TITLE PAGE
CONSTRUCTION OF DC
VOLTAGE DUOBLER
BY
ENG/107150115 IGHOJOSEWE THOMPSON ONORIODE
A PROJECT WORK SUBMITTED TO THE DEPARTMENT OF
ELECTRICAL/ELECTRONICS ENGINEERING, AUCHI POLYTECHNIC, AUCHI
IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE
AWARD OF NATIONAL DIPLOMA (ND) IN ELECTRICAL/ELECTRONICS ENGINEERING.
JUNE
2017.
CERTIFICATION
This
is to certify that this technical report “Construction of Dc Voltage Duobler” was carried out and submitted by
ENG/107150115 IGHOJOSEWE THOMPSON ONORIODE
________________________ _________________
Project Supervisor Date
________________________ _________________
Program Co-ordinator Date
________________________ _________________
Head of Department Date
DEDICATION
I dedicate this project work to Almighty God for his
mercies, grace, strength, guidance, protection and loving kindness shown unto
me throughout my academic pursuit in the polytechnic.
ACKNOWLEDGEMENT
My special gratitude goes to Almighty God for making
it possible for me to successfully complete our programme.
I also sincerely appreciate the effort of our Head
of Department, Electrical Electronics Engineering: Engr. Abdulazeez Isah
Watson, our project supervisor Engr. Usidame Imuzeze, and all lecturers
Electrical Electronics Engineering whose guidance and suggestion made this
project a successful one.
My profound gratitude also goes to all my Parents and
all my family members and those who have one way or the other help in our
academic pursuit. May the Almighty God richly bless them all.
ABSTRACT
A voltage doubler is an electronic circuit which
charges capacitors from the input voltage and switches these charges in such a way
that, in the ideal case, exactly twice the voltage is produced at the output as
at its input.
The simplest of these circuits are a form of rectifier which
take an AC voltage as input and outputs a doubled DC voltage. The switching
elements are simple diodes and they are driven to switch state merely by the
alternating voltage of the input. DC-to-DC voltage doublers cannot switch in
this way and require a driving circuit to control the switching. They
frequently also require a switching element that can be controlled directly,
such as a transistor, rather than relying
on the voltage across the switch as in the simple AC-to-DC case.
Voltage doublers are a variety of voltage multiplier circuit. Many, but not all, voltage doubler circuits
can be viewed as a single stage of a higher order multiplier: cascading
identical stages together achieves a greater voltage multiplication.
TABLE OF CONTENT
TITLE PAGE
CERTIFICATION
DEDICATION
ACKNOWLEDGEMENT
ABSTRACT
CHAPTER ONE
1.0 INTRODUCTION
1.1 BACKGROUND OF
STUDY
1.2 BASIC PRINCIPLES
CHAPTER TWO
2.0 COMPONENTS OF THE DC DOUBLER
2.1 555 TIMER IC
2.2 BASIC CONCEPTS
2.3 FUNCTION OF DIFFERENT PINS
2.4 RESISTOR
2.5 CAPACTOR……………………………………………………………..18
2.6
DIODE…………………………………………………………………...19
CHAPTER THREE
3.0 VARIOUS SECTIONS OF THE DC DOUBLER CIRCUIT
3.1 THE OSCILLATOR UNIT
3.2 Basic Astable 555
Oscillator Circuit
3.3 555 Oscillator Cycle
Time
3.4 555 Oscillator
Frequency Equation
3.5 555 Oscillator Duty
Cycle
3.6 THE DIODE-CAPACITOR NETWORK………..……………………….
CHAPTER FOUR
4.0 THE PRACTICAL CIRCUITS
4.1 PRACTICAL
DEMONSTRATION CIRCUIT……...…………………..
