DESIGN AND DEVELOPMENT OF 30W SMPS WITH THE

SPECIFICATIONS OF Vin:85-265V (AC), V0: 5V, 15V (DC)

Report submitted to the SASTRA Deemed to be

University as the requirement for the course

EEE327: Electrical Vehicle Charging Systems

Submitted by

Pragya Majji – 125159036

Sahana Maddukuri – 125159041

School of Electrical & Electronics Engineering

SASTRA DEEMED TO BE UNIVERSITY

(A University established under section 3 of the UGC Act, 1956)

Tirumalaisamudiram

Thanjavur-613401

NOVEMBER 2024

1
 BONAFIDE CERTIFICATE
This is to certify that the report titled “Design and Development of an 30W
SMPS with the specifications of Vin:85-265V (AC), V0: 5V, 15V (DC)” is a
bonafide record of the work done by
Ms. Pragya Majji (Reg. No: 125159036)
Ms. Sahana Maddukuri (Reg.No:125159041)
Students of final year B.Tech., Electrical & Electronics Engineering (Smart
Grid and Electrical Vehicles), in partial fulfillment of the requirements towards
Project Based Evaluation of the Course titled “Electrical Vehicle Charging
Systems”

Name of the course coordinator: Dr. S. Lenin Prakash

Signature

Project Viva-voce held on:

Examiner – I Examiner- II
2
 DECLARATION
We declare that the report titled “Design and Development of a 30W SMPS with the
specifications of Vin:85-265V (AC), V0: 5V, 15V” submitted by us is an original work done
by us under the guidance of Dr. Lenin Prakash, School of Electrical and Electronics
Engineering, SASTRA Deemed to be University during the seventh semester of the
academic year 2024-2025, in the school of Electrical and Electronics Engineering. The work
is original and wherever we have used materials from other sources, we have given due credit
and cited them in the text of the report. This report has not formed the basis for the award of
any degree, diploma, associateship, fellowship, or other similar title to any candidate of any
university.

Signature of the candidate(s):

Name of the candidate(s): Pragya Majji

Sahana Maddukuri

Date:

3
 Acknowledgements

First and foremost, we are thankful to God Almighty for giving us the potential and strength
to work on this project fruitfully. We express our gratitude to Dr. S.
VAIDHYASUBRAMANIAM, Vice- Chancellor, SASTRA Deemed to be University for
providing us with an encouraging platform for the course of study. We also thank Dr. R.
CHANDRAMOULI, Registrar, SASTRA Deemed University, for providing us the
opportunity to work in the SEEE, SASTRA Deemed to be University for the course of the
work.

We render our solicit thanks to Dr. K. THENMOZHI, Dean, SEEE and Dr. A.
KRISHNAMOORTHY, Associate Dean – Academics, SASTRA Deemed to be University
for their motivation and support.

We owe a debt of earnest gratitude towards our guide Dr. LENIN PRAKASH, Asst.
professor-II for his continued support and guidance throughout the course of our work.

We also extend our sincere thanks to our parents and friends for their continuous support.

4
 Abstract (125159036)

In recent years, power efficiency has become critical in power supply systems, especially in
low-power applications like the 30W SMPS (Switched-Mode Power Supply). This project
focuses on designing and optimizing a 30W SMPS with wide input voltage range capabilities,
ensuring stable and efficient DC output. The SMPS uses a flyback topology, which is chosen
for its simplicity, cost-effectiveness, and efficiency in low-power applications. To minimize
switching losses and improve performance, an RCD snubber circuit is implemented, with future
upgrades planned to include an active snubber for enhanced efficiency. The system’s
performance is simulated, and the results demonstrate the effectiveness of the design in
reducing energy losses, ensuring steady output, and maximizing power delivery to the load.

Specific Contribution

• Developed MATLAB simulations for the power circuit, focusing on stability and
efficiency

• Led the circuit design and PCB layout for the 30W SMPS using KiCad

• Responsible for soldering and assembling the hardware components for the SMPS on the
PCB

Specific Learning

• Deep understanding of SMPS design processes, including component selection and

snubber circuit implementation.

