TITLE:
THYROID -TRANSISTOR DC DRIVE
NAME:
LUKAS KIBICHII
INDEX NUMBER:
5231020158
COURSE:
DIPLOMA IN ELECTRICAL ENGINEERING
(POWER OPTION)
PAPER NO:
2601/306
PRESENTED TO:
THE KENYA NATIONAL EXAMINATION COUNCIL
EXAM SERIES:
NOVEMBER 2022
CENTRE NAME:
ALDAI TECHNICAL TRAINING INSTITUTE
SUPERVISORS NAME:
MR.CORNELLIUS MUTAI
i
ABSTRACT
When the circuit is switch on the main a voltage is step down to 12v this is then filtered and
stabilized, part of this voltage issued to operate the firing circuit which utilizes a pulse
transformer, this allows smooth alteration between thyristor and other component. The objective
of this project is to demonstrate an experiment work of a DC motor control system using
athyristor. In this project DC motor control system has two kinds of circuit. The first circuit uses
two sources the 12v DC voltage is connected to universal motor series with are sistor and scr.
While the DC variable voltage source of 0 to 1.5v is connected in parallel connection with
acapacitor and resistor.
ii
DECLARATION
I, Lukas kibichii , do hereby declare that this report is my original work and to the best of my
knowledge, it has not been submitted for any academic award in any learning institution.
Signature.................................
Date.........................................
Supervisor: Mr. Cournellius Mutai
Signature:………………………..
Date............................................
iii
PREFACE
This project consists of three different chapters, chapter one deals with the introduction,
objectives, aims, specifications and block diagram.
Chapter two deals with the theory of components and circuit design and in respective blocks
indicating the types of components, component parameters and values
Chapter three deals with the project assembly, schematic circuit diagram, circuit operation,
component layout on PCB, performance test points, cost analysis, conclusion and
recommendations.
iv
ACKNOWLEDGEMENT
I wish to express my warmest thanks to all who have participated in any way for the completion
of this project and in particular to the following individuals.
Firstly special thanks go to Mr Cornellius Mutai for his tireless assistance and encouragement for
the Preparation of this project. I am also grateful to my friends and relatives who have
contributed a lot of preparation of this project.
Finally I am greatly indebted to my parents who contributed a lot. May God bless in a special
way.
v
DEDICATION
I honorably dedicate this project to my beloved parents and family friends.
vi
Table of Contents
DECLARATION ...................................................................................................................... iii
PREFACE ............................................................................................................................... iv
ACKNOWLEDGEMENT .......................................................................................................... v
DEDICATION ......................................................................................................................... vi
CHAPTER ONE ....................................................................................................................... 1
1.0 INTRODUCTION ............................................................................................................... 1
1.2PROBLEM STATEMENT .................................................................................................... 1
1.3 OBJECTIVES .................................................................................................................... 1
1.4 SPECIFICATION............................................................................................................... 2
CHAPTER TWO ...................................................................................................................... 3
CHAPTER THREE .................................................................................................................. 4
METHODOLOGY ............................................................................................................... 4
3.0 CIRCUIT ANALYSIS AND DESIGN ................................................................................... 4
3.1 POWER SUPPLY UNIT ..................................................................................................... 4
Power transformer.................................................................................................................. 4
3.2
RECTIFIER ................................................................................................................... 6
DC4081 AND GATE IC........................................................................................................... 8
3.4 POWER SUPPLY .............................................................................................................11
3.4.0 Output dc voltage .............................................................................................................11
3.4.2 PIV rating .......................................................................................................................12
3.3 FILTERS ...........................................................................................................................12
3.5 VOLTAGE STABILIZER ................................................................................................13
RESISTOR (R4)......................................................................................................................15
FIRING CIRCUIT .................................................................................................................16
SCR BRIDGE CIRCUIT ..........................................................................................................20
OUTPUT VOLTAGE ..............................................................................................................23
Figure 9:CIRCUIT DIAGRAM ..................................................................................................25
CHAPTER FOUR ...................................................................................................................26
4.0.0 DATA ANALYSIS .........................................................................................................26
4.2.0 RECOMMENDATIONS ................................................................................................29
4.3.0 CONCLUSION .............................................................................................................30
vii
4.4.0 REFERENCES .........................................................................................................31
LIST OF TABLES
Table 3.1:TABLE OF TESTING .......................................................................................... 27
TABLE3.2:TABLE OF PERFORMANCE .......................................................................... 27
TABLE3.3:COST ANALYSIS ............................................................................................ 28
viii
CHAPTER ONE
1.0 INTRODUCTION
In the past traditional electric power mechanical control circuits were greatly in a wide use. Of
late, electronic control circuits have become very popular for controlling the speed of ac and dc
machines. This is because of the fact they have high accuracy, quick response, greater reliability
and also higher efficiency as there is no power loss, arcing contacts and moving parts which
cause friction and wear.
