequency that is
programmed by one timing resistor, RT, and one timing capacitor,
CT. RT establishes constant charging current for CT. This result in a
linear voltage ramp at CT, which is fed to the comparator providing
leaner control of the output pulse duration (width) by the error
amplifier. The SG2524 contains an onboard 5-V regulator that serve
as a reference, as will as supplying the SG2524 internal regulator
control circuitry. The internal reference voltage is divided externally
by a resistor ladder network to provide a reference within the
common-mode range of the amplifier as shown in figure 6 or an
external reference can be used. The output sensed a second resistor
divider network and the linear signal is amplified. This voltage is then
compared to the linear ramp at CT. The resulting modulated pulse
out of the high-gain comparator is then steered to the appropriate
output pass transistor (Q1 or Q2) by the pulse-steering flip-flop,
which is synchronously toggled by the oscillator output. The oscillator
output pulse also serve as blanking pulse to ensure both output are
never ON simultaneously during the transition times. The duration of
the blanking pulse is controlled by the value of CT. The outputs may
be applied in a push-pull configuration in which their frequency is half
that of the base oscillator, or paralleled for single-ended applications
in which the frequency is equal to that of the oscillator. The output of
the error amplifier shares a common input to the comparator with the
current-limiting and shut-down circuitry and can be overridden by
signals from either of these inputs. This common point also is
available externally and can be employed to control the gain, to
compensate the error amplifier, or to provide additional control to the
regulator.
CHAPTER THREE
3.10 METHODOLOGY
The approach adopted in the project work is a study of the material that
relates to the design of the UPS. The main aim relying mostly on articles and
scientific materials for the design of the inverter, and in most cases the
contemporary authors of these theories have tested and proven these designs
which are adopted today.
In my research the following or electrical measuring instruments were used
in order to achieve a calibrated process and a lasting design. Theses devices
are discussed briefly below, they include
 electronic work bench software
 Galvanometer
 Oscilloscope
 Volt meter
 Amp meter
 Watt meter
3.11 ELECTRONIC WORKBENCH
The Electronic Work bench is a simulation soft ware which runs on almost
any windows platform and be used to design and simulate a circuitry to see
if there are errors in the design layout. In this tool, a signal source can be
attached to the input and when switched ON, the output waveform can be
viewed on an oscilloscope plot on the screen of the computer. It is very
essential tool for designing and test-running circuitry before the main
construction process can start. It is also a known fact that when a workable
design has been accomplished, 70% of the job is said to be done.
3.12 GALVANOMETER
Early Scientists Experimenting on electricity and magnetism noticed that an
electric current produces a magnetic field. This discovery was probably an
accident, but it got the curiosity of scientist. When a magnetic compass is
placed near a wire carrying a direct electric current, the compass does not
point toward magnetic north, the needle is displaced. The extent of the error
depends on how close the compass is brought to the wire, and also on how
much current the wire is carrying. Scientific experimenters are like children.
They first observed, the scientist tried different arrangements to see how
much the compass needle could be displaced, and how small a current could
be detected. An attempt was made to obtain the greatest possible currentdetecting sensitivity. Wrapping the wire in a coil around resulted in a device
that would indicate a tiny electric current. This effect is known as galvanism,
and the meter so devised was called a galvanometer
Fig 3.12 a galvanometer
In the circuit arrangement shown above, the galvanometer output is obtained
be varying the potentiometer. In the design of the UPS the actual output
voltage across a potentiometer can be achieved be varying the galvanometer
by connecting the potentiometer as shown above.
3.13 OSCILLOSCOPE
This measures and records quantities that vary rapidly at rates of hundreds,
thousands, or millions of times per second. It creates a “graph” by throwing
a beam of electrons at a phosphor screen. A cathode-ray tube, similar to the
kind in a television seat, is employed. Oscilloscopes are useful for looking
at the shapes of signal waveforms, and also for measuring peak signal levels
(rather than just the effective levels). An oscilloscope can also be used to
approximately measure the frequency of a waveform.
The horizontal scale instantaneous shows time, and the vertical scale shows
instantaneous voltage. An oscilloscope can indirectly measure power or
current, by using a known value of resistance across the input terminals.