• Learned SMPS circuit design, KiCad PCB layout, and MATLAB simulation for
power electronics, focusing on stability analysis and efficiency optimization.

Technical Limitations & Challenges

• High output ripple and voltage spikes were observed initially, which were mitigated by
optimizing the snubber circuit design.

• Thermal management and component selection were crucial to prevent overheating and
ensure longevity.

Keywords: SMPS, flyback converter, power efficiency, snubber circuit, DC output stability.

5
 Abstract (125159041)

In recent years, power efficiency has become critical in power supply systems, especially in
low-power applications like the 30W SMPS (Switched-Mode Power Supply). This project
focuses on designing and optimizing a 30W SMPS with wide input voltage range capabilities,
ensuring stable and efficient DC output. The SMPS uses a flyback topology, which is chosen
for its simplicity, cost-effectiveness, and efficiency in low-power applications. To minimize
switching losses and improve performance, an RCD snubber circuit is implemented, with future
upgrades planned to include an active snubber for enhanced efficiency. The system’s
performance is simulated, and the results demonstrate the effectiveness of the design in
reducing energy losses, ensuring steady output, and maximizing power delivery to the load.
Specific Contribution
• Initial design concept and specifications for the SMPS, analysing load requirements,
input/output constraints

• Conducted MATLAB simulations.

Specific Learning
• Deep understanding of SMPS design processes, including component selection and
snubber circuit implementation.
• Improved skills in SMPS design specification, parameter optimization,
and MATLAB simulation
Technical Limitations & Challenges
• High output ripple and voltage spikes were observed initially, which were mitigated by
optimizing the snubber circuit design.
• Thermal management and component selection were crucial to prevent overheating and
ensure longevity.
Keywords: SMPS, flyback converter, power efficiency, snubber circuit, DC output stability

6
 TABLE OF CONTENTS

Title Page
Title page 1
Bona-fide Certificate 2
Declaration 3
Acknowledgment 4
Abstract 5
Table of contents 7
List of Figures and Tables 8
Abbreviations 9
1. CHAPTER 1
1.1 Introduction to SMPS 11
1.2 Introduction to Flyback Converter 12
1.3 Methodology 13
1.4 Flyback converter circuit 13
2. CHAPTER 2
2.1 Simulation Modes 15
2.2 Design Equations 15
2.3 MATLAB Simulations 19
2.4 Simulation Results 21
3. CHAPTER 3
3.1 Introduction to the chapter 25
3.2 Details of the controller 17
3.3 KiCAD Schematic 17
3.4 Gerber files of power circuit 28
3.5 Gerber files of control circuit 30
3.6 Bill of materials (BOM) 33
4. CHAPTER 4
4.1 Power Circuit PCB Board Assembly Using Soldering 34
4.2 Control Circuit PCB Board Assembly Using Soldering 35
5. CHAPTER 5
5.1 Conclusion 36
5.2 Future Scope 37
6. APPENDEX
6.1 References 38

7
 LIST OF FIGURES

Fig No Title Page No

1.1 13
Block diagram
1.2 Circuit of Fly Back Converter 13
2.1 Fly Back Simulation model 19
2.2 Primary Current and Secondary Current 21
2.3 Waves forms of pulse generator and voltage across the MOSFET 21
2.4 Wave forms of voltage and current of diode 22
2.5 Output wave forms of voltage and current of converter 22
2.6 Primary Current and Secondary Current 23
2.7 Waves forms of pulse generator and voltage across the MOSFET 23
2.8 Wave forms of voltage and current of diode 24
2.9 Output wave forms of voltage and current of converter 24
3.1 Schematic Diagram of Fly Back Power circuit 27
3.2 Schematic Diagram of Fly Back drive circuit 27
3.3 3D View of power circuit 32
3.4 3D View of control circuit 32
4.1 Front View of Soldered power circuit PCB 34
4.2 Back View of Soldered power circuit PCB 34
4.3 Front View of Soldered control circuit PCB 35

