KATHMANDU UNIVERSITY SCHOOL OF ENGINEERING

DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING

PROJECT REPORT

Design and Construction of a DC Voltage Supplier with Seven

Segment Display

by:

Sujeet Kumar Jha[22009]

Rupa Rokaya[22022]

Manish Karn [22035]

Divya Mishra[22039]

Ahmed Raja Khan[22432]

August 2015

TABLE OF CONTENTS

S.No. Chapter Description Page No.

1 List of Figures ii

2 List of Tables iii

3 Abstract iv

4 Acknowledgement v

3 1 Introduction 1.1.Background 1.2.Objectives 1.3.Brief Working Mechanism

1

4 2 Literature Survey 2.1. Hardware Required 2.1.1. Transformer 2.1.2. Rectifier 2.1.3. Filter 2.1.4. Seven-Segment Display 2.1.5. Regulators 2.1.6. A/D Converters and Display Driver 2.1.7. Multisim 2.1.8. Heat Sink

2-4

5 3 Discussion 3.1. System Overview 3.2. Digital Display Panel 3.2.1. Digital Voltmeter 3.2.2. Digital Ammeter 3.3. Calculation Part

5-8

6 4 Task Accomplished 4.1. Task Accomplished

9

7 5 Gantt Chart 10

8 6 Conclusion 11

9 7 References 12

10 Appendices 1. Circuit of dual DC voltage supplier 2. Circuit of current regulator circuit 3. ICL7107 test circuit 4. LM337 5. LM338 6. LM7805 7. A/D Converters

13-27

ii | P a g e

LIST OF FIGURES

S.No. Fig. No. Description Page No.

1 2.1.1. Transformer 2

2 2.1.2. Diode as Rectifier 3

3 2.1.3. Filter Circuit 3

4 2.1.4. Seven-Segment Display 3

5 2.1.5. IC Regulator 4

6 3.1. Block diagram of DC power supply 5

7 3.2.1. Block Diagram of Digital Voltmeter 6

iii | P a g e

LIST OF TABLES

S.No. Table No. Description Page No.

1 1 Gantt Chart 10

iv | P a g e

ABSTRACT

This project highlights the design and control of DC voltage supplier with seven-segment

display. A Variable DC Power Supply is a device that supplies electric power to an electrical

load and as the name implies, allow the user to vary or change the DC output voltage within

the specified ranges. The most frequently used device in electronic 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 variable voltage regulator LM338 and LM7805 as

constant voltage regulator. Also LM337 is employed for current regulation. The AC mains

supply is stepped down by transformer to deliver a secondary output of 12V-0-12V AC, 3A.

The output of the transformer is rectified by a full-wave rectifier comprising diodes. Capacitors

are also used as filters to eliminate ripple. Here both negative and positive half cycles are used

to obtain positive as well as negative DC output. The display section uses CMOS IC

ICL7107CPLZ which is typical a/d converter measure the voltage and current regulation.

v | P a g e

ACKNOWLEDGEMENT

We would like to thank Department of Electrical and Electronics to provide us the opportunity to work on this project, which will help us to explore our creativity and knowledge. We would also like to thank our Project Supervisor Mr. Parash Acharya for his guidance and time to

guide us throughout the project.

At last we would like to acknowledge our colleague and seniors at Kathmandu University for giving their valuable suggestion and technical help to complete the recommended proposal.

1 | P a g e

CHAPTER 1

INTRODUCTION

1. Introduction

1.1. Background This report intend to show the progress of the project work as required for the course

EEEG 212 offered by Department of Electrical and Electronics Engineering. If electrical

systems can convert AC power upstream of individual devices, the means and size of

these converters become more efficient and cost-effective. Main aspect of current project

is to convert AC main voltage to variable DC voltage. The project aim to work on that

aspect and develop an electrical device i.e. DC power supply.

1.2. Objectives

To be familiar with electric equipments. To develop teamwork quality. To transform high voltage AC current to low voltage DC. To increase the flexibility of using dual fixed and variable voltage. To develop a safe, efficient and economical device.

1.3. Brief Working Mechanism The operation of this device starts with 220V AC input, which is than treated with step-

down transformer to transform the high voltage input to low voltage. Further, it is

supplied through rectification diode that allow the passage of electric current only in one

specified direction. After that, the filter capacitor is used for smoothing frequency pulse

and results to the synthesis of smooth DC voltage. This DC voltage is than supplied to

fixed and variable voltage outputs using fixed and variable regulator respectively. A

separate current regulator is also derived. The visual indication of voltage and current

through seven segment implemented.

