1

CUK CONVERTER USING LM2611

Project report submitted in partial fulfillment of the requirements

For the award of the degree of

BACHELOR OF TECHNOLOGY

IN

ELECTRICAL AND ELECTRONICS ENGINEERING

By

S.ANKUSH REDDY (08241A0259)

P.RAJ KUMAR (08241A0285)

N.SANTOSH KUMAR (08241A0296)

P.SIVA TARUN (08241A02A2)

Under the guidance of

Mr.SRIKANTH

Assistant Professor

Department of Electrical and Electronics Engineering

GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING &

TECHNOLOGY, BACHUPALLY, HYDERABAD-72

2012

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GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING AND

TECHNOLOGY

Hyderabad, Andhra Pradesh.

DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING

C E R T I F I C A T E

This is to certify that the project report entitled CUK CONVERTER USING LM2611

that is being submitted by Mr. S.ANKUSH REDDY, Mr.P.RAJ KUMAR, Mr.N.SANTOSH KUMAR and P.SIVA TARUN in partial fulfillment for the award of the

Degree of Bachelor of Technology in Electrical and Electronics Engineering to the Jawaharlal Nehru Technological University is a record of bonafide work carried out by

him under my guidance and supervision. The results embodied in this project report have not

been submitted to any other University or Institute for the award of any graduation degree.

Mr.P.M.Sarma Mr. SRIKANTH HOD, EEE Assistant Professor.

GRIET, Hyderabad GRIET, Hyderabad

(Internal Guide)

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Acknowledgement

This is to place on record my appreciation and deep gratitude to the persons without

whose support this project would never seen the light of day.

I have immense pleasure in expressing my thanks and deep sense of gratitude to my

guide MR. SRIKANTH, Assistant Professor Department of Electrical

Engineering, and G.R.I.E.T for his guidance throughout this project.

I also express my sincere thanks to Mr.P.M.Sarma, Head of the Department, and

Mr.M.Chakravarthy Associate Proffessor G.R.I.E.T for extending his help.

I express my gratitude to The Dr.S.N.Saxena, Project Supervisor G.R.I.E.T for his

valuable recommendations and for accepting this project report.

Finally I express my sincere gratitude to all the members of faculty and my friends

who contributed their valuable advice and helped to complete the project

successfully.

S.ANKUSH REDDY (08241A0259)

P.RAJ KUMAR (08241A0285)

N.SANTOSH KUMAR (08241A0296)

P.SIVA TARUN (08241A02A2)

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Abstract

The CUK converter is a DC-DC converter. Switch-mode DC-DC converters are commonly

used to convert an unregulated DC input into a controlled DC output at a desired voltage

level. The voltage magnitude that is either greater or less than the input voltage magnitude.

It consists of dc input voltage source VS, input inductor L, controllable switch S, energy

transfer capacitor C, diode D, lter inductor L, lter capacitor C, and load resistance R. An important advantage of this topology is a continuous current at both the input and the output

of the converter. Disadvantages of the Cuk converter are a high number of reactive

components and high current stresses on the switch, the diode, and the capacitor C. The main

waveforms in the converter are presented in Fig. 1. When the switch is on, the diode is off

and the capacitor C is discharged by the inductor L current. With the switch in the off state,

the diode conducts currents of the inductors L and L, whereas capacitor C is charged by the

inductor L current.

Analytic models for a bidirectional coupled-inductor Cuk converter operating in sliding mode

are described. Using a linear combination of the converter four state variable errors as a

general switching surface, the expression for the equivalent control is derived and the

coordinates of the equilibrium point are obtained. Particular cases of the general switching

surface are subsequently analyzed in detail: (1) surfaces for ideal line regulation, (2) surfaces

for ideal load regulation, and (3) surfaces for hysteretic current control. Simulation results

verifying the analytical predictions are presented

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CONTENTS

S.NO TITLE Page No.

a) Abbreviations Vi

b)

List of Figures 5i

c) List of Tables 5i

1. Introduction

1.1 History

1.2 Aim of this Project 1.3 Methodology 1.4 Outline

1

2. DC-to-DC Converter

2.1 Definition

2.2 Usage

2.3 Conversion methods

2.3.1 Electronic

2.3.2 Electrochemical

2

2

2

2

2

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3. CUK Converter 3.1 Introduction

3.2 Principle of operation of isolated Cuk converter 3.3 Non Isolated Cuk converter

3.3.1 Principle of operation of Non Isolated Cuk converter

3.3.2 Continuous Mode

3.3.3 The two operating states.

3.3.3 Dis Continous Mode.

6

6

7

7

8

9

10

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4. Pulse Width Modulation. 4.1 Introduction

4.2 Principle

4.2.1 Delta 4.2.2 Delta-sigma

4.2.3 Space vector modulation

4.2.4 Direct torque control (DTC)

4.2.5 Time proportioning

4.2.6 Types 4.2.7 Spectrum

4.3 Applications

4.3.1 Telecommunications

4.3.2 Power delivery

4.3.3 Voltage regulation

4.3.4 Audio effects and amplification

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11

12

13

13

14

14

14

15

15

16

16

16

17

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5. IC LM2611

5.1 Introduction

5.2 Features

5.3 Applications

5.4 Typical application of LM2611

5.5 Connection Diagram And Pin Discription

5.5.1 Connection Diagram

19

19

19

19

20

21

21

6

5.5.2 Ordering

5.5.3 Pin Description

5.5.4 Block Diagram

5.6 Absolute Max Ratings

5.7 Operating

5.8 Electrical Characteristics

5.9 Typical Performance Characteristics

5.10 Application Circuits Of LM2611 In Cuk Converter

5.11 Physical Dimensions

21

22

22

23

23

24

25

27

27

6. Operation Of Cuk Converter 6.1 Output and input indicator

6.2 Switch current limit

6.3 Input capacitor

6.4 Output capacitor

6.5 Improving transient response

6.6 Hysteric mode

6.7 Thermal shutdown

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28

30

31

31

31

33

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7. Simulation of Practical Circuit

7.1 Intoduction to PSIM software

7.1.1 Tool for Model-Based Design

7.2 The obtained wave forms

7.3 Simulation results

7.3.1 Inference

7.4 Simulation circuit of the CUK Converter

35

35

35

37

39

39

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8. Hardware Implementation

8.1 Circuit Specification

8.2 Circuit Description 8.2.1 Starting Power Supply

8.2.2 Complete circuit

8.3 Hardware Output Waveforms

41

41

41

41

42

42

9. Applications

1.1 Digital cam 1.2 LCD Multiplex Ratio 1.3 LCD Bias

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45

46

46

10 Conclusion and Scope for Future 48

11 REFERENCES 49

APPENDEX-A 50

APPENDEX-B 52

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APPENDEX-C 53

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Abbreviations

1. IC : Integrated circuit 2. UC: Unitrode circuit 3. TL: Texas Laboratories 4. PWM: Pulse Width Modulation 5. SMPC: Switched Mode Power Converter 6. CCM: Continuous Conduction Mode 7. SM: Sliding Mode 8. HM: Hysteresis Modulation 9. PCB: Printed Circuit Board