4.2 MORE USEFUL VERSION OF THE CIRCUIT
4.3 CASCADED ‘VOLTAGE
DOUBLER’ CIRCUIT
CHAPTER FIVE
5.1 CONCLUSION
5.3 RECOMMENDATION
REFERENCES
CHAPTER
ONE
1.0 INTRODUCTION
1.1 BACKGROUND OF STUDY
In many modern
battery-powered electronic circuits, a DC supply is needed that is of either a
larger voltage value than that of the main battery, or is of reverse polarity;
a circuit that is powered from a six-volt battery may, for example, incorporate
a single op-amp stage that needs +12V and -6V supply lines. In such cases, the
required voltages may be generated via one or more special DC voltage converter
circuits.
Most electronic DC
voltage converters operate in one or another of four basic ways and use a
DC-powered oscillator to drive either a simple diode-capacitor ‘voltage
multiplier’ network, or a step-up transformer and rectifier network, or a
‘flying capacitor’ voltage converter, or a ‘diode-steered charge pump,’ which
produces the desired final DC output voltage or voltages.
This
project explains the operating principles of — and shows practical examples of
a DC-powered
oscillator to drive either a simple diode-capacitor ‘voltage multiplier’ network.
1.2 BASIC PRINCIPLES
Conventional DC ‘voltage multiplier’ types of voltage converter circuits are based on a simple two-section diode-capacitor type of rectifier network that was originally designed way back in the 1930s for use in high-value AC-to-DC voltage conversion applications, and is still widely used today.
Conventional DC ‘voltage multiplier’ types of voltage converter circuits are based on a simple two-section diode-capacitor type of rectifier network that was originally designed way back in the 1930s for use in high-value AC-to-DC voltage conversion applications, and is still widely used today.
To understand this circuit’s basic operation and terminology
(which can sometimes be rather confusing), it is necessary to start off by
looking at a simple AC-to-DC power conversion circuit, as follows:
The simplest AC-to-DC power conversion circuit is the basic
half-wave rectifying type shown in Figure 1, which depicts a
circuit that uses a transformer with a secondary voltage value of 250V rms.
FIGURE 1. Basic details of a simple 250V half-wave rectified DC
power supply.
Here, the AC voltage applied to the input of rectifier D1
swings alternately above and below the 0V value, rising to a positive Vpeak (Vpk)
value +353V in the positive half-cycle, and falling to a negative Vpeak value
of -353V in the negative half-cycle.
D1 is forward-biased during each positive half-cycle and
thus charges capacitor C1 to a peak value of (ignoring D1’s forward volt drop)
+353V, but is reverse-biased during each negative half-cycle, which thus has no
practical effect on the circuit.
This circuit produces a positive output voltage, but can be
made to generate a negative output voltage by simply reversing the polarities
of D1 and C1.
The really important thing to note about the Figure
1 half-wave rectifier circuit is that D1 and C1 act together as a
peak-voltage detector that makes the circuit give an output equal to the
positive peak value of T1’s secondary voltage.
The same basic action occurs in all conventional full-wave
rectifier circuits, which also give an output equal to the peak value of the
transformer’s secondary voltage.
During the early 1930s, engineers needed a cheap, reliable,
and safe way of generating high-value low-power DC voltages from low-cost
non-lethal transformers, and devised a simple two-section ‘voltage multiplier’
circuit to do this job. Figure 2 shows such a circuit, driven
from the secondary winding of a 250V transformer.
FIGURE 2. Basic details of a transformer-driven
‘voltage-doubling’ voltage multiplier circuit.
Here, the C1-D1 section acts as a diode clamp that, when fed
with a normal AC input that swings symmetrically about the 0V value, produces
an output waveform that is of identical shape, but has its peak negative point
clamped to the 0V ‘reference’ value, as shown in the diagram.
This waveform’s peak output value equals the peak-to-peak (Vp-p)
value of the AC input voltage, and is fed directly into the input of the simple
D2-C2 peak voltage detector section, which thus produces a DC output voltage
equal to the Vp-p value (rather than the peak value) of the AC
input voltage.
This circuit thus gives twice as much output voltage as a
conventional half-wave or full-wave rectifier circuit, and is thus known as a
‘voltage-doubling’ voltage multiplier.
