ANALYSIS OF FLYBACK CONVERTER

1. A
MINOR PROJECT REPORT ON
“ANALYSIS OF FLYBACK CONVERTER”
Submitted in partial fulfillment of the requirement for the degree of
Bachelor of technology
In
ELECTRICAL ENGINEERING
BY
RITU RAJ (1473720028)
Under the supervision of
Mr. PREM NARAYAN VERMA
In the
Department of Electrical Engineering
RAJKIYA ENGINEERING COLLEGE,
AMBEDKARNAGAR
Affiliated to
Dr. A.P.J ABDUL KALAM TECHNICAL
UNIVERSITY,LUCKNOW

2. Table of Contents
Declaration……………………………………………………………….1
Certificate………………………………………………………………...2
Acknowledgement………………………………………………………..3
Abstract…………………………………………………………………..4
List of figures…………………………………………………………….5
CHAPTER 1……………………………………………………………..6
 INTRODUCTION
CHAPTER 2……………………………………………………………..7
 AIM & OBJECTIVE
CHAPTER 3……………………………………………………………..8
 PROJECT PLANNING
CHAPTER4…………………………………………………………..9-12
 PRINCIPLE OF OPERATION OF FLYBACK CONVERTER
CHAPTER 5………………………………………………………...13-15
 SIMULATION OF FLYBACK CONVERTER
CHAPTER 6……………………………………………………………16
 RESULT AND DESCUSSION
CHAPTER 7………………………………………………………….. 17
 CONCLUSION
REFERENCES………………………………………………………………………………………18

3. DECLARATION
I RITU RAJ hereby declare that the report of the project entitled “Analysis of Flyback
Converter” is my own work and that to be best of my knowledge and believe, it contains no
material previously published or written by another person, nor material which to be a substantial
extent has been excepted for the award of any degree or the diploma of the university or the
institute of higher learning, except where due acknowledgement has been made in the text.
Signature:
Name: RITU RAJ
Roll No.: 1473720028
Date: 01/12/2016

4. CERTIFICATE
It is certified that RITU RAJ has carried out the research work presented in this project entitled
“ANALYSIS OF FLYBACK CONVERTER” for the award of Bachelor of Technology from
Uttar Pradesh Technical University, Lucknow under my supervision. The project embodies result
of original work and studies carried out by student himself and contents of theproject do not form
the basis for the award of any other to the candidate or to anybody else.
Supervised By:
DATE:……………
(Mr. Prem Narayan Verma)
Assistant Professor
REC, AMBEDKAR NAGAR
Approved By:-
(Mr. Sonu Kumar)
HOD
Electrical Engineering Department
Rajkiya Engineering College, Ambedkar Nagar
External Examiner:

5. ACKNOWLEDGEMENT
We wish to thank Mr. PREM NARAYAN VERMA, Assistant Professor of Department of
Electrical Engineering, Rajkiya Engineering College Ambedkarnagar, for his help and valuable
suggestions for preparation of this report.
We wish to thank Mr. SONU KUMAR, Head of Department of Electrical Engineering,Rajkiya
Engineering College Ambedkarnagar, for his help and valuable suggestions for preparation of this
report.
RITU RAJ
(1473720028)
B.Tech 3rd year(EE)

6. ABSTRACT
THE PURPOSE OF THIS PROJECT IS TO DESIGN A FLYBACK CONVERTER THAT HAS AN INPUT VOLTAGE
OF 12V DC AND THE OUTPUT VOLTAGE OF 240V DC. FLYBACK CONVERTER IS ONE OF THE
SWITCHING DC POWER SUPPLIES APPLICATIONS WITH ELECTRICAL ISOLATION.
THETRANSFORMATIONOF DC VOLTAGE FROM 12V DC TO 240V DC IS ACCOMPLISHED BY USING DC-
TO-DC CONVERTER CIRCUITS. THE SWITCHING ELEMENT USED IN THIS FLYBACK CONVERTER IS
MOSFET (METAL OXIDE SEMICONDUCTOR FIELD EFFECT TRANSISTER), WHICH IS
OPERATINGCOMPLETELY OFF OR COMPLETELY ON.THIS IS BECAUSE MOSFET HAS HIGH POWER
RATING AND HIGH SWITCHING SPEED . THE OUTPUTOF THE MOSFET IS FED TO HIGH FREQUENCY
TRANSFORMER. THE SNUBBER CIRCUIT IS CONNECTED PARALLELTO THE MOSFETFOR PROTECTION.
THE INPUT VOLTAGE OF 12V DC WILL BE STEP UP TO 240V DC. A HIGH SPEED
ISOLATIONTRANSFORMER PROVIDES THE ELECTRICAL ISOLATION IN FLYBACKCONVERTER. THE HIGH
SPEED TRANSFORMERS WERE USED DUE TO THE SMALL SIZE AND SMALL WEIGHT. CONSEQUENTLY,
THE DESIGN CIRCUIT WILL DELIVER ACURATE VALUE WITH LOW POWER LOSSES ON THE WHOLE, THE
UNDER TAKEN TASK WOULD PROVIDE TO UNDERSTAND THE OPERATION OF FLYBACK CONVERTER
CIRCUIT PRACTICALLY.