10. DTC: Dead Time Control

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LIST OF FIGURES

1. Fig.3.1 Basic schematic CUK converter

2. Fig.3.2 Schematic of a CUK converter

3. Fig.3.3 The two operating states of a non isolating cuk converter

4. Fig.4.1 A simple method to generate the PWM pulse train corresponding

to a given signal is the intersective PWM

5. Fig.4.2 Principle of Delta PWM

6. Fig.4.3 Principle of delta sigma PWM.

7. Fig.4.4 Waveforms of different types of pulses

8. Fig.5.1 Typical application of lm2611

9. Fig.5.2 Pin diagram

10. Fig.5.3 Block diagram

11. Fig.5.4 Typical Characteristics

12. Fig.5.5 Physical Dimensions

13. Fig.6.1 Operating cycle of a Cuk converter

14. Fig.6.2 Voltage and current wave forms in inductor L1

15. Fig.6.3 Voltage and current wave forms in inductor L2

16. Fig.6.4 Switch Current waveform in a Cuk Converter

18. Fig.6.5 Transient response of Cuk converter

19. Fig.7.1 Representation of a system in PSIM 20. Fig.7.2 Output Voltage waveform

21. Fig.7.3 Waveform near switch

22. Fig.7.4 Simulation circuit

23. Fig.8.1 Power Supply Board

24. Fig.8.2 Completely Soldered Hardware Circuit

25. Fig.8.3 Reference Voltage

26. Fig.8.4 PWM pulses

27. Fig.8.5 Varying Pulse width

28. Fig.8.6 Output DC Voltage

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LIST OF TABLES

1. Table-2.1 Different Topologies 2. Table-5.1 Function Table

3. Table-5.2 Ordering Table

4. Table-5.3 Pin Description Table

5. Table-5.4 Electrical Characteristics

6. Table-7. Input voltage variation

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1. INTRODUCTION The ukconverter. Is a type of DC-DC converter that has an output voltage magnitude that is either greater than or less than the input voltage magnitude.

1.1 HISTORY It is named after Slobodan uk of the California Institute of Technology, who first

presented the design.

The Four BoostBuck Topologies

1. Boost-Buck Switching Converter

2. Cuk Converter

3. Coupled Inductor Cuk Converter

4. Integrated Magnetics Cuk Converter

1.2 Aim Of This Project

The initial aim of this project is to generate a DC voltage whose magnitude is greater

than or less than the input voltage magnitude.

Here we use LM2611 as the switching regulator.

1.3 Methodology

A CUK converter is designed using LM2611 IC which is used as a PWM switching

regulator. Where the whole circuit is used to obtain the desired DC output for the given DC

input.

1.4 Outline Of This Report

In this report, the following chapters will cover the different types of DC-DC converters,

PWM, LM2611IC, integration of lm2611 IC with CUK converter, applications of CUK

converter, future scope.

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2. DC-TO-DC CONVERTER

2.1 DEFINITION A DC-to-DC converter is an electronic circuit which converts a source of direct

current (DC) from one voltage level to another. It is a class of power converter.

2.2USAGE DC-to-DC converters are important in portable electronic devices such as cellular

phones and laptop computers, which are supplied with power from batteries primarily. Such

electronic devices often contain several sub-circuits, each with its own voltage level

requirement different from that supplied by the battery or an external supply (sometimes

higher or lower than the supply voltage). Additionally, the battery voltage declines as its

stored power is drained. Switched DC-to-DC converters offer a method to increase voltage

from a partially lowered battery voltage thereby saving space instead of using multiple

batteries to accomplish the same thing.

Most DC-to- DC converters also regulate the output voltage. Some exceptions include

high-efficiency LED power sources, which are a kind of DC to DC converter that regulates

the current through the LEDs, and simple charge pumps which double or triple the input

voltage

2.3CONVERSION METHODS

2.3.1 Electronic

2.3.1.1Linear

Linear regulators can only output at lower voltages from the input. They are

very inefficient when the voltage drop is large and the current is high as they dissipate heat

equal to the product of the output current and the voltage drop; consequently they are not

normally used for large-drop high-current applications.

The inefficiency wastes power and requires higher-rated, and consequently more expensive

and larger, components. The heat dissipated by high-power supplies is a problem in itself as it

must be removed from the circuitry to prevent unacceptable temperature rises. They are

practical if the current is low, the power dissipated being small, although it may still be a

large fraction of the total power consumed. They are often used as part of a simple regulated

power supply for higher currents: a transformer generates a voltage which, when rectified, is

a little higher than that needed to bias the linear regulator. The linear regulator drops the

excess voltage, reducing hum-generating ripple current and providing a constant output

voltage independent of normal fluctuations of the unregulated input voltage from the

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transformer / bridge rectifier circuit and of the load current. Linear regulators are

inexpensive, reliable if good heat sinking is used and much simpler than switching regulators.

As part of a power supply they may require a transformer, which is larger for a given power

level than that required by a switch-mode power supply. Linear regulators can provide a very

low-noise output voltage, and are very suitable for powering noise-sensitive low-power

analog and radio frequency circuits. A popular design approach is to use an LDO, Low Drop-

out Regulator that provides a local "point of load" DC supply to a low power circuit.

2.3.1.2Switched-mode conversion

Electronic switch-mode DC-to-DC converters convert one DC voltage level to

another, by storing the input energy temporarily and then releasing that energy to the output

at a different voltage. The storage may be in either magnetic field storage components

(inductors, transformers) or electric field storage components (capacitors). This conversion

method is more power efficient (often 75% to 98%) than linear voltage regulation (which

dissipates unwanted power as heat). This efficiency is beneficial to increasing the running

time of battery operated devices. The efficiency has increased since the late 1980s due to the

use of power FETs, which are able to switch at high frequency more efficiently than power

bipolar transistors, which incur more switching losses and require a more complicated drive

circuit. Another important innovation in DC-to-DC converters is the use of synchronous

rectification replacing the flywheel diode with a power FET with low "On" resistance,

thereby reducing switching losses. Most DC-to-DC converters are designed to move power in

only one direction, from the input to the output. However, all switching regulator topologies

can be made bi-directional by replacing all diodes with independently controlled active

rectification. A bi-directional converter can move power in either direction, which is useful in

applications requiring regenerative braking. Drawbacks of switching converters include

complexity, electronic noise (EMI / RFI) and to some extent cost, although this has come

down with advances in chip design. DC-to-DC converters are now available as integrated

circuits needing minimal additional components. DC-to-DC converters are also available as a

complete hybrid circuit component, ready for use within an electronic assembly.

2.3.1.2.1 Magnetic

In these DC-to-DC converters, energy is periodically stored into and released from

a magnetic field in an inductor or a transformer, typically in the range from 300 kHz to

10 MHz By adjusting the duty cycle of the charging voltage (that is, the ratio of on/off time),

the amount of power transferred can be controlled. Usually, this is applied to control the

output voltage, though it could be applied to control the input current, the output current, or

maintain a constant power. Transformer-based converters may provide isolation between the

input and the output. In general, the term "DC-to-DC converter" refers to one of these

switching converters. These circuits are the heart of a switched-mode power supply. Many

topologies exist. This table shows the most common.