Although the electronic controls of motors have the above mention merits, speed fluctuation has
been a great drawback ever since. Thus, for a précised work to be achieved there is a need to
control and maintain these machines.
The speed of the motor without overheating of the coil and over-current and surging voltages
during the switching operation in addition, change of direction that is clockwise and anticlockwise, is achieved for Convenience purposes.
1.2PROBLEM STATEMENT
When we use machines in our day to day work it help us through increase in production.
Therefore, by keeping the speed constant and independent of the load, the dc motor can operate
satisfactorily by using the thyristor device. This actually uses the principle of RC timing network
by which the voltage across the capacitor is applied to the gate.
1.3 OBJECTIVES
 To design, construct and test the servo motor speed control unit.

To be able to design a circuit which is more convenient to use.

To be able to reduce failures associated with analog controller circuit.
1
1.4 SPECIFICATION
Input voltage: 12V dc
Input current: 400mA
IC CD4081 CMOS Nand gate IC
Motor power rating: 2W. 12V
Thyristor / SCR C106D or equivalent
D1 1N5401 3A 100V diode
D2,D3 1N4004 1A 400V diode
C1 1uF 16v capacitor
C2 220uF 16v capacitor
VR 5K potentiometer
R1 5.6k resistor
2
CHAPTER TWO
LITERATURE REVIEW
In 1834, Moritz Von jacobi, a Russian engineer invented the first rotating Dc motor. Jacobi's motor
became well known for its power which would later set a world record.Jacobi went on to create an even
more powerful motor.The invention of this motor, by jacobi went on to further inspire other to expand
and produce more DC motors of the same power.Even with all of the developments throughout the
19th century.Julian sprague again invented a DC motor that was capable of maintaining a constant
speed under variable loads.This would lead to the commercial use of the DC motor.
These tradition DC motors was being controlled manually e.g by varying the flux and by varying the
current through field windings again by varying the armature voltage and the armature resistance and
this could cost much time and more labour since the working DC motor was to be dismantle and starting
varying the flux and field windings which could needs some extra time for the process leading to pausing
of the work. Other motors was made to run at a constant speed you couldn't change the speed by these
particular methods.
But in our today life since motors have become more beneficiary in industry and even in other
commercial works.It has become more difficult and waste of time in controlling DC motors using those
varying methods and also costly. The thyroid-transistor DC drive is one of the most cheapest way to
control this DC motor by use of thyristor corresponding with variable resistor hence varying the speed of
motor.This will be one of the easiest and cheapest method if implemented.Going to the future their will
be a well implemented thyristor control DC drive that will be more advanced compared to this current
one that will be more cheaper and easy implemented to control the output (DC motors).
3
CHAPTER THREE
METHODOLOGY
3.0 CIRCUIT ANALYSIS AND DESIGN
The speed control process of the motor or the machines in general involves a number of stages
normally represented in form of block diagrams. The desired and the result of this process
explained in the blocks will eventually be attained.
3.1 POWER SUPPLY UNIT
The power supply unit t of power transformer and full wave rectifiers and filters.
Power transformer
The main ac input voltage is transformed into a low ac voltage, the methods that are used to
achieve this include; use of power transformer or a resistor are isolation transformer, instrument
transformer, audio transformer, phase transformer, radio frequency transformer. A step- down
power transformer is suitable because, power loss is minimal, has a longer life span as it does not
undergo wear and tear and performs transformation of voltage from one level to another with
ease.