The circuit can be made to generate a negative (rather than
positive) output voltage by simply reversing the polarities of C1-D1 and D2-C2.
One very important point to note about the basic Figure
2 circuit is that its output voltage actually equals Vp-p plus
the common ‘reference’ voltage (Vref) of D1-C2, which in this
particular example is 0V. Thus, if this circuit is modified so that Vref is
somehow raised to (say) +1000V, the 706V output of C2 will be added to that of
Vref to give a final output voltage of 1,706V, and so on.
The heart of the Figure 2 circuit is the
actual C1-D1-D2-C2 voltage doubler network. Figure 3(a) shows
the conventional diagram of this network and Figure 3(b) shows
it redrawn as a ‘standard’ voltage-doubling voltage multiplier section.
FIGURE 3. (a) Conventional voltage-doubler diagram,
and (b) the circuit redrawn in ‘standard’ form.
A major feature of the voltage-doubler is that numbers of
‘doublers’ can easily be interconnected to give various values of voltage
multiplication, and such circuits are best drawn by using the standard Figure
3(b) representation.
Figure 4,
for example, shows three of these ‘doubler’ stages interconnected to give a
voltage sextupler action in which the final output voltage is six times greater
than the peak value of the original 250V rms input voltage.
FIGURE 4. Three ‘doublers’ interconnected to give x6 voltage
multiplication.
Here, each ‘doubler’ section generates an individual output
(across its C2, C4, or C6 capacitor) of 706V, but the output of the first
doubler acts as the Vref point of the second doubler, and the
output of the second doubler acts as the Vref point of the
third doubler, the net effect being that the three individual output voltages
add together to give a final DC output of +2118V from the 250V AC input.
Note in the Figure 4 circuit that the input
capacitor of each section is fed directly from the AC input voltage, and needs
an absolute minimum voltage rating equal to that section’s output-to-ground
voltage, e.g., C5 needs a minimum rating of 2118V.
In the mid 1930s a modified version of the voltage
multiplier was designed to overcome this snag. Known as the Cockcroft-Walton
voltage multiplier, it uses standard voltage-doubler stages interconnected in
the manner shown in Figure 5.
FIGURE 5. This three-stage Cockcroft-Walton circuit gives x6
voltage multiplication.
This circuit is similar to that of Figure 4,
except that the input of each doubler (except the first) is fed from the
‘clamped’ AC voltage point of the preceeding doubler.
Consequently, the ‘minimum voltage rating’ requirement of
each component used in each doubler stage equals the peak-to-peak value of the
original AC input voltage.
A weakness of the Cockcroft-Walton voltage multiplier is
that its output impedance is rather high (it is proportional to the sum of the
impedances of the various input capacitors), and it can thus supply only small
output currents.
In practice, this type of voltage multiplier was originally
designed simply to generate a very high (up to about 30KV) accelerator voltage
on the final anode of cathode-ray tubes, an application which requires very
little energizing current.
Note that a 10-stage circuit of this type — when driven by a
500V AC input — generates a DC output of over 14KV, but the components used in
each stage have minimum voltage rating requirements of less than 1.5KV.
CHAPTER TWO
2.0
COMPONENTS OF THE DC DOUBLER
The circuit of the DC doubler
consists of the following components;
COMPONENTS
|
QUANTITY
|
555
Timer IC
|
1
|
3.3kΩ
Resistor
|
1
|
18kΩ
Resistor
|
1
|
10nf
Capacitor
|
1
|
100uf
Capacitor
|
1
|
10uf
Capacitor
|
2
|
Diode
IN4148
|
2
|
These components will now be
treated separately.
2.1 555
TIMER IC
IC 555 timer is a well-known component in the electronic
circles but what is not known to most of the people is the internal circuitry
of the IC and the function of various pins present there in the IC. Let me tell
you a fact about why 555
timer is called so, the timer
got its name from the three 5 kilo-ohm resistor in series employed in the
internal circuit of the IC.