LIST OF TABLES

Table No Name of the Table Page No

2.1 Design Specifications 15
2.2 Design for Vo=15 Volts 18
2.3 Design for Vo=5 Volts 18
3.1 BOM of Power Circuit 33
3.2 BOM of Control Circuit 33

8
 ABBREVIATIONS

• Po (W) - Output Power (Watts)

• Vin_min (AC) (V) - Minimum Input Voltage (AC)

• Vin_max (AC) (V) - Maximum Input Voltage (AC)

• Vo (V) - Output Voltage

• Vin_min (DC) (V) - Minimum Input Voltage (DC)

• Vin_max (DC) (V) - Maximum Input Voltage (DC)

• Dlim - Duty Cycle Limit

• Vf (V) - Forward Voltage Drop (typically of a diode)

• fs (sec) - Switching Frequency

• Conservative efficiency estimate - Estimated Efficiency

• Load Step - Change in Load (possibly step size in load transients)

• Vd (V) - Diode Voltage Drop

• Np2s - Turns Ratio of Primary to Secondary

• Vmosfet_max (V) - Maximum Voltage across MOSFET

• Dmax - Maximum Duty Cycle

• Dmin - Minimum Duty Cycle

• %RIP - Ripple Percentage

• Ipri (A) - Primary Current

• I_ripple (A) - Ripple Current

• Lpri (H) - Primary Inductance

• L_leakage (H) - Leakage Inductance

• Ipri_peak (A) - Peak Primary Current

• Ipri_sat (A) - Saturation Primary Current

9
• Ipri_rms (A) - RMS Primary Current

• Isec_rms (A) - RMS Secondary Current

• E_leakage_inductance - Energy stored in leakage inductance

• Vsn=Vclamp (V) - Snubber Voltage (equal to Clamp Voltage)

• Psn (W) - Snubber Power

• Rsn (ohm) - Snubber Resistance

• RippleVoltage_Vsn (V) - Ripple Voltage of Snubber

• Csn (F) - Snubber Capacitance

• NcIk - Number of Clock Cycles or Controller Current information

• Vo_Ripple (V) - Output Voltage Ripple

• Co (F) - Output Capacitance

• ESRCo - Equivalent Series Resistance of Output Capacitor

• Ico_rms (A) - RMS Current through Output Capacitor

• Al - Core Al factor (magnetic core characteristic)

• Np - Primary Turns

• Ns - Secondary Turns

• Extra across MOSFET (V) - Additional Voltage Stress on MOSFET

• Ro - Output Resistance

10
 CHAPTER 1

1.1 Introduction to SMPS

• Switched-Mode Power Supplies (SMPS) are an integral part of modern electronics,

known for their high efficiency, compact size, and versatility in a wide range of
applications. They operate by converting an unregulated input voltage (AC or DC) into a
regulated output voltage through high-frequency switching techniques. Unlike linear
power supplies, SMPS achieve higher efficiency by switching the input power on and off
rapidly, reducing energy loss in the form of heat.
• A Switched-Mode Power Supply (SMPS) is an electronic power supply that uses
switching regulators to efficiently convert electrical power. It has wide applications that
require high efficiency, compact size, and lightweight power supplies. SMPS transfers
energy from source to load with fewer losses. SMPS converts AC to DC by rectifying the
input to HVDC and chops the DC voltage using switches like MOSFETs, and produces
an HVAC signal, which is transformed and rectified again to DC output.

• This project focuses on the design and development of a 30W SMPS with an input voltage
range of 85V to 265V AC and dual output voltages of 5V and 15V DC. The wide input
voltage range ensures that the SMPS can operate effectively under varying grid
conditions, making it suitable for use in global applications.
• The SMPS design will involve two main stages:
• AC to DC Conversion with Rectification and Filtering: This stage rectifies the
AC input voltage into a high-voltage DC output and filters it to reduce ripple.
• DC-DC Conversion with Regulation: The second stage uses switching
techniques to step down the high-voltage DC to the required 5V and 15V outputs,
maintaining precise voltage regulation and high efficiency.