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Table-2.1 Different Topologies

Forward

Energy goes from the input,

through the magnetics and to the

load, simultaneously

Flyback

Energy goes from the input and stored in the magnetics

Later, it is released from the magnetics to the load

No

transformer

Non-

isolated

Step-down (Buck) - The output voltage is

lower than the input voltage, and of the

same polarity

Non-inverting: The output voltage is the same polarity as the input

Step-up (Boost) - The output voltage is higher than the input voltage

SEPIC - The output voltage can be lower or higher than the input

Inverting: the output voltage is of the opposite polarity as the input

Inverting (Buck-Boost)

uk - Output current is continuous

True Buck-Boost - The output voltage is the same polarity as the input and can be lower or higher

Split-Pi (Boost-Buck) - Allows bidirectional voltage conversion with the output voltage the same polarity as the input and

can be lower or higher

With

transformer

May be

Half bridge - 2 transistors drive

Full bridge - 4 transist

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In addition, each topology may be:

Hard switched - transistors switch quickly while exposed to both full voltage and full

current

Resonant - an LC circuit shapes the voltage across the transistor and current through it so

that the transistor switches when either the voltage or the current is zero

Magnetic DC-to-DC converters may be operated in two modes, according to the current in its

main magnetic component (inductor or transformer):

Continuous - the current fluctuates but never goes down to zero

Discontinuous - the current fluctuates during the cycle, going down to zero at or before

the end of each cycle

A converter may be designed to operate in Continuous mode at high power, and in

Discontinuous mode at low power.

The Half bridge and Fly back topologies are similar in that energy stored in the magnetic core

needs to be dissipated so that the core does not saturate. Power transmission in a

flybackcircuit is limited by the amount of energy that can be stored in the core, while forward

circuits are usually limited by the I/V characteristics of the switches.

Although MOSFET switches can tolerate simultaneous full current and voltage

(although thermal stress and electromigration can shorten the MTBF), bipolar switches

generally can't so require the use of a snubber (or two).

2.3.1.2.2 Capacitive

Switched capacitor converters rely on alternately connecting capacitors to the input

and output in differing topologies. For example, a switched-capacitor reducing converter

might charge two capacitors in series and then discharge them in parallel. This would

produce an output voltage of half the input voltage, but at twice the current (minus various

inefficiencies). Because they operate on discrete quantities of charge, these are also

sometimes referred to as charge pump converters. They are typically used in applications

requiring relatively small amounts of current, as at higher current loads the increased

efficiency and smaller size of switch-mode converters makes them a better choice. They are

also used at extremely high voltages, as magnetics would break down at such voltages 2.3.2Electrochemical

A further means of DC-to-DC conversion in the kilowatt to many Megawatts range is

presented by using redox flow batteries such as the vanadium redox battery, although this

technique has not been applied commercially to date.

isolated

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3. CUK CONVERTER

3.1 INTRODUCTION The circuit of the C`uk converter is shown in Fig. 13.12a. It consists of dc input

voltage source VS, input inductor L, controllable switch S, energy transfer capacitor C, diode

D, lter inductor L, lter capacitor C, and load resistance R. An important advantage of this topology is a continuous current at both the input and the output of the converter.

Disadvantages of the C`uk converter are a high number of reactive

components and high current stresses on the switch, the diode, and the capacitor C. The main

waveforms in the converter are presented in Fig. 13.12b. When the switch is on, the diode is

off and the capacitor C is discharged by the inductor L current. With the switch in the off

state, the diode conducts currents of the inductors Land L, whereas capacitor C is charged by

the inductor L current.

Fig.3.1 Basic schematicC'UK converter

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3.2PRINCIPLE OF OPERATION OF ISOLATED CUK

CONVERTER.

The basic principle of the Buck-Boost converter is fairly simple:

While in the On-state, the input voltage source is directly connected to the inductor (L1).

This results in accumulating energy in L1. In this stage, the capacitor C2 supplies energy

to the output load.

While in the Off-state, the inductor is connected to the output load and capacitor, so

energy is transferred from L to C and R.

Compared to the buck and boost converters, the characteristics of the Buck-Boost converter

are mainly:

polarity of the output voltage is opposite to that of the input;

The output voltage can vary continuously from 0 to (for an ideal converter). The

output voltage ranges for a buck and a boost converter are respectively 0 to and

to

Fig.3.2Schematic of a CUK converter

3.3 NON ISOLATED CUK CONVERTER.

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There are variations on the basic Cuk converter. For example, the coils may share

single magnetic core, which drops the output ripple, and adds efficiency. Because the power

transfer flows continuously via the capacitor, this type of switcher has minimized EMI

radiation. The Cuk converter enables the energy flow bidirectionally, by adding a diode and a

switch.

3.3.1 PRINCIPLE OF OPERATION OF NON ISOLATED CUK

CONVERTER.

A non-isolated uk converter comprises two inductors, two capacitors, a switch

(usually a transistor), and a diode. Its schematic can be seen in figure 1. It is an inverting

converter, so the output voltage is negative with respect to the input voltage.

The capacitor C is used to transfer energy and is connected alternately to the input and

to the output of the converter via the commutation of the transistor and the diode (see figures

2 and 3).

The two inductors L1 and L2 are used to convert respectively the input voltage source

(Vi) and the output voltage source (Co) into current sources. Indeed, at a short time scale an

inductor can be considered as a current source as it maintains a constant current. This

conversion is necessary because if the capacitor were connected directly to the voltage

source, the current would be limited only by (parasitic) resistance, resulting in high energy

loss. Charging a capacitor with a current source (the inductor) prevents resistive current

limiting and its associated energy loss.

As with other converters (buck converter, boost converter, buck-boost converter) the

uk converter can either operate in continuous or discontinuous current mode. However,

unlike these converters, it can also operate in discontinuous voltage mode (i.e., the voltage

across the capacitor drops to zero during the commutation cycle).

Fig 3.3

THE TWO OPERATING STATES OF A NON-ISOLATING CUK CONVERTER

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3.3.2 CONTINOUS MODE

In steady state, the energy stored in the inductors has to remain the same at the

beginning and at the end of a commutation cycle. The energy in an inductor is given by:

This implies that the current through the inductors has to be the same at the beginning

and the end of the commutation cycle. As the evolution of the current through an inductor is

related to the voltage across it:

it can be seen that the average value of the inductor voltages over a commutation

period have to be zero to satisfy the steady-state requirements.

If we consider that the capacitors C and Co are large enough for the voltage ripple across

them to be negligible, the inductor voltages become:

in the off-state, inductor L1 is connected in series with Vi and C (see figure 2).

Therefore . As the diode D is forward biased (we consider zero voltage

drop), L2 is directly connected to the output capacitor. Therefore

in the on-state, inductor L1 is directly connected to the input source.

Therefore . Inductor L2 is connected in series with C and the output capacitor,

so

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The converter operates in on-state from t=0 to t=DT (D is the duty cycle), and in off state

from DT to T (that is, during a period equal to (1-D)T). The average values of VL1 and

VL2 are therefore:

As both average voltage have to be zero to satisfy the steady-state conditions we can write,

using the last equation:

So the average voltage across L1 becomes:

Which can be written as:

It can be seen that this relation is the same as that obtained for the Buck-boost converter.

