Low Cost High current waveform generator

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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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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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



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Approach 3 .............................................................................................................. 23

Construction of an air cored inductor ..................................................................... 25

Approach 1 .............................................................................................................. 27


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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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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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).


digitalWrite (pinB, LOW); // set pin B to low (0V).


digitalWrite (pinB, HIGH); // set pin B to high (5V).


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}

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:


2013

24

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:


2013

25

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,


2013

26

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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27

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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28

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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29

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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30

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:


2013

31

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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32

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 =


2013

33

=

= 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


2013

34

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:


2013

35

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:


2013

36

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


2013

37

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


2013

38

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


2013

39

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)


2013

40

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)


2013

41

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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42

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)


2013

43

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.


2013

44

Reference

[1] ADD2. Low Voltage Tester Ground Offset Vehicle Battery Simulator,

Version 3, p.1-20.

[2] V. Madhuravasal; S. Venkataraman; C.G. Hutchens. Buck-Converter

Design for Power in Plus 275??C Environments. IEEE Transactions on

Aerospace and Electronic Systems, 2012, 48 (1), pp. 304 312.

[3] M.Ponugubati. DC-DC Converters. Lecture delivered in Power Systems,

Energy Converters and Drives, Unit code: EEC_6_491_1213. London

Southbank University, 2012/13.

[4] B. Hauke. Basic calculation of a Buck Converters Power stage. [ Aug 2012]. [Online] Available from:

http://www.ti.com/lit/an/slva477a/slva477a.pdf [ Accessed 25Apr 2013].

[5] J. Segura, C. Hawkins. CMOS Electronics: How It Works, How It Fails.

Wiley-IEEE Press, 2004. [Online] Available from:

http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=5237840&cont

entType=Books+%26+eBooks&refinements%3D4291944823%26searchField

%3DSearch_All%26queryText%3Dhow+capacitor+works [Accessed 25 Apr

2013].

[6] Murata Manufacturing Co. Basic Facts about Inductors [Lesson 1]

Overview of inductors - "How do inductors work?", 12 Dec 2010. [Online]

Available from:

http://www.murata.com/products/emicon_fun/2010/12/inductor_en15.html

[Accessed 25 Apr 2013].

[7] R. Nave. The Schmitt Trigger, [no date]. [Online] Available from:

http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/schmitt.html [Accessed

08 Apr 2013].

[8] ISOCOM Components. High density Phototransistor Optically Coupled

Isolator, [no date]. [Online]. Available from: http://docs-

europe.electrocomponents.com/webdocs/0265/0900766b802655bc.pdf


[9] S. Portz. Transistor, [no date]. [Online]. Available from:

http://www.physlink.com/education/askexperts/ae430.cfm [Accessed 14 Apr

2013].


2013

45

[10] Circuits Today. Working of a capacitor, [14 Dec 2009]. [Online].

Available from: http://www.circuitstoday.com/working-of-a-capacitor


[11] Arduino Uno SMD Rev3, [no date]. [Online] Available from: http://docs-

europe.electrocomponents.com/webdocs/11af/0900766b811af13a.pdf .


[12] RS Online. TDS2004B oscilloscope, 60mHz, colour, [no date].[Online].

Available from: http://uk.rs-online.com/web/p/digital-oscilloscopes/6170082/


[13] National Semiconductor. CD40106BM/CD40106BC Hex Schmitt

Trigger, [Feb 1988]. [Online]. Available from:

http://www.pablin.com.ar/electron/circuito/auto/baliza/cd40106.pdf [Accessed

14 Apr 2103].

[14] ST Microelectronics. ST. N-CHANNEL 100V - 0.115 W - 15A TO-

220/TO-220FP/D2PAK LOW GATE CHARGE STripFET II POWER MOSFET, [no date]. [Online] Available from:

http://www.datasheetcatalog.org/datasheet/stmicroelectronics/7779.pdf


[15] LCB Systems. Inductor Calculators, [no date]. [Online]. Available from:

http://lcbsystems.com/InduCalc.html [Accessed 25 Apr 2013].

[16] RS Online. Solid Al cap Radial NS series 25V 22uF, [no date]. [Online].

Available from: http://uk.rs-online.com/web/p/aluminium-

capacitors/7149635P/?searchTerm=7149635P&relevancy-

data=636F3D3126696E3D4931384E525353746F636B4E756D6265724D504

E266C753D656E266D6D3D6D61746368616C6C26706D3D5E5C647B362C

377D5B4161426250705D2426706F3D313426736E3D592673743D52535F53

544F434B5F4E554D424552267573743D37313439363335502677633D4E4F

4E4526 [Accessed 26 Apr 2013].

[17] D. Gao; Q. Lu; J. Lou. A new scheme for on-load tap-changer of

transformers. Power System Technology, 2002. Proceedings. PowerCon,

2002, vol. 2, pp. 1016-1020.


2013

46

Appendix

Approach 1 software code


2013

47

Approach 2 software code


2013

48

CD40106B Hex Schmitt Trigger datasheet


2013

49

P14NF10 N-channel mosfet datasheet


2013

50

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


2013

51

Gantt chart

Milestone 1: Submission of progression report

Milestone 2: Christmas break

Milestone 3: Submission of interim report.

Milestone 4: End of project.

Documents

Low Cost High current waveform generator