Key characteristics of SMPS:

• High efficiency - SMPS operates at high frequencies, and reduces powerlosses
so efficiency is improved.
• Compact size - Due to its high-frequency operation it allows for a reduction in
the size of the transformers, leading to compact size.
• Multiple outputs - It can able to provide multiple output voltages
• Multiple topologies - It can be designed in various topologies like a buck,
flyback, boost, and forward converters.

Applications: SMPS is widely used in computers, TVs, LED lighting, mobile phone
chargers, and industrial power supplies due to its reliability and energy efficiency.
Introduction to flyback converters

11
1.2 Introduction to Flyback converter

• A flyback converter is a type of SMPS used for low to medium-power applications, offering both
voltage conversion and electrical isolation between input and output through a transformer. Its
simple design and efficiency make it suitable for AC-DC adapters and isolated power supplies.

• In operation, the transformer in a flyback converter stores energy during the ON phase of the switch
and releases it during the OFF phase. This makes the flyback converter cost-effective, as it requires
fewer components than other converter types.

Key Characteristics of Flyback Converters:

• Simple and Cost-Effective Design: Fewer components reduce complexity and cost.

• Electrical Isolation: The transformer provides isolation between input and output.

• Efficient Energy Transfer: Energy is stored and released efficiently through the switching process.

Applications: Flyback converters are commonly used in power adapters for laptops and mobile phones,
battery chargers, and small power supplies for household electronic

1.3 METHODOLOGY

• Define the key electrical specifications, including input voltage range, output voltage,
power rating, and switching frequency.

• Calculate the required turns ratio, magnetizing inductance, and leakage inductance based
on the specified input and output parameters.

• Select appropriate MOSFETs and diodes considering voltage and current ratings,
efficiency, and thermal performance.

• Design and optimize a snubber circuit to protect the switching components from voltage
spikes and to reduce electromagnetic interference (EMI).

• Simulate the converter circuit using appropriate software tools to verify the design,
optimize component values, and ensure performance under various load conditions.

• Build a prototype of the converter and test it under different operating conditions to
validate the design and performance.

• Compare the converter's performance with existing designs in terms of efficiency,

thermal management, and reliability to ensure it meets or exceeds industry standards.
12
 • The control of power converter will be implemented using a Texas instrument
TMS320FF28069 Microcontroller

BLOCK DIAGRAM

Fig 1.1 Schematic diagram

1.4 Flyback converter circuit

Fig 1.2 Flyback converter circuit

13
Figure 1.2 shows the power circuit of a flyback SMPS. A switched-mode power supply (SMPS)
is an electronic converter that uses switches to efficiently transform electrical power. The main
components of the circuit include a rectifier, switching element, transformer, and filter.

Rectifier and Filter: This section of the circuit converts the input AC from the mains into DC.
The rectifier is composed of diodes followed by a filter capacitor. The AC input voltage (85-
265V) is converted into a DC voltage (around 120-375V). The rectifier is typically a bridge
rectifier, which converts AC to DC, while the capacitor smooths the output to provide a stable
DC voltage.

Switching Element: This part includes a MOSFET switch, which is controlled by a PWM signal.
The MOSFET regulates the energy flow to the transformer by rapidly switching on and off at a
frequency of about 250 kHz. When the MOSFET is on, energy is stored in the transformer's
primary winding. When it is off, the stored energy is transferred to the secondary side.

Snubber Circuit (Rsn, Csn, D_Snubber): The snubber circuit protects the MOSFET from high-
voltage spikes that result from transformer leakage inductance. The RC combination and snubber
diode help dissipate the excess energy.

Load (R_load): This resistor simulates the load connected to the SMPS output. It draws the
output power, and the regulated output voltage is measured across it.

Transformer: The transformer is the heart of the energy transfer in the converter. It has a primary
winding connected to the MOSFET and a secondary winding that supplies the output voltage.
The transformer provides voltage transformation and isolation between the input and output,
which makes the flyback converter ideal for applications requiring galvanic isolation.