3.3.3 The two operating states of a non-isolated uk converter. In this figure, the diode and the switch are either replaced by a short circuit when

they are on or by an open circuit when they are off. It can be seen that

when in the Off state, the capacitor C is being charged by the input source

through the inductor L1. When in the On state, the capacitor C transfers

the energy to the output capacitor through the inductance L2.

3.3.4 DISCONTINOUS MODE

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Like all DC-DC converters Cuk converters rely on the ability of the inductors in the

circuit to provide continuous current, in much the same way a capacitor in a rectifier filter

provides continuous voltage. If this inductor is too small or below the "critical inductance",

then the current will be discontinuous. This state of operation is usually not studied in much

depth, as it is not used beyond a demonstrating of why the minimum inductance is crucial.

The minimum inductance is given by:

Where is the switching frequency.

4. PULSE WIDTH MODULATION

4.1INTRODUCTION

Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a commonly

used technique for controlling power to inertial electrical devices, made practical by modern

electronic power switches.

The average value of voltage (and current) fed to the load is controlled by turning the

switch between supply and load on and off at a fast pace. The longer the switch is on

compared to the off periods, the higher the power supplied to the load is.

The PWM switching frequency has to be much faster than what would affect the load,

which is to say the device that uses the power. Typically switchings have to be done several

times a minute in an electric stove, 120 Hz in a lamp dimmer, from few kilohertz (kHz) to

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tens of kHz for a motor drive and well into the tens or hundreds of kHz in audio amplifiers

and computer power supplies.

The term duty cycle describes the proportion of 'on' time to the regular interval or

'period' of time; a low duty cycle corresponds to low power, because the power is off for most

of the time. Duty cycle is expressed in percent, 100% being fully on.

The main advantage of PWM is that power loss in the switching devices is very low.

When a switch is off there is practically no current, and when it is on, there is almost no

voltage drop across the switch. Power loss, being the product of voltage and current, is thus

in both cases close to zero. PWM also works well with digital controls, which, because of

their on/off nature, can easily set the needed duty cycle.

PWM has also been used in certain communication systems where its duty cycle has

been used to convey information over a communications channel.

4.2PRINCIPLE

Pulse-width modulation uses a rectangular pulse wave whose pulse width is

modulated resulting in the variation of the average value of the waveform. If we consider a

pulse waveform f (t) with a low value ymin, a high value ymax and a duty cycle D (see figure 1),

the average value of the waveform is given by:

As f (t) is a pulse wave, its value is ymax for

and ymin for

The above expression then becomes:

This latter expression can be fairly simplified in many cases where ymin = 0 as

. From this, it is obvious that the average value of the signal ( ) is

directly dependent on the duty cycle D.

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Fig.4.1A simple method to generate the PWM pulse train corresponding to a given signal is

the intersective PWM

The simplest way to generate a PWM signal is the intersective method, which requires

only a sawtooth or a triangle waveform (easily generated using a simple oscillator) and

a comparator. When the value of the reference signal (the green sine wave in figure 2) is

more than the modulation waveform (blue), the PWM signal (magenta) is in the high state,

otherwise it is in the low state.

4.2.1Delta

In the use of delta modulation for PWM control, the output signal is integrated, and

the result is compared with limits, which correspond to a reference signal offset by a

constant. Every time the integral of the output signal reaches one of the limits, the PWM

signal changes state.

Fig.4.2 Principle of Delta PWM

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4.2.2Delta-Sigma

In delta-sigma modulation as a PWM control method, the output signal is subtracted

from a reference signal to form an error signal. This error is integrated, and when the integral

of the error exceeds the limits, the output changes state.

Fig.4.3Principle of delta sigma PWM.

4.2.3Space Vector Modulation

Space vector modulation is a PWM control algorithm for multi-phase AC generation,

in which the reference signal is sampled regularly; after each sample, non-zero active

switching vectors adjacent to the reference vector and one or more of the zero switching

vectors are selected for the appropriate fraction of the sampling period in order to synthesize

the reference signal as the average of the used vectors.

4.2.4Direct Torque Control (DTC)

Direct torque control is a method used to control AC motors. It is closely related with

the delta modulation (see above). Motor torque and magnetic flux are estimated and these are

controlled to stay within their hysteresis bands by turning on new combination of the device's

semiconductor switches each time either of the signal tries to deviate out of the band.

4.2.5Time proportioning

Many digital circuits can generate PWM signals (e.g. many microcontrollers have

PWM outputs). They normally use acounter that increments periodically (it is connected

directly or indirectly to the clock of the circuit) and is reset at the end of every period of the

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PWM. When the counter value is more than the reference value, the PWM output changes

state from high to low (or low to high).This technique is referred to as time

proportioning, particularly as time-proportioning control which proportion of a fixed cycle

time is spent in the high state.

The incremented and periodically reset counter is the discrete version of the

intersecting method's sawtooth. The analog comparator of the intersecting method becomes a

simple integer comparison between the current counter value and the digital (possibly

digitized) reference value. The duty cycle can only be varied in discrete steps, as a function of

the counter resolution. However, a high-resolution counter can provide quite satisfactory

performance.

4.2.6 Types

Three types of pulse-width modulation (PWM) are possible:

1. The pulse center may be fixed in the center of the time window and both edges of

the pulse moved to compress or expand the width.

2. The lead edge can be held at the lead edge of the window and the tail edge

modulated.

3. The tail edge can be fixed and the lead edge modulated.

Fig.4.4 Waveforms of different types of pulses

4.2.7Spectrum

The resulting spectra (of the three cases) are similar, and each contains

a dc component, a base sideband containing the modulating signal and phase

modulated carriers at each harmonic of the frequency of the pulse. The amplitudes of the

26

harmonic groups are restricted by a sinx / x envelope (sinc function) and extend to infinity.On

the contrary, the delta modulation is a random process that produces continuous spectrum

without distinct harmonics.

4.3APPLICATIONS

4.3.1Telecommunications

In telecommunications, the widths of the pulses correspond to specific data values

encoded at one end and decoded at the other.

Pulses of various lengths (the information itself) will be sent at regular intervals

(the carrier frequency of the modulation).

The inclusion of a clock signal is not necessary, as the leading edge of the data signal

can be used as the clock if a small offset is added to the data value in order to avoid a data

value with a zero length pulse.

4.3.2Power Delivery

PWM can be used to adjust the total amount of power delivered to a load without

losses normally incurred when a power transfer is limited by resistive means. The drawback

is the pulsations defined by the duty cycle, switching frequency and properties of the load.

With a sufficiently high switching frequency and, when necessary, using additional

passive electronic filters the pulse train can be smoothed and average analog waveform

recovered.

High frequency PWM power control systems are easily realizable with semiconductor

switches. As has been already stated above almost no power is dissipated by the switch in

either on or off state. However, during the transitions between on and off states both voltage

and current are non-zero and thus considerable power is dissipated in the switches. Luckily,

the change of state between fully on and fully off is quite rapid (typically less than 100

nanoseconds) relative to typical on or off times, and so the average power dissipation is quite

low compared to the power being delivered even when high switching frequencies are used.

Modern semiconductor switches such as MOSFETs or Insulated-gate bipolar

transistors (IGBTs) are quite ideal components. Thus high efficiency controllers can be built.