Technicians and engineers develop a sense of what a signal waveform
should look like, and them they can often tell, by observing the oscilloscope
display, whether or not the circuit under test is behaving the way it should.
This is a subjective kind of measurement, since it is qualitative as well as
quantitative.
If a wave shape looks wrong, it might indicate distortion in a circuit, or
possibly even cause a burned-out of component someplace. In this design I
used the oscilloscope on the electronic workbench in circuit stimulation.
3.14 VOLTMETER
Current is a flow of charge carriers. Voltage, or electromotive force (EMF),
or potential difference, is the “pressure” that makes a current possible. Given
a circuit whose resistance is constant, the current that will flow in the circuit
is directly proportional to the voltage placed across it. Early electrical
experimenters recognized that an ammeter could be used to measure voltage,
since an ammeter is a form of constant–resistance circuit. If you connect an
ammeter directly across a source of voltage a battery, the meter needle will
deflect. In fact, a millimeter needle will probably be “pinned” if you do this
with it, and a micrometer might well be wreaked by the force of the needle
striking the pain at the top of the scale.
For this reason, you should never connect millimeter or micro ammeters
directly across voltage sources. An ammeter, perhaps with a range of 0-10
A, might not deflect to full scale if it is placed across a battery, but it is still a
bad idea to do this, because it will rapidly drain the battery. Some batteries,
such as automotive lead-acid cells, explode under these conditions.
This is because all ammeters have low internal resistance. They are
designed that way deliberately. They are meant to be connected in series
with other parts of a circuit, not right across the power supply.
But if you place a large resistor in scribes with an ammeter, and then
connect the ammeter across a battery or other types of power supply, you no
longer have a short circuit. The ammeter will give an indication that is
directly proportional to the voltage of the supply. The smaller the full-scale
reading of the ammeter, the larger the resistance to get a meaningful
indication the meter. Using a micro ammeter and a large value of resistor in
series, a voltmeter can be devised that will draw only a little current from the
source. It is always good when a voltmeter has a high internal resistance.
The reason for this is that you don’t want the meter to draw much current
from the power source. This current should go, as much as possible, towards
working whatever circuit is hooked up to the supply, and not into just getting
a reading of the voltage. Also, might not want, or need, to have the voltmeter
constantly connected in the circuit. You do not want the behavior of the
circuit to be affected the instant you connect the voltmeter to the supply. The
less current a voltmeter draws, the less it will affect the behavior of anything
that is working from the power supply.
Fig 3.14 a diagram of a Voltmeter
In this project work the voltmeter is place or installed across the out put of
the UPS to display the output potential at all time.
3.15 AMP METER
Sometimes, it is desirable to have an ammeter that will allow for a wide
range of current measurements. The full-scale deflection of a meter
assembly cannot easily be changed, since this would mean changing the
number of coil turns and/or the strength of the magnet. But all ammeters
have a certain amount of internal resistance. If a resistor, having the same
internal resistance as the meter, is connected in parallel with the meter, the
resistor will take half the current. Then take twice the current through the
assembly to deflect the meter to full scale, as compared with the meter alone.
By choosing a resistor of just the right value, the full-scale deflection of an
ammeter can be increased by a factor of 10, or 100, or ever 1000. This
resistor must be capable of carrying the current without burning up. It might
have to take practically all of the current flowing through the assembly,
leaving the meter to carry only 1/10,or 1/100 of the current. This is called a
shunt resistance or meter shunt. Meter shunts are frequently used when it is
necessary to measure very large currents, such as hundreds of amperes. They
allow micro ammeters or millimeter to be used in a versatile millimeter, with
many current ranges.
3.16 WATTMETER
The measurement of electrical power requires that voltage and current both
be measured simultaneously. Remember that power is the product of the
voltage and current. That is, watts (P) equals volts (E) times amperes (I),
written as p= EL In fact, watts are sometimes called volt-amperes in a dc
circuit. You might think that you can just connect a voltmeter in parallel
with a circuit, thereby getting a reading of the voltage across it, and also
hook up an ammeter in series to get a reading of the current through the
circuit, and then multiply volts time's amperes to get watts consumed by the
circuit Infact, for practically all dc circuits, this is an excellent way to
measure power.