14
 CHAPTER 2

2.1Simulation modes
The flyback converter operates in two distinct phases:

• On Phase (MOSFET Switch ON):

When the MOSFET switch turns ON, current flows through the primary
winding of the transformer, and energy is stored in its magnetic field. During
this phase, no energy is transferred to the output as the diode on the secondary
side (D2) is reverse biased.
• Off Phase (MOSFET Switch OFF):
When the MOSFET turns OFF, the magnetic field in the transformer
collapses, inducing a voltage in the secondary winding. This voltage forward-
biases the secondary diode (D2), allowing current to flow through the load.
The output capacitor (Co) filters this current to provide a smooth DC output.

Design specifications

S.NO SPECIFICATION SYMBOL VALUE

1. Output power Po 30W
2. Input voltage range (AC) Vin 85-265V
3. Rectifier output voltage range Vdc 120-375V
4. Output voltages (DC) Vo 3.3V, 5V, 15V
5. Switching frequency Fs 50 KHz
6. Maximum duty cycle Dmax 50%
7. Efficiency η 80%
8. MOSFET Voltage rating Vds 800V
9. Maximum Output current I0 3A

Table 2.1

2.2 Design Equations

1 Calculation of Transformer Turns Ratio

The turn ratio is chosen to limit the duty cycle to a maximum of 50%. Reasons to do
this are, that it reduces stress on the rectifying diode and output capacitors, and it avoids the
possibility of sub-harmonic oscillation inherent to current mode control.
Np2s = (Vin_dc_min X Dmin)/ (Vo + VD)(1-Dma
15
 2 Calculation of permissible MOSFET Drain to Source voltage
VMosfet_Max = (Vin_dc_max +(Vo + VD) x Np2s)/0.8

The MOSFET is chosen such that its drain to source voltage is greater than the above
voltage considering a safety margin of a further 20%. An 800V MOSFET will be an appropriate
choice.

3 Maximum and Minimum value of Duty cycle:

Dmax = ((Vo + VD) x Np2s)/ (Vin_dc_min + (Vo + VD) x Np2s)

Dmin = ((Vo + VD) x Np2s)/ (Vin_dc_max + (Vo +VD) x Np2s)

4 Transformer primary magnetizing inductance
Lpri = (Vin_dc_max x Dmin)/ (Iripple x Fs)
One method to choose the inductance is to limit the current ripple to a percentage of the
average current through the primary winding during the on-time of the switch. A fairtrade-off
between size and efficiency is achieved with a percent ripple (RIP%) between 60%and 90%.

Iripple = %Ripple x (Vo x Io)/ (η x Vin_dc_max x Dmin)

5 Transformer leakage inductance
It is desirable, that the leakage inductance must be limited to less than 2 % of the
magnetizing inductance to minimize the snubber losses and increase the overall efficiency.
Lleakage <= 20Uh

6 Current ratings of Transformer

The minimum recommended saturation current rating is 20% higher than the

calculated peak current under full load.

Ipri_peak = ((Vo x Io)/ (Vin_min x Dmax x η)) + (Iripple/ 2)Ipri_sat = 1.2 x

Ipri_peak

Ipri_rms = (D{((Vo x Io)/ (Vin x D))2 + I2ripple/3})(1/2)Isec_rms = ((1-D) (I2o

2 / 3)) (1/2)
+ (Iripple x Np2s)

7 Transformer leakage inductance

It is desirable, that the leakage inductance must be limited to less than 2 % of the
16
 magnetizing inductance to minimize the snubber losses and increase the overall efficiency.
Lleakage <= 20uH

8 Current ratings of Transformer

The minimum recommended saturation current rating is 20% higher than thecalculated
peak current under full load.
Ipri_peak = ((Vo x Io)/ (Vin_min x Dmax x η)) + (Iripple/ 2)Ipri_sat = 1.2 x
Ipri_peak

Ipri_rms = (D{((Vo x Io)/ (Vin x D))2 + I2ripple/3})(1/2)Isec_rms = ((1-D) (I2o

+ (Iripple x Np2s)2 / 3)) (1/2)