IC 555 timer
is a one of the most widely used IC in electronics and is used in various
electronic circuits for its robust and stable properties. It works as
square-wave form generator with duty cycle varying from 50% to 100%, Oscillator
and can also provide time delay in circuits. The 555 timer got its name from
the three 5k ohm resistor connected in a voltage-divider pattern which is shown
in the figure below. A simplified diagram of the internal circuit is given
below for better understanding as the full internal circuit consists of over
more than 16 resistors, 20 transistors, 2 diodes, a flip-flop and many other
circuit components.
The 555 timer
comes as 8 pin DIP (Dual In-line Package) device. There is also a 556 dual
version of 555 timer which consists of two complete 555 timers in 14 DIP and a
558 quadruple timer which is consisting of four 555 timer in one IC and is
available as a 16 pin DIP in the market.
2.2 BASIC CONCEPTS
· Comparator:
The Comparator are the basic electronic component which compares the two input
voltages i.e. between the inverting (-) and the non-inverting (+) input and if
the non-inverting input is more than the inverting input then the output of the
comparator is high. Also the input resistance of an ideal comparator is
infinite.
· Voltage
Divider: As we know that the input resistance of the comparators is infinite
hence the input voltage is divided equally between the three resistors. The value
being Vin/3 across each resistor.
· Flip/Flop:
Flip/Flop is a memory element of Digital-electronics. The output (Q) of the
flip/flop is ‘high’ if the input at ‘S’ terminal is ‘high’ and ‘R’ is at ‘Low’
and the output (Q) is ‘low’ when the input at ‘S’ is ‘low’ and at ‘R’ is high.
2.3 Function of different Pins:-
1. Ground:
This pin is used to provide a zero voltage rail to the Integrated circuit to
divide the supply potential between the three resistors shown in the diagram.
2. Trigger:
As we can see that the voltage at the non-inverting end of the comparator is Vin/3,
so if the trigger input is used to set the output of the F/F to ‘high’ state by
applying a voltage equal to or less than Vin/3 or any negative
pulse, as the voltage at the non-inverting end of the comparator is Vin/3.
3. Output:
It is the output pin of the IC, connected to the Q’ (Q-bar) of the F/F with an
inverter in between as show in the figure.
4. Reset:
This pin is used to reset the output of the F/F regardless of the initial
condition of the F/F and also it is an active low Pin so it connected to ‘high’
state to avoid any noise interference, unless a reset operation is required. So
most of the time it is connected to the Supply voltage as shown in the figure.
5. Control
Voltage: As we can see that the pin 5 is connected to the inverting input
having a voltage level of (2/3) Vin. It is used to override the
inverting voltage to change the width of the output signal irrespective of the
RC timing network.
6. Threshold:
The pin is connected to the non-inverting input of the first comparator. The
output of the comparator will be high when the threshold voltage will be more
than (2/3) Vin thus resetting the output (Q) of the F/F from
‘high’ to ‘low’.
7. Discharge:
This pin is used to discharge the timing capacitors (capacitors involved in the
external circuit to make the IC behave as a square wave generator) to ground
when the output of Pin 3 is switched to ‘low’.
8. Supply:
This pin is used to provide the IC with the supply voltage for the functioning
and carrying of the different operations to be fulfilled with the 555 timer.
2.4
RESISTOR
A resistor is an electrical
components especially designed and having the property of resistant known as
resistance. It is used to control the amount of current flows in a particular
part of a circuit. Resistors are of two (2) types; fixed and variable
resistors.
Fixed resistors have their ohmic
value set by the manufacturer and cannot be easily changed. Examples of these
are the carbon composition, film and wire wound resistor.
The most commonly used is the carbon
composition resistor, which is made from a mixture of carbon black
(non-conductor), which are pressed and molded into rods by heating.
Variable resistor are designed in a
way that their resistance value can easily
be changed with a manual or an automatic adjustment.
There are basically two types which
are potentiometer and rheostat. Their schematic symbols are shown fig 3.4.
