Chethan DC-DC Convertor Full

8/14/2019 Chethan DC-DC Convertor Full

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DC-DC

CONVERTORS

SUBMITTED


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DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

EAST POINT COLLEGE OF ENGINEERING & TECHNOLOGY

BANGALORE

SEMINAR REPORTON

DC-DC CONVERTORS

SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTFOR THE AWARD OF THE DEGREE OF B.E IN ELECTRONICS AND

COMMUNICATION

SUBMITTED BY:

CHETHAN.C (1EP06EC401)8 th SEMESTER, B.E

ACADEMIC YEAR-2010

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EAST POINT COLLEGE OF ENGINEERING AND TECHNOLIOGYBANGALORE 560 049

(Affiliated to Visveswaraya Technological University)DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

CERTIFICATE

Certified that seminar work entitled DC-DC CONVERTORS is a bonafide

work carried out by CHETHAN.C(1EP06EC401) of VIII Semester Electronicsand Communication Engineering in partial fulfillment of the requirements for Bachelor of Engineering of Visveswarayya Technological University during theacademic year 2009-2010.

Prof. Elumalai Dr. A.R. Reddy

Dept. of ECE SEMINAR CO-ORDINATOR

Name of student University Seat Number CHETHAN.C 1EP06EC401

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CONTENTS

1. INTRODUCTION2. TYPES OF CONVERTORS3. BUCK TYPE CONVERTOR 4. BOOST TYPE CONVERTOR 5. CUK TYPE CONVERTOR 6. BUCK-BOOST CONVERTOR 7. ISOLATED CONVERTORS

1.FLYBACK CONVERTOR 2.FORWARD CONVERTOR

8.APPLICATIONS

9.CONCLUSION

10.REFERENCES

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8.

ABSTRACT

A DC-to-DC converter is a device that accepts a DC input voltage and produces a DC output voltage. Typically the output produced is at a different voltage level than the input.

In addition, DC-to-DC converters are used to provide noise isolation, power bus regulation, etc.

This is a summary of some of the popular DC-to-DC converter topolopgies

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INTRODUCTION

DC-dc converters are used to convert unregulated dc voltage to regulatedor variable dc voltage at the output.

Early DC-DC converters were known as choppers with silicon-controlledrectifiers (SCRs) used as the switching mechanical

The output voltage in DC-DC converters is generally controlled using aswitching concept

Modern DC-DC converters employ insulated gate bipolar transistors(IGBTs) and metal oxide silicon field effect transistors (MOSFET)

Saving space instead of using multiple batteries.

Offer a method of generating multiple controlled voltagesfrom a single battery voltage.

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DC-DC conve

Types of Dc- Isolated convertors

1.Flyback convertors2.Forward convertors

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STEP DOWN (BUCK COVERTORS)

A step-down converter produces an average output voltage, which islower than the DC input voltage (Vin)

The basic circuit of a step-down converter is shown below

Buck convertor circuit

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BUCK convertors:

High efficiency, simple

No transformer

Low switch stress

Small output filter, low ripple

No isolation between input and output

Only one output possible

High input ripple current

Switiching states: switch open (a); switch closed (b)

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CONTINOUS MODE :

The continuous-conduction mode of operation occurs when the currentthrough the inductor in the circuit is continuous. This means that theinductor current is always greater than zero.

As the conduction of current through the inductor occurs during theentire switching period, the average output voltage is the product of theduty ratio and the DC input voltage.

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DISCONTIOUS MODE:

The discontinuous mode of operation occurs when the value of the loadcurrent is less than or equal to zero at the end of a given switching period.

The boundary point between continuous- and discontinuous-currentconduction occurs when the average inductor current over one switching

period is half of the peak value, as illustrated in figure below

Diagram :

Inductor current at boundary point for

discontinuous mode of buck converter.

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Buck Converter

Conversion ratio:

For the Buck converter the conversion ratio is D

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STEP UP(BOOST CONVERTORS)

Step-up conversion

Produces an output voltage greater than the source

Same components as the buck converter

High efficiency, simple

No transformer Regulator loop hard to stabilize

High output ripple. Unable to control short circuitcurrent.

Power-factor correction. Battery up-converters.

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Boost convertor circuit

Boost converter switch states: (a) switch closed; (b) switch open

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CONTINUOUS MODE

The continuous-conduction mode of operation occurswhen the current through the inductor in the circuitalways greater than zero.

The operation of the circuit in steady state consists of twostates

The first state with the switch closed has current charging theinductor from thevoltage source. The switch opens at the end of the on-time andthe inductor discharges current to the load with the inputvoltage source still connected. This results in an output voltageacross the capacitor larger than the input voltage.

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Diagram: Inductor voltage and current waveforms for continuous mode of boostconverter.

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Discontinuous-Conduction Mode

The discontinuous mode of operation occurs when the value of the load current is less than or equal to zero at the end of agiven switching period.

Assuming a linear rise and fall of current through the inductor,the boundary point between continuous- and discontinuous-current conduction occurs when the average inductor currentover one switching period is half the peak value.

The average inductor current at the boundary point iscalculated using Eq.

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Boost convertors

Conversion Ratio :

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CUK-CONVERTOR:

Simple, low ripple input and output current.

Capacitative isolation protects against switch failure.

High drain current.

C1 has high ripple current requirement.

High voltage required for switch.

Voltage inversion. Low noise, inverse output voltages.

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CUK CONVERTOR CIRCUIT:

(a) (b)

Ck converter switch states: (a) switch open; (b) switch closed.