7. LIST OF FIGURES
FIGURENO. PAGE NO. FIGURENAME
1 9 Circuit diagram of flyback converter
2 13 Simulation circuit of flyback converter
3 13 Output voltage Waveform of flyback
converter
4 14 Output current and input voltage waveform
of flyback converter
5 15 Inputcurrent waveform of flyback converter

8. CHAPTER – 1
INTRODUCTION
Fly-back converter is the most commonly used SMPS circuit for low output
power applications where the output voltage needs to be isolated from the input main
supply. The output power of fly-back type SMPS circuits may vary from few watts to
less than 100 watts. The overall circuit topology of this converter is considerably
simpler than other SMPS circuits. Input to the circuit is generally unregulated dc
voltage obtained by rectifying the utility ac voltage followed by a simple capacitor
filter. The circuit can offer single or multiple isolated output voltages and can operate
over wide range of input voltage variation. In respect of energy-efficiency, fly-
back power supplies are inferior to many other SMPS circuits but its simple topology
and low cost makes it popular in low output power range.
The commonly used fly-back converter requires a single controllable switch
like, MOSFET and the usual switching frequency is in the range of 100 kHz. A two-
switch topology exists that offers better energy efficiency and less voltage stress across
the switches but costs more and the circuit complexity also increases slightly. The
present lesson is limited to the study offly-back circuit of single switch topology.

9. CHAPTER – 2
Aim:-
1- Analysis of flyback converter.
Objective:-
The main objective of this project is to study the flyback boost converter and its operation under
continuous and discontinuous modes of operation and to obtain its waveform. And design the
simulation circuit and observe the output voltage and current waveform. The switching element
use in the flyback converter is MOSFET which is operating completely OFF or completely ON this
is because MOSFET has high power rating and high switching speed.

10. CHAPETER – 3
PROJECT PLANNING
Exactly what was planned in the project?
 To design a fly back boost converter
 To get correct amplitude of gate pulse
 To calculate the width and frequency of gate pulse
 To get the output voltage waveform of fly back converter
 To get the output current waveform of fly back converter
 To get the input voltage waveform of fly back converter
 To get the input current waveform of fly back converter
What is achieved?
 We designed a fly back boost converter
 We get correct amplitude of gate pulse
 We calculate the width and frequency of gate pulse
 We get the output voltage waveform of fly back converter
 We get the output current waveform of fly back converter
 We get the input voltage waveform of fly back converter
 We get the input current waveform of fly back converter

11. CHAPTER – 4
PRINCIPLE OF OPERTION:-
During its operation fly-back converter assumes different circuit-configurations. Each of these
circuit configurations have been referred here as modes of circuit operation. The complete
operation of the power supply circuit is explained with the help of functionally equivalent circuits
in these different modes.
As may be seen from the circuit diagram of Fig.1, when switch ‘S’ is on, the primary winding of
the transformer gets connected to the input supply with its dotted end connected to the positive
side. At this time the diode ‘D’ connected in series with the secondary winding gets reverse biased
due to the induced voltage in the secondary (dotted end potential being higher). Thus with the
turning on of switch ‘S’, primary winding is able to carry current but current in the secondary
winding is blocked due to the reverse biased diode. The flux established in the transformer core
and linking the windings is entirely due to the primary winding current. This mode of circuit has
been described here as Mode-1 of circuit operation. shows (in bold line) the current carrying
part of the circuit and shows the circuit that is functionally equivalent to the fly-back circuit
during mode-1. In the equivalent circuit shown, the conducting switch or diode is taken as a
shorted switch and the device that is not conducting is taken as an open switch. This
representation of switch is in line with our assumption where the switches and diodes are assumed
to have ideal nature, having zero voltage drop during conduction and zero leakage current during
off state.