Fig.
2.4
In the circuit, a potentiometer is
used.
For the carbon, their values are
indicated by use of colour codes. eg |
|
||||
Fig
2.5 Diagram Showing Color Codes
The tolerance gives a range of
values that can be used in place of the given value. That is for a resistor
marked 470
5%,
any resistor that falls in the range of 446.5Ω to 493.5Ω can be used in place
of it.
5%,
any resistor that falls in the range of 446.5Ω to 493.5Ω can be used in place
of it.
The colour coding are given in table 1.
Table
1
Resistance value for
fist three band.
|
0
|
Black
|
1
|
Brown
|
|
2
|
Red
|
|
3
|
Orange
|
|
4
|
Yellow
|
|
5
|
Green
|
|
6
|
Blue
|
|
7
|
Violet
|
|
8
|
Grey
|
|
9
|
White
|
|
0.01
|
Silver
|
|
0.1
|
Gold
|
|
Tolerance
value for fourth band.
|
2%
|
Red
|
5%
|
Gold
|
|
10
|
Silver
|
|
20%
|
No
Band
|
The value of resistor is ohms (Ω).
2.5 CAPACTOR
A capacitor consist of two metal
surface separated by a dielectric. It is arranged in such a way that it has the
ability of storing electricity. This is termed capacitance. It is the constant of
proportionality between charge and potential difference (P.D.) of a system. The
unit of capacitances is called farad (F).
There are different types of
capacitor; air, paper, mica, ceramic and electrolytic capacitor. In this
project work, the electrolytic capacitor is used.
The electrolytic capacitor is the
most commonly used capacitor. It consists of two Aluminum foils, one with an
oxide foil and the other without any foil. They are separated with a paper
saturated with suitable electrolyte. The foil with the oxide is the positive
plate, the oxide layer is dielectric, the paper is the electrolytic and the
other aluminum foil, is the negative plate.
The electrolyte is used due to the
fact that it is suitable for comparatively high capacitance value ranging from
a few micro-farads to several thousands of micro-farads. The circuit symbol of
a capacitor is shown in fig. 3.6.
2.6 DIODE
A
diode is a specialized electronic component with two electrodes called
the anode and the cathode. Most diodes are made
with semiconductor materials such as silicon, germanium, or
selenium. Some diodes are comprised of metal electrodes in a chamber evacuated
or filled with a pure elemental gas at low pressure. Diodes can be used as
rectifiers, signal limiters, voltage regulators, switches,
signal modulators, signal mixers, signal demodulators, and oscillators.
The
fundamental property of a diode is its tendency to conduct
electric current in only one direction. When the cathode is
negatively charged relative to the anode at a voltage greater than a
certain minimum called forward break over, then current flows
through the diode. If the cathode is positive with respect to the anode, is at
the same voltage as the anode, or is negative by an amount less than the
forward break over voltage, then the diode does not conduct current. This is a
simplistic view, but is true for diodes operating as rectifiers, switches, and
limiters. The forward break over voltage is approximately six tenths of a volt
(0.6 V) for silicon devices, 0.3 V for germanium devices, and 1 V for selenium
devices.
The
above general rule notwithstanding, if the cathode voltage is positive relative
to the anode voltage by a great enough amount, the diode will conduct current.
The voltage required to produce this phenomenon, known as the avalanche
voltage, varies greatly depending on the nature of the semiconductor
material from which the device is fabricated. The avalanche voltage can range
from a few volts up to several hundred volts.
CHAPTER THREE
3.0 VARIOUS SECTIONS OF THE DC DOUBLER
CIRCUIT
The DC doubler circuit consists of
or better still divided into four major parts. These are;
Ø The
Oscillator Unit.
Ø The
Diode-Capacitor Network.
These units are further discussed below.