Typically frequency converters used to control AC motors have efficiency that is better than

98 %. Switching power supplies have lower efficiency due to low output voltage levels (often

even less than 2 V for microprocessors are needed) but still more than 70-80 % efficiency can

be achieved.

Variable-speed fan controllers for computers usually use PWM, as it is far more

efficient when compared to a potentiometer or rheostat. (Neither of the latter is practical to

operate electronically; they would require a small drive motor.)

Light dimmers for home use employ a specific type of PWM control. Home-use light

dimmers typically include electronic circuitry which suppresses current flow during defined

portions of each cycle of the AC line voltage. Adjusting the brightness of light emitted by a

light source is then merely a matter of setting at what voltage (or phase) in the AC half cycle

27

the dimmer begins to provide electrical current to the light source (e.g. by using an electronic

switch such as a triac). In this case the PWM duty cycle is the ratio of the conduction time to

the duration of the half AC cycle defined by the frequency of the AC line voltage (50 Hz or

60 Hz depending on the country).

These rather simple types of dimmers can be effectively used with inert (or relatively

slow reacting) light sources such as incandescent lamps, for example, for which the

additional modulation in supplied electrical energy which is caused by the dimmer causes

only negligible additional fluctuations in the emitted light. Some other types of light sources

such as light-emitting diodes (LEDs), however, turn on and off extremely rapidly and would

perceivably flicker if supplied with low frequency drive voltages. Perceivable flicker effects

from such rapid response light sources can be reduced by increasing the PWM frequency. If

the light fluctuations are sufficiently rapid, the human visual system can no longer resolve

them and the eye perceives the time average intensity without flicker (see flicker fusion

threshold).

In electric cookers, continuously-variable power is applied to the heating elements

such as the hob or the grill using a device known as a Simmerstat. This consists of a thermal

oscillator running at approximately two cycles per minute and the mechanism varies the duty

cycle according to the knob setting. The thermal time constant of the heating elements is

several minutes, so that the temperature fluctuations are too small to matter in practice.

4.3.3Voltage Regulation

PWM is also used in efficient voltage regulators. By switching voltage to the load

with the appropriate duty cycle, the output will approximate a voltage at the desired level.

The switching noise is usually filtered with an inductor and a capacitor.One method measures

the output voltage. When it is lower than the desired voltage, it turns on the switch. When the

output voltage is above the desired voltage, it turns off the switch.

4.3.4Audio Effects and Amplification

PWM is sometimes used in sound (music) synthesis, in particular subtractive

synthesis, as it gives a sound effect similar to chorus or slightly detuned oscillators played

together. (In fact, PWM is equivalent to the difference of two sawtooth waves.) The ratio

between the high and low level is typically modulated with a low frequency oscillator, or

LFO. In addition, varying the duty cycle of a pulse waveform in a subtractive-synthesis

instrument creates useful timbral variations. Some synthesizers have a duty-cycle trimmer for

their square-wave outputs, and that trimmer can be set by ear; the 50% point was distinctive,

because even-numbered harmonics essentially disappear at 50%.A new class of audio

28

amplifiers based on the PWM principle is becoming popular. Called "Class-D amplifiers",

these amplifiers produce a PWM equivalent of the analog input signal which is fed to

the loudspeaker via a suitable filter network to block the carrier and recover the original

audio. These amplifiers are characterized by very good efficiency figures ( 90%) and

compact size/light weight for large power outputs. For a few decades, industrial and military

PWM amplifiers have been in common use, often for driving servo motors. They offer very

good efficiency, commonly well above 90%. Field-gradient coils in MRI machines are driven

by relatively-high-power PWM amplifiers.Historically, a crude form of PWM has been used

to play back PCM digital sound on the PC speaker, which is driven by only two voltage

levels, typically 0 V and 5 V. By carefully timing the duration of the pulses, and by relying

on the speaker's physical filtering properties (limited frequency response, self-inductance,

etc.) it was possible to obtain an approximate playback of mono PCM samples, although at a

very low quality, and with greatly varying results between implementations.In more recent

times, the Direct Stream Digital sound encoding method was introduced, which uses a

generalized form of pulse-width modulation called pulse density modulation, at a high

enough sampling rate (typically in the order of MHz) to cover the whole acoustic frequencies

range with sufficient fidelity. This method is used in the SACD format, and reproduction of

the encoded audio signal is essentially similar to the method used in class-D amplifiers.

5. IC LM2611

5.1INTRODUCTION

The LM2611 is a current mode, PWM inverting switching regulator. Operating from a

2.7 - 14V supply, it is capable of producing a regulated negative output voltage of up to (36-

VIN(MAX)). The LM2611 utilizes an input and output inductor, which enables low voltage

ripple and RMS current on both the input and the output. With a switching frequency of

1.4MHz, the inductors and output capacitor can be physically small and low cost. High

efficiency is achieved through the use of a low RDS(ON)FET. The LM2611 features a

shutdown pin, which can be activated when the part is not needed to lower the Iq and save

battery life. A negative feedback (NFB) pin provides a simple method of setting the output

voltage, using just two resistors. Cycle-by-cycle current limiting and internal compensation

further simplify the use of the LM2611.

5.2 FEATURES n 1.4MHz switching frequency n Low RDS(ON) DMOS FET n 1mVp-p output ripple n 5V at 300mA from 5V input n Better regulation than a charge pump n Uses tiny capacitors and inductors n Wide input range: 2.7V to 14V n Low shutdown current:

29

5.3 APPLICATIONS n MR Head Bias n Digital camera CCD bias n LCD bias n GaAs FET bias n Positive to negative conversion.

5.4 TYPICAL APPLICATION OF LM2611

30

Fig 5.1 typical application of lm2611

The LM2611 is available is a small SOT23-5 package. It comes in two grades:

Table-5.1 Function Table

Grade A Grade B

Current Limit 1.2A 0.9A

RDS(ON) 0.5 0.7

5.5 CONNECTION DIAGRAM AND PIN DISCRIPTION

5.5.1PIN DIAGRAM

31

Fig 5.2 pin diagram

5.5.2ORDERING Table-5.2 Ordering Table

5.5.3 PIN DESCRIPTION Table-5.3 Pin Description Table

32

Pin Nam

e Function

1 SW

Drain of internal switch. Connect at the node of the input inductor and

Cuk capacitor.

2 GND Analog and power ground.

3 NFB

Negative feedback. Connect to output via external resistor divider to set

output voltage.

4

SHD

N Shutdown control input. VIN = Device on. Ground = Device in shutdown.

5 VIN

Analog and power input. Filter out high frequency noise with a 0.1 F

ceramic capacitor

placed close to the pin.

