Introduction to ELECTENG 311

## ELECTENG 311
# Electronics Systems Design 
### An Introduction

.TitleAuthor[Duleepa J Thrimawithana]

---

.logo-slide[]
.footer[[Duleepa J Thrimawithana](https://www.linkedin.com/in/duleepajt), Department of Electrical, Computer and Software Engineering (2026)]

---

# Learning Objectives

- What is a power converter?
 - Power converter types
 - Desirable features of a power converter
- Power electronics research at UoA
- Design project details
 - What is to be designed
 - Specifications & system architecture
- Assessment details and learning resources
- Fundamentals of linear and switched-mode DC to DC power supplies
 - Operating principles 
 - Key differences between linear regulators and SMPSs
 - Pulse width modulation
 - Power supply specifications

---

# What Are Power Electronics Converters?
### An Introduction

---

.logo-slide[]
.footer[[Duleepa J Thrimawithana](https://www.linkedin.com/in/duleepajt), Department of Electrical, Computer and Software Engineering (2026)]

---

# Background

- Power conversion systems or power electronics converters play a vital role in the modern society
 - A vital component of modern medical equipment, consumer electronics and appliances
 - A key enabling technology that would help achieve a zero-carbon future

.center[
<iframe width="560" height="315" src="https://www.youtube.com/embed/2bXn2F58OsM" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
]

---

# What is a Power Converter?

- A power converter takes an energy source as the input and produce an output that is suitable to feed a load (e.g. electronic/electrical circuit or a motor)
- As an example, a power converter may be designed to take an input from a battery and produce a constant current (even when the battery voltage changes as it discharges) to feed an LED light bulb
 - We may also want to control the current setpoint to change the brightness of the LED bulb

---

# Important Features of a Power Converter

- Designing a power converter involves improving 5 key performance features 
 - Losses need to be minimized to achieve higher efficiency
 - Weight and volume need to be minimized to achieve higher density
 - Failure rate needs to be minimized to achieve higher reliability
 - Costs need to be minimized so that its ready to market within an acceptable time frame and a budget
 - Controllability needs to be improved so that it can produce a distortion-less output 
- These performance features are related to each other 
 - E.g., improving efficiency can often lead to an increase in cost and restrict controllability 
- Depending on the application, a power electronics engineer often has to tradeoff some features for others 
 - E.g., we may decide to go with a less efficient design to reduce cost

---

# Types of Power Converters

.left-column[
- Based on the nature of the input source and the output produced, power converters can be broadly categorized as
 - *DC to DC* converters where input source is DC and output is DC
 - *DC to AC* converters where input source is DC and output is AC
 - *AC to DC* converters where input source is AC and output is DC
 - *AC to AC* converters where input source is AC and output is AC
- These 4 types of power converters can be categorized further as *isolated* and *non-isolated* converters
 - An isolated converter often employs a transformer to provide galvanic isolation between input source and load in situations where for example we need to ensure user safety
- E.g., your phone charger employs an *isolated AC to DC converter* to derive power from wall power socket and output 5V DC
]

.right-column[
.center[<img src="img/ConverterTypes.png" width="260px">
.credits[
Apple 18W Charger Teardown [[1]](https://www.chargerlab.com/apple-18w-usb-c-power-adapter-a1695-teardown-review-beautiful-inside-and-out/)
]
]
]

---

# Future of Power Electronics

- Power electronics is a multidisciplinary field that encompasses the study of power converter topologies, modulation schemes, embedded control techniques, power semiconductors, magnetics, thermal management, CAD, system level optimization, etc. 
 - Hope is to develop better performing power converters to meet future demand
- Power electronics engineering roles are applied and practical
 - Growing demand for *skilled* power electronics engineers due to increasing use of electronics systems in areas such as renewable generation and electrified transportation

.center[
<iframe width="355" height="200" src="https://www.youtube.com/embed/KPpYTnD_ZHw" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
]

---

# Power Electronics Research at UoA
### An Overview

---

.logo-slide[]
.footer[[Duleepa J Thrimawithana](https://www.linkedin.com/in/duleepajt), Department of Electrical, Computer and Software Engineering (2021)]

---
name: S7

# Power Electronics Research Themes

- Power electronics research group at ECSE is at the forefront of PE research
 - Long history dating back to the late 1980's
 - Considered global leaders and pioneers of near field wireless power transfer technology