3.1 THE
OSCILLATOR UNIT
The 555
Timer IC can be connected either in its Monostable mode thereby
producing a precision timer of a fixed time duration, or in its Bistable mode
to produce a flip-flop type switching action. But we can also connect the 555
timer IC in an Astable mode to produce a very stable 555 Oscillator circuit
for generating highly accurate free running waveforms whose output frequency
can be adjusted by means of an externally connected RC tank circuit consisting
of just two resistors and a capacitor.
The 555
Oscillator is another type of relaxation oscillator for generating
stabilized square wave output waveforms of either a fixed frequency of up to
500kHz or of varying duty cycles from 50 to 100%. In the previous 555 Timer
tutorial we saw that the Monostable circuit produces a single output one-shot
pulse when triggered on its pin 2 trigger input.
Whereas
the 555 monostable circuit stopped after a preset time waiting for the next
trigger pulse to start over again, in order to get the 555 Oscillator to
operate as an astable multivibrator it is necessary to continuously re-trigger
the 555 IC after each and every timing cycle.
This
re-triggering is basically achieved by connecting the trigger input
(pin 2) and the threshold input (pin 6) together, thereby
allowing the device to act as an astable oscillator. Then the 555 Oscillator
has no stable states as it continuously switches from one state to the other.
Also the single timing resistor of the previous monostable multivibrator
circuit has been split into two separate resistors, R1 and R2 with
their junction connected to the discharge input (pin 7) as
shown below.
3.2 Basic Astable 555
Oscillator Circuit
In
the 555 Oscillator circuit above, pin 2 and pin 6 are
connected together allowing the circuit to re-trigger itself on each and every
cycle allowing it to operate as a free running oscillator. During each cycle
capacitor, C charges up through
both timing resistors, R1 and R2 but discharges itself only through
resistor, R2 as the other side
of R2 is connected to the discharge terminal,
pin 7.
Then
the capacitor charges up to 2/3Vcc (the upper comparator limit) which is
determined by the 0.693(R1+R2)C combination
and discharges itself down to 1/3Vcc (the lower comparator limit) determined by
the 0.693(R2*C) combination. This
results in an output waveform whose voltage level is approximately equal
to Vcc – 1.5V and whose output
“ON” and “OFF” time periods are determined by the capacitor and resistors
combinations. The individual times required to complete one charge and
discharge cycle of the output is therefore given as:
Astable 555 Oscillator Charge and Discharge Times
Where, R is in Ω and C in
Farads.
When
connected as an astable multivibrator, the output from the 555
Oscillator will continue indefinitely charging and discharging between
2/3Vcc and 1/3Vcc until the power supply is removed. As with the monostable
multivibrator these charge and discharge times and therefore the frequency are
independent on the supply voltage.
The
duration of one full timing cycle is therefore equal to the sum of the two
individual times that the capacitor charges and discharges added together and
is given as:
3.3 555 Oscillator Cycle
Time
The
output frequency of oscillations can be found by inverting the equation above
for the total cycle time giving a final equation for the output frequency of an
Astable 555 Oscillator as:
3.4 555 Oscillator
Frequency Equation
By
altering the time constant of just one of the RC combinations,
the Duty Cycle better known as the “Mark-to-Space” ratio of
the output waveform can be accurately set and is given as the ratio of
resistor R2 to resistor R1. The Duty Cycle for the 555 Oscillator, which
is the ratio of the “ON” time divided by the “OFF” time is given by:
3.5 555 Oscillator Duty
Cycle
The
duty cycle has no units as it is a ratio but can be expressed as a percentage
( % ). If both timing resistors, R1 and R2 are equal in value, then the output duty
cycle will be 2:1 that is, 66% ON time and 33% OFF time with respect to the
period.
555 Oscillator Example No1
An Astable
555 Oscillator is constructed using the following components, R1 = 1kΩ, R2 =
2kΩ and capacitor C = 10uF.