In this design, wattmeter of the above principle was used to determine the
power in watts that the inverter may be able to accommodate from the
diagram shown below
wattmeter
fig 3.5 diagram of a wattmeter arrangement
an electric iron might consume 1000 W, or a current of 1000/117 = 8.55 A.
and a large heating unit might gobble up 2000 W, requiring a current of
2000/ 117 = 17.1 A. this might below a fuse or breaker, since these devices
are often rated for only 15 A. you have probably had an experience where
you hooked up too many appliances to a single circuit, blowing the fuse or
breaker. The reason was that the appliances, combined, drew too much
current for the house wiring to safely handle, and the fuse or breaker,
detecting the excess current, opened the circuit.
3.17 MULTIMATE’S
In the electronics lab, a common piece of test equipment is the millimeter, in
which different kinds of meters are combined into a single unit. The voltohm-millimeter (VOM) is the most often used. As its name implies, it
combines voltage, resistance and current measuring capabilities. You should
not have too much trouble envisioning how a single millimeter can be used
for measuring voltage, current and resistance. The preceding discussions for
measurements of these quantities have all included method in which a
current meter can be used to measure the intended quantity. Commercially
available multimeters have certain limits in the values they can measure.
The maximum voltage is around 1000 V; larger voltages require special
leads and heavily insulated wires, as well as other safety precautions. The
maximum current that a common VOM can measure is about 1 A. the
maximum resistance is on the order of several mega ohms or tens of mega
ohms. The lower limit of resistance indication is about an ohm.s
CHAPTER FOUR
4.10 Designs and the construction of a ups
4.11 Complete circuit diagram of ups
4.12 Stage by stage design is divided into five sections, they are
 The oscillator section.
 The device/switching section.
 The output section.
 The change over section.
 The low battery cut-off section
4.12.1 OSCILLATOR SECTION
THE IC SG3524 is used in the oscillation section of this UPS. This IC
is used to generate the 50Hz frequency required to generate AC
supply by the inverter. To start this process, battery supply is given
to the pin-15 of the SG324 through on/off switch which passes
through the normally close contact of the relay. Pin-8 is connected to
the negative terminal of the battery. A voltage regulator LM7812 is
connected across the battery through two capacitors connected in
parallel and grounded as shown in the circuit below. This regulates
the 12V supply from the battery.
Pin-5 and 7 of the IC are the oscillation section pins. The frequency
produced by the IC depends on the value of the capacitor and
resistor connected at these pins. The two capacitors (each 0.1 uf) are
connected to pin-7. These capacitors decide the 50Hz frequency
output by the IC. Pin-5 is timing resistance pin. The resistance at this
pin keeps the oscillator frequency constant. Preset variable resistor
is connected to ground from pin-6 of the IC this preset is used so
that the value of the output frequency can be adjusted to a constant
50Hz. A fixed resistor of is connected in series with the variable
resistor to give a given frequency as shown by the relation:
F=1.30/RT*CT
Where F is the frequency in KHz
RT is the total resistance at pin-6
CT is the total capacitance at pin-7
Therefore to obtain a frequency of 50Hz
Given CI +C2 =CT
CT=0.1+0.1=0.2
Making RT subject formula
Therefore we have that RT=1.31/0.05*0.2
RT=1.31/0.01=131K
Therefore we have that RT must be varied at 131k to obtain a
frequency of 50Hz.
In my design I a fixed resistor of 100K and a variable resistor of 20k.
Signal generated at the oscillator section of the IC reaches the flipflop section if the IC. This section converts the incoming signal into
signal with changing polarity. This signal with changing polarity
means that when the first signal is positive the second would be
negative and when the first signal goes negative the second would
be positive.
Therefore to achieve a frequency of 50Hz this process most repeat
50 times per second at a regular interval i.e an alternating signal with
50Hz frequency is generated inside the flip-flop section of the IC.
This 50Hz frequency alternating signal has an output at pin-11 and
14 of the IC. This alternating signal may also be known as the MOS
drive signal. This MOS drive signal at pin-11 and 14 are between 34V. Voltage at these pins should be same, because any variation in
the voltage at these pins could damage the MOSFET at the output.
