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Low Cost High Current Waveform Generator
2013
London South Bank University
Final Project Report
Department of Engineering and Design,
BEng (Hons) Project in Electrical
Engineering (SES)
Title: Low Cost High Current Waveform Generator
Author: Rahat Hasan
Academic Session: 2012/13
Supervisor: Dr. G.H. Shirkoohi
Course Title: BEng Electrical and Electronic Engineering
Mode of Study: Full Time
Date: 10/05/2013
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Low Cost High Current Waveform Generator
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TITLE: LOW COST HIGH CURRENT WAVEFORM GENERATOR
NAME: RAHAT HASAN
ID: 2822815
COURSE: BENG ELECTRICAL AND ELECTRONICS
ENGINEERING (SES)
SUBMISSION DATE: 10/03/2013
This report has been submitted for assessment towards a Bachelor
of
Engineering Degree in Electrical and Electronic Engineering in
the
Department of Engineering and Design, London South Bank
University.
The report is written in the authors own words and all sources
have been
properly cited.
Authors signature:
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Low Cost High Current Waveform Generator
2013
Table of Contents Introduction
..................................................................................................................
1
Project Aim
...................................................................................................................
2
Project Objectives
........................................................................................................
2
Deliverables
..................................................................................................................
2
Technical Background and Context
.............................................................................
3
Buck converter and components
..............................................................................
3
How Buck converter (synchronous) works
...............................................................
4
Calculation of synchronous buck converters power stage
...................................... 5
What is Mosfet and how it works
.............................................................................
6
What is inductor and how it works
...........................................................................
7
What is Schmitt trigger and how it works
.................................................................
9
What is optocoupler and how it works
...................................................................
10
What is a transistor and how it works
....................................................................
11
What is capacitor and how it works
........................................................................
11
Technical approach
....................................................................................................
14
Scope of the project
................................................................................................
14
Specification of the product
....................................................................................
14
Design of the product
.............................................................................................
14
Generation of PWM waveform
...............................................................................
14
Approach 1
..............................................................................................................
15
Problem with Approach 1
.......................................................................................
17
Approach 2
..............................................................................................................
17
Procedure of measurement
....................................................................................
19
Apparatus information (TDS 2004B Four Channel Oscilloscope)
........................... 19
Mosfet Driver Circuit (Generation of synchronous PWM
waveforms)................... 19
Approach 1
..............................................................................................................
19
Problem with the approach
....................................................................................
21
Approach 2
..............................................................................................................
21
Problem with the approach
....................................................................................
23
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Low Cost High Current Waveform Generator
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Approach 3
..............................................................................................................
23
Construction of an air cored inductor
.....................................................................
25
Approach 1
..............................................................................................................
27
Problem with the approach
....................................................................................
28
Approach 2
..............................................................................................................
28
The size of the wire used
........................................................................................
29
Measurement of the inductance
............................................................................
30
Determining the capacitor for the buck converter
................................................. 30
Issue with the capacitive value
...............................................................................
31
Construction of a capacitor bank
............................................................................
31
Measurement of the capacitance
...........................................................................
32
Time constant of the LC circuit
...............................................................................
32
Device under Test
...................................................................................................
33
How the whole circuit is expected to work
............................................................ 33
Initial rejected solution for the project
...................................................................
34
Solution 1
................................................................................................................
34
Solution 2
................................................................................................................
35
Research on similar product in the market
............................................................ 36
Cost of the Product
.................................................................................................
37
Results and Discussion
...............................................................................................
38
Conclusion and Recommendations for Further Work
.............................................. 43
Reference
....................................................................................................................
44
Appendix
.....................................................................................................................
46
Approach 1 software code
......................................................................................
46
Approach 2 software code
......................................................................................
47
CD40106B Hex Schmitt Trigger datasheet
..............................................................
48
P14NF10 N-channel mosfet datasheet
...................................................................
49
Project Planning
.........................................................................................................
50
Work breakdown structure
.....................................................................................
50
Gantt chart
..............................................................................................................
51
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Low Cost High Current Waveform Generator
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Abstract
The idea of the project is to develop a product which is capable
of fluctuating
the input voltage to a user defined output voltage. To achieve
this, the
hardware parts of the product was designed according to the
concept of a
synchronous buck converter, which converts a fixed input voltage
into a
regulated output voltage which is equal to or lower than the
input voltage. The
main problem encountered in designing the hardware was to
operate it at a
high frequency as mentioned in the specification. Since the
components used
cannot handle high frequency, the operating frequency of the
whole product
was brought down to a low value. The hardware part was then
interfaced with
the PC using an Arduino UNO development board which will allow
the user to
define the output voltage in a specified period in order to
generate a sample of
test waveforms.
The product was tested by altering the duty cycle to observe the
output voltage
which was not exactly same as the expected value due to the
mismatch of the
operating frequency between parts of the hardware and this
resulted in the
failure to generate test waveforms. Also a research was
conducted on similar
products that exist in the market and a brief comparison was
then made
between products.
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Introduction
The most common issue seen in cars is normally caused by
disturbances in the
car battery which is due to the faulty conditions arising when
the car is in
crank mode. This can result in damage to all the electronic
components
working in multiple buses such as FM/AM radio, speedometer, etc.
To
overcome this problem, automotive manufacturing industries have
to ensure
that their products are tested for tolerance to faulty
conditions before they are
fitted inside the car. Replicating similar faulty conditions on
a test bench can
be a problem due to the unavailability of proper
instruments.
The idea of this project is to come up with a product which is
capable of
replicating the faulty conditions on test bench by generating
waveforms which
can then be tested on the electronic components in the car to
improve their
tolerance. The waveforms need to be generated to test the faulty
conditions are
crank waveform, voltage drop out waveform, ramp up and ramp
down
waveform. The outcome product from this project would be able to
create all
these waveforms and also repeat them in sequence. [1] The Low
Cost High
Current Waveform Generator (LCHCWG) provides the user with
four
benefits mentioned below:
The capability to generate waveforms with a high transient
current of
0-50A which can then be tested across the device under test
(DUT).
The ability to generate waveforms with high voltage range,
normally
from 0 to 12V. This will allow the user to create a wide range
of
waveforms similar to the faulty conditions.
The ability of the hardware part of the product to interface
with PC via
user-friendly software which makes it easier for the user to
vary the
output voltage.
The capability to produce stable output.
