ACKNOWLEDGEMENT

I take this opportunity to present my votes of thanks to all those guideposts who really
acted as lightening pillars to enlighten my way throughout this project that has led to
successful and satisfactory completion of this study.

I am really grateful to Dr.Narbada Prasad Gupta for providing me with an

opportunity to undertake this project and providing me with all the facilities. I am
highly thankful to sir for his active support, valuable time and advice, whole-hearted
guidance, sincere cooperation and pains-taking involvement during the study and in
completing the assignment of preparing the said project within the time stipulated.

Lastly, I am thankful to all those, particularly the various friends , who have been
instrumental in creating proper, healthy and conductive environment and including
new and fresh innovative ideas for me during the project, without their help, it would
have been extremely difficult for me to prepare the project in a time bound framework.
 ABSTRACT

Variable power supply with digital control through voltmeter display is the most frequently
used device in electronics workshops and laboratories is a universal power supply that
provides a variable, fluctuation-free output. Here we present a variable power supply with
digital control that is simple and easy to construct. The circuit is built around an adjustable 3-
terminal positive-voltage regulator IC LM317T. The AC main supply is stepped down by
transformer x1 to deliver a secondary output of 12V-0-12V AC, 1A. The output of the
transformer is rectified by a full-wave rectifier comprising diodes D1 through D4. Capacitor
C1 and C2 are connected to rectifier diodes to bypass undesired spikes and provide smooth
and fluctuation-free power. By using a properly calibrated digital multimeter you can easily
adjust the presets to obtain 1.5V to 12 V. Assemble the circuit on any general-purpose PCB
and enclosed it in a suitable cabinet. Use suitable heat-sink for regulator IC.
 CONTENTS

Acknowledgement ...... (i)

Abstract …… (ii)
Contents ……... (iii)
Introduction .…....... 01
Project Description .……… 02
Working .……. (a)
Circuit Diagram ……...(b)
Block Diagram …….(c)
Component Required ……(d)
Component Description …...….(e)
Result & Discussion ………. 03
Conclusion .……… 04
Reference ………. 05
 INTRODUCTION

The project Variable regulated power supply plays a very important role in the laboratory
functions and that is mainly to the electronics laboratory. As in electronics all the
instruments, components work on a particular regulated dc supply, so a project which an
provide this supply by converting the alternating current to direct current that too into a great
range of regulated power keep its own preference. As it can produce a range of 0- 13.5V
direct current by regulating and converting alternating current is has a vast application too.
Such converters are also known as SMPS (Switch mode power supply). AC to DC converters
generally comprise a rectifier bridge to rectify the AC current of the input line and a
regulating device supplying on output of one or more regulated DC voltages. Just the simple
ac current is applied and through potentiometer you get the desired regulated dc power
supply.
All circuits require some source of power to operate and the most convenient source of such
power in an AC outlet. Unfortunately, many electronics circuits cannot make use of ac
directly such as the mobile phone, laptop, radio, etc. Instead, some way to convert the ac to
dc is required. Sometimes, the source of dc power for electronic equipment is a battery, but
more usually, the power is obtained from a unit that converts the normal single phase ac
mains supply (240V at 50Hz) to some different value of dc voltage. The function of power
supply are to provide necessary dc voltage and current, with good stability and regulation. In
other words it must provide a stable dc output voltage, irrespectively of changes in the mains
input voltage and of changes in the load current.
A further important requirement of a modern unit is that it should be able to limit the
available output current in the event of an overload (current limiting) and also limit the
maximum output voltage. Damage to sensitive components, such as IC, in the instrument can
easily occur if excessive appears on the power supply lines.
 PROJECT DESCRIPTION

a. WORKING

The 11OV-AC coming from the power cord is fed to the transformer TR1 via the on-off
Switch and the 500mA fuse. The 30v ac output (approximately) from the transformers
presented to the BR1, the bridge-rectifier, and here rectified from AC (Alternating Current) to
DC (Direct Current). If you don’t want to spend the money for a Bridge Rectifier, you can
easily use four general purpose 1N4004 diodes.
The pulsating DC output is filtered via the 2200mF capacitor (to make it more
Manageable for the regulator) and fed to IN-put of the adjustable LM317 regulator
(IC1). The output of this regulator is your adjustable voltage of 1.2 to 30 volts varied
via the Adj pin and the 5k pot meter Pl. The large value of C1 makes for a good,
low ripple output voltage.
Why exactly 1.2V and not 0-volt? Very basic, the job of the regulator is two-fold; first,
it compares the output voltage to an internal reference and controls the output voltage
so that it remains constant, and second, it provides a method for adjusting the output
voltage to the level you want by using a potentiometer. Internally the regulator uses a
zener diode to provide a fixed reference voltage of 1.2 volt across the external
resistor R2. (This resistor is usually around 240 ohms, but 220 ohms will work fine
without any problems.