---
name: S8

# The Power Electronics Research Group

---
name: S9

# Pioneers in Wireless Power Transfer (WPT)

.center[
<iframe width="784" height="441" src="https://www.youtube-nocookie.com/embed/G1q1HZLQ528?" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
]

---
name: S10

# PE Group Connections

- Power electronics research group at ECSE is well connected with top ranking universities as well as industry (a few of these connections are shown below)

---

# Design of a Smart Power Bank
### Project Information

---

.logo-slide[]
.footer[[Duleepa J Thrimawithana](https://www.linkedin.com/in/duleepajt), Department of Electrical, Computer and Software Engineering (2026)]

---
name: S11

# The Project

- What is this course about and what should you expect to learn?
 - Gives you an opportunity to design and develop a system incorporatingpower electronics converters, analog and digital control, and a user interface
 - During this process you will gain knowledge, experience, skill-set and professional behavior needed to succeed in more challenging projects you will engage as an engineer
- What would you design and engineer during this course?
 - Sub-systems of a smart power bank depending on your team's interest and skill-sets to develop
- How would you achieve this task?
 - All teams must develop a *Boost Converter* to derive a 5V output from the energy storage element
 - The boost converter will be controlled using an ATMega328PB MCU and an UC3843 controller
 - Depending on your team's interest, you can choose to develop the other sub-systems such as the *Charger*, *User Interface* or other features
 - The charger can be a linear converter implemented using discrete components, while the user interface subsystem contains protection, battery management and touch control features

---
name: S12

# A Typical Smart Power Bank

- There are many commercially available power banks in the market with many smart features
 - Modern devices have a USB-C PD interface to charge and to provide a 5V output to the devices
 - Often has a user interface and modern devices include wireless charging

.center[<img src="img/TearDown.png" height="290">
.credits[
Tear Down of a Smart Power Bank [[2]](https://www.chargerlab.com/teardown-of-apple-iphone-air-magsafe-battery-a3466/)
]
]

---
name: S13

# Architecture of a Modern Power Bank (PI)

- Charging the power bank and deriving a 5V output is done through the USB-C PD interface
- A bi-directional buck-boost converter interface the USB-C PD and the energy storage element 
 - When in the charging mode, to takes energy from the input and charge the energy storage element
 - When in the discharging mode, a 5V output is generated using energy from the storage element
- Sensing circuitry measure voltages, currents and temperatures to ensure safe operation 
 - Isolation switch physical isolate the storege element under unsafe conditions

---
name: S14

# Architecture of a Modern Power Bank (PII)

- A microcontroller (MCU) implements user interface and to manage the operation of the power bank
 - Battery management system (BMS) monitors the storage element to ensures safe operation 
 - Touch interface allows the user to turn-on/off the power bank
 - Control logic controls the buck-boost converter

---
name: S15

# Suggested System Architecture

- We have divided the suggested system architecture into 3 sub-systems, 
 - A separate charging sub-system 
 - A boost converter sub-system for deriving 5V output
 - An smarts sub-system to implement user interface, monitoring and protection

---
name: S15b

# Suggested Boost Converter Architecture

- The boost converter converts the 2.5V to 3.5V DC from the energy storage element to a 5V DC output
 - Employs a UC3843 current mode controller to control the boost converter
 - An ATmega328PB microcontroller is used to implement a PI controller to regulate the 5V output
 - Includes a hardware protection feature for over-voltage

---
name: S15c

# Suggested Charger Architecture

- A linear regulator charges the energy storage element from 0V to 3.5V DC
 - Discrete components implements a linear regulator with both current and voltage control
 - Fully analog design using an OpAmp to implement feedback control
 - Should use a low dropout design to charge the energy storage element to 3.5V from a 5V input
- A PCB needs to be designed to implement the linear regulator 
 - Should include an isolation switch to isolate the energy storage element under unsafe conditions

---
name: S15d

# Suggested Smarts Architecture

- An ATmega328PB implements the user interface and manages the operation of the power bank
 - A capacitive touch sensor is used to turn on/off the power bank
 - Voltages, currents and temperatures are monitored to ensure safe operation of the power bank
 - Implements a battery management system (BMS) to track the state of charge (SOC) 
- Hardware protection circuitry is implemented to provide an independent layer of protection

---
name: S16

# Initial System Specifications (PI)

- The boost converter should be designed to meet following minimum specifications
 - In your proposal you would expand on these specifications