The circuit diagram of the oscillation section is shown below.
1.2K
4v
6v
47uf
5K
8
5
7
6
1.2k
1k
22uf
10k
3
100k
47 
10k
1
104uf 2
16
15
OSC14
4
5
13
12
6
OSC11
10
9
7
8
Pin 3 Pre – Driver
4.7K
Pin 5 Pre – Driver
102uf
Fig4.12.1 oscillator circuit
4.7uf
4.12.2 DRIVER/ SWITCHING SECTION
The MOS drive signal from the pin-11 and 14 of the IC are given to
the base of the transistor T1 and T2. This results in the MOS drive
signal getting separated into two different channels. Transistor T1
and T2 amplify the 50Hz MOS drive signal at their base to a sufficient
level and output them from the emitter while the collector are
grounded.
50Hz signal from the emitter of T1 is given to the gate of each
MOSFET in the MOSFET channel, through resistance RA4-2K. Each
MOSFET gate receives the 50Hz signal through a resistor (RA6-RA9).
And also 50Hz signal from the emitter of T2 is given to the gate of
each MOSFT in the second MOSFET channel, through resistance
RA19-2K. Each MOSFET gate receives the 50Hz signal through a
resistor (RA14 –RA17). When the first MOSFET is on, the current
flows through the first half of the inverter transformer bifilar winding.
When the second MOSFET channel turns ON, the current flows
through the second half of the inverter transformer winding. This
switching on/off of the MOSFET channels will start an alternating
current in the bifilar winding of inverter transformer. This AC current
in the bifilar winding will induce an AC current of 50Hz, in the 220
and 240v tapings of the transformer. The AC voltage output from the
transformer is connected to the normally close of the relay to the
output socket. This can be shown by the circuit below.
Fig 4.12.2 drive/switching section
4.12.3 THE OUTPUT SECTION
The 50Hz alternating MOS drive signal reaches each MOSFET channel
separately. This result in the MOSFET channels being alternating on
and off i.e. when the first channel is ON the second channel will be
OFF, and when the second channel is ON, the first will be OFF. This
on/off switching is repeated 50 times per second. The drain (D) of all
the MOSFETs of one channel is connected together and one end of
the inverter transformer’s bifilar winding is connected to this
connection. Likewise the drain of the MOSFET of the second channel
is also connected together and the other end of the inverter
transformer’s bifilar winding is connected to this connection. The
position terminal of the battery is connected to the center tapping of
the bifilar winding. This results in the positive supply reaching drain
of each MOSFET transistor through each end of the bifilar winding.
Source (S) terminal of each MOSFET is connected to the negative
terminal of the battery through a shunt of low value resistance.
Because polarity of the 50Hz MOS drive signal at pin-11 and 14 are
different, at a time only one channel from the output channel
remains ON, the other channel stays OFF.
4.12.4 THE CHANGEOVER SECTION
The changeover section is used to

Switch on the inverter when the AC mains supply switches
off and

Switch off the inverter when the AC mains supply returns.
When the UPS receives AC mains supply, it stops drawing the
battery supply, and the AC mains supply at the UPS input is
directly sent to the UPS output socket.
The change over circuit adopted for this design is very simple. It
consists of 12V step down transformer. This change over as the
name implies can be divided into two states i.e when there is Power
supply from AC source the inverter would be switch off and
When there is no supply it goes back and switches the inverter.
This process happens like this, when there is AC supply, the oscillator
which is connected to the output of the normally close of the relay
connects the oscillator with power sources and the switching process
starts. But when power supply comes back on, a 12V signal is sent to
the coil of the relay through the diodes D1 and D2. The common of
transformer is connected to the negative terminal of a 220uf
capacitor and the positive terminal is connected to the cathode of D1.
The coil energizes in the process and contacts the normally open the
relay thereby connected the load to the AC supply.
During this process a 12V signal is sent to the shutdown pin of the IC
SG3524 to shutdown the inverter and hence stop its switching
process. This is shown by the circuit bellow
220k
1
2
N
3
4N35
L
6
VCC
5
4
IN4007
BD135
.
.