The designed product LCHCWG is based on the concept of a
synchronous
buck converter which consists of two gate driven mosfets, an
inductor and
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capacitor. The mosfets are controlled via a TTL signal from a
software
development board allowing the user to output the desired
voltage levels. By
changing the voltage to different levels, the user can then
simulate vehicle
battery disturbances waveforms.
One of the key benefits that can be gained by performing this
project is that it
will allow automotive companies to manufacture product testing
tools at a
lower price which means they can purchase more tools within the
company
budget and will allow the company to test more of their products
at a short
time.
Project Aim
The aim of this project is to identify a way of producing a
cost-effective
product which is capable of generating waveforms used to test
the tolerance of
car components.
Project Objectives
Generation of waveforms used for testing tolerance of
electronic
components in car.
Research on similar products that already exists in the
market.
Production of a cost-effective hardware which is capable of
fluctuating
input voltage.
Interfacing the hardware to the PC using user friendly
software.
Comparison between the market product and the outcome product
from
this project.
Deliverables
Progression, Interim and Final reports.
The presentation talk.
Simulating waveforms similar to faulty conditions such as crank
waveform, voltage drop out waveform, ramp up and ramp down
waveform with the help of a synchronous buck converter.
Controlled variation of voltage over a time period with the help
of an Arduino UNO development board.
Generate very fast output transitions of high currents, thus
exceeding the transient performance of power supplies.
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Stable ripple free output.
Able to interface with PC and/or possibly via vehicle control
interface.
Technical Background and Context
The main aim of this project is to allow automotive companies to
test their
products within a short time and in a cost effective way which
would be
beneficial as it will reduce the man hour required for
testing.
The most common problem is when a car is subjected to high
current surge
caused by disturbances in the car battery during crank mode.
This can result in
damage to all the electronic components working in multiple
buses such as
FM/AM radio, speedometer, etc. In order to solve this problem,
automotive
manufacturing industries have to ensure that their products are
tested for
tolerance to faulty conditions by applying a test waveform
across the
electronic components.
The main benefits obtained from this project is that it will
allow automotive
companies to manufacture product testing tools at a low price
which means
they can manufacture more testing tools within the company
budget and will
allow the company to test more of their products at a short time
period as most
of the test sequence is automatic and can be run for 24 hours
without the need
for human presence.
Buck converter and components There are two components to the
project: hardware and software. The
hardware part of this project is based on synchronous buck
converter. A
synchronous buck converter is step-down dc to dc converters
which converts a
fixed input voltage into a regulated output voltage which is
equal to or lower
than the input voltage. They are mostly used in electronics for
achieving an
ideal low voltage level for a particular component from a
constant input
voltage level.
A synchronous buck converter consists of two switches- a high
side switch
and a low side switch (nowadays switches are replaced with
mosfets to reduce
power loss), an inductor and a capacitor. The output voltage
from the
converter is then fed into a resistive load. A basic design of a
synchronous
buck converter is shown below in figure 1. [2]
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Figure 1: A basic synchronous buck converter [2]
How Buck converter (synchronous) works In synchronous buck
converter, the duty cycle in the two Mosfets used
controls the output voltage by varying the ON and OFF durations
for the
mosfets where the frequency at which the two mosfets operates is
kept
constant. The two mosfets are operated via a TTL PWM (Pulse
Width
Modulaion) signals which are complementary to each other, i.e.
when Q1 is
on, Q2 is off. When the Mosfet Q1 is on, the energy is
transferred from the d.c
supply to the inductor and the amount of energy that is
transferred depends on
the Mosfet Q1 ON time. This produces a voltage drop across the
inductor, the
capacitor and the load. The voltage that is developed across the
inductor
during the Q1, the time is equals to (Vin Vo). The circuit for
the Mosfet Q1
on time is shown below in figure 2. [3]
Figure 2: Circuit when Q1 is on
When Mosfet Q1 is switched off and Mosfet Q2 is turned on, the
supply is
removed from the circuit and all the energy in the inductor is
then passed to
the capacitor and the load. At this point, the voltage across
the inductor equals
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to Vo. The circuit for the Mosfets Q1 off and Q2 on is shown
below in figure
3. [3]
Figure 3: Circuit when Q1 is off and Q2 is on
When the inductor is in steady state, the average current
flowing through it is
equal to the average output current as the average current in
the capacitor is
zero. In synchronous buck converter, there are two different
types of
operations: continuous and discontinuous conduction mode, where
continuous
conduction mode is the most preferred mode of operation. In
discontinuous
conduction mode, current in the inductor reaches zero due to all
the energy
stored in the inductor being transferred to the capacitor before
mosfet Q1 is
turned on again. In continuous conduction mode, the mosfet Q1 is
turned on
again before the current in the inductor reaches zero. [3]
Calculation of synchronous buck converters power stage The
parameters required to calculate the power stage are as
follows:
Input voltage
Nominal output voltage
Maximum output current
Switching frequency
The first step is to calculate the inductor ripple current ( )
which is often
estimated to be 20% to 40% of the output current of the buck
converter.
.eq1.
Where = Maximum output Current
The next step to then to determine the inductor value. A higher
inductor value
will allow larger maximum current output as the ripple current
of the converter
is reduced. Therefore, a smaller inductor will give a smaller
solution size. It is
often recommended to use an inductor with higher current rating
than the
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maximum output current as the current will increase when the
inductance
decreases. The equation for the inductor is shown below:
eq2.
Where = Input voltage; = Output voltage; = Switching
frequency;
= Inductor ripple current.
The last step is to calculate the value of the capacitor for the
filter. It is
required to use a capacitor with low Effective Series Resistance
(ESR) value
as it will reduce the output voltage ripple. In most cases,
ceramic capacitors
are preferred. For a converter with internal compensation, the
output capacitor
value has to be adjusted in the ratio of L and C whereas for a
converter with
external compensation, the equation shown below is used to
adjust the value of
the capacitor for a desired output voltage ripple:
.eq3.
Where = Ripple output voltage; = Switching frequency; =
Inductor
ripple current. [4]
What is Mosfet and how it works A mosfet is a metal oxide
semiconductor field effect transistor normally found
in digital ICs. Mosfet consists of a gate (G), a source (S) and
a drain (D).
Mosfets are normally categorized into two types: then MOS
transistor and the
MOS transistor where the polarity of the conduction is opposite
to each other.
Figure of a basic mosfet and the different types of mosfets are
shown below:
Figure 4: Structure of a basic mosfet, nMOS and pMOS.