5.5.4 BLOCK DIAGRAM Fig 5.3 Block diagram

5.6Absolute Maximum Ratings

If Military/Aerospace specified devices are required, please contact the National

33

Semiconductor Sales Office/ Distributors for availability and specifications. VIN 14.5V

SW Voltage 0. 4V to 36V NFB Voltage +0. 4V to 6V SHDN Voltage 0. 4V to 14.5V Maximum Junction 125C Temperature

Power Dissipation (Note

2) Internally Limited

Lead Temperature 300C ESD Susceptibility

Human Body Model 2kV

Machine Model 200V

5.7 Operating

condition

Operating Junction

Temperature Range 40C to +125C Storage Temperature 65C to +150C Supply Voltage 2.7V to 14V

ja 256C/W

5.8Electrical Characteristics

Specifications in standard type face are for TJ = 25C and those with boldface type

34

apply over the Temperature Range TJ = 40C to +85C, unless otherwise specified. VIN = 5.0V and IL = 0A, unless otherwise specified. Table 5.4 Electrical characteristics

Symbol Parameter Conditions

Min Typ Max

Units

(Note 4) (Note 5) (Note 4)

VIN Input Voltage 2.7 14 V

ISW Switch Current Limit Grade A 1 1.2 2 A

Grade B 0.7 0.9 RDSON Switch ON Resistance Grade A 0.5 0.65

Grade B

0.7 0.9

SHDNTH Shutdown Threshold Device enabled 1.5 V

Device disabled 0.50

ISHDN

Shutdown Pin Bias

Current VSHDN = 0V

0.0 A

VSHDN = 5V 0.0 1.0

NFB Negative Feedback VIN = 3V 1.205 1.23 1.255 V Reference

INFB NFB Pin Bias Current VNFB =1.23V 2.7 4.7 6.7 A

Iq Quiescent Current VSHDN = 5V, Switching 1.8 3.5 mA

VSHDN = 5V, Not Switching 270 500 A

VSHDN = 0V 0.024 1 A

%VOUT/

Reference Line

Regulation 2.7V VIN 14V 0.02 %/V

VIN

fS Switching Frequency 1.0 1.4 1.8 MHz DMAX Maximum Duty Cycle 82 88 %

IL Switch Leakage Not Switching 1 A

VSW = 5V

Note 1: Absolute maximum ratings are limits beyond which damage to the device may

occur. Operating Ratings are conditions for which the device is intended tobe functional,

but device parameter specifications may not be guaranteed. For guaranteed specifications

and test conditions, see the Electrical Characteristics. Note 2: The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(MAX), the junction-to-ambient thermal resistance,JA,and the ambient temperature, TA. See the Electrical Characteristics table for the thermal resistance of various layouts. The maximum allowable power dissipation at any ambient temperature is calculated using: PD (MAX) = (TJ(MAX) TA)/JA. Exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. Note 3: The human body model is a 100 pF capacitor discharged through a 1.5kresistor into each pin. The machine model is a 200pF capacitor dischargeddirectly into each pin. Note 4: All limits guaranteed at room temperature (standard typeface) and at temperature

extremes (bold typeface). All room temperature limits are 100% testedor guaranteed

through statistical analysis. All limits at temperature extremes are guaranteed via

35

correlation using standard Statistical Quality Control (SQC) methods. All limits are used

to calculate Average Outgoing Quality Level (AOQL).

Note 5: Typical numbers are at 25C and represent the expected value of the parameter.

5.9Typical Performance Characteristics Fig 5.4 Typical Characteristics

36

37

5.10 APPLICATION CIRCUITS OF LM2611 IN CUK

CONVERTER 1. 5V to -5V Inverting Converter 2. 9V to -5V Inverting Converter 3. 12V to -5V Inverting Converter 4. Operating with Separate Power and Biasing Supplies

38

5.11 Physical Dimensionsinches (millimeters)unless otherwise noted Fig 5.5 Physical Dimensions

39

6. OPERATION OF CUK CONVERTER

Fig 6.1 Operating cycle of a Cuk converter

The LM2611 is a current mode, fixed frequency PWM switching regulator with a

1.23V reference that makes it ideal for use in a Cuk converter. The Cuk converter inverts

the input and can step up or step down the absolute value. Using inductors on both the input

and output, the Cuk con-verter produces very little input and output current ripple. This is a

significant advantage over other inverting topolo-gies such as the buck-boost and flyback. The operating states of the Cuk converter are shown in Figure 1.During the first

cycle, the transistor switch is closedand the diode is open. L1 is charged by the source and L2 is charged by CCUK, while the output current is provided by L2. In the second cycle, L1 charges CCUK and L2 discharges through the load. By applying the volt-second balance to either of the inductors, the relationship of VOUT to the duty cycle (D) is found to be:

The following sections review the steady-state design of the LM2611 Cuk converter.

6.1 Output and Input Inductor

Figure 2and Figure 3showthe steady-state voltage andcurrent waveforms for L1 and L2, respectively. Referring to Figure 1(a),when the switch is closed, VINis applied acrossL1. In the next cycle, the switch opens and the diode be-comes forward biased, and VOUT is applied across L1 (the voltage across CCUK is VIN VOUT.

40

FIG 6.2 Voltage and current wave forms

The voltage and current waveforms of inductor L2 are shown in Figure 3. During the first cycle of operation, when the switch is closed, VIN is applied across L2. When the switch opens, VOUT is applied across L2.

41

The following equations define values given in Figure 2 and Figure 3:

IL2

= IOUT

Use these equations to choose correct core sizes for the inductors. The design of the

LM2611s internal compensa-tion assumes L1 and L2 are equal to 10 - 22 H, thus it

is recommended to stay within this range.

6.2 Switch Current Limit

The LM2611 incorporates a separate current limit compara-tor, making current limit

independent of any other variables. The current limit comparator measures the switch current

versus a reference that represents current limit. If at any time the switch current surpasses the

current limit, the switch opens until the next switching period. To determine the maxi-mum

load for a given set of conditions, both the input and output inductor currents must be

considered. The switch current is equal to iL1 + iL2, and is drawn in Figure 4. In summary:

ISW(PEAK) must be less than the current limit (1.2A typical), but will also be limited by the thermal resistivity of the LM2611s SOT23-5 package (JA = 265C/W).

Fig 6.4 Switch Current waveform in a Cuk Converter

FIGURE 4. Switch Current Waveform in a Cuk Converter. The peak value is equal to

the sum of the average currents through L1 and L2 and the average-to-peak current

ripples through L1 and L2.

42

6.3 Input Capacitor

The input current waveform to a Cuk converter is continuous and triangular, as shown

in Figure 2. The input inductor insures that the input capacitor sees fairly low ripple cur-

rents. However, as the input inductor gets smaller, the input ripple goes up. The RMS current

in the input capacitor is given by: The input capacitor should be capable of handling the RMS current. Although the

input capacitor is not so critical in a Cuk converter, a 10F or higher value good quality

capacitor prevents any impedance interactions with the input supply. A 0.1F or 1F ceramic

bypass capacitor is also recom-mended on the VIN pin (pin 5) of the IC. This capacitor must

be connected very close to pin 5 (within 0.2 inches).