<table class="tg" style="undefined;table-layout: fixed; width: 647px; margin-left:auto; margin-right:auto;">
 <colgroup>
 <col style="width: 333px">
 <col style="width: 314px">
 </colgroup>
 <thead>
 <tr>
 <th class="tg-dzaw">Parameter</th>
 <th class="tg-dzaw">Value</th>
 </tr>
 </thead>
 <tbody>
 <tr>
 <td class="tg-jayl">Input Voltage Range</td>
 <td class="tg-jayl"> 2.5 VDC to 3.5 VDC </td>
 </tr>
 <tr>
 <td class="tg-sabo">Output Voltage</td>
 <td class="tg-sabo"> 5 VDC </td>
 </tr>
 <tr>
 <td class="tg-ig71">Load Regulation</td>
 <td class="tg-ig71"> 5% </td>
 </tr>
 <tr>
 <td class="tg-sabo">Output Power</td>
 <td class="tg-sabo">0.5 W to 5 W</td>
 </tr>
 <tr>
 <td class="tg-ig71">Output Voltage Ripple</td>
 <td class="tg-ig71">50 mV or Less</td>
 </tr>
 <tr>
 <td class="tg-ig71">Switching Frequency</td>
 <td class="tg-ig71">100 kHz</td>
 </tr>
 </tbody>
</table>

---
name: S16b

# Initial System Specifications (PII)

- The charger should be designed to meet following minimum specifications
 - In your proposal you would expand on these specifications

<table class="tg" style="undefined;table-layout: fixed; width: 647px; margin-left:auto; margin-right:auto;">
 <colgroup>
 <col style="width: 333px">
 <col style="width: 314px">
 </colgroup>
 <thead>
 <tr>
 <th class="tg-dzaw">Parameter</th>
 <th class="tg-dzaw">Value</th>
 </tr>
 </thead>
 <tbody>
 <tr>
 <td class="tg-jayl">Input Voltage</td>
 <td class="tg-jayl"> 5 VDC </td>
 </tr>
 <tr>
 <td class="tg-sabo">Output Voltage Range</td>
 <td class="tg-sabo"> 0 VDC to 3.5 VDC </td>
 </tr>
 <tr>
 <td class="tg-ig71">Voltage Regulation</td>
 <td class="tg-ig71"> 5% </td>
 </tr>
 <tr>
 <td class="tg-sabo">Output Current</td>
 <td class="tg-sabo">0.5 ADC</td>
 </tr>
 <tr>
 <td class="tg-ig71">PCB</td>
 <td class="tg-ig71">2-Layer PTH with SMT and TH Devices</td>
 </tr>
 <tr>
 <td class="tg-ig71">PCB Size</td>
 <td class="tg-ig71">Smaller than 100 mm x 100 mm</td>
 </tr>
 </tbody>
</table>

---
name: S19

# Working in Teams

- You will work in a team of 4 to 8 members
 - You can chose your team members and register your team details on Canvas by the end of 1st week
 - All team members should attend lab sessions together 
 - Team size and task division needs to be justified when you present your project proposal
- Throughout the project work as a team and aim to support each other
 - You need to report the contribution of each team member including hours spent
- Plan your work, document your work and communicate regularly with your team members
 - Use a logbook and [Slack](https://slack.com/intl/en-nz/) to plan and document your work 
 - Use [Slack](https://slack.com/intl/en-nz/) and [Zoom](https://zoom.us)/[Hangouts](https://hangouts.google.com) for team communications
 - Use [GitHub](https://github.com) and [G Suite](https://gsuite.google.com)/[Office 365](https://www.library.auckland.ac.nz/services/it-essentials/computer-facilities/software-personal-use/microsoft-student-advantage-office-365) products to collaborate with team members
- Be patient with your team members even if they are not making much progress during the initial stage
 - If things are not working out, after about 1-2 weeks, let us know
 - If a member is not engaging in team work we will ask that person to work alone