RELAY
Fig 4. 12. 4 changeover circuit of the UPS
4. 12.5 THE LOW BATTERY CUT-OFF SECTION
When the battery becomes discharged i.e. the battery voltage falls
below a set voltage level, the UPS should switch off cause if the it
continues to draw current from a discharges battery, the battery will
get damaged.
Therefore to switch off the UPS in low-battery condition, a low
battery cut circuit is put to use. This circuit is made of pin-2,3 and 4
of an IC2 (LM339). Pin-4 of the IC2 is given a 5V reference voltage
goes below a set point,pin-2 of the IC2 outputs a low-battery signal.
This low battery signal is uses to drive T15 and SCR T10 (XL08), and
sends a shut down signal at the shutdown pin-10 of PWM controller
IC(SG3524).
When the PWM controller IC2 receives low-battery shutdown signal
at its pin-16, its oscillation section stops the operation and the UPS
will automatically shutdown as shown by the circuit below
12v
v
100 
Pin 16 (OSC)
47K
Pin 10 (OSC) short down
10K
2
v
47k
lv
4
3
1
.
12 v
Fig 4.12.5 low battery cut-off circuit
4.13 COMPONENT JUSTIFICATION
I would like to explain the reason for using some of those
components in my design work.
44.13.1 MOSFETS
MOSFETS are used in the design in place of bipolar junction
transistors in building inverters and UPS because
 MOSFETS device can work on very small drive power whereas
bipolar transistors require large drive power for its operation.
 Safe operating area of MOSFET is larger than that of bipolar
transistor, because of this, MOSFET devices do not get easily
damaged.
 The temperature affects switching time of bipolar transistor
whereas temperature has very little effect on MOSFET devices.
A MOSFET device can withstand higher peak current compared to
the bipolar transistor.
4.13.2 SG3524 OSCILLATOR
The SG3524 oscillator was used in this design due to its steady
oscillatory characteristic that gives out a steady pulse at the output
of the driver circuit. It is known to give a constant pulse of 4V at pin-
11- 14 that helps to reduce sparks delay in the output that could
affect the MOS switch.
4.13.3 OPTO-COUPLER
The opto-coupler was adopted in the design mainly because of its
flexibility and most importantly its sensitivity to signal from an input
potential to the phototransistor.
4.13.4 RESISTORS
Fixed and variable resistors where used in this design to help finetune the output of the oscillator to a constant 50Hz frequency.
4.14 TEST AND ANALYSIS
Before a new UPS is assembled, it needs to be tested properly; its
various presets should be set properly.
When testing a UPS, one should test its inverter section (the section
which operates on battery supply) first. Next, is the charging section
(section which operates on AC mains supply). Requirement for the
testing inverter section:
 Connect a fully charged battery to the inverter
 A current meter or ampere meter is required to check the load
current and charging current. For this, connect a 50 Amp
Meter in series between the positive terminal of inverter.
 Connect a 0 -300V AC voltmeter parallel to the inverter output
socket.
 To check the AC supply frequency of inverter output, connect a
frequency meter parallel to the output socket
4.14.1 TESTING AND SETTING THE INVERTER SECTION
 Remove the battery wires from this section.
 Outer ends of 12-0-12 winding 0f inverter–cum charger
transformer are connected to the heat sink. Remove these
connections from the heat sink. Now, if the battery is
reconnected, MOSFET drains will not receive any battery
supply.
 Reconnect the battery
 Remove the 3- pin MOSFET drive connector between the
mains PCB and the MOSFET PCB.
 Do not connect the inverters mains supply from reaching the
inverter.
Without AC mains supply, 220V/18V transformer will not
produce the 18V AC supply. Without 18V AC supply, 12V
Regulated DC supply is not produced and the charging circuit
will not operate.
 Switch on the inverter switch. 12V supply from battery will
reach pin -15 of IC (SG3524).
 If the oscillator section is operating, pin -11 and 14 should have
equal MOS drive voltage
 To check the MOS drive voltage, set the millimeters at 10V AC
range, and check the voltage between pin – 11 of IC2 ground.