Calculate the output frequency from the 555 oscillator and the duty cycle of
the output waveform.
t1 –
capacitor charge “ON” time is calculated as:
t2 –
capacitor discharge “OFF” time is calculated as:
Total
periodic time ( T ) is therefore calculated as:
The
output frequency, ƒ is therefore
given as:
Giving
a duty cycle value of:
As
the timing capacitor, C charges
through resistors R1 and R2 but only discharges through resistor R2 the output duty cycle can be varied
between 50 and 100% by changing the value of resistor R2. By decreasing the value of R2 the duty cycle increases towards 100% and
by increasing R2 the duty cycle
reduces towards 50%. If resistor, R2 is
very large relative to resistor R1 the
output frequency of the 555 astable circuit will determined by R2 x C only.
The
problem with this basic astable 555 oscillator configuration is that the duty
cycle, the “mark to-space” ratio will never go below 50% as the presence of
resistor R2 prevents this. In
other words we cannot make the outputs “ON” time shorter than the “OFF” time,
as (R1 + R2)C will always be
greater than the value of R1 x C. One
way to overcome this problem is to connect a signal bypassing diode in parallel
with resistor R2 as shown below.
Improved 555 Oscillator Duty Cycle
By
connecting this diode, D1 between
the trigger input and the discharge input,
the timing capacitor will now charge up directly through resistor R1 only, as resistor R2 is effectively shorted out by the diode.
The capacitor discharges as normal through resistor, R2.
An
additional diode, D2 can be connected
in series with the discharge resistor, R2 if
required to ensure that the timing capacitor will only charge up through D1 and not through the parallel path of R2. This is because during the charging process
diode D2 is connected in reverse
bias blocking the flow of current through itself.
Now
the previous charging time of t1 =
0.693(R1 + R2)C is modified to take account of this new charging
circuit and is given as: 0.693(R1 x C).
The duty cycle is therefore given as D =
R1/(R1 + R2). Then to generate a duty cycle of less than 50%,
resistor R1 needs to be less than
resistor R2.
Although
the previous circuit improves the duty cycle of the output waveform by charging
the timing capacitor, C1 through
the R1 + D1 combination and then
discharging it through the D2 + R2 combination,
the problem with this circuit arrangement is that the 555 oscillator circuit
uses additional components, i.e. two diodes.
We
can improve on this idea and produce a fixed square wave output waveform with
an exact 50% duty cycle very easily and without the need for any extra diodes
by simply moving the position of the charging resistor, R2 to the output ( pin 3 ) as shown.
50% Duty Cycle Astable Oscillator
The
555 oscillator now produces a 50% duty cycle as the timing capacitor, C1 is now charging and discharging through
the same resistor, R2 rather than
discharging through the timers discharge pin 7 as before. When the output from
the 555 oscillator is HIGH, the capacitor charges up through R2 and when the output is LOW, it discharges
through R2. Resistor R1 is used to ensure that the capacitor
charges up fully to the same value as the supply voltage.
However,
as the capacitor charges and discharges through the same resistor, the above
equation for the output frequency of oscillations has to be modified a little
to reflect this circuit change. Then the new equation for the 50% Astable 555
Oscillator is given as:
50% Duty Cycle Frequency Equation
Note
that resistor R1 needs to be
sufficiently high enough to ensure it does not interfere with the charging of
the capacitor to produce the required 50% duty cycle. Also changing the value
of the timing capacitor, C1 changes
the oscillation frequency of the astable circuit.
3.6 THE DIODE-CAPACITOR NETWORK
CHAPTER
FOUR
4.0 THE PRACTICAL CIRCUITS
A DC voltage can easily be converted into one of greater value or of reversed polarity by using the DC supply to power a free-running 1KHz to 30KHz square wave generator that has its output fed to a voltage multiplier of one of the basic types already described, which thus provides the desired ‘converted’ DC output voltage.
A DC voltage can easily be converted into one of greater value or of reversed polarity by using the DC supply to power a free-running 1KHz to 30KHz square wave generator that has its output fed to a voltage multiplier of one of the basic types already described, which thus provides the desired ‘converted’ DC output voltage.