6.4 Output Capacitor

Like the input current, the output current is also continuous, triangular, and has low

ripple (see IL2 in Figure 3). The output capacitor must be rated to handle its RMS current: For example, ICOUT(RMS) can range from 30mA to 180mA with 10H L1,2 22H,

10V VOUT 3.3V, and 2.7V VIN 30V (VIN may be 30V if using separate power and analog supplies, see Split

Supply Operation in the APPLI-CATIONS section). The worst case conditions are with L1,2, VOUT(MAX), and VIN(MAX). Many capacitor technologies will provide this level of RMS

current, but ceramic capacitors are ideally suited for the LM2611. Ceramic capacitors provide a good combination of

capacitance and equivalent series re-sistance (ESR) to keep the zero formed by the

capacitance and ESR at high frequencies. The ESR zero is calculated as:

A general rule of thumb is to keep fESR>80kHz for LM2611 Cuk designs. Low ESR

tantalum capacitors will usually be rated for at least 180mA in a voltage rating of 10V or

above. However the ESR in a tantalum capacitor (even in a low ESR tantalum capacitor) is

much higher than in a ceramic capaci- tor and could place fESR low enough to cause the LM2611 to run unstable.

6.5 Improving Transient Response/Compensation

The compensator in the LM2611 is internal. However, a zero-pole pair can be added to the open loop frequency response by inserting a feed forward capacitor, CFF, in par-allel to the top feedback resistor (RFB1). Phase margin and bandwidth can be improved with the added zero-pole pair. This inturn will improve the transient response to a step load change (see Figure 5 and Figure 6). The position of the zero-pole pair is a function of the feedback

43

resistors and the capacitor value:

(1)

(2) The optimal position for this zero-pole pair will vary with circuit parameters such as D, IOUT, COUT, L1, L2, and CCUK. For most cases, the value

for the zero frequency is between 5 kHz to 20 kHz. Notice how the pole position, p, is depen-dant on the feedback

resistors RFB1 and RFB2, and therefore also dependant on the output voltage. As the output voltage becomes closer to 1.26V, the pole moves towards the zero, tending to cancel it out. If the absolute magnitude of the output voltage is less than 3.3V, adding the zero-pole pair will not have much effect on the response.

Fig 6.5 Transient response of Cuk converter

20018120

) LEVEL 3 FIGURE 5. 130mA to 400mA Transient Response of the circuit in Figure 9

with CFF= 1nF

44

) LEVEL 3

FIGURE 6. 130mA to 400mA Transient Response of the circuit in Figure 9 with CFF

disconnected

6.6 Hysteretic Mode

As the output current decreases, there will come a point when the energy stored in the

Cuk capacitor is more than the energy required by the load. The excess energy is absorbed by

the output capacitor, causing the output voltage to in-crease out of regulation. The LM2611

detects when this happens and enters a pulse skipping, or hysteretic mode. In hysteretic

mode, the output voltage ripple will increase, as illustrated in Figure 7 and Figure 8.

FIGURE 7. The LM2611 in PWM mode has very low ripple

45

THERMAL SHUTDOWN If the junction temperature of the LM2611 exceeds 163C, it will enter the thermal

shutdown. In thermal shutdown, the part deactivates the driver and the switch turns off. The

switch remains off until the junction temperature drops to 155C,at which point the part begins switching again. It will typically take 10ms for the junction temperature to drop from

163C to 155C

46

7. SIMULATION OF PRACTICAL CIRCUIT

7.1INTRODUCTION TO PSIM SOFTWARE

PSIM is the leading simulation and design software for power electronics, motor

drives, and dynamic system simulation. With fast simulation and easy-to-use interface, PSIM

provides a powerful and efficient environment to meet your simulation needs:

Aerospace and Defense

Automotive

Communications

Electronics and Signal Processing

Medical Instrumentation

7.1.1Tool for Model-Based Design

A system is represented in PSIM in the following way:

Fig 7.1 Representation of a system in PSIM

Based on this representation, a sensor must be used to send a power circuit quantity (it

could be voltage, current, torque, or speed sensor) into the control circuit. Similarly, a

switch controller or an interface block must be used to send a control circuit quantity

into the power circuit. Circuits should be built based on this convention.

The power circuit and the control circuit are solved separately, and there is one time

step delay between these two solutions.

47

The following are the power circuit elements:

- All the elements under the Elements/Power menu; - All the elements under the Elements/Other/Probes menu; - All the elements under the Elements/Sources menu

The following are the control circuit elements:

- All the elements under the Elements/Control menu; - Independent voltage sources under the Elements/Sources/Voltage menu, including dc source, single-phase and 3-phase sine source, triangular

source, square-wave source, step source, piecewise linear source, and random

source.

The following elements are common to both power and control circuits:

- ABC-DQ0 transformation blocks;

- External DLL blocks;

- Voltage probe in Elements/Other/Probes; - Time element Time under the Elements/Sources menu;

The following are the sensor elements:

- All the elements under the Elements/Other/Sensors menu.

The following are the switch controllers and interface block:

- All the elements under the Elements/Other/Switch Controllers menu. - Control-power interface block under the Elements/Other menu.

Based on this definition:

- All the RLC branches, switches, transformers, electric machines, and

mechanical loads are power elements.

- All the current sources, controlled voltage/current sources, and nonlinear

sources (such as "voltage source (multiplication)") are power elements.

- Switch gating blocks is a power element. Note that the gating block can be

connected to the gate node of a switch ONLY. It can not be connected to any

other elements.

- All the function blocks (such as multiplier, sine function block, etc.), s-

domain and z-domain transfer function blocks and elements, and logic

elements are control elements.

- Op. amp. is an exception. Op. amp.is a subcircuit which is modeled using

voltage-controlled voltage source, resistor, diodes, and dc voltage sources.

48

Based on above definition, it is a power element. However, op. amp.is a

control element in the conventional sense. That is why op. amp. is placed

under the Elements/Control menu rather than under Elements/Power.

- The gate node of a controlled switch (such as MOSFET, IGBT) can be

connected to a switch gating block or the output of a switch controller ONLY.

It cannot be connected to any other elements.

In order to make the power-control interface easier and more transparent to

users, PSIM does allow a power circuit node to be connected directly to the input

node of a control element. In this case, a voltage sensor is inserted automatically by

the program.

However, PSIM does not allow the output node of a control element to be

connected directly to a power element. The user would have to connect a control-

power interface block from the control node to the power node. (Exception: Direct

connection of the control element output to a RLC branch is allowed. In this case, a

control-power interface block is inserted automatically by the program.)

We do not automatically insert control-power interface blocks for all other

elements because doing so might result in indiscriminate use of the power and control

elements in mixture (such as the case where an op. amp. is followed by a comparator

or a control element, which is followed by another op. amp., and another comparator).

In this case, the delay in the solution is more than one time step, and this could cause

problems in certain situations.

49

7.2 The obtained wave forms.

Fig.7.2 OutputVoltage waveform

Fig.7.3Waveformnear switch

50

The Output voltage gets lower than input voltage only when the ON-time of the PWM pulse

is less 50percent of the total time period.

7.3 Simulation Results In the simulation variation of the output voltage,pulse width with input voltage, inductor,

capacitor are observed and noted down in the table as follows,

7.3.1 Inference 1. The Output voltage is directly proportional to the resistance R3 in the circuit.

2. Circuit works as a boost for pulse width greater than 50% and as a buck for less than

50% pulse width.

Table-7.1 Input voltage

variation

Input Voltage Output voltage

Pulse width

12 -4.5 74.2%

10 -4.2 60.64%

8 -2.985 40.60%

5 -1.984 37.38%

9 -3 41.46%

51

7.4 The simulation circuit of the Cuk converter

Fig 7.4 Simulation circuit

52

8. HARDWARE IMPLEMENTATION

8.1 CIRCUIT SPECIFICATION This section covers a simple closed loop controlled Buck-Boost converter with the following

specifications.