9 Transformer leakage inductance

It is desirable, that the leakage inductance must be limited to less than 2 % of the
magnetizing inductance to minimize the snubber losses and increase the overall efficiency.
Lleakage <= 20uH

10 Current ratings of Transformer

The minimum recommended saturation current rating is 20% higher than thecalculated
peak current under full load.
Ipri_peak = ((Vo x Io)/ (Vin_min x Dmax x η)) + (Iripple/ 2)Ipri_sat = 1.2 x
Ipri_peak

Ipri_rms = (D{((Vo x Io)/ (Vin x D))2 + I2ripple/3})(1/2)Isec_rms = ((1-D) (I2o

+ (Iripple x Np2s)2 / 3)) (1/2)

11 Design of RCD clamp snubber circuit

Eleakage_inductance = (Lleakage/2) x I2pri_peakVsn = Vclamp = Vmosfet_max – Vin_dc_max

Psn = (Vsn/ (Vsn – (Vo x Np2s))) x Fs x Eleakage_inductanceRsn = (Vsn x Vsn)/ Psn
Snubber Capacitor Ripple Voltage CVsn = 0.05 x Vsn
Csn = Vsn/ (CVsn x Rsn x F)

17
DESIGN FOR Vo = 15 V

Table 2.2

DESIGN FOR Vo = 5 V

Table 2.3

18
 2.3 MATLAB Simulation

Fig 2.1 Flyback simulation model

Fig 2.2 depicts the MATLAB simulation model of a 30W SMPS (Switched-Mode Power
Supply) based on a flyback converter topology with output voltages of 15V and 5V. Here’s an
explanation of each section of the circuit:
• Input DC Voltage Source (Vdc):

• This represents the DC input voltage supplied to the flyback converter. It could
be derived from an AC-DC rectifier stage if this were a complete power supply.

• Snubber Circuit (Csn, Rsn, D_Snubber):

• The snubber circuit (comprising a capacitor CsnC_{sn}Csn, resistor

RsnR_{sn}Rsn, and diode DsnubberD_{snubber}Dsnubber) is connected across
the MOSFET to protect it from high-voltage spikes caused by the leakage
inductance of the transformer. It dissipates excess energy, preventing voltage
stress on the switching MOSFET.
• Switching Element (MOSFET):

• The MOSFET acts as a switch controlled by a pulse generator, which generates

the PWM (Pulse Width Modulation) signal. This signal determines the on/off state
of the MOSFET at a specific frequency.

• When the MOSFET turns on, current flows through the primary winding of the
transformer, storing energy in its magnetic field. When the MOSFET turns off,
this energy is transferred to the secondary winding to supply the load.

19
• Pulse Generator:

• The pulse generator provides the switching signal for the MOSFET, enabling it to
switch on and off at the desired frequency. This frequency is typically high (in the
kHz range) for efficient power transfer.
• Transformer (Linear Transformer):

• The transformer has a primary and a secondary winding, and it’s the core
component of energy transfer in the flyback converter.

• When the MOSFET is on, energy is stored in the magnetic field of the transformer.
When the MOSFET turns off, the stored energy is released to the secondary
winding. The transformer also provides isolation between the input and output.

• Secondary Diode (D2):

• This diode allows current to flow only when the MOSFET is off. When the stored
energy in the transformer is transferred to the secondary winding, D2D2D2
conducts and supplies power to the output capacitor and load.

• The diode blocks the current flow when the primary side is active, thus isolating
the output during the on period of the MOSFET.

• Output Capacitor (Co):

• The capacitor CoC_{o}Co filters the pulsating DC from the secondary side of the
transformer, providing a smooth DC output voltage across the load.

• Load (R_load):

• RloadR_{load}Rload represents the output load connected to the SMPS. The

output voltage and current are measured across this load.
• Measurement Blocks:

• Various blocks are included to measure the key parameters, such as:

• Primary and Secondary Current – Measuring current through the

primary and secondary windings of the transformer.

• Voltage across MOSFET and Diode – Monitoring the voltages across

the MOSFET and secondary diode to ensure they remain within safe
limits.