12. Mode-1
Under Mode-1, the input supply voltage appears across the primary winding inductance and the
primary current rises linearly. The following mathematical relation gives an expression for current
rise through the primary winding:where EDC is the input dc voltage, LPr i is inductance of the
primary winding and iPri is the instantaneous current through primary winding.
Linear rise of primary winding current during mode-1 is shown in fig. As described later, the fly-
back circuit may have continuous flux operation or discontinuous flux operation. The waveforms
inand correspond to circuit operations in continuous and discontinuous flux respectively. In case
the circuit works in continuous flux mode, the magnetic flux in the transformer core is not reset to
zero before the next cyclic turning ON of switch ‘S’. Since some flux is already present before ‘S’
is turned on, the primary winding
current in Fig.3(a) abruptly rises to a finite value as the switch is turned on. Magnitude of
thecurrent-step corresponds to the primary winding current required to maintain the previous flux
in the core. At the end of switch-conduction (i.e., end of Mode-1), the energy stored in the
magnetic field of the fly back inductor-transformer is equal to LPr i IP2 2 , where I P denotes the
magnitude of primary current at the end of conduction period. Even though the secondary winding
does not conduct during this mode, the load connected to the output capacitor gets uninterrupted
current due to the previously stored charge on the capacitor. During mode-1,assuming a large
capacitor, the secondary winding voltage remains almost constant and equals
to VSec = EDC ×N 2 / N1 .
During mode-1, dotted end of secondary winding remains at higher potential than the
other end. Under this condition, voltage stress across the diode connected to secondary winding
(which is now reverse biased) is the sum of the induced voltage in secondary and the output
voltage
(Vdiode = VO + EDC × N2 / N1 ).

13. Mode-2 of circuit operation starts when switch ‘S’ is turned off after conducting for some time.
The primary winding current path is broken and according to laws of magnetic induction, the
voltage polarities across the windings reverse. Reversal of voltage polarities makes the diode in
the secondary circuit forward biased. Fig.3(a) shows the current path (in bold line) during mode- 2
of circuit operation while Fig.3(b) shows the functional equivalent of the circuit during this mode.
Vpri = VO*N1/N2 , Vsec= VO
In mode-2, though primary winding current is interrupted due to turning off of the switch ‘S’, the
secondary winding immediately starts conducting such that the net mmf produced by the windings
do not change abruptly. (mmf is magneto motive force that is responsible for flux production in
the core. Mmf, in this case, is the algebraic sum of the ampere-turns of the two
windings. Current entering the dotted ends of the windings may be assumed to produce positive
mmf and accordingly current entering the opposite end will produce negative mmf.) Continuity of
mmf, in magnitude and direction, is automatically ensured as sudden change in mmf is not
supported by a practical circuit for reasons briefly given below.
Flux linked by the windings remain zero until the next turn- on of the switch, and the circuit is
under discontinuous flux mode of operation. Alternately, if the off period of the switch is small,
the next turn on takes place before the secondary current decays to zero. The circuit is then under
continuous flux mode of operation
Mode 3.
During discontinuous mode, after complete transfer of the magnetic field energy to the output, the
secondary winding emf as well as current fall to zero and the diode in series with the winding
stops conducting. The output capacitor however continues to supply uninterrupted voltage to the
load. This part of the circuit operation has been referred to as Mode-3 of the circuit

14. operation. Mode-3 ends with turn ON of switch ‘S’ and then the circuit again goes toMode-1 and
the sequence repeats.

15. CHAPTER – 5
SIMULATIONOF FLYBACK CONVERTER
SIMULATION CIRCUIT OF FLY BACK CONVERTER:-
OUTPUT WAVEFORM:-
Output voltage waveform:

16. Outpute current waveform:
Input voltage waveform:

17. Input current waveform:

18. CHAPTER – 6
CONCLUSION:-
The simplified and idealized fly back converter circuit high voltage drop and losses.
The coupling between the primary and secondary winding will not be ideal. Due to
the non-ideal coupling between the primary and secondary winding when the
primary side switch is turned off some energy is trapped in the leakage inductance
of the winding the flux associated with the primary winding leakage inductance ill
not link the secondary winding and hence the energy associated with the leakage
flux need to dissipated in an external circuit. The switching element used in fly
back converter is MOSFET which is operating completely OFF completely ON this is
because MOSFET has high rating and high switching speed. The output of the
MOSFET is fed to high frequency transformer. And the all waveform are studied as
shown in chapter 5.

19. CHAPTER – 7
REFERENCES:-
I. Billings, Keith (1999), Switch mode Power Supply Handbook (Second ed.),
McGraw-Hill,
II. Power electronics(Dr. P.S. Bhimbhra)
III. www.electrical4u.com
IV. www.wikipedia.org
V. P.C. Sen., Principlesof electric machine & power electronics,wiley1999.
VI. M.M.R. Ahmed and M. soliman,”flyback converter”