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The operation of the basic nonisolated Ck converter in steadystate consists of two transistor states,

In the first state when the transistor is off, the inductor currentsflowthrough the diode and energy is stored in the transfer capacitorfrom the input and the inductor L1. The energy stored in theinductor L2 is transferred to the output. As a result, both of theinductor currents are linearly decreasing in the off-state.

In the second state when the transistor is on, the inductorcurrentsflow through the transistor and the transfer capacitordischarges while energy is stored in the inductor L1.

As the transfer capacitor discharges through the transistor,energy is stored in the inductor L2. Consequently, both of theinductor currents are linearly increasing in the on-state.

The voltage and current ratio for the nonisolated Ck convertercan be derived by assuming the inductor currents, whichcorrespond to the input current and output current, are ripple-free .

This results in an equal charging and discharging of the transfercapacitor during the off-state and the on-state.

The charging and discharging are defined in terms of theproduct of current and time by the equation

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Diagram 1: Inductor 1, voltage and current waveforms

for Ck converter.

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Diagram 2: Inductor 2, voltage and current waveformsfor Ck converter.

CUK-CONVERTOR:

Conversion Ratio :

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BUCK-BOOST CONVERTORS :

Voltage inversion without using a transformer

Simple, high frequency operation.

No isolation between input and output.

Only one output is possible.

Regulator loop hard to stabilize.

High output ripple.

High input ripple current.

Inverse output voltages.

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BUCK-BOOST CONVERTOR CIRCUIT :

The operation of this converter is nonlinear and discrete;however, it can be represented by a cyclic change of powerstage topologies.

The buckboost converter has cyclic changes in topology due tothe switching action of the semiconductor devices.

During a cycle of operation, the main power switch is turned onand off; the diode responds to this by switching off and on.

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Isolated DC-DCConverter

Isolated DC-DC requires isolation transformer

Advantages of switched mode over linear powersupply-Efficient (70-95%)-Weight and size reduction

Disadvantages-Complex design-EMI problems

However above certain ratings,SMPS is the only feasible choice

Types of SMPS-Flyback-forward

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FLYBACK CONVERTOR

Drain current reduced by turns ratio of transformer.

Low parts count.

Isolation. Has no secondary output inductors.

Poor transformer utilization.

Transformer stores energy.

High output ripple.

Diode needs fast reverse recovery.

Low output power. Supports multiple outputs.

CIRCUIT DIAGRAM:

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FORWARD CONVERTOR

Drain current reduced by turns ratio of transformer.

Low output ripple.

Poor transformer utilization. Poor transientresponse.

Transformer design is critical.

Transformer reset limits duty ratio.

High voltage required for switch. High inputcurrent ripple.

Low-to-moderate output power.

Supports multiple outputs

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CIRCUIT DIAGRAM:

The concept behind the foward converter is that of the ideal transformer converting the input AC voltage to an isolated secondary output voltage.

when the transistor is ON, Vin appears across the primary and then generates

The diode D1 on the secondary ensures that only positive voltages are appliedto the output circuit while D2 provides a circulating path for inductor current if the transformer voltage is zero or negative.

The problem with the operation of the circuit in Fig 15 is that only positivevoltage is applied across the core, thus flux can only increase with theapplication of the supply. The flux will increase until the core saturates whenthe magnetising current increases significantly and circuit failure occurs. Thetransformer can only sustain operation when there is no significant DCcomponent to the input voltage. While the switch is ON there is positive voltageacross the core and the flux increases. When the switch turns OFF we need tosupply negative voltage to reset the core flux.

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The circuit shows a tertiary winding with a diode connection to permit reversecurrent. Note that the "dot" convention for the tertiary winding is opposite thoseof the other windings. When the switch turns OFF current was flowing in a"dot" terminal. The core inductance act to continue current in a dotted terminal,thus the circuit is shown below

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APPLICATIONS

Laboratory equipment, test Instruments, desktop PC's,static telecomms

To drive dc motors Hybrid Electric Vehicles (HEV) Battery Powered Application of Chip Dc Power supplies SMPS In vehicle instrumentation In spacecrafts for optical communications power supply Radio instruments and communications LCD display

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CONCLUSION

There are many different types of DC-DC converter, each of which tends to bemore suitable for some types of application than for others. For conveniencethey can be classified into various groups, however. For example someconverters are only suitable for stepping down the voltage, while others are onlysuitable for stepping it up.

Another important distinction is between converters which offer full dielectricisolation between their input and output circuits, and those which dont.

Needless to say this can be very important for some applications, although itmay not be important in many others.

In the above data sheet we have looked briefly into each of the main types of DC-DC converter in current use, to give you a good overview. Well start firstwith those which dont offer input-output isolation, and then progress to thoseWhich do.

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REFERENCES:

[1] Rasid Hadzimusic, Design of Low Voltage Low Power and Highly Efficient DC-DC Converters, Master thesis inElectronics Systems at Linkping Institute of Technology,Reg nr: LITH-ISY-EX-3404-2004, 2004.

[2] "Power Electronics: Converters, Applications and Design",Mohan, Undeland and Robbins, Wiley, 1989.

[3] Maxim Integrated ProductsDC-DC Converter Tutorial,

Application Note 2031: http://www.maxim-ic.com/an2031,Oct 19, 2000.

[4]Muhammad H.Rashid: power electronics circuits,Devices and applications(second edition), pearson education

[5]www.hindwai.com/journals

[6]Google search
http://www.hindwai.com/journalshttp://www.hindwai.com/journals

Chethan DC-DC Convertor Full

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