---
name: S20

# Course Calendar

---
name: S21

# How to Get an Excellent Grade

- Is the project challenging?
 - Yes, design and developing your first power electronics systems can be quite challenging
 - You need to have a good mastery of circuit analysis techniques, magnetics, control, digital logic, analog circuitry and embedded programming
- What are the most challenging aspects?
 - Time management, planing and team work are the key challenges
 - As in a real life project, resources are limited (time, teams' availability, lab space, equipment, software licenses, etc.) and therefore last minute frantic endeavour will not help
- How could I get an excellent grade?
 - Enjoy designing a real-world product and be passionate about your design (this is the key ingredient)
 - Plan and manage your and your team members' time well
 - Throughout the semester you are expected to spend about 12 hours a week on the project 
 - Make full use of all lab work sessions (there are 3 sessions a week 9am to 11am)

---
name: S22

# Are Design Courses Useful?

- Engineering a solution to solve a real-life problem helps you to understand the importance of the theoretical concepts you have learnt, and teaches you how to use these theories to achieve an output that could help the society

.center[
<iframe src="https://geo.dailymotion.com/player.html?video=x8x6204&startTime=420&autoplay=false"
 width="560" height="315" frameborder="0"
 allowfullscreen allow="web-share"
 title="Feynman - The Pleasure of Finding Things Out"></iframe>
]

---

# Assessment Components
### Details on How to Prepare

---

.logo-slide[]
.footer[[Duleepa J Thrimawithana](https://www.linkedin.com/in/duleepajt), Department of Electrical, Computer and Software Engineering (2026)]

---
name: S23

# Assessment Components

- All assessment components except the *Design Challenge* are compulsory
 - It is compulsory to satisfactorily complete all components except the design challenge to obtain a passing grade
 - To obtain a passing grade for this course, the average score of the 2 tests MUST be over 40%.
 - To be eligible for the bonus marks you must satisfactorily complete the entire project
 - Although this project will be undertaken in design teams of 4 to 8, you will be assessed individually

<table class="tg" style="undefined;table-layout: fixed; width: 647px; margin-left:auto; margin-right:auto;">
 <colgroup>
 <col style="width: 383px">
 <col style="width: 264px">
 </colgroup>
 <thead>
 <tr>
 <th class="tg-dzaw">Component</th>
 <th class="tg-dzaw">Weighting</th>
 </tr>
 </thead>
 <tbody>
 <tr>
 <td class="tg-jayl">Tests (Theory and Practical)</td>
 <td class="tg-jayl"> 45% </td>
 </tr>
 <tr>
 <td class="tg-sabo">Lecture Quizzes </td>
 <td class="tg-sabo"> 5% </td>
 </tr>
 <tr>
 <td class="tg-ig71">Progress Reviews</td>
 <td class="tg-ig71"> 18% </td>
 </tr>
 <tr>
 <td class="tg-ig71">Final Interview</td>
 <td class="tg-ig71">12%</td>
 </tr>
 <tr>
 <td class="tg-sabo">Project Deliverables </td>
 <td class="tg-sabo">20%</td>
 </tr>
 <tr>
 <td class="tg-ig71">Bonus Marks (optional)</td>
 <td class="tg-ig71">5%</td>
 </tr>
 </tbody>
</table>

---
name: S24

# Test, Lecture Quizzes & Progress Reviews

- Two tests will be conducted during weeks 7 and 10 of the semester in the laboratories
 - The theory test on week 7 will assess your understanding of fundamental concepts 
 - The practical test on week 10 will assess your ability to use design tools to complete a practical task
- We will conduct 0.5% lecture quizzes using Canvas to evaluate your engagement and understanding
 - Quizzes will be available for 6 hours and you are allowed 2 attempts
 - The maximum marks you can get will be capped to 5%
- The 3 progress reviews are to make sure you complete critical tasks on time
 - You are required to present your design proposal with supporting initial design calculations and literature review at the 1st review 
 - You are required to present your theoretical design along with supporting design
calculations, simulation results and PCB designs at the 2nd review
 - You are required to present preliminary experimental results at the 3rd review
 - We will check the progress and quality of work completed (4%), as well as your understanding and engagement(2%)

---
name: S25

# Final Interview & Deliverables

- During the last week there will be an interview to evaluate your understanding of the subject matter (12%) 
 - Theoretical and practical knowledge of hardware and firmware concepts you gained during the project will be assessed 
 - Though you will participate in the interviews as a team, you will be assessed individually 
 - You will be assessed based on technical accuracy and completeness of the answers given as well as your ability to confidently explain technical concepts 
 - The experience gained through this process will be invaluable to do well in technical job interviews
- During the last week of the semester you will be given an opportunity to demonstrate your final design
 - Design will be evaluated based on performance (8%), quality (6%) and report detailing test plan and results (6%)