4
Figure 1:POWER TRANSFORMER
5
TRANSFORMER PARAMETERS
The maximum expected input voltage is 220V, 50Hz
The maximum expected output is 12v
Therefore the transformer ratio
Vp/Vs = Np/Ns =1800:1
Power ratings
The maximum expected input current is 5A
Power rating (VA) =VpIp
200*5
=1000VA
This is an assumption that the power factor is unity
Ampere turns IpNp = IsNs
Assuming that there is no magnetic leakage within the core
18*5
=90AT
3.2
RECTIFIER
6
Rectification is process of converting ac to dc. This is required because the electronic circuits
operate with dc while the mains supply is ac. There are three typical methods of retification.
a) HALF-WAVE RECTIFIER
In this method of rectification a single diode is used with a transformer as shown above.
The rectified output waveform is also shown above. This gives an output voltage of half
the transformer output.
b) centre tapped full wave rectification
A center tapped transformer makes it possible to use two diodes to have all the advantages of a
bridge rectifier. The peak inverse voltage of the diodes must exceed the peak voltage of the
transformer secondary coil. Even though this method gives the required full wave rectification
the transformer is is uneconomically used. Therefore its uneconomical to use.
7
c) bridge rectification
Figure 2:FULL WAVE BRIDGE RECTIFIER:
DC4081 AND GATE IC
8
The 4081 is a member of the 4000 series cmos range and contains four independent cmos AND
gates, each with two input.The pinout diagram, given on the above ,is the standard two-input
logic gate IC layout;

pin 7 is the negative supply

pin 14 is the positive supply

pins 1&2,5&6,8&9,12&13 are gate inputs

pins 3,4,10,11 are gate output
9
3.3 THYRISTOR / SCR
10
Thyroid transistor are semiconductor device that can operate only in the switching mode. Silicon
Controlled Rectifiers (SCR) known commonly as thyristor are three-junction PNPN
semiconductor devices which can be regarded as two interconnected transistors that can be used
in the switching of heavy electrical loads.
Characteristics of a thyristors
 thyristor are semiconductor device that can operate only in the switching mode.
 Thyristor are current operated devices, a small gate current controls a larger Anode
current.
 Conducts current only when forward biased and triggering current applied to the Gate.
 Thyristor acts like a rectifying diode once it is triggered “ON”.
 Anode current must be greater than holding current to maintain conduction.
 Blocks current flow when reverse biased, no matter if Gate current is applied.
3.4 POWER SUPPLY
3.4.0 Output dc voltage
The input voltage is an rms value voltage hence it must be converted into maximum voltage
=16.97V
Vdc=2*16.97=12V
11
3.4.2 PIV rating
Since it is a bridge rectifier PIV = Vmax, As Vmax is 16.97V the PIV rating of each diode is
17V
Ripple factor =0.5043
Form factor =
Power rating of each diode P =
Since silicon diode is used
The input current is 5 Ma which is rsm value, the equivalent maximum value
1max =0.707A
P=0.707*0.7=0.5
3.3 FILTERS
The ripple content present in the rectifier is undesirable and has to be eliminated, a filter is
therefore required to achieve this function, types of filters include; capacitor filter, induction
filter, induction capacitor filter and pie filter. In this design a capacitor filter is used, this is
because it provides a simple circuit design, has good filtering characteristic, it can withstand
effectively high charging and discharging current, the cost of the filter circuit is low.
Ripple factor of this filter is given by=0.5043
The frequency f will be the same as the main input ac. Ripple factor will be the same as
that of the bridge rectifier 0.4949 as calculated earlier
The minimum expected load will have an impedance of 60.2 for the maximum transfer tooccur
between the source and the load.
C=100µF
12
Voltage Rating
The output de voltage from the rectifier should be equal to the capacitor voltage rating,
Source Vdc is 12V, and Vdc should not be less than 12V. For this design Vdc is selected to be
16V
The type of capacitor use in an electrolytic capacitor as they are the most suitable for
Power supply circuit.
3.5 VOLTAGE STABILIZER
The operating voltage for the speed control circuit must be kept very constant to avoid
fluctuations in speed due to slight voltage variations
Many types of voltage regulator utilized the Zener diode as it provide a simple circuit
design therefore it has to be used.