A mosfet can be used as a digital switch where the gate terminal
is similar to a
switch on the wall. At a high gate voltage, the mosfet acts as a
closed switch
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and electricity flows from the drain to the source. A mosfet
requires a certain
voltage for the drain and the source to be electrically
connected which is the
mosfets threshold voltage. For the nMOS, the threshold voltage
is positive
whereas for pMOS, the threshold voltage is negative.
When a mosfet acts as a switch, there are only two conducting
states on and
off which are normally controlled via the gate voltage. At the
on state, there is
no resistance across the drain and the source whereas at off
state, the
resistance is infinite. In non-ideal condition, the resistance
during on state is
non-zero and there is a delay during the change of state.
In an nMOS, at an input voltage lower than the gate-source
voltage, the device
stops conducting and it acts as an open switch. At an input
voltage higher than
the gate-source voltage, the drain and the source become
electrically
connected and the device acts as a closed switch. For a pMOS,
the signals
have an opposite polarity so during an off state, the
gate-source voltage
becomes higher than the input voltage and during on state, the
gate-source
voltage becomes lower than the input voltage. The different
states of nMOS
and pMOS are shown below in figure 5: [5]
Figure 5: Different states of nMOS and pMOS. [5]
What is inductor and how it works An inductor is a passive
device which stores electrical energy in the form of
magnetic field. In an inductor, a conductor is coiled into a
core where
electricity flows from left to right which produces a magnetic
field in the
clockwise path. The direction of the magnetic field is shown
below in figure 6:
[6]
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Figure 6: Direction of the magnetic field. [6]
One of the main properties of the inductor is dependent on the
number of turns
of conductor used. The more the number of turns coiled around
the core, the
more magnetic fields are produced. The magnetic field is also
proportional to
the cross-sectional area of the coil i.e. the larger the
cross-sectional area the
more the magnetic field produced. The equation used to calculate
the
inductance of an inductor is shown below:
Where:
L = Inductance required.
= Permeability of free space, 4 .
= Relative permeability, 1 (Due to the presence of air
core).
A = Cross-sectional area of the coil.
l = Length of the coil.
N = Number of turns of the coil. [6]
The behaviour of an inductor is very different when an AC
current flows
through it. The magnetic field produced when the AC current
flows through it
cuts the conductor winding and therefore producing an induced
voltage which
hinders any current change. When there is a rise in the current,
an
electromotive force is produced in the opposite direction which
then hinders
the current to rise. The behaviour of an inductor to current
change is shown
below in figure 7: [6]
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Figure 7: The behaviour of an inductor to current change.
[6]
When a DC current is applied across an inductor, no magnetic
field is
produced and as a result, no induced voltage is generated.
Therefore, an
inductor only allows a DC current to flow through it. The
behaviour of an
inductor under DC current is shown below in figure 8:
Figure 8: The behaviour of an inductor under DC current. [6]
What is Schmitt trigger and how it works A Schmitt trigger is a
type of comparator which produces a negative output
when the input fed into it is positive compared to the reference
voltage. Using
the negative feedback built into it, it stays in that state
until the input is lower
compared to the threshold voltage. A schematic diagram of the
Schmitt trigger
and the input and output waveforms are shown below in figure
9:
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Figure 9: A schematic diagram of the Schmitt trigger and the
input and
output waveforms.
The main function of a Schmitt trigger is to produce a stable
level-crossing
switch. [7]
What is optocoupler and how it works Optocoupler is a device
used to transfer signals from one part of the subsystem
to another without a direct electrical connection. An
optocoupler normally
contains two devices: a light-emitting diode (LED) and a photo
transistor.
When current flows through the LED, it shines light onto the
base of the photo
transistor which then allows current to flow through the
collector and the
emitter. The optocoupler can be operated as a switching device
by switching
the LED on and off and therefore output an on-off controlled
signal from the
phototransistor. A schematic diagram of a phototransistor is
shown below in
figure 10: [8]
Figure 10: A schematic diagram of an optocoupler. [8]
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What is a transistor and how it works A transistor is normally
used as an amplifier or a switch. There are three parts
in a transistor: base, collector and emitter. The base is where
signals are
applied to trigger the transistor. The collector is the positive
part of the
transistor and the emitter is the negative part. The amount of
current flow in
the transistor can be controlled by applying different levels of
current at the
base of the transistor. A schematic diagram of a NPN transistor
is shown
below in figure 11: [12]
Figure 11: A schematic diagram of a NPN transistor. [9]
There are two different types of junction transistor: NPN and
PNP. In this
report, the main focus is on the NPN transistor. In an NPN
transistor, the
middle layer is P-type whereas the outside layer is N-type. In
order for the
NPN transistor to operate, the base voltage has to be more
positive than the
emitter voltage and the collector voltage has to be more
positive than the base
voltage. This allows electrons to flow from the emitter to the
base and
therefore electricity will flow through the transistor.
What is capacitor and how it works A capacitor is a device which
is capable of storing electrical energy in the
form of electrons. It consists of two conducting plates
separated by a dielectric
which is a non-conducting substance. Depending on the type of
dielectric
used, the capacitor is capable of handling high voltages. A
picture of dielectric
used in between a two conducting plates in a capacitor is shown
below in
figure 12: [10]
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Figure 12: A picture of dielectric used in between a two
conducting plates in a
capacitor. [10]
When a capacitor is connected across a battery with voltage V, a
capacitance
of C and a current of I is produced. The electrons flow from the
metal plate
which is connected to the negative side of the battery to the
metal plate which
is connected to the positive part of the battery. The charging
equation of a
capacitor is shown below:
dQ = C dV and I = C dV/dt.
Where: dQ = Minute change in charge.
dV = Minute change in voltage.
The figure 13 below shows a circuit where a capacitor is
connected across a
battery. [10]
Figure 13: A capacitor connected across a battery. [10]
When two capacitors C1 and C2 are connected across a battery of
voltage V,
the voltage is distributed between C1 and C2 depending on the
capacitance.
The current I remains the same throughout the series
circuit.
Total voltage, V = V1 + V2.
Total capacitance, C total =
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The total capacitance for a circuit with n capacitors connected
in series:
When two capacitors are connected in parallel across a battery
of voltage V,
the voltage across the capacitors remain same whereas, the
charge flowing
through the capacitor is distributed between C1 and C2.
Total charge, Q = Q1 + Q2.
Total capacitance, C total =
C total = C1 + C2.