---
name: S26

# Bonus Marks & Industry Judging

- Based on the performance throughout the semester the top 5 design teams will be selected 
- Industry judges from [Fisher & Paykel](https://www.fisherpaykel.com) will interview the top teams 
 - F&P visit to learn about current industry practices and meet engineers
 - They will decide the top PIII EEE design team
- The top 5 teams can also get up to 5% bonus marks awarded for demonstrated personal growth over the course of the project
 - We will be looking at both technical and soft skills (e.g., passion, coachability, emotional maturity, attention to ethical and social responsibilities, ability to clearly communicate with staff and peers, accountability, and adaptability)

---
name: S27

# Collaborating with Team Members

- To be a good engineer you also need to develop a number of *soft-skills*
 - Some of the key skills you should aim to develop are management, teamwork and communication 
- One of the primary responsibilities you will have as an engineer is to tell other engineers how to build, service, use and update a product you have been involved in designing/developing/building/testing/etc.
 - Thus, engineers are expected to document all details about their work in a logbook 
 - The information recorded in a logbook include, design notes, design decisions, calculations, software flow diagrams, schematics, meeting minutes, etc. 
- In industry, many different digital tools are used to help with managing teamwork work, communicating with team members and documenting details of the project
 - Slack and GitHub are a few such most commonly used and simple to use tools 
- In this project all students are expected to use a logbook together with Slack and GitHub to effectively plan, manage and document the work
 - We will regularly check how you use these tools as part of the assessment process

---
name: S28

# Resources & Flexible Learning

- Duleepa Thrimawithana (course director) and Moon Kim, from the academic staff, will be looking after this course
 - Howard Lu is your technical facilitators 
- Teaching assistance (TAs) will be available during support sessions to help with the project
 - Charley Shi (PhD), Frank He (PhD), Tharindu Dharmakeerthi (PhD), Sree Bommineni (PhD), Alex Skilton (PIV), Ella Wilson (PIV), Sam Ye (PIV) and Taha Basar (PIV) are your TAs
- You will get in-person support/training during the dedicated lab sessions shown on the course planner 
 - You are expected to attend all labs from 9am to 11am with your team members
- We will also provide support remotely using EdDiscussions, Slack and Zoom 
 - You may also request additional staff assisted evening support/tutorial sessions (online or on-campus)
- Recorded media will be provided to support your learning 
- We will communicate all course related information via Canvas and Slack

---
name: S28B

# Winter & Respiratory Viruses

- The course will be predominantly delivered in person unless UoA protocols change during the semester 
- Health and safety of everyone is a priority and so, if a TA is ill we would have to find replacements 
- We need to try and minimize the spread of respiratory viruses especially since it is winter
 - Students should wear face masks and try to minimize the spread of viruses 
 - If you are sick, you can participate virtually in support and assessment sessions (or in some cases you can request to reschedule your assessments)
- At times we may have TA shortages and might be forced to conduct support and assessment sessions virtually (or reschedule assessment times)
 - We will discuss with affected students and organize alternatives 
- If you test positive for COVID and think you have had contact with TAs during infectious time period notify Duleepa

---
name: S29

# Enrolment & Software Installation

- Prerequisite for this course is ELECTENG 310 
 - If you have failed ELECTENG 310, please contact us to check if your enrolment is still valid
- In some cases, even if you do not meet the prerequisite, after an interview, we may allow you to continue with the course, but we will have to partner you with a suitable team 
 - Contact Duleepa for more information
- Follow details on Canvas or the [course website](https://uoa-ee311.github.io/extra.html) to get setup on EdDiscussions, Slack and GitHub
 - Guides detailing how to obtain and install your personal copy of the software we will use in this course (Atmel Studio, Proteus VSM, Altium Designer, LTspice, Plecs and GitHub Desktop) are available
 - Ansys is only available via FlexIT

---
name: S30

# Building a Prototype

- This is a design project and you are expected to develop a hardware prototype 
 - This includes PCB design, building a prototype, testing hardware, rework, etc.
- We will provide resources and tools to get started on the project 
 - You can use Proteus VSM and the Xplained Mini development boards to develop and validate most of your firmware
 - We will provide a generic PCB for Boost Converter and a Xplained Mini to experimentally validate your design
 - You will need to develop your own PCBs for other subsystems
- The lab benches in MDLS E&I labs will be equipped with suitable bench-top equipment 
 - MDLS E&I is booked specifically for this course during times shown on the planner 
- You are expected to work from MDLS E&I with your team during the dedicated support sessions
 - If you are sick and connot attend please inform us and your team via Slack  
- We will have a number of workshops to teach you how to build and test your hardware