13
Figure 3:VOLTAGE STABILIZER
14
RESISTOR (R4)
It performs the function of current limiting for Zener diode the maximum expected
Current that will flow through resistor (R4) i.e. IR4 = Idc
Idc = 2Imax/
But Imax =
=
= 0.707A
Idc = 2* 0.707/ = 0.51A
The maximum expected voltage drop across resistor R4 is 2.4V, therefore
R= VR4/IR4
= 2.4/0.51
= 4.7Ω
This is a dropper resistor and its power rating will be
p=I2 R
=0.51*4.7
=2W
15
FIRING CIRCUIT
The silicon control rectifier should be triggered into conduction therefore a firing circuit
Is required that will supply sufficient gate current to each respective SCR
It is also important that there is isolation during conduction period of each respective SCR such
that when one set is conducting the other set is off hence the use of the phase transformer.
The operation of this SCR will be such that Qı operates with Q4 and Q3 operates with Q2
Types of firing include: burst firing, phase firing, and voltage firing. In this design phase firing is
utilized this is because it is more accurate and has minimal power losses.
Figure 4:FIRING CIRCUIT
16
RESISTOR (RI)
17
It sets the instants at which the SCR will be triggered into conduction.
RESISTOR (R2)
It acts as a current limiting resistor by dropping voltage to safe value thereby protecting
the SCR and the Zener diode against high voltages hence high currents.
Typical practical values selected for resistor R, in order to achieve reasonable firing
angles that will create speed variation range which should be between 0 and 50k In this
Potentiometer is chosen to be in the range 0 -20kΩ
The maximum voltage expected across the resistor R2 is equal to 4.7V
The maximum current expected to flow through resistor R2 will be:
IR1=10mA
R2 = VR2/ IR?
= 4.7/10*10^-3
= 4.7 kΩ
DIODE (D)
This diode will break down only when a given terrestrial voltage equals to its breakdown
Voltage has been reached
At this point gate signal will flow through the gate terminal of SCR5 putting it into conduction
hence taking away power from section of the coil of the phase transformer to another section
18
e.g. T-T2 and vice versa.
The diode used is zener diode, it will be selected to have a breakdown voltage equal to 6V, and
the reason for this is because a phase transformer ideally operates on maximum voltage of 6V.
RESISTOR (R3)
It forms a voltage divider network with the Zener diode in order to take-up part of the remaining
voltage so that the Zener diode operates with voltage of 6V at all times. VR3 is the maximum
voltage across resistor R3 is equal to 2V
The maximum current expected to flow through resistor R3 i.e. 1R3 which is equal to
2Ma = 2/2* = 1000Ω
SCR PARAMETERS
The maximum expected gate current 1g will be given by
1g =1D5-1R3
=2.8m A-2mA
=0.8mA
The maximum anode current expected to flow through the rectifier:
=1R2- 1Ds
= 10*10^-3 -2.8* 10^-3
= 7mA
The maximum reverse breakdown voltage of the SCR will be the same as Vdc out 12V
CAPACITOR (C1)
It acts as a coupling device between the pulse transformer and SCR The maximum voltage
expected across this capacitor is 6V The maximum charge expected at this capacitor for proper
operation of SCR is 30Mc
Where
C=Q/V
= 30*10
19
=5
PULSATING TRANSFORMER
It is a special transformer used to provide isolation between complimenting SCR of a given
bridge particularly when they are to be fired into conduction alternatively.
SCR BRIDGE CIRCUIT
Silicon control rectifiers are used as power control devices hence with ultimate speed
Controllers of the motor.
They are preferable because they have a very low drop out voltage hence can conduction
Very high currents with relatively very low heat dissipation.
They also have excellent inverse voltage holding capacity and are therefore ideal for use
in high power application when fully conduction, they have negligible voltage drop across them
and do not suffer from leakage currents.