Input: 5V

Output: INVERTED DC VOLTAGE

Topology:-CUK Converter using LM2611 IC

Controller: LM2611

Switching Frequency:50kHz

Protection: None

8.2CIRCUIT DESCRIPTION

8.2.1 Starting Power Supply The starting power supply is obtained from a 18V transformer connected to a rectifier circuit.

The rectifier circuit consists of 1000microfarad capacitors, 7805 voltage regulators for

obtaining positive voltage. Consists of 10nf capacitors and also jumpers to connect to the

circuit.

Fig.8.1.Power Supply Board

53

8.2.2 Complete circuit

Fig.8.2 Completely Soldered Hardware Circuit

8.3 HARDWARE OUTPUT WAVEFORMS The waveforms obtained from the hardware circuit are shown below,

Fig.8.3 Reference Voltage

54

Fig.8.4 PWM pulses

Fig.8.5 Varying Pulse width

55

Fig.8.6 Output DC Voltage

56

9.APPLICATIONS

The CUK converter is used in. MR Head Bias Digital camera CCD bias LCD bias GaAs FET bias

Positive to negative conversion The description of various applications are

9.1 Digital cam

What is a CCD? In a digital camera the traditional photographic film is replaced by a Charge Coupled

Device (CCD).

A CCD is a mosaic of tiny light sensitive detectors called pixels or 'photosites'. The pixels are arranged as a flat rectangular surface onto which an image is projected

using a camera or telescope lens. Each pixel accumulates an electrical charge

depending on the amount of light falling upon it.

When an image is 'captured' the electrical charge from each pixel is measured and converted to a number (digitised) by the electronic circuits within the camera. These

numbers are transmitted to a computer (immediately or at some later time) where they

are used to control the brightness of points on the computer screen (screen pixels),

thus reproducing the original image projected onto the CCD.

Sets of numbers representing a complete image are stored in the computer as 'image files'. There are many powerful software programs available to process these files and

enhance the image by adjusting the contrast, colour balance etc.

Signal and Noise The efficiency with which CCD pixels can capture faint images is much better than

traditional photography, but there are problems that need to be understood. Most of

these are relate to 'noise'.

The variation in the brightness of pixels across the image shows the 'picture' to our eyes. The greater the variation, the greater the contrast. However, variation can come

from:

Signal: Pixel variation due to the features of the object being photographed. Noise: Pixel variation due to other unwanted causes. For a good image we need to have a good signal-to-noise ratio. If there is too much

noise we will have an image with poor contrast, speckles or other unpleasant features.

(See this example of a noisy image of C/2004 Q4)

A CCD will introduce noise through bias, dark current, quantum noise and inhomogeneities, each of which is described below. Modern, cooled cameras

developed for astrophotography will suffer relatively little from these problems, but

for long exposures they can still degrade image quality. Webcams and ordinary digital

cameras are generally very 'noisy'.

57

Bias (offset)

Each CCD pixel will have a certain minimum electrical charge even if the exposure is

of zero duration. This means that pixel values will always be greater than zero even for the

shortest exposures. This is called 'bias' or 'offset'.

9.2 LCD MULTIPLEX RATIO

The configuration for Liquid Crystal Display Multiplex Drive technique differs from

a Static Drive technique is that it uses more than a single "backplane" or segment common.

With this configuration, each segment control line can be connected to as many segments as

there are backplanes, providing that each of the segments that it is connected to are tied to a

separate backplanes. This method "Multiplexes" each of the segment control lines and

minimizes the number of interconnects. This is the method used with complex displays that

have limited interconnection surface area or available drive circuits. This reduction in the

number of external connections enhances device reliability and increases the potential display

density. The liability of a higher multiplex rate will effect display quality, operational

temperature range, and the increased complexity of drive circuitry (or perhaps

microprocessor software) may necessary for their operation.

The method of drive for multiplexed displays is essentially a time division multiplex

with the number of time divisions equal to twice the number of common planes used in a

given format. As is the case with conventional LCDs, in order to prevent irreversible

electrochemical action from destroying the display, the voltage at all segment locations must

be caused to reverse polarity periodically so that zero net DC voltage is applied. This is the

reason for the doubling in time divisions: Each common plane must be alternately driven with

a voltage pulse of opposite polarity.

As is the case with non multiplexed displays, the drive frequency should be chosen to be

above the flicker-fusion rate, i.e. >30 Hz. Since increasing the drive frequency significantly

above this value increases current demand by the CMOS drive electronics, and to prevent

problems due to the finite conductivity of the display segment and common electrodes, an

upper drive frequency limit of 60-90 Hz is recommended.

8.3 LCD BIAS

The control signals that drive an LCD are AC in nature. The basic configuration of

how to generate a waveform to control an LCD are covered in the sections "LCD Multiplex

Ratio (above)" and "LCD Static Drive Technology". But to control LCDs with a larger

multiplex ratio, we need to provide the waveform generator with multiple bias voltage level

points. The resulting waveform sent to the LCD segment/dot control lines and backplane

commons will contain a stair-stepped waveform that will maintain specific ac voltages across

any given segment/dot to keep it in it's "on" or "off" state (or in a grayscale module, states

between those two points). The LCD Bias number (example: 1/5 bias) will indicate how

many voltage reference points are created to drive a specific LCD. The table below shows the

relationship between the number of driving bias voltages and the display multiplex ratios

typically used:

Mux

RatioStatic1/21/31/41/71/81/111/121/141/161/241/321/64Biases23

58

1/2 Bias4

1/3 Bias5

1/4 Bias6

1/5 Bias

The necessary bias voltages are usually generated by the use of a resistor dividing

network, and example of which is shown below using Vdd at 5 volts, and the number of

resistors in the ladder determined using the table above.

The values of the resistors is determined by the required voltage reference points and possible

waveform distortion. Because an LCD is a capacitive load, the values should be decreased to

decrease distortion, or with larger displays, buffering the voltage reference points with op-

amps.

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10. CONCLUSION AND SCOPE FOR FUTURE WORK

We obtained an inverted voltage -1.64V with an input supply of 5V thus working as a

Cuk converter.

Future scope:

Development of multi-stage cuk converter for photo voltaic regulation

Analysis and design of multi-stage, multi-leave, DC-DC converter with input-output bypass capacitor

Simulation and Hardware implementation of Incremental Conductance. MPPT (Maximum Power Point Tracking) with Direct Control method using CUK

converter.

Power Factor Improvement Using DCM (Discontinuous Conduction mode) CUK converter with Coupled Inductor.

Photovoltaic Power converter for military and space applications. Dynamic Maximum power point tracking of Photo voltaic arrays using ripple

correlation control.

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REFERENCES

1. Mohan/ unde land/ Robbins, Power Electronics: Converters, Applications and Design.

2. Muhammad H.Rashid, Power Electronics: Circuits, Devices and applications

3. MDSingh /Khanchandani, Power Electronics, Tata-Mcgrawhill publications.

4. Wikepedia.org, CUK converter,

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APPENDEX-A

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63

APPENDEX-B

64

APPENDEX-C

65