Because of this the voltage at the output can never decrease below 1.2 volts potentiometer
(Pl) increases in resistance the voltage across it, due to current from the
regulator plus current from R2, its voltage increases. This increases the output

Dl is a general purpose 1N4001 diode, used as a feedback blocker. It steers any

current that might be coming from the device under power around the regulator to
prevent the regulator from being damaged. Such reverse currents usually occur when
devices are powered down.

The ON Led will be lit via the 18k resistor Rl. The current through the led will be
between 12-2OmA @ 2V depending on the type and colour Led you are using.

C2 is a 0.1 mF (l00nF) decoupler capacitor to filter out the transient noise which can be
induced into the supply by stray magnetic fields. Under normal conditions this capacitor
is only required if the regulator is far away from the filter cap, but I added it anyway.

C3 improves transient response. This means that while the regulator may perform
perfectly at DC arid at low frequencies, (regulating the voltage regardless of the load
current), at higher frequencies it may be less effective. Adding this1uF capacitor
should improve the response at those frequencies.
b. CIRCUIT DIAGRAM

c. BLOCK DIAGRAM
d. COMPONENTS REQUIRED

1. Capacitor (C1) = 4700uf, 25V

2. Capacitor (C2) = 1uf, 63V
3. Capacitor (C3) = 10uf, 63V
4. Resistor (R1) = 3.3k
5. Resistor (R2) = 240 ohms
6. 5k Potentiometer
7. 230V Switch
8. 3V Led
9. Diode ( 1N4007 )
10. Transformer (Step down) =12V or 24V (1A)
11. Box
12. PCB Board
13. Banana Cable
14. Potentiometer Knob
15. LM317T (Voltage Regulator)
 COMPONENTS DESCRIPTIOPN

1. LM317T (Voltage Regulator)

The LM317 series of adjustable 3-terminal positive voltage regulators is capable of supplying
in excess of I.5A over a 1.2V to 37V output range. They are exceptionally easy to use and
require only two external resistors to set the output voltage. Further, both line and load
regulation are better than standard fixed regulators. Also, the LM317 is packaged in standard
transistor packages which are easily mounted and handled. In addition to higher performance
than fixed regulators. The LM3I7 series offers full overload protection available only in IC’s.
Included on the chip are current limit, thermal overload protection and safe area protection.
All overload protection circuitry remains fully functional even if the adjustment terminal is
disconnected.
Normally, no capacitors are needed unless the device is situated more than 6 inches from the
input filters capacitors in which case an input bypass is needed. An optional output capacitor
can be added to improve transient response. The adjustment terminal can he bypassed to
achieve very high ripple rejection ratios which are difficult to achieve its standard 3-
terminal regulators. Besides replacing fixed regulators. The LM3I7 is useful in a wide variety
of other applications. Since the regulator is floating and sees only the input-to-output
differential voltage, supplies of several hundred volts can be regulated as long as the
maximum input to output differential is not exceeded. i.e., avoid short-circuiting the output.
Also, it makes an especially simple adjustable switching regulator, a programmable output
regulator, or by connecting a fixed resistor between the adjustment pin and output, the
LM317 can be used as a precision current regulator. Supplies with electronic shutdown can
be achieved by clamping the adjustment terminal to ground which programs the output to
1.2V where most loads draw little current. For applications requiring greater output current.

2. TRANSFORMER 230/(12V-0- 12V)

A transformer is a device that transfers electrical energy from one circuit to another through
inductively coupled conductors the transformer’s coils or “windings”. Transformer is used
here to step down the supply voltage to a level suitable for the low voltage components.
The transformer used here is a 230/(12V-0- 12V) step down transformer.
 3. RESISTOR

A resistor is a two-terminal electronic component designed to oppose an electric

current by producing a voltage drop between its terminals in proportion to the current, that is,
in accordance with Ohm’s law: V = IR. The resistance R is equal to the voltage drop V across
the resistor divided by the current I through the resistor. A resistor is a passive two-terminal
electrical component that implements electrical resistance as a circuit clement. The current
through a resistor is in direct proportion to the voltage across the resistor’s terminal thus,
the ratio of the voltage applied across a resistor’s terminal to the intensity of current through
the circuit is called resistance. 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 lager and ma require heat sinks. In a
high-voltage circuit attention must sometimes be paid to the rated maximum working voltage
of the resistor.
Practical resistors have a series inductance and a small parallel capacitance: these
specifications can be important in high-frequency applications. In a low-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