---
class: title-slide
layout: false
count: false
.logo-title[]

# Switched-Mode DC to DC Converters
### Fundamentals

---
layout: true
name: template_slide

.logo-slide[]
.footer[[Duleepa J Thrimawithana](https://www.linkedin.com/in/duleepajt), Department of Electrical, Computer and Software Engineering (2026)]

---
name: S31

# DC to DC Converters

- A DC to DC converter can be implemented as a linear regulator or as a switched-mode converter 
- A linear regulator uses a switch such as a BJT, that is operated in its active region 
 - In a series type linear regulator, the switch creates a voltage drop across it when its conducting current that flows from the source to the load
 - The voltage drop across the switch is controlled to achieve the desirable output 
 - Since the switch always has a certain voltage drop across it while also conducting current, the switch dissipates part of the power supplied by the source as losses
- A switched-mode converter uses a switch such as a BJT, that is continuously *switched* back and forth between the cut-off and saturation (or ohmic) regions
 - In cut-off region, though there is voltage across the switch, it has no current flowing through it
 - In saturation region, though there is current through the switch, voltage drop across it is insignificant
 - As such, the switch does not dissipate power as loss when its either in the cut-off or saturation regions
- Lets explore these two types of converters further with the aid of a case study

---
name: S32

# Linear Regulator Example (PI)

- As a case study, consider a power converter designed using a series type linear regulator to produce either a constant 5V or a 10V output from a 20V input source
 - Assume the load resistance is 5Ω and a BJT is used as the *series pass device* 
 - The *controller* takes user input, which indicates whether the output should be controlled to 5V or 10V and controls the base current, Ib, to produce the correct output voltage
 - Note that in practice the controller may also observe the output voltage and employ a *closed-loop* controller to produce the correct output

---
name: S33

# Linear Regulator Example (PII)

- Since the BJT of the linear regulator is operating in the active region we can model it as a variable resistance, Rce, where Rce can be controlled using Ib
 - Note that in a BJT `\(I_{e} \approx I_{c} = \beta I_{b} \)`, from which we can deduce `\(I_{out} \approx I_{in} = \beta I_{b} \)`
 - Value of Rce thus can be thought of as `\( \left ( V_{in} - V_{out} \right ) / I_{c} \)` or `\( \left ( V_{in} - V_{out} \right ) / \beta I_{b} \)`
- To produce a 5V output from the 20V input, as per voltage divider theory Rce should be set to 15Ω
 - Iout and therefore approximately Iin are both equal to `\(V_{out} /R_{L} = 1A \)`
- To produce a 10V output from the 20V input, as per voltage divider theory Rce should be set to 5Ω

---
name: S34

# BJT Operation in Linear Regulator Example

- For the BJT of the linear regulator to behave as a variable resistor it needs to be operated within its active region
- Lets assume that the β of the BJT employed in our example linear regulator is 100
 - When the linear regulating is producing 5V across the 5Ω load, Iout is 1A and thus Ib should be 10mA, while Vce is 15V, correspondingly BJT operates at point __'A'__
 - When the linear regulating is producing 10V across the 5Ω load, Iout is 2A and thus Ib should be 20mA, while Vce is 10V, correspondingly BJT operates at point __'B'__

---
name: S35

# Linear Regulator Efficiency

- As we saw from the operating points, the BJT always has a certain voltage drop (Vce) across it while also conducting current (Iout) 
 - Thus the BJT dissipate a significant portion of the power supplied by the source as losses 
- The efficiency of a series type linear regulator can be given by 
\\[ \eta = \frac {V\_{out}I\_{out}} {V\_{in}I\_{in}} \approx \frac {V\_{out}} {V\_{in}} \quad \left [ \because I\_{out} \approx I\_{in} \right ]\\]
- Our example regulator will be about 25% efficient when Vout is 5V, and 50% efficient when Vout is 10V