The total capacitance for a circuit with n capacitors connected
in parallel:
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14
Technical approach
Scope of the project The scope of the project is to design a
waveform generating unit which is
capable of producing power disturbances waveform such as random
cranking
waveform, fast transient burst, multi-step Square waves, ramp
waveform, etc.
One possible way of achieving the project is by using Buck
Converters [4]
where the input voltage from the battery supply is regulated to
give output
voltage which ranges from 0 to input voltage. Using Pulse Width
Modulation
technique, the user is capable of creating any desired waveforms
by changing
the level of the voltage over a period of time.
Moreover, in order to make the product user friendly,
microcontroller based
control is introduced in to the product. The development board
used to control
the buck converters is Arduino Uno. The main feature of the
board is the
capability to have six PWM outputs which can be used to control
the Buck
Converters [5].
Specification of the product
The input voltage of the product, . The nominal output voltage
of the product, at a
resolution of 0.1 steps.
The maximum output current of the product,
Design of the product The product is composed of two important
parts: the hardware and the
software. The hardware part of the product contains a buck
converter, a circuit
to generate synchronous waveforms to drive the buck converter
and a software
development board. The buck converter consists of two mosfets,
an inductor
and a capacitor. The two mosfets used are synchronised i.e. when
one mosfet
is on, the other mosfet is off.
Generation of PWM waveform Arduino Uno SMD board is used for the
purpose of generating high frequency
PWM waveform. It is designed with an ATmega328 microcontroller
with 14
digital input/output pins of which 6 output PWM waveform. One of
the timers
(TimerOne is used in this case) embedded in the board are used
to output
PWM at high frequency through one of the six PWM pins (pin 10 is
used in
this project). A snapshot of the Arduino board used is shown in
figure 14: [11]
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Figure 14: Arduino SMD development board. [11]
The step by step procedure to generate the high frequency PWM
waveform is
described below:
The Arduino Uno software is installed on laptop from the
official website of Arduino.
The library for timer1 is downloaded from
http://arduino.cc/playground/Code/Timer1. The maximum PWM
frequency that can be achieved from Timer 1 is 1 MHz and the
PWM
waveform can be varied from a duty cycle range of 128 - 1024
bits.
Approach 1 The code used to generate high frequency PWM is
compiled and uploaded
into the Arduino board. The code used to generate high frequency
PWM is
shown below:
# include TimeOne.h // select TimerOne in the Arduino Uno
board.
void setup ()
{
pinMode (10, OUTPUT); // select digital pin 10 and use it as an
output
Timer1.initialize (1); // set the period of the PWM waveform in
us.
Timer1.pwm (10, 512); // set the duty cycle of the PWM waveform
from pin
10.
}
void loop (){
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}
The actual code in the Arduino software window is shown below in
figure 15:
Figure 15: Code in the Arduino software window.
The PWM waveform obtained from the Arduino board was distorted
at a
higher frequency. As a result, the period of the PWM waveform
was increased
to 100 us. The waveform observed is shown below in figure
16:
Figure 16: A PWM waveform with a period of 100 us.
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Problem with Approach 1 The main problem with approach 1 is that
it produced PWM signal from pin
10 only and therefore the PWM signal has to be divided into two
and then
inverted in the hardware before they are passed into the gate of
the two
Mosfets in the buck converter. This will not allow any
propagation delay
between the two signals which might cause the mosfets to short
out.
Approach 2 Approach 2 involves generating two out of phase PWM
signals from pin 9 and
pin 10 of the Arduino board. The code shown below is capable of
generating
two PWM waveforms: one at 70% duty cycle and another at 30% duty
cycle.
int pinA = 9; // introducing a variable pin A.
int pinB = 10; // introducing a variable pin B.
void setup()
{
pinMode (pinA, OUTPUT); // set pin A to be output.
pinMode (pinB, OUTPUT); // set pin B to be output.
}
void loop()
{
digitalWrite (pinA, LOW); // set pin A to low (0V).
delayMicroseconds (70); // set a delay of 70 us.
digitalWrite (pinA, HIGH); // set pin A to high (5V).
delayMicroseconds (1); // set a delay of 1 us.
digitalWrite (pinB, LOW); // set pin B to low (0V).
delayMicroseconds (30); // set a delay of 30 us.
digitalWrite (pinB, HIGH); // set pin B to high (5V).
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delayMicroseconds (1); // set a delay of 1 us.
}
The outputs from pin 9 and pin 10 are then passed into a Mosfet
driver circuit
which then generates two out of phase PWM waveforms of 70% and
30% duty
cycle to be passed to the gates of the two Mosfets in the buck
converter. The
waveforms produced are at a frequency of about 10 kHz which
provides a
suitable frequency as well as a propagation delay between the
switching of the
two Mosfets. The actual code in the Arduino software window is
shown below
in figure 17:
Figure 17: Code in the Arduino software window.
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Procedure of measurement The procedure of observing the PWM
waveform generated by the Arduino
Uno board is by connecting channel 1 of TDS 2004B Four
Channel
Oscilloscope to pin 10 of the Arduino board and then pressing
Autoset on
the oscilloscope.
Apparatus information (TDS 2004B Four Channel Oscilloscope) The
main application of this apparatus is for designing, debugging
and
educational purposes. It is capable of performing full sample
rate and full
record length which is important for accurate acquisition. One
of the important
features is a front panel USB port which makes it easier to
analyse the data by
transferring it to PC. Other features include multipurpose
knob,
AUTORANGE function and AUTOSET button used to detect a
waveform.
The other specifications of the apparatus are listed below:
[12]
Bandwidth 60MHz.
Time base (maximum) 50s/div.
Vertical sensitivity (maximum) 2V/div.
Time base (minimum) 5ns/div.
Vertical sensitivity (minimum) 2mV/div.
Sample rate 1Gsps.
Vertical resolution 8bit.
Mosfet Driver Circuit (Generation of synchronous PWM
waveforms) Two methods are being proposed to generate two PWM
waveforms that are
complementary to each other, i.e. when one waveform is high, the
other
waveform is low. The methods used are mentioned below:
Approach 1 In this circuit, a Schmitt trigger is used to
generate two synchronous
waveforms and it works in conjunction with approach. It is used
to generate
PWM waveform from the Arduino board. The schematic diagram of
the
Schmitt trigger used is shown below in figure 18:
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Figure 18: A schematic diagram of CD40106B Hex Schmitt Trigger.