2 | P a g e

CHAPTER 2

LITERATURE SURVEY

2.1 Literature survey A high quality power supply is a electronic device with a continuous variable stabilized

output adjustable at any value between zero (approx.) and 20V DC. The circuit also

incorporates a different electronic output current limiter that effectively controls the

output current from a few mill amperes (2 mA) to the maximum output of 3 amperes that

the circuit can deliver. This feature makes this power supply indispensable in the

experimenter’s laboratory, as it is possible to limit the current to the typical maximum

that a circuit under test may require, and power it up then, without any fear that it may be

damaged if something goes wrong. There is also a visual indication for the voltage and

current supplied.

2.1 Hardware Required

2.1.1. Transformer

A transformer is an electronic device, which is used to step up or step down the input

AC voltage. The used transformer is one primary two secondary (1p2s ) configuration

of rating 12v-0-12 v, 3A. It used to step down the main AC 220v to 12-0-12 V.

Fig.2.1.1. Transformer

3 | P a g e

2.1.2. Rectifier

It is an electrical that converts alternating current (AC), which periodically reverses

direction, to direct current (DC), which flows in only one direction. In our case, we have

designed bridge rectifier using diode 1N4007.

Fig.2.1.2. Diode as a Rectifier

2.1.3. Filter

Filters are electronic circuits which perform signal processing functions. To remove

unwanted frequency components from the signal, to enhance wanted ones, or both. Filter

comprising one or more capacitors, resistors, and sometimes inductors. The capacitor of

4700uf is used (Calculation is shown in chapter 3).

Fig. 2.1.3. Filters Circuit

2.1.4. Seven- Segment Display

It is an output device for presentation of information in visual or tactile form when input

information is supplied. A seven-segment display is a set of seven bar-shaped LED (light-

emitting diode) elements, arranged to form a squared-off figure 8. Seven-segment

displays are widely used in digital clocks, electronic meters, basic calculators, and other

electronic devices that display numerical information.

Fig.2.1.4. Seven-Segment Display

4 | P a g e

2.1.5. Regulators

It is a circuit that helps maintain a fixed or constant output voltage. Voltage ratio of transformation can be adjusted, or an electronic circuit that produces a defined voltage. The regulator fixes the output voltage to the desired level then maintains that value despite any output or input variations. IC LM338 and LM 7805 as variable and constant voltage regulator respectively is used. Also LM 337 is employed for current regulation. The further information about these IC is attached to the corresponding datasheet in appendices.

Fig.2.1.5. IC Regulator

2.1.6. A/D Converters and Display Driver

The ICL7107CPLZ, the analog to digital converters have very high input impedances

and require no external display drive circuitry. On-board active components include

polarity and digit drivers, segment decoders, voltage reference and a clock circuit. The

ICL7107 will directly drive a common anode light emitting diode (LED) display. It is

used for the visual indication of voltage. It has following benefit over others.

No need to add external display diver.

Great accuracy.

Portable and small size. It fitted into 35*50 mm board.

Further, more detail found in datasheet attached in appendices.

2.1.7. Multisim

Multisim is an electronic schematic capture and simulation program that is part of a suite

of circuit design programs. Multisim is used for simulation of circuits followed by

implementation of circuit in breadboard.

2.1.8. Heat Sink Heat sink is the metallic case that is used to draw the excessive heat from the IC and help

to cool it off. The heat sink is used to prevent the thermal overload of IC regulator.

5 | P a g e

CHAPTER 3

DISCUSSION

3.1. SYSTEM OVERVIEW

A main supply (220v, 50Hz) is supplied directly to the one primary and two secondary(1s2p) transformer and transformer steps down it to about 12-0-12 These voltages are rectified through the bridge rectifier, which is at once after the transformer. Rectified signal is the continuous pulsating DC, then capacitors filters the pulsating DC into the smooth non-pulsating DC .Now this DC is regulated by the IC’s.

LM 7805- IC regulates about constant 5V.

LM 337 - Variable regulators capable of supplying in excess of 5A over a 1.2-32 V.

LM 338- Variable regulators capable of supplying in excess of 5A over a 1.2-32 V and current regulation.

Therefore, user can easily get the desired voltages from the output pins of the different regulators. In the circuit, The separate output pins for positive, negative voltage, and common ground pin of the whole circuit is available in the circuit.

In order to avoid the risk of damage due to short circuit a fuse of 1.5A is put across the series of the transformer. In order to prevent the damage due to overheating of the ICs the cooling system is provided to them. Cooling system is comprise of Heat Sink and cooling fan. The corresponding output voltage and current is simultaneously displayed by the display section. The display section consists of ICL7107CPLZ that is high performance, low power, 31/2digit A/D converters. Included are seven segment decoders, display drivers, a reference, and a clock. In addition, common anode seven segment display.

Fig.3.1. Block diagram of DC power supply

6 | P a g e

3.2. Digital Display Panel

3.2.1. Digital Voltmeter It displays the measurement of dc output voltages from the supply as discrete numerals

through the seven segment displays.