20
Figure 5:SCR
BRIDGE CIRCUIT
Figure 6:Triggering pulses
21
22
OUTPUT VOLTAGE
If the firing angle is considered to be 90° and the input voltage rms value equal to 12V
Vdc=Vmax/ (1+Cosø)
If the firing angle is considered to be 90' and the input voltage rms value equal to 12V
Vmax = V2*12
= 16.97V
Vdc = 16.97/1 (1+ Cos90)
= 12V
For another different speed angle of a different angle is used e g 30"
Vdc = Vmax/(1+Cosø)
= 16.97/1 (1+Cos30)
= 10.07V
23
The reverse breakdown voltage for each SCR will be given by
PIV = 2Vmax
= 2* 16.97
= 33V
Power rating of SCR
P=V/*Id
= 0.707*0.7
= 0.5W
1.5 Figure 1 BLOCK DIAGRAM OF THYROID_TRANSISTOR DC DRIVE
POWER
SUPPY
PULSE
OSCILLATOR
24
THYROID_TR
ANSISTOR
OPERATED
CIRCUIT
DC
MOTO
R
Figure 7:CIRCUIT DIAGRAM
25
CHAPTER FOUR
4.0.0 DATA ANALYSIS
When the circuit is switch on the mains ac voltage is step down to 12v this is then filtered
and stabilized, part of this voltage is used to operate the firing circuit which utilizes a
pulse transformer, this allows smooth alteration between each pair of SCR that work
together, this isolation is important to eliminate sparking and shorting of live and neural.
SCR Q1 and Q4 are triggered simultaneously thereby providing electrical power to the armature.
In the next half SCR3 and SCR2 are triggered and at the same time the latter
SCR commutated to off the armature recovers the electrical power and the motor rotates.In order
to vary the speed of the motor potentiometer R is varied this change the instant at which the SCR
are fired the circuits incorporates speed direction, variations and this is achieved by use of switch
S1.
4.1.0 TABLESS OF RESULTS
26
1Table 3.1:TABLE OF TESTING
T E S T
P O I N T VOLTAGE EXPECTED VOLTAGE MEASURED
T
P
1
1 6 V
1 6 . 8 V
T
P
2
2.5V
2 . 7 V
T
P
3
MAX :16.3V
MIN:1.3V
T
P
4
2 . 5 V
2 . 7 V
2TABLE3.2:TABLE OF PERFORMANCE
27
PENTIOMETER SETTING
M
0
1
8
0
0
1
0
0 1
6
0
0
2
0
0 1
4
0
0
3
0
0 1
2
0
0
4
0
0 1
0
0
0
5
0
0 8
0
0
6
0
0 5
0
0
7
0
0 3
0
0
8
0
0
3TABLE3.3:COST ANALYSIS
28
2
O
T
O
R
S
P
E
E
D
0
COMPONENTS T
Y
P
E QUATITY
PRICE UNIT(KSHS)
Strip board
1
1
R e s i s t o r
3
3
0
I N 5 4 0 4
4
5
5 2
I N 5 2 6 2
2
2
4 4
Capacitor
2
5
0 1
0
0
S
R 2 N 4 1 7 2
4
1
0
0 4
0
0
2 N 5 0 6 2
1
1
5
0 1
5
0
D i o d e s
C
0
TOTAL(KSHS)
0 1
0
0
9
0
2
0
8
Copper wire
I M E T R E 2
0
2
0
Soldering
1 M E T R E
0
1
0
1
T y p i n g
1
Binding/Photocopy
3
T O T A L
3
2
5
5
6
0
0
7
8
4.2.0 RECOMMENDATIONS
There are other forms of speed control apart from electronic speed control like rotor speed control
29
but in terms of cost implication the electronic speed control is cheaper when compared to other
forms.
4.3.0 CONCLUSION
Despite the various problems that were encountered during the preparation of this project, the
entire work was successful. Different operating values were achieved by varying the resistor VR.
Some of the approximate speeds achieved by varying VR1 is tabulated as follows
Firing angle(degrees)
Speed(rpm)
0
1 5 0 0
3 0
1400
4 0
1 2 0 0
6
1000
From this table, it can be concluded that as the firing angle increases, the speed limit
decreases and vice-versa.
30
4.4.0 REFERENCES
Electrical Technology by S.K The raja
Success in Electronics by Tom Duncan
Basic s of Electronics Motors by Schuler
Power Electronics by P. C. SEN
Digital Fundamentals (4th Edition) by T.L Floyd
Electric Motors, Application and Control by M.V
E lectronic speed control casing sections
Top casing (not to scale)
31
32
33