[13]
Pin 1 of the Schmitt trigger is connected to the output from the
Arduino
development board (pin 10). The input to the Schmitt trigger is
a Pulse Width
Modulated (PWM) waveform with a period of 100 us. Pin 14 of the
Schmitt
trigger is connected to the supply voltage of 5V from the
Arduino board while
pin 7 is connected to the ground. The output from pin2 is an
inverted PWM
waveform with a period of 100 us. Pin 2 and pin 3 are connected
together in
order to obtain a waveform from pin 4 which is the same as the
input
waveform. As a result, two waveforms are generated which are out
of phase or
opposite to each other.
The measurements of the waveforms shown above are carried out
using a TDS
2004B Four Channel Oscilloscope. Channel 1 is connected to pin 4
of the
Schmitt trigger whereas channel 2 is connected to pin 2. Once
connected, the
Autoset button on the oscilloscope is pressed in order to
observe the
waveforms shown below in figure 19:
Figure 19: Two out of phase PWM waveforms.
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Problem with the approach The main error that occurred with this
approach is that the logic pulses are not
enough to trigger the two mosfets as it is less than the gate
threshold voltage.
As a result, another approach is taken to overcome this
problem.
Approach 2 The circuit used to generate synchronous waveforms
works in conjunction
with approach 1 used to generate PWM waveform from Arduino board
and it
consists of two main components: transistor and optocoupler. A
PWM (Pulse
Width Modulated) waveform is applied to the input of the
circuit. The
waveform is fed into the base of a BC547 NPN transistor which
output an in
phase 5V peak to peak PWM waveform at the emitter side of the
transistor.
The 5V peak to peak waveform is then passed to two separate
BC547 NPN
transistors, both of which are connected to pins 2 and 3 of
ISD74 High Density
Phototransistor Optically Coupled Isolators which contains two
separate
optocoupler. A schematic diagram of High Density Phototransistor
Optically
Coupled Isolators is shown below in figure 20:
Figure 20: A schematic diagram of ISD 74. [8]
Pins 1 and 4 of the LED part of the device are connected to a
12V supply. Pins
6 and 7 of the phototransistor part of the optocoupler are
connected to the
positive 12 V rail whereas pin 8 is connected to the source of a
mosfet and pin
5 is connected to the ground rail. The output waveform from pin
7 is an
inverted 12V peak to peak PWM waveform and the output waveform
from pin
5 is a 12V peak to peak PWM waveform which is in phase with the
input
waveform. A schematic diagram of the circuit is shown below in
figure 21:
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1 K
470
1 K
1 K
1 K
1 K
330
330
12V
12V
12V
12V
12V
Optocoupler
Optocoupler
Figure 21: Circuit to generate two synchronous waveforms
A picture of the original circuit described above is shown in
figure 22:
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Figure 22: Shows picture of the mosfet driver circuit with
transistor and opto-
coupler.
Problem with the approach The main flaw in this circuit is that
the phototransistor used cannot provide the
gate voltage required to trigger the two Mosfets which is 11V
PWM for the
mosfet connected to the positive side of the power supply and 5V
PWM for
the mosfet connected to the ground.
Approach 3 The third approach involves a much simpler mosfet
driver circuit which works
with the code from approach 2 of the generation of PWM waveform.
It
consists of two transistors with their base voltage being
supplied from pin 9
and pin 10 from the Arduino board. The gate signals to the
Mosfets are
provided from the collector side of the transistors which means
the output
waveforms are inverted compared to the input waveforms from the
Arduino
board. The two outputs from the mosfet driver circuit are 11V
PWM
waveform to drive the mosfet connected to the positive supply
and 5V PWM
waveform to drive the mosfet connected to the ground. A
schematic diagram
of the circuit is shown below in figure 23:
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12V 12V
1K
1K
1K2K2
2K2
100uF
Figure 23: A schematic diagram of the circuit for approach
3.
Mosfets
The mosfets used in the development of the buck converter are
STP14NF10,
N-channel. The maximum voltage that are allowed across drain and
source is
100V, the on time resistance across drain and source is 0.13 and
the
maximum pulsed drain current is 60A.[14] The mosfets are being
triggered by
applying two 5V and12V peak to peak TTL signals which are
complementary
to each other on the gates of the mosfets. The maximum
gate-source voltage
for this type of mosfets is +/- 20V. The duty cycle and the
period of the signals
can be varied using the software that interface with the
software development
board (Arduino Uno Board). Heat sinks are attached to the
mosfets in order to
prevent the mosfets from getting too hot. The switching
frequency of the
mosfets is determined using the calculation shown below:
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The two N-channel mosfets are driven at a gate voltage of 5V
from its source
voltage. Therefore, the mosfet connected to the positive side of
the supply is
driven by an 11V PWM signal and the mosfet connected to the
ground is
driven by a 5V PWM signal. The voltage levels at the gates of
the mosfets are
shown below in figure 24:
0V
6V6V
12V
5V
5V
11V
Figure 24: Voltage level of the gates in the Mosfets.
Construction of an air cored inductor The first step to make an
inductor for the buck converter or step down
converter is to determine the inductance required for a
particular ripple
current. In this project, the input and output parameters are
defined in the
specification as shown below:
Input voltage,
Nominal output voltage,
Maximum output current,
Switching frequency,
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Therefore, using equation 1 and 2 from the technical background
the value of
inductance required can be calculated. The first step is to
calculate the inductor
ripple current using equation 1:
Then the next step is to calculate the inductance using equation
2:
The different values of inductance required for the nominal
output voltage
range is shown below in figure 25:
Inductance calculation
Vin Vout D Fsw I ripple L L in uH
12 0 0 240000 15 0 0
12 1 0.083333 240000 15 2.5463E-07 0.255
12 2 0.166667 240000 15 4.62963E-
07
0.463
12 3 0.25 240000 15 0.00000062
5
0.625
12 4 0.333333 240000 15 7.40741E-
07
0.741
12 5 0.416667 240000 15 8.10185E-
07
0.81
12 6 0.5 240000 15 8.33333E-
07
0.833
12 7 0.583333 240000 15 8.10185E-
07
0.81
12 8 0.666667 240000 15 7.40741E-
07
0.741
12 9 0.75 240000 15 0.00000062
5
0.625
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12 10 0.833333 240000 15 4.62963E-
07
0.463
12 11 0.916667 240000 15 2.5463E-07 0.255
12 12 1 240000 15 0 0
Figure 25: The inductance calculation for different output
voltage or duty
cycle.