4.1 PRACTICAL DEMONSTRATION CIRCUIT
Figure 6 shows a practical
demonstration circuit of this type.
FIGURE
6. Basic ‘voltage
doubler’ demonstration circuit.
The Figure 6 circuit uses a
type-555 ‘timer’ IC (which can supply fairly high output currents) as a
free-running squarewave generator that operates at about 3KHz (determined by
the R1-R2-C2 values), and directly drives the C3-D1-D2-C4 ‘doubler’ stage,
which (ideally) produces a DC output equal to the peak-to-peak output of the
squarewave, which (ideally) equals the Vcc value.
In practice, the squarewave’s peak-to-peak
value is slightly less than Vcc, and the ‘doubler’ loses another 1.2V in
volt-drops in D1 and D2, the net result being that the actual output (when very
lightly loaded) is about 1.6V less than Vcc, e.g., 8.4V with a 10V supply. The
circuit can use any supply in the range 5V to 15V.
4.2 MORE USEFUL VERSION OF THE CIRCUIT
Figure 7 shows a far more useful version of the
basic Figure 6 ‘voltage-doubler’ circuit.
FIGURE
7. DC
voltage-doubling circuit. (Project
Circuit Diagram)
In this version, the C3-D1-D2-C4 ‘doubler’ is
tied to the positive (rather than 0V) supply line, and its output voltage is thus
added to that of the supply line, thus giving a DC output voltage (when lightly
loaded) of almost two times Vcc.
In practice, the prototype circuit gives an
output of almost 19V when using a 10V supply.
4.3 CASCADED ‘VOLTAGE
DOUBLER’ CIRCUIT
Figure 8 shows the Figure 7 circuit
modified for use with a cascaded pair of ‘doubler’ stages, in a configuration
that is known (because it generates a DC output four times greater than a basic
peak AC input voltage) as a ‘voltage quadrupler.’
FIGURE
8. Cascaded
‘voltage doubler’ circuit.
Here, the output of the new C5- D3-D4-C6
‘doubler’ stage (which is a couple of volts less than Vcc) is added to that of
the basic Figure 7 circuit, thus giving a DC output voltage
(when lightly loaded) of almost three times Vcc.
In practice, the prototype circuit gives an
output of 27V when using a 10V supply.
CHAPTER
FIVE
CONCLUSION/RECOMMENDATION
AND REFERENCE
5.1 CONCLUSION
The circuit worked
perfectly well when I the load was below 70mA. The circuit efficiency reduces
when loaded above 70mA, there the circuit the maximum load must not exceed 70
mA.
On lower current ratings, the voltage is higher.
If a stable voltage lever is desired, a 3 pin voltage regulator IC can be added at the output. The regulator IC’s own current consumption must be added to the total current consumption which must not exceed 70 mA.
On lower current ratings, the voltage is higher.
If a stable voltage lever is desired, a 3 pin voltage regulator IC can be added at the output. The regulator IC’s own current consumption must be added to the total current consumption which must not exceed 70 mA.
5.2
RECOMMENDATION
The
school management should be the availability of good and current textbooks to
aid students in projects like this.
Ø The
department should endeavor to ensure that components of different values are
made available to students at a considerable amount to check the risk involved
in travelling or transportation to get the required components.
Ø The
department should endeavor to ensure the availability of constant power supply
in the workshops.
Ø This
project is recommended for schools and academic laboratories and also for
students that want embark on this type of project work.
Ø It
is also recommended that the government should render assistance to
5.3
REFERENCES
M.
Nelkon, (1977), Principle of Physics, 7th Edition, Hart-Davis
Educational.
Hughes
E., (1987) Electrical Technology, Longman Scientific Publication, London Group,
London.
Theraja
B. L. and Theraja A. K., (2002), A textbook of Electrical Technology, S. Chand
& Co. Ltd, New Delhi.
Odunsi
J. A., Electrical Maintenance and Repairs, Ayenbros Enterprises, Lagos.
www.wikipedia.org
and other websites via Google search.
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