恒流驱动led文章，超长巨详
LUTW Project: LED Current SourcesBy
Nino Johansson
The School of Information Technology and Electrical
Engineering
The University of Queensland
Submitted for the degree of Bachelor of Engineering
in the division of Electrical Engineering
October 2003ഊii
October, 2003
The Dean
School of Engineering
The University of Queensland
St. Lucia, QLD 4072
Dear Professor Simmons,
In accordance with the requirements of the degree of Bachelor of Engineering in the
division of Electrical Engineering, I present the following thesis entitle “LUTW: LED
Current Sources”. This work was developed under the supervision and guidance of Dr.
Geoffrey Walker.
I declare that the work presented in this document is my own original work, except where
acknowledged otherwise, and has not previously been submitted for academic merit in
another course at The University of Queensland or any other institution.
Yours sincerely,
Nino Johanssonഊiii
Abstract
Access to light is something that many in the western nations take for granted and much
of this light is produced by using incandescent and fluorescent forms of lighting. Light
Up The World (LUTW) is an organisation, based in Canada, which aims to assist poor
and remote villages in developing countries obtain a reliable and affordable means of
lighting their homes by leading the way in utilizing low energy White Light Emitting
Diodes (WLED’s) to provide an efficient, reliable, and safe form of lighting.
The WLED’s being used in this project are a revolutionary, energy efficient and ultra
compact new light source, combining the lifetime and reliability advantages of Light
Emitting Diodes with the brightness of conventional lighting. These WLED’s require
more power than conventional LED’s and to ensure optimum light output, they must be
driven at a constant current.
A typical household may install up to three WLED’s for the lighting of the entire home
and thus, the aim of this thesis is to provide a means of powering 3 LED’s from a single
driving circuit, so as to reduce the cost of having a driver for each LED. It is hoped that
by designing a single device which is capable of driving up to 3 Luxeon LED’s that it
will assist LUTW in it’s goal of providing efficient, reliable and safe lighting to those in
developing countries.ഊiv
Acknowledgements
I would like to thank these people for their assistance in making this thesis possible:
Mr. Geoffrey Walker, for his supervision, patience and technical thesis advice.
Mr. Peter Allen for maintaining and supervising the thesis laboratory.
Mr Keith Bell for running and maintaining the electronics workshop and keeping it well
stocked and supplied.
My friends, for putting up with me and for the good stories and jokes that they tell.
And finally, my family, for their non-stop support in everything I do.
Thank you for your assistance during this project.ഊv
Table Of Contents
Chapter 1 – Introduction.................................................................................................. 1
1.1 Light Up The World Project ..................................................................................... 1
1.2 What Is This Thesis About?...................................................................................... 1
1.3 Overview of Document............................................................................................. 2
Chapter 2 – Background Information and Product Review......................................... 4
2.1 Luxeon Light Emitting Diodes ................................................................................. 4
2.2 DC-DC Converter Theory......................................................................................... 7
2.2.1 Buck Converter Operation ................................................................................. 7
2.2.2 Continuous Conduction Mode ........................................................................... 9
2.2.3 Converter Control .............................................................................................. 9
2.3 Currently Available Products.................................................................................. 10
2.3.1 Xitanium LED Drivers..................................................................................... 10
2.3.2 Lumidrives Series ............................................................................................ 11
2.3.3 LED Dynamics................................................................................................. 12
2.3.4 Table of Feature Comparisons of Luxeon LED Drivers.................................. 13
2.4 Summary................................................................................................................. 13
Chapter 3 – Product Specifications ............................................................................... 14
3.1 Separating the Device into Subsystems .................................................................. 14
3.2 Hardware Specifications ......................................................................................... 15
3.2.1 Power Supply ................................................................................................... 15
3.2.2 Controller ......................................................................................................... 16
3.2.3 Power Electronics ............................................................................................ 16
3.2.4 Luxeon LED’s.................................................................................................. 16
3.2.5 User Input/Output ............................................................................................ 17
3.3 Software Specifications .......................................................................................... 17
3.3.1 Software Subsystems ....................................................................................... 17
3.4 Summary................................................................................................................. 18
Chapter 4 – Implementation Plan and Schedule ......................................................... 19
4.1 Project Goals........................................................................................................... 19
4.2 Project Schedule...................................................................................................... 20ഊvi
4.3 Planned Method of Implementation........................................................................ 21
4.3 Summary................................................................................................................. 22
Chapter 5 – Hardware Implementation ....................................................................... 23
5.1 Power Supply.......................................................................................................... 23
5.1.1 Operation from 12V......................................................................................... 23
5.1.2 Operation from 230VAC ................................................................................. 25
5.2 Micro-Controller ..................................................................................................... 26
5.3 Power Electronics ................................................................................................... 27
5.3.1 MOSFET and BJT Selection ........................................................................... 28
5.3.1.1 Switch Operation .......................................................................................... 28
5.3.2 Inductor Selection ............................................................................................ 29
5.3.3 Capacitor Selection .......................................................................................... 29
5.3.4 Diode Selection................................................................................................ 30
5.4 Luxeon LED’s......................................................................................................... 30
5.5 User Input/Output ................................................................................................... 32
5.6 Schematics and Printed Circuit Board Design........................................................ 33