Multimeter should show a voltage between 4V- 5V
 Voltage at pin – 11 and 14 should be equal
 If these voltage are OK then reconnect the 3-pin connector
between the mains PCB and the MOSFET
 Make sure that the voltage at pin- 11 and 14 of 1C2 (SG3524)
should be equal. If there is difference in the voltage on these
pins, or if the MOS drive voltage is missing, then there is some
fault in the circuit.
 If the MOS drive voltage is OK at pin – 11 and 14 of 1C2 then
check the MOSFET transistor gates for MOS drive voltage.
 If the MOS drive voltage is missing from all the MOSFET gates,
then check that the 3- pin connector joining the output plate
with MOS drive signal
 If the MOS drive signal is missing from one of the MOSFET gate
then check the 22E resistance at the gate.
 If the MOS drive signal is missing from all the MOSFETs in one
channel, then check the transistors and other components in
that channel.
 When proper MOS drive signal is available at the gate of all the
MOSFET transistors of both channels, switch off the inverter
 Remove the battery connection
 Reconnect the end points of 12-0-12 inverter cum-charger
transformer to the heat sinks, i.e. to the MOSFET drain.
 Keeping the inverter on/off switch in off position connect the
battery to the inverter.
 Connect the voltmeter and frequency meter to the inverter
output. Connect two 100W/ 250 V bulbs to the UPS output
socket.
 Switch on the UPS. If the bulb starts to glow, the UPS is
working properly. All the components of the UPS MOSFET
transistor, relay, inverter transformer, changeover circuit, etc.
are working properly.
 If the bulb does not glow than check the inverter transformer
for 220V AC supply.
 270V tapping of inverter transformer is connected to the N/O-2
terminal of relay. Check the AC supply by keeping the
Multimeter in 250V AC range.
4.15 BILL OF ENGINEERING MEASUREMENT AND
EVALUATION
S/NO Item Specification
Quantity
Unit cost
Total cost
1
RESISTORS
20
N5
N 100
2
Capacitor 10 uf
2
N20
N 40
3
Capacitor 0.1uf
6
N20
N 120
4
Capacitor 47 uf
2
N20
N 40
5
10000uf 35v capacitor
2
N 80
N 160
6
MOSFET IRT 3205
2
N 200
N 400
7
Transformer step-up
1
N 3000
N 3000
8
220-12v step-down
1
N 500
N 500
2
N 300
N600
N 250
N250
Transformer
9
Relay
10
Connecting Wires
11
A digital multi meter
1
N 900
N 900
12
A voltmeter
1
N 150
N150
13
AC socket
1
N100
N 100
14
Transistor BC557B
3
N 50
N50
15
Battery IC
1
N 3000
N3000
16
SG3524 IC
1
N 600
N600
17
Opto coupler 4N35
1
N 250
N250
18
Rocker on/off switch
1
N 50
N50
19
Transport
N 300
N300
20
Variable resistor
2
N 20
N40
21
Vero board
2
N 200
N200
N10,850.00
TOTAL COST
CHAPTER FIVE
5.10 CONCLUSION
It is obvious that UPS are indispensable power units in virtually every
scale of establishment. Its features such as noiseless working
condition, availability of storage elements, numerous
system
compatibility etc, have not in any way marred its acceptance. This
device is really dominating in computer establishment but in no due
time will find use in many other applications where it is still under
consideration.
5.11 RECOMMENDATION
I strongly recommend a restructuring in our department’s project
condition. I think conducting these project in group will give a room
for wider and in-depth research, sharing of ideas between group
members and taking and non-execution of infant projects or better
still low-grade projects.
BIBLIOGRAPHY.
Edward
Hughes.(1997), Electrical Technology. Addison –Wesley
Publishers,7th edition.
BL.THERAJA.(2000).A Textbook of Electrical Technology S. Chand &
Company, New Delhi.
Deboo,
G.J
and
C.N.
Burro.(1971)
integrated
Circuits
and
Semiconductors Devices Thorny and Application. New York:
McGraw-Hill.
Horowitz,P, Klinfield, H. (1995).The Art of Electronics. Cambridge
University Press, London.
Sloich Matsumoto.(2000). Understanding and Using DC-AC Inverters.
Jay car Electronics. New York.
Kelvin R. Sullivan(1992) Mosfets devices ,Physics and operation IEEE
Trans. New York: McGraw-Hill.