It can be seen that the maximum inductance value required for
the buck
converter is 0.833 uH. The approaches taken to design the
windings and length
of the inductor coil are described below:
Approach 1 The first approach used to design an air-cored
inductor is by using the Wheeler
formula.
Where: L is inductance in uH.
N is the number of turns.
D is the diameter of the coil in inches.
L is the length of the coil in inches. [15]
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 1 2 3 4 5 6 7 8 9 10 11 12
L in
uH
Vout
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Assuming length of the coil, l = 0.7 inch and diameter of the
coil, d = 3 inch.
The number of turns, n required to achieve an inductance of
0.833 uH :
An approximate of 3 turns is required to achieve an inductance
of 0.833uH.
Problem with the approach The main problem with approach 1 is
that Wheeler formula for inductance
calculation is normally used to make air-cored inductors for RF
circuit
whereas the inductor designed in this project is for a power
circuit. Another
problem is that the formula is only valid for inductors where
the diameter to
length ratio is less than 0.8 and the assumption made for the
diameter and the
length of the constructed inductor gives a ratio of about 4.3.
Therefore, the
formula mentioned above cannot be used to design the inductor
for the buck
converter.
Approach 2 The next approach used to design the coil of an air
cored inductor is by using
the basic inductance formula. The number of turns required to
achieve the
desired inductance of 0.833 uH is determined using equation
6:
Inductance required, L = 0.833uH.
Permeability of free space, = 4
Relative permeability, = 1 (Due to the presence of air core)
The radius of the coil is assumed to be r = 0.0381m.
The cross sectional area of the coil = = 0.00456 .
The length of the coil is assumed to be l = 0.0178 m.
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Therefore, the number of turns required for the desired
inductance:
1.61
Therefore, it will take 1.6 turns to get an inductance of
0.833uH with a coil
length of 0.0178m and a cross sectional area of 0.00456
The formula used above is valid for determining the size of any
air cored coil
i.e. both power and RF inductors.
The size of the wire used
The next step is then to determine the diameter of the wire
needed to make the
inductor coil. It is a known factor that the current carrying
capacity of a copper
wire under normal condition is 6 A/ As a result, for a current
of 50A it
will take a wire cross-sectional area of 8.33 . Therefore, the
diameter of
the wire is calculated as follows:
The wire was then winded around a 0.0762 m in diameter base and
taped
together so that the windings are as close as possible. A
picture of the inductor
is shown below in figure 26:
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Figure 26: A picture of the designed 0.833uH inductor.
Measurement of the inductance
The inductance of the designed inductor is measured using the
Wayne Kerr
Automatic Precision Bridge B905A instrument. Before measuring
the
inductance, the instrument was setup to measure inductance in
series and then
calibrated by connecting the two positive test plugs together
and then pressing
CE Trim. The two positive test plugs are then connected to two
ends of the
inductor and the value displayed on the instrument screen is
recorded.
The desired inductance value for the buck converter =
0.833uH.
The measured inductance value using Wayne Kerr instrument =
0.886uH.
Determining the capacitor for the buck converter
In order to determine the value of capacitor required for the
buck converter,
the following parameters are determined below:
Ripple current, .
Ripple output voltage,
Switching frequency,
Therefore, using equation 3 from the theoretical background the
output
capacitance for the filter can be calculated:
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The above calculation shows that a capacitive value of 156 uF is
required to
filter out a waveform with a ripple current of 15A and a ripple
voltage of 50
mV.
Issue with the capacitive value The main issue was that a
capacitor of 156 uF with the capability to handle a
ripple current of 15 A is unavailable in the market. And as a
result of this,
smaller capacitors with high enough ripple current were selected
and
connected in parallel to achieve the desired capacitance and
ripple current.
Construction of a capacitor bank The most suitable capacitors
available for this purpose are Functional Polymer
Aluminium Solid Electrolytic Capacitors with a capacitance of 22
uF and a
ripple current of 3.4 A. Other features of the capacitors
include a low ESR
(Equivalent series resistance) of 0.028 , a leakage current of
110 A,
tolerance of +/- 20%, maximum operating temperature of +105C,
minimum
operating temperature of -55C and a voltage of 25V dc. [16]
Total number of capacitor required for the bank =
= 7 capacitors.
Total ripple current of the capacitor bank = 7 3.4 = 23.8 A.
Therefore, 7 capacitors are connected in parallel to achieve a
capacitive value
of 154 uF which is very close to the desired value of 156 uF and
the capability
to handle a ripple current of 23.8 A to that of 15A. A picture
of the capacitor
bank is shown below in figure 27:
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Figure 27: A picture of the capacitor bank for the buck
converter.
Measurement of the capacitance The capacitance of the designed
capacitor bank is measured using the Wayne
Kerr Automatic Precision Bridge B905A instrument. Before
measuring the
capacitance, the instrument is setup to measure capacitance in
parallel and
then calibrated by connecting the two positive test plugs
together and then
pressing CE Trim. The two positive test plugs are then connected
to two
ends of the capacitor bank and the value displayed on the
instrument screen is
recorded.
The desired capacitive value for the buck converter = 156
uF.
The measured capacitive value using Wayne Kerr instrument =
144.5 uF.
The capacitance of the buck converter is designed within the 20%
tolerance
value.
Time constant of the LC circuit The time constant of the
inductor and capacitor bank used as a filter in the
buck converter are calculated below:
Time Constant, T =
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=
= 11.4 us
This is the time constant for one complete cycle. And therefore,
the two
mosfets should be driven at a period lower than this in order
for the inductor to
get fully discharged.
Device under Test The device under test (DUT) used to test the
product is a combination of two
1 power resistors connected in series which can draw a current
of 6A from
the battery or supply.
How the whole circuit is expected to work The main purpose of
the circuit is to be able to output different levels of the
input voltage which are being specified by the user in the form
of duty cycle.
This will allow the user to generate a waveform of different
voltage levels
over a period of time.
The first approach to generate a waveform is to define the duty
cycles of the
PWM waveform required for different voltage levels in the
Arduino software
window as well as the period of the waveform and the output pin.
Once the
parameters are being defined, the code is compiled and uploaded
in the
Arduino development board. This will produce a user defined 5V
peak to peak
PWM waveform from the specified pins.