4. DIODE
A diode is a two terminal electronic component with asymmetric transfer
characteristic, with low (ideally zero) resistance to current flow in one direction, and high
(ideally infinite) resistance in the other. A semiconductor diode, the mast common type
today, is a crystalline piece of semiconductor material with a p-n junction connected to two
electrical terminals, A vacuum tube diode, now rarely used except in some high-power
technologies and by enthusiasts. is a vacuum tube with two electrodes, a plate (anode) and
cathode. The most common function of a diode is to allow an electric current to pass in one
direction (called the diodes forward direction), while blocking current in the opposite
direction (the reverse direction. This, the diode can be thought of as an electronic version of
a check valve. This unidirectional behaviour is called rectification, and is used to convert
alternating current to direct current, including extinction of modulation from radio signals
 5. CAPACITOR

A capacitor originally known as condenser is a passive two-terminal electrical

component used to store energy in an eclectic field. The forms of practical capacitors vary
widely, but all contain at least two electrical conductors separated by a dielectric insulator:
for example, one common construction consists of metal foils separated by a thin layer of
insulating film. Capacitors arc widely used as parts of electrical circuits in many common
electrical devices.

When there is a potential difference (voltage) across the conductors, a static electric field
develops across the dielectrics, causing positive charge to collect on one plate and
negative charge on the other plate, energy i stored in the electrostatic field. An ideal
capacitor is characterized by a single constant value, capacitance, measured in farads. This is
the ratio of the electric charge on each conductor to the potential difference between them
 6. POTENTIOMETER

The measuring instrument called a potentiometer is essentially a voltage divider used for
measuring electric potential (voltage); the component is an implementation of the same
principle, hence its name. Potentiometers are commonly used to control electrical devices
such as volume controls on audio equipment.

7. LED

A light-emitting diode (LED) is a semiconductor light source that emits light

when current flows through it. Electrons in the semiconductor recombine with electron holes,
releasing energy in the form of photons. The colour of the light (corresponding to the energy
of the photons) is determined by the energy required for electrons to cross the band gap of the
semiconductor. White light is obtained by using multiple semiconductors or a layer of light-
emitting phosphor on the semiconductor device.
Appearing as practical electronic components in 1962, the earliest LEDs emitted low-
intensity infrared light.Infrared LEDs are used in remote-control circuits, such as those used
with a wide variety of consumer electronics. The first visible-light LEDs were of low
intensity and limited to red. Modern LEDs are available across the visible, ultraviolet,
and infrared wavelengths, with high light output.
Early LEDs were often used as indicator lamps, replacing small incandescent bulbs, and
in seven-segment displays. Recent developments have produced high-output white light
LEDs suitable for room and outdoor area lighting. LEDs have led to new displays and
sensors, while their high switching rates are useful in advanced communications technology.
LEDs have many advantages over incandescent light sources, including lower energy
consumption, longer lifetime, improved physical robustness, smaller size, and faster
switching. LEDs are used in applications as diverse as aviation lighting, automotive
headlamps, advertising, general lighting, traffic signals, camera flashes, lighted
wallpaper, plant growing light, and medical devices.
RESULT & DISCUSSION
 CONCLUSION

Variable Power Supply with Digital Control with voltmeter display is one of the
application of electronic to increase the facilities of life. And it is the most frequently used
device in electronic workshops and laboratories is a universal power supply that provides a
variable. Fluctuation-free output.
With the knowledge of new techniques in Electronics’ we are able to make our life more
comfortable. One such application of electronics is used in “Rf power amplifier”.RF power
amplifiers can save much energy if they are supplied with a variable voltage as described in
the slate of the art. The design of the power supply of these amplifiers is challenging since
many requirements have to be accomplished: very low output voltage ripple: wide output
voltage variation at khz frequencies: fast load current steps: etc. A typical solution is the use
of a multiphase dc-dc convener based on the buck topology. In this paper,
The main advantage is that current loops are removed. The design of this control circuit and
main Trade-offs are discussed.
 REFERENCE

Harper C.AL Handbook of components for electronics.(1977)

Christos C.H and jacob. M (1987) integrated electronics, analogue ad digital circuits and

systems, U.S.A. Mc(imo hill )

Oakes. I.: Management of Electronics Assembly Design,(1992).

First Edition, Reed International Book Page 1003

Jackson, K.G. and Feinberg R.: Dictionary of Electrical

Engineering (1981) Buffer Worth Publishers Ltd. Second Edition Page 107.

Malcolm, P.: Basic Electronics 91998)

Second Edition. Hodder and Stoughton. Page 411

Michael. T.: Electric Circuits Handbook. (1993)

Second Edition, Longman, Page 367.

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