The display section uses CMOS IC ICL7107CPLZ which is typical a/d converter measure

the voltages based on the dual slope technique. It is complete integrated package of

Integrator Level comparator A basic clock Counters Display Driver

Fig:-3.2.1. Block Diagram of Digital Voltmeter

3.2.2. Digital Ammeter

In same way as the digital voltmeter, it also measure the dc output current of the supply. It

uses same IC ICL7107CPLZ with slight modification in the passive components. The block

diagram is somehow same to block diagram of digital voltmeter as shown in fig.3.2.1.

3.3. Calculation Part:

3.3.1. Design of variable DC Circuit: In this part, we intend to produce positive as well as negative voltage. It uses two end of

bridge rectifier i.e. is one for positive and other for negative. From transformer that step down

the voltage to 12 volts. In addition, voltage drop from diode is 0.7*2 = 1.4 volts. Now we

need to calculate peak-to-peak voltage because we will need that value later for choosing a

smoothing capacitor value. To calculate peak-to-peak voltage value we need to multiply that

voltage by 1.414.

i.e. (V)rms = (V)p / 1.414

7 | P a g e

So, peak-to-peak voltage after bridge rectifier would be about (V)p = 12*1.414 =16.968 volts.

If we subtract voltage drop from diode i.e. 1.4 volts from peak-to-peak voltage, we will get

15.57 volts.

The rectified DC voltage has so many ripples so that we cannot actually power anything

useful with it. That’s why we need smoothing capacitor. After smoothing capacitor, output

will have less ripple under load. Size of that ripple depends on amount of capacitance (C),

voltage (V), load current (I) and AC frequency (f)

3.3.2. To calculate capacitance For

ripple(r) = 0.167

Frequency(f) = 50 Hz

Maximum Load (R) = Rated voltage / Rated current (For Transformer)

= 12/3

= 4 Ohms

We Know,

r = 1 / (4*1.732*f*C*R)

or, C = 1 / (4*1.732*f*r*R)

= 1 / (4*1.732*50*0.167*4)

= 4.3 milli-farad

We chose the capacitor of 4700 microfarad. Similarly we one independent capacitor of 4700

microfarad for negative section.

That means, at 220-volt AC supply into transformer, the maximum possible rectified voltage

after smoothing is 15.57 volts and that goes to LM338 and LM337.

Now, Vin = 15.57 volts

Vout =13 volts(max.)

So, it ranges from 1.25 volts to 13 volts.

In order to make lower limit, we add zener diode of 1.5 volt and it becomes

0 – 11.5 volts (theoretically)

For positive section: 0.4 – 10 volts (practically)

For negative section: -0.2 - -10.1 volts (practically)

Now for selection of R1 and R2 for voltage regulator

Here,

Vout = 10 volts

Vref = 1.25 volts

From formula,

8 | P a g e

Vout = Vref (1+ (R1/R2))

This implies, R1/R2 = 7

So, R1/R2 must be greater than 7.

3.3.3. Calculation for unknown output voltage (Reference to Fig:-3.2.1.

Block Diagram of Digital Voltmeter, page no.6)

The unknown voltage fed to integrator through switch S be Vx for the time T. The time is

determined by clock frequency in the decimal counter.

During time period T capacitor across integrator is charged at rate proportional to Vx .

At the end of time interval T, the switch S is shifted to reference voltage Vref (100 mv) which

is observed for the time t. The t is determined by counting pulse from the clock until the

capacitor voltage reaches its basic reference level.

Now from the similar triangle we derive the relation

(insert the equation Vx /T = Vref /t

Vx = T/t * Vref

The count after t, which is proportional to Vx, is displayed

as the measured voltage.

Volt

Time

T t

Slope,

Vx

Slope,

Vref

9 | P a g e

CHAPTER 4

TASK ACCOMPLISHED

4.1. Task accomplished

Step down transformer was connected to the ac mains and was step-down to 12-0-

12v. Step-down low voltage was rectified to the pulsating dc by using bridge rectifier.

Each end of rectifier gives +ve pulsating Dc and -ve pulsating DC. There after pulse of each dc signal was smoothened using filter electrolytic capacitor

(47mf). Each of filter DC signal was fed to corresponding IC +ve to LM 338,LM7805 and

-ve to LM337. LM338 gives output (+0.4v to +10v). LM337 gives output (-0.4v to -10v). LM7805 gives constant 5v. Overall the system can deliver upto dc 20v. Output voltage is displayed by using ICL7107cplz. PCB designing, printing, etching is completed. Testing and implementation of ICL7107 as current measuring and displaying.

Fabrication of the PCB.

Assembling the unit in the case.

10 | P a g e

CHAPTER 5

GANTT CHART

Table.1 Gantt chart

Task Sept. Nov. Dec. Jan-Feb.

March April- May

June- Aug.