The waveform is then fed into a mosfet driver circuit which
converts low
power 5V peak to peak TTL output from the Arduino development
board into
a high output voltage which is equal to the supply voltage. The
mosfet driver
circuit produces a 12V peak to peak PWM waveform and a 5V peak
to peak
PWM both of which are out of phase to each other. The two
waveforms are
then applied to the gates of the two mosfets in the buck
converter. This will
allow the two mosfets to switch at a synchronous rate, i.e. when
one mosfet is
on; the other mosfet is off. When the mosfet connected to the
positive side
of the 12 V supply is on, the energy from the supply flows into
the 0.833 uH
inductor in the buck converter which will charge up the
inductor. At that time,
the voltage across the inductor is equals to (Vin Vo).
When the mosfet connected to the ground is switched on, the
other mosfet
will switch off. At that point, the energy stored in the
inductor is being
transferred to the 156 uF capacitor bank and the load. The
voltage across the
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inductor at that point is equals to Vo. The voltage across the
capacitor bank
and the load is equal to Vo as they are parallel to each other.
For example, in
order for the buck converter to output a pulse waveform where
the voltage
level changes between 0V and 6 V with a delay of 1ms between the
change in
voltage level, the user has to define the duty cycles of the
output PWM
waveform from pins of the Arduino board which is 50% and 100% in
this
case. A delay of 1ms is also defined in between the two duty
cycles. This will
result in the buck converter to output a 0-6 V pulse with a 1ms
delay. An
information flow diagram of the whole process is shown below in
figure 28:
PC
USERARDUINO
SOFTWARE
PIN 10
ARDUINO
DEVELOPMENT
BOARD
SYNCHRONOUS BUCK CONVERTER
MOSFET
DRIVER
CIRCUIT
DC
LO
AD
Figure 28: An information flow diagram of the whole process.
Initial rejected solution for the project
Solution 1
The first solution considered before the Arduino controlled buck
converter is
using an on-load tap changers to control the voltage level from
a DC battery.
The idea was to use a software development board like Arduino to
switch
specified connection points in the tap changer. One form of the
tap changer
circuit is shown below in figure 29:
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Figure 29: Tap changer circuit. [17]
The main issue with the tap changer solution was the high number
of taps
required to be able to change the input DC voltage to 320
different levels
which will make the product expensive and bulky. At the same
time, it is
difficult to create an interface between the tap selectors of
the tap changer with
the software development board. As a result, this method was
rejected due to
the failure of generating fast transient waveforms.
Solution 2 The other alternative solutions considered for this
project was the use of a
resistor bank to fluctuate the voltage level in the battery.
Each resistor in the
resistor bank is connected on parallel to a solid state switch
which is being
controlled from the input/ output pins on the software
development board.
This method is based on the principle of potential divider
circuit where the
output voltage depends on the value of the resistor across the
load. A circuit
diagram of the solution is shown below in figure 30:
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PC
SOFTWARE
SOFTWARE
DEVELOPMENT
BOARDUSER LOAD
12V
SOLID STATE SWITCH
RESISTOR BANK
SIGNAL FROM SOFTWARE BOARD TO
SOLID STATE SWITCH
Figure 30: The circuit diagram of the resistor bank and the sold
state switch
solution.
The main issue with this solution was that the resistors in the
resistor bank can
get hot when connected to a 12 V supply and will result in power
dissipation
from the resistors which will bring down the efficiency of the
entire system
and this will drain the power from the battery which is not
suitable. To
overcome this problem, the resistors must be attached to large
heat sinks but it
will make the product expensive to manufacture and also heavy to
carry
around. Considering all the above drawbacks, solution 2 was
rejected.
Research on similar product in the market A comparison is done
between the market product and the product developed
from this project.
Feature and Cost Evaluation between products
Feature LVTGO-VBS LCHCWG (expected)
Generation of test
waveform
YES YES
Generation of Ground
offset voltage
YES NO
Used in vehicle testing YES YES
Used in System testing YES YES
User defined voltage YES YES
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fluctuation
Tolerant High transient
current
YES YES
Used in Capacitive loads
testing
YES YES
Use car battery as a
supply
YES YES
CAN feature YES NO
Cost of manufacturing 2000 50
Cost of the Product
Components used Price ()
Arduino Development board 18.04
Transistor 2 0.30
1K resistor 3 0.20
2.2K resistor 2 0.15
100 uF capacitor 1 0.14
P14 NF10 mosfet 2 1.156
Wire for inductor coil 18
22uF capacitors 7 11.76
Total 49.75
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Results and Discussion
1. An analysis was done on the continuous PWM waveform
obtained
from pin 10 of the Arduino development board. Since the PWM
waveform generated was a continuous waveform, a part of the
waveform was analysed and the measurements taken using the
oscilloscope are tabulated below:
Time (us) Expected logic voltage Actual logic voltage
0 0 0
1 0 0
1.999 0 0
2.001 5 4.7
3 5 4.7
3.999 5 4.7
4.001 0 0
5 0 0
5.999 0 0
6.001 5 4.7
7 5 4.7
7.999 5 4.7
8.001 0 0
9 0 0
9.999 0 0
10.001 5 4.7
11 5 4.7
11.999 5 4.7
12.001 0 0
13 0 0
13.999 0 0
14.001 5 4.7
15 5 4.7
15.999 5 4.7
16.001 0 0
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A graph of the expected and actual voltage PWM waveforms is
shown
below in figure 31:
Figure 31: A comparison of expected logic voltage (coloured red)
and
actual voltage (coloured green).
From the graph it is seen that the actual logic voltage from pin
10 of
the Arduino board is 0.3V off the expected logic voltage. This
has an
insignificant effect as a logic voltage of 0 4.7V peak to peak
is
enough to drive any mosfet driver circuit.
2. An analysis was then done of the two continuous out of phase
PWM
waveform obtained from the Mosfet Driver Circuit which is a
Schmitt
trigger. Since the two PWM waveforms generated were
continuous
waveforms, a part of the waveforms i.e. four pulses were
analysed and
the measurements taken using the oscilloscope are tabulated
below:
Time (us) Expected
voltage from
pin 4
Actual
voltage from
pin 4
Expected
voltage from
pin 2
Actual
voltage from
pin 2
0 0 0 5 4.7
1 0 0 5 4.7
1.999 0 0 5 4.7
2.001 5 4.7 0 0
3 5 4.7 0 0
0
1
2
3
4
5
6
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
25
Time (us)
Logic voltage (V)
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3.999 5 4.7 0 0
4.001 0 0 5 4.7
5 0 0 5 4.7
5.999 0 0 5 4.7
6.001 5 4.7 0 0
7 5 4.7 0 0
7.999 5 4.7 0 0
8.001 0 0 5 4.7
9 0 0 5 4.7
9.999 0 0 5 4.7
10.001 5 4.7 0 0
11 5 4.7 0 0
11.999 5 4.7 0 0
12.001 0 0 5 4.7
13 0 0 5 4.7
13.999 0 0 5 4.7
14.001 5 4.7 0 0
15 5 4.7 0 0
15.999 5 4.7 0 0
16.001 0 0 5 4.7
A graph of the expected and actual voltage of two out of phase
PWM
waveforms from pin 2 and pin 4 of the Schmitt trigger is shown
below
in figure 32:
Figure 32: Comparison of the expected and actual waveforms from
pin
2 (coloured violet and blue) and pin 4 (coloured red and green)
of
Schmitt trigger.