---
name: S36

# Improving Linear Regulator Efficiency

- To improve the efficiency of our example linear regulator, we need to make sure Vin is as close as possible to Vout (i.e., reduce Vce as much as possible)
 - However, Vce cannot be too small as we need to make sure BJT operates in the active region 
 - Minimum Vce required is called the *headroom voltage* and can be as much as a few volts
- If you had an AC input source, a transformer with taps can be used to switch in a Vin that's close to each Vout level we like to have
 - In this example, the *tap selector* selects 7V tap when needing a Vout of 5V (`\( \eta \approx 71\% \)`) while the 12V tap is selected when outputting 10V (`\( \eta \approx 83\% \)`)

---
name: S36

# Closed Loop Control of Linear Regulator

- The output voltage of a linear regulator can be controlled using an analog closed-loop controller 
 - The controller observes the output voltage and adjusts Ib to regulate the output voltage
- An OpAmp can be used to implement this closed loop controller 
 - The negative feedback path is through the base-emitter junction of the BJT 
- Since the inverting input is kept at the same voltage as the non-inverting input, the output voltage is

\\[ V\_{out} = V\_{ref} \frac {R\_{a}+R\_{b}} {R\_{b}} \\]

---
name: S36b

# Instability of the Controller

- The linear regulator in the previous slide can be unstable since the OpAmp introduces a pole (up to 90° phase lag) in addition to the pole formed by the load resistor and output capacitor 
 - We can model the circuit in frequency domain first by representing it as in the block diagram below

\\[ T\_{p}(s) \approx \frac {\beta \gamma} {1 + sC\_{o}R\_{g}\gamma } \quad \text{where} \quad \gamma = \frac {R\_{L}} {\beta R\_{L} + R\_{g}} \\]
 
\\[ T\_{c}(s) = \frac {A\_{OL}} {1 + s/\omega\_p} \quad \text{and} \quad F\_{b} = \frac {R\_{b}} {R\_{a}+R\_{b}}  \\]

---
name: S37

# Compensating the Controller

- We can add a capacitor from OpAmp output to its inverting input to slow the response of the controller and thus improve stability 
 - Zf is the impedance of the capacitor 
 - It can also be a resistor in series/parallel with a capacitor
- A capacitor across Ra can also help stability by introducing a phase lead

---
name: S38

# Constant Current Limiting

- A second BJT can be added to the linear regulator to implement a constant current limiting
 - When the voltage across Ri reaches 0.7V, this BJT shunts the base current of the series pass BJT, limiting the output current to

\\[ I\_{limit} \approx \frac {0.7V} {R\_{i}} \\]

- Foldback current limiting reduces the output voltage when the load current exceeds a certain limit

---
name: S39

# Switched-Mode Converter Example (PI)

- As a second case study, consider a power converter designed using a buck type switched-mode converter to produce either an *average* 5V or a 10V output from a 20V input source
 - Assume the load resistance is 5Ω and a BJT is used as the *on/off switch* 
 - The *controller* takes user input, which indicates whether the output should be 5V or 10V and controls the on-time, Ton, with respect to a constant time period, Ts, to produce the correct *average* output
 - Note that in practice the controller may also observe the output voltage and employ a *closed-loop* controller to produce the correct output

---
name: S38

# Switched-Mode Converter Example (PII)

- Since the BJT of the switched-mode converter is operated either in the cut-off or saturation regions we can model it as an on/off switch
 - When in cut-off region, its a turned-off switch, thus `\(I_{in} = I_{out} = 0\)`, `\(V_{out} = 0 \)` and `\(V_{ce} = V_{in} \)`
 - When in saturation region, its a turned-on switch, thus `\(V_{ce} \approx 0 \)`, `\(V_{out} \approx V_{in} \)` and `\(I_{in} \approx I_{out} = V_{out}/R_{L} \)`
 - In either case (i.e., on/off) power dissipated in BJT is negligible since `\(P_{BJT\_loss} \approx V_{ce}I_{in} \approx 0W \)`
- To produce an *average* 5V or 10V output from the 20V input, on-time, Ton, is varied with respect to a constant time period, Ts, where `\(T_{s} = T_{on} + T_{off} \)`