Study of possible project

Project Title Selection

Literature Review

Proposal Writing And Defense

Circuit design and implementation of the circuit

Mid-Term Report

Hardware and PCB development

Testing and evaluation of the system

Work Accomplished

Work Remaining

11 | P a g e

CHAPTER 6

CONCLUSION

6. Conclusion Due to the need for most domestic and laboratory equipment of small ratings to be powered

by electricity in one form or the other coupled with the problem of insufficiency of number

of specially designed power supply for the needed domestic application or laboratory

experiment as well as electrical project design, a multi-output power supply unit was

developed. The variable DC output produced values ranging from 0-20V while the

regulated and regulated dual outputs produced 5V and ±10V respectively. The output

measurements showed that the developed power supply was effective and measured values

gave minima variation from the nominal designed values. The developed system is cheap,

robust and very useful for domestic application and laboratory experimental purposes.

12 | P a g e

CHAPTER 7

REFERENCES

1. wikihow. (2014, 12 20). www.wikihow.com. Retrieved from wikihow: www.wikihow.com/Make-an-AC-DC-Converter

2. wikipedia. (2014, 12 20). Retrieved from www.wikipedia.com

3. John Palmisano, “ Electronics Components And Hardware I (CFS)” , part 1 & 2. 4. Sedra & Smith, Microelectronic Circuits, CBS College Publishing, USA, 1987

5. Shoewu, O., Olaniyi, O.M. and Ogunleye, O.M. (2011). Design and Development of an Intelligent Variable Power Supply Device. Pacific Journal of Science and Technology. 12(1):30-37

6. Wikipedia. (2015). Power Supplies. Retrieved February 2012 from: (http://en.wikipedia.org/wiki/power_supply)

7. Williams, O.A. (1995). Design and Construction of a Regulated Power Supply Unit. Cambridge Press:Cambridge, UK

8. Theraja, B.L. and Theraja, A.K. (2002). A Textbook of Electrical Technology. 23rded. S. Chand: New Delhi, India.

9. National. (2012). LM338 Regulator Datasheet Data Sheet. Retrieved November, 2014, from(http://www.national.com/pf/LM/LM338.html )

10. National. (2012). LM317 Regulator Datasheet Data Sheet. Retrieved November, 2014, from(http://www.national.com/pf/LM/LM337.html )

11. National. (2012). LM7805 Regulator Datasheet Data Sheet. Retrieved November, 2014, from (http://www.national.com/pf/LM/LM7805.html )

12. Maxim(2015).ICL7106&ICL7107 Datasheet. Retrived March 29,2015,from( http://www.datasheet.com/archive/ICL7106&07/data.pdf)

13. Scribd. Voltmeter (2015). Voltmeter Panel. Retrived on June 18,2015, from (https://www.scribd.com/doc/61586687/Digital-Voltmeter.html)

0

0

1

1

2

2

3

3

4

4

5

5

6

6

7

7

8

8

A A

B B

C C

D D

E E

F F

G G

V1

220Vrms 60Hz 0°

T1

220:12:12

C1

4700µF

D1

3N246

1

2

4

3

LED1

R11kΩ R2

1kΩ

U1LM338K

LINE VREG

COMMON

VOLTAGE

C2

2.2uF

R3

10kΩKey=A

100 %

1

1kΩ

C3

4700µF R61kΩ

LED2

U2LM337K

LINE VREG

COMMON

VOLTAGE

R10

1kΩKey=A

100 %C4

2.2uF R71kΩ

R5

1kΩKey=A

31 %

Title:

Designed by:

Checked by:

Approved by:

Document No:

Date:

Sheet of

Revision:

Size:

Dual DC volt supplier 0-20v Project 2nd year Electric and electronics

1

3/32015

1 5

A

Desc.:

Electronics Workbench801-111 Peter StreetToronto, ON M5V 2H1(416) 977-5550

circuit 1:- Dual Dc Voltage Supplier 0-20 v

C7

0.1uF

R8

10kΩKey=A

10 %

R9

1kΩ

D21.5V

R11

680Ω

D3

1.5V

R12

680Ω Probe1

V: I: Freq.:

Probe2 V:

I:

0

0

�

�

�

�

�

�

�

�

�

�

�

�

�

�

�

�

� �

� �

� �

� �

11

������

GGGG GGGG

�����G

G�G��GG

�1�

1�������

1

�1

�

��

�� ���� � ��

1�

1� ��

�1 ��

� ��

�1

� �� ��

1�������

�

������

��������� ���

���� ���

��������� ���

�������� ���

�����

'��� �'

���������

'�'��

+�������� +�+��� '����� ������� ���������

����

��

��

000�

��/0�/�0��

� �

�10

�

���1�

���������� �������0������+�����'�������������������+���������� �������0

111111

����1�����

����������