0
1
2
3
4
5
6
1 3 5 7 9 11 13 15 17 19 21 23 25
Voltage
Time (us)
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From the graph, it is seen that the waveform from pin 2 is
inverted
compared to the input waveform whereas the waveform from pin 4
is
the same as the input waveform. Both waveforms are expected to
be 0
5V peak to peak but the outputs from the pins in Schmitt trigger
are 0
4.7 V as a result of the input waveform to the Schmitt trigger
which
is 0 4.7 V from the Arduino board. The output waveforms from
the
Schmitt trigger are not enough to trigger the two Mosfets in the
buck
converter as the gate threshold voltage of the Mosfets are
higher than
the applied voltages. Therefore, the approach of using a Schmitt
trigger
as a Mosfet Driver Circuit is rejected.
3. Another analysis was done on the actual inductance value and
the
measured value using Wayne Kerr Automatic Precision Bridge
B905A
instrument. The theoretical inductance value for the buck
converter is
0.833 uH whereas the measured inductance value is
0.886uH.The
difference between the theoretical and the measured inductance
is
within the tolerance level of the circuit which is 20% and
therefore
have insignificant effect on the operation of the buck converter
circuit.
4. The next analysis was done on the capacitive value of both
actual and
experimental, using the Wayne Kerr Automatic Precision
Bridge
B905A instrument. The theoretical capacitive value for the
buck
converter is 156 uF whereas the measured value is 144.5uF.
The
difference between the theoretical and measured capacitance has
an
insignificant effect on the operation of the buck converter
circuit as it
is within the tolerance limit of 20%.
5. A final analysis was then done on the relationship between
the duty
cycle and the output voltage from the buck converter. This is
important
as the user determines the voltage level required for creating
a
waveform in the code in the form of duty cycle. The duty cycle
of the
PWM waveform at the gate of the Mosfet is varied within a range
of
10-90% and the output voltages from the converter are
tabulated
below:
Duty Cycle
%
Expected output voltage(V) Actual Output voltage (V)
10 1.2 1.28
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20 2.4 2.54
30 3.6 3.5
40 4.8 4.4
50 6 5.34
60 7.2 6.3
70 8.4 7.32
80 9.6 8.3
90 10.8 9.2
The graph in figure 33 below shows the relationship between the
duty
cycle and the output voltage.
Figure 33: The relationship between the duty cycle and the
output
voltage.
From the graph, it is seen that there is significant difference
between
the expected and the actual output voltage for each duty cycle.
The
difference between them varies from 0.08 1.6 V. The main reason
for
this is that the inductor and the capacitor of the buck
converter are
designed for the switching frequency defined in the
specification of the
project whereas the mosfets are switched at a much lower
frequency as
the waveforms at the gates of the mosfets get distorted at the
specified
frequency. This will result in losses across the inductor and
the
capacitor as the charging and discharging time of the filters
(inductor
and capacitor) is much lower than the switching time of the
mosfets.
0
2
4
6
8
10
12
10 20 30 40 50 60 70 80 90
Expectedoutputvoltage(V)
Actual Outputvoltage (V)
Duty cycle (%)
Output voltage (V)
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Conclusion and Recommendations for
Further Work
The aim of the project is achieved successfully by following
five key
objectives which involve benchmarking of the product,
identifying the
advantage of the product over other market products, building
cost-effective
hardware, driving the product with software and generating a
sequence of test
waveforms.
A market research on the product resulted in the finding of
LVTGO-VBS
which has similar functionalities to the product mentioned and a
brief
comparison between the two products is also tabulated in the
report. The
hardware of the product is driven by an Arduino development
board which
allows the user to control the output voltage from the product.
A cost-effective
hardware for the product was designed where limitations in the
component
used limited the product to reach its full potential. This is
due to the
incapability of the Mosfets to handle high frequency signal and
as a result, the
product is driven at a much lower frequency. Therefore, the
output voltage
from the product is not exactly same as the expected output
voltage which
resulted in the failure of generating a sequence of test
waveforms.
Future works on the product involve the following:
Improving the frequency at which the product works.
Introducing CAN (controller area network) feature in the
product.
Generating sequence of test waveforms.
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Low Cost High Current Waveform Generator
2013
44
Reference
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[Accessed
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Low Cost High Current Waveform Generator
2013
45
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data=636F3D3126696E3D4931384E525353746F636B4E756D6265724D504
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Low Cost High Current Waveform Generator
2013
46
Appendix
Approach 1 software code
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47
Approach 2 software code
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48
CD40106B Hex Schmitt Trigger datasheet
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P14NF10 N-channel mosfet datasheet
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Project Planning
Work breakdown structure
Low cost High Current w
aveform generator
Low Cost High Current W
aveform Generator
Interface with PC
Connection
with PC via
USB
Development
interface
User
Interface
Software
Installation
Process
Development
Code e.g.,
defining the
parameter
Programm
ing Language:
using an environment
based on the original
Arduino
IDE
Simple U
ser
Comm
and
Graphical
Interface
Easy to Use
Store Data
Microcontroller
PIC
32MX
320F12
PIC
32MX
320F12
Voltage Control
Pulse Width
Modulation
Switching
speed
1ms step
Current
70A
Voltage
Lower lim
it = 0V
Nom
inal = 16V
Upper lim
it = 32V
Accuracy
Cable
Rated 70A
Constant Current
and Voltage
Current = 70A Voltage = 0-32V
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Low Cost High Current Waveform Generator
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51
Gantt chart
Milestone 1: Submission of progression report
Milestone 2: Christmas break
Milestone 3: Submission of interim report.
Milestone 4: End of project.