• Output Voltage and Current – Measuring the output voltage and current
delivered to the load.

• Output I-V Characteristics – This allows observation of the load's

voltage and current behavior.

20
The flyback converter operates by switching the MOSFET on and off. When the MOSFET is
on, energy is stored in the transformer's magnetic field. When it turns off, the energy is released
to the output through the secondary winding. This allows the converter to regulate the output
voltage and current, making it suitable for applications needing isolation, such as SMPS
designs for various electronic devices

2.4 Simulation Results

i) Vo = 15V,
Duty Cycle = 24%

Fig 2.2 Primary current/ Secondary current

Fig 2.3 Waveforms of the pulse generator and voltage across the MOSFET
21
 Fig 2.4 Waveforms of the voltage and current of the diode

Fig 2.5 Output waveforms of the voltage and current of the converter

22
ii) Vo = 5V
Duty Cycle = 12%

Fig 2.6 Primary current/ Secondary current

Fig 2.7 Waveforms of the pulse generator and voltage across the MOSFET

23
 Fig 2.8 Waveforms of the voltage and current of the diode

Fig 2.9 Output waveforms of the voltage and current of the converter

24
 CHAPTER 3

3.1 Introduction to the chapter

This chapter offers an in-depth examination of the flyback SMPS converter design
utilizing the UC3844AN PWM controller. It outlines the structure of the power supply system,
featuring a block diagram, subsystem details, and the PCB schematic. The subsystems are
thoroughly described, focusing on critical components like the input rectifier, PWM controller,
switching element, transformer, output filter, and feedback loop. The PCB schematic section
illustrates the physical arrangement of the circuit elements and demonstrates the hardware
implementation of the design.

3.2 Details of the controller

In the flyback converter, the controller is responsible for regulating the output voltage
by controlling the duty cycle of the switch. The UC3844AN is the most commonly used fixed-
frequency, current-mode PWM controller specifically designed for off-line and DC-to-DC
converters.
Internal structure and pin configuration
➢ COMP
• This pin is the output of the internal error amplifier, that controls the dutycycle of
the PWM signal.
• It connects to external compensation components to stabilize the feedbackloop and
control the response to load changes.

➢ VFB
• It is a feedback input pin for voltage regulation
• It receives the feedback signal from the output voltage, through the voltagedivider
network, and it compares it to an internal reference voltage to regulate the
output.

➢ I_sense
• It is the current sense input pin.
• It constantly monitors the current through the MOSFET and provides peakcurrent
feedback to the controller. This also gives protection against overcurrent
conditions and stable operation under different loads.

➢ RT/CT
• This pin connects to an external timing capacitor and resistor that sets the Fsof the
PWM signal.
• The operating frequency ranges from 20KHz to 500KHz depending on thevalues
of the RT and CT.

25
 ➢ Ground
• It is the ground reference for the controller.

➢ Out
• This pin is the output pin that drives the gate of the MOSFET switch.
• It generates the PWM signal, controlling the ON and OFF of the switch toregulate
power conversion in the converter.

➢ VCC
• It is the supply voltage pin, that powers the controller.
• It operates from a DC supply ranging from 11V to 25V

➢ VREF
• It provides a 5V reference voltage for internal circuits and external use in the
feedback network.

Functional blocks of UC3844AN

• Error amplifier: It compares the feedback voltage with a precise internal reference
voltage. The output of the error amplifier adjusts the duty cycle of thePWM signal to
maintain a constant output voltage.
• PWM comparator and latch: The PWM comparator compares the error amplifier
output with the Isense signal. When the Isense signal is greater than the setvalue by the
COMP pin, the PWM latch is reset and turns OFF the switch. This ensures stable
operation under varying loads.
• Oscillator: It sets the switching frequency of the PWM signal. The RT and CT define
the timing characteristics.