---
name: S39

# BJT Operation in the SMPS Example

- For the BJT of the switched-mode regulator to behave as an on/off switch it needs to be operated either in the cut-off or saturation regions 
- Lets assume that the β of the BJT employed in our example SMPS is 100
 - When working as a tuned-on switch, the voltage across the 5Ω load is 20V, Iout is 4A and thus `\(I_{b} >> 40mA \)`, while `\(V_{ce} \approx 0 \)`, correspondingly BJT operates at point __'A'__
 - When working as a tuned-off switch, the voltage across the 5Ω load is 0V, Iout is 0A and thus `\(I_{b} = 0 \)`, while `\(V_{ce} = 20V \)`, correspondingly BJT operates at point __'B'__

---
name: S40

# Pulse Width Modulation

- Varying the on-time, Ton, of the switch of an SMPS, while keeping the time period, Ts, constant, is referred to as pulse width modulation (PWM) 
 - Note that `\(T_{s} = T_{on} + T_{off} \)` and thus varying Ton has the opposite effect on Toff since Ts is constant
- PWM allows us to change the average value of Vout, Vout(av), between 0V and Vin since,
\\[ V\_{out(av)} = \frac{1}{T\_s} \int\_{0}^{T\_s} V\_{out}dt = \frac{1}{T\_s} \left[ V\_{in}T\_{on} + 0 \right] = \frac{T\_{on}}{T\_s} V\_{in} \\]
 - For example, if switch is always on, then Vout(av) is 20V, while if it is always off Vout(av) is 0V

---
name: S41

# Duty Cycle

- A new parameter called the *duty cycle*, which is also referred to as *D*, is introduced in SMPS terminology to help us easily quantify the ratio `\( T_{on} / T_{s} \)` and thus,
\\[ D = \frac{T\_{on}}{T\_s} \quad \text{where} \quad 0 \leqslant D \leqslant 1 \\]
- Using D, we could express Ton and Toff as `\( T_{on} = DT_{s} \)` and `\( T_{off} = (1-D)T_{s} \)`
- The average output voltage can now be simply written as `\( V_{out(av)} = D V_{in} \)` where `\( 0 \leqslant D \leqslant 1 \)`

---
name: S42

# SMPS Efficiency

- If we use an ideal switch, theoretically there is [no power losses](#S38), leading to a 100% efficient converter
- In real life, for example when using a BJT as the switch, Vce(sat) will not be exactly 0V when turned-on 
 - Small voltage drop across switch when turned-on and conducting will lead to some power loss
 - This type of loss is referred to as the *conduction loss* of the switch
- Also when the switch transitions from on to off state and vice versa, it passes through the active region 
 - This means momentarily there will be voltage across the device while also conducting current leading to some power loss
 - This type of loss is referred to as the *switching loss* 
- We use some form of a passive filter to obtain a smooth Vout(av) by removing pulsation in Vout 
 - This filter also introduces losses 
- A modern SMPS can achieve efficiencies over 99% but often practical converters have slightly lower efficiencies
 - Note efficiency is not the only important feature of a power converter as previously [discussed](#S4)

---
name: S43

# Example: Importance of Efficiency

.questions[
A remote sensor that is measuring environmental CO2 requires a regulated 3.3V supply. The sensor draws a constant 0.1mA current. The sensor is to be powered using a battery pack that has a nominal voltage of 6.6V. The battery pack has a capacity of 3.3Wh. A power converter is to be designed to convert the battery voltage to a regulated 3.3V output to supply the sensor. 
- If a linear regulator is used as the power converter, how many hours can the sensor operate before needing a battery replacement? Assume the battery voltage is constant.

- If a buck type switched-mode converter is used as the power converter, how many hours can the sensor operate before needing a battery replacement? Assume the converter efficiency is 95%.
]

---
name: S44

# Power Converter Specifications

- A number of different specifications are typically used to highlight the performance of a power supply 
 - Input voltage range 
 - Output voltage and current range 
 - Operating temperature range
 - Efficiency
 - Isolation rating
 - No load input current 
 - Line regulation: Change in output voltage when input voltage changes from minimum to maximum
 - Load regulation: Change in output voltage when load current changes from minimum to maximum
 - Output ripple voltage: Pulsation in output voltage around its average value
 - Settling time: Time taken for output of power supply to settle as operating conditions change
 - Protection features: Under/over voltage, current limiting, over temperature, short-circuit, etc.
- You are expected to develop a set of specifications for the power supply you will design

---

# Demo: A Simple SMPS

.questions[
Explore the behavior of this circuit when the duty cycle and load resistance change. Derive an expression for RMS & average current through switch as a function of D and validate using this simulation model.
]

---

# Questions?