Operation modes
• Continuous conduction mode:
In this mode, the current through the inductor or transformer primary winding never
drops to zero. It is most commonly used in high-power applications where energy is
transferred continuously.
• Discontinuous conduction mode:
In this mode, the current through the inductor or transformer primary drops to zero
during the switching cycle. This has more applications in lower-power applications

26
3.3 KiCAD SCHEMATIC

Fig 3.1 Schematic diagram of the flyback power circuit

Fig 3.2 Schematic diagram of the flyback drive circuit

27
3.4 GERBER FILES OF POWER CIRCUIT

FRONT COPPER

BACK COPPER

LAYOUT
28
THT COMPONENTS IN FRONT COPPER

THT COMPONENTS IN BACK COPPER

29
3.5 GERBER FILES OF CONTROL CIRCUIT

FRONT COPPER

BACK COPPER

LAYOUT
30
THT COMPONENTS IN FRONT COPPER

THT COMPONENTS IN BACK COPPER

31
Fig 3.3 3D VIEW OF POWER CIRCUIT

Fig 3.4 3D VIEW OF CONTROL CIRCUIT

32
3.6 BILL OF MATERIALS

BOM OF POWER CIRCUIT

Table 3.1

BOM OF CONTROL CIRCUIT

Table 3.2
33
 CHAPTER 4

HARDWARE AND TESTING

4.1 Power Circuit PCB Board Assembly Using Soldering

Fig 4.1 Front View

Fig 4.2 Back View

34
4.1 Power Circuit PCB Board Assembly Using Soldering

Fig 4.3 Front View

35
 CHAPTER 5

CONCLUSION AND FUTURE SCOPE

5.1 CONCLUSION

(125159036)

The design and development of the 30W SMPS with dual output voltages of 15V and 5V DC
was successfully completed, achieving stable performance across an input range of 85–265V
AC. Testing with an RCD snubber circuit effectively controlled voltage spikes, ensuring
reliable operation and protecting the components from transient stress. Using KiCad for PCB
design allowed for efficient layout and component placement, contributing to overall circuit
stability and performance. This project demonstrates the importance of efficient power
conversion in low-power applications and provides a foundation for further improvements,
such as enhanced efficiency measures and increased power handling.

(125159041)

In this project, a 30W SMPS with dual outputs of 15V and 5V DC was designed and tested,
showing reliable performance across an input range of 85–265V AC. The implementation of
an RCD snubber circuit controlled transient spikes effectively, enhancing the system's
stability. Designing the PCB in KiCad enabled efficient layout organization, supporting both
functionality and reliability. This SMPS design provides a dependable solution for low-power
applications and lays the groundwork for potential upgrades, such as enhanced efficiency and
increased output power.

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5.2 FUTURE SCOPE

➢ Power Capacity Expansion: To handle higher loads, the SMPS can be upgraded with
additional modules or parallel power sources, making it adaptable for larger
applications or grid export capabilities.

➢ DC-to-AC Flexibility: Adding an inverter in future phases will allow seamless DC-to-
AC conversion, enabling compatibility with AC systems and broader applications.The
project's future plans include incorporating electric cars (EVs) into the system and
bringing the "vehicle-to-grid" (V2G) idea to life. In line with smart grid and sustainable
mobility technology, this bidirectional energy flow enables EVs to both inject excess
energy back into the microgrid and take energy from it.

➢ Enhanced Efficiency with Active Snubber: Introducing an active snubber circuit can
further improve efficiency by reducing switching losses, making the system more
energy-efficient and reliable.

➢ Electric Vehicle (EV) Integration: Future integration with EVs, including vehicle-to-
grid (V2G) functionality, would enable bidirectional energy flow, supporting
sustainable energy use and grid stability.

➢ Modular Development: Designed for phased development, the project can adapt to
evolving needs by adding components incrementally, supporting both technical
advancements and sustainability goals.
.

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 APPENDEX

REFERENCES

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D. Ð. Vračar and P. V. PEJOVIĆ, "Active-Clamp Flyback Converter as Auxiliary Power-

Supply of an 800 V Inductive-Charging System for Electric Vehicles," in IEEE Access, vol.
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W. -S. Choi, C. -F. Jin, J. -W. Park, S. -J. Park and D. -S. Jo, "A new topology of flyback
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