5.6.1 PCB Layout Considerations............................................................................. 33
5.7 Summary................................................................................................................. 35
Chapter 6 – Software Implementation.......................................................................... 36
6.1 Software Development............................................................................................ 36
6.1.1 Software Basics................................................................................................ 36
6.1.2 Generating PWM Signals ................................................................................ 36
6.1.3 Enabling Analogue to Digital Conversion....................................................... 38
6.2 Software Design...................................................................................................... 39
6.3 Final Code............................................................................................................... 42
6.4 Summary................................................................................................................. 42
<P>这是个毕业论文之类的东西，网上一大堆，废话更是一大堆。我说它废话一堆是因为：我自己也经常写废话:D:D.</P><P>虽然对于电筒这个没有什么用，但是12V/市电对于商用角度是很好的。特别是在照明系统里。</P> <P>我发现这个论坛没有真正讨论技术多深的文章，高手基本都不说话，有时候说几句，还要被一堆人类问来问去，导致这个论坛的技术性就差了很多</P> <P>tingni你想怎么讨论啊？我很期待有强人能告诉我DB、BB之类是怎么弄出来的。</P><P>如果自动焊，我想它们应该没有这么大的量，而且那些元件摆放得也不是很好；手动焊，又觉得焊不了这么好，特别是那些贴片电阻＋电容。那个圆形的PCB一看就是自己切的，不过不知道怎么切最好。有人知道吗？</P> Chapter 7 – Product Evaluation.................................................................................... 43
7.1 Evaluation of the device Against the Specifications of Chapter 3.......................... 43
7.1.1 Quick Checklist of Device Against the Specifications .................................... 43
7.1.2 Detailed Checklist of the Device Against the Specifications .......................... 44
7.2 Device Efficiency.................................................................................................... 46ഊvii
7.3 Evaluation of the Author’s Performance as an Engineer........................................ 52
Chapter 8 – Future Developments and Improvements ............................................... 53
Chapter 9 – Conclusion .................................................................................................. 55
9.1 What was set to Achieve? ....................................................................................... 55
9.2 What was Achieved?............................................................................................... 55
Bibliography ....................................................................................................................57
Re 59
A 60
Appendix A - Schematics ............................................................................................... 61
Appendix B – Printed Circuit Board Designs .............................................................. 65
Appendix C – Software Code......................................................................................... 69
Appendix D – Efficiency Results ................................................................................... 75ഊviii
List of Figures
Figure 1: Luxeon Light Emitting Diodes............................................................................ 4
Figure 2: Various Luxeon Packages, from left to right; Star, Star/C, Star/O and Emitter.
5
Figure 3 – Relative Light Output of 5mm White LED’s and Luxeon LED’s ............... 6
Figure 4: Buck Converter .............................................................................................. 8
Figure 5: Circuit diagram when the switch is: (a) on; (b) off ....................................... 8
Figure 6: Xitanium Driver Module ............................................................................. 10
Figure 7: Microdriver3/9 LED Driver Module ........................................................... 11
Figure 8: MicrolV3/9 LED Driver Module ................................................................. 12
Figure 9: PowerPuck Luxeon LED Driver .................................................................. 12
Figure 10: Subsystem Diagram........................................................................................ 15
Figure 11: 12V to 5V step-down converter to power the MCU....................................... 24
Figure 12: LM2594HV-5 Step-Down Converter.............................................................. 24
Figure 13: 230VAC to 12VDC Adapter Schematic ......................................................... 25
Figure 14: 230VAC to 12VDC Adapter ........................................................................... 25
Figure 15: Pin Configuration of the ATmega8L............................................................... 26
Figure 16: ATmega8L Micro-Controller .......................................................................... 27
Figure 17: A Single Buck Converter Channel .................................................................. 27
Figure 18: Three Buck Converter Channels ..................................................................... 30
Figure 19: Voltage and Current Protection Circuitry ....................................................... 31
Figure 20: Fuse Housing with Zener Diode and BJT ....................................................... 32
Figure 21: Daughter Board for User Input and Output..................................................... 33
Figure 22: Isolation Switches and Programming Connection .......................................... 34
Figure 23: Final PCB ........................................................................................................ 35
Figure 24: CodeWizardAVR Window Showing PWM Options ...................................... 37
Figure 25: CodeWizardAVR Window Showing ADC Options ....................................... 38
Figure 26: Main Software Flowchart Diagram................................................................. 40
Figure 27: Power Mode Control Flowchart Diagram ....................................................... 41
Figure 28: Final Product ................................................................................................... 46
Figure 29: Efficiency at 12VDC Input and Daughter Board Connected.......................... 48ഊix
Figure 30: Efficiency at 12VDC Input, No Daughter Board Connected at High Power
Output ....................................................................................................................... 49
Figure 35: Printed Circuit Board Layout of 240VAC Adapter......................................... 69
Figure 36: Efficiency at 12VDC Input and Daughter Board Connected.......................... 78
Figure 36: Efficiency at 12VDC Input and Daughter Board Connected.......................... 78
Figure 37: Efficiency at 12VDC Input, No Daughter Board Connected at High Power
Output ....................................................................................................................... 79
Figure 37: Efficiency at 12VDC Input, No Daughter Board Connected at High Power
Output ....................................................................................................................... 79
Figure 38: Efficiency at 12VDC Input, No Daughter Board Connected at Low Power
Output ....................................................................................................................... 80
Figure 38: Efficiency at 12VDC Input, No Daughter Board Connected at Low Power
Output ....................................................................................................................... 80
Figure 39: Efficiency at 230VAC Input and Daughter Board Connected........................ 81ഊx
List Of Tables
Table 1: Comparison of Luxeon LED Drivers ................................................................. 13
Table 2: Product Subsystems Classification .................................................................... 14
Table 3: Efficiency at 12VDC Input and Daughter Board Connected ............................ 47
Table 4: Efficiency at 12VDC Input, No Daughter Board Connected at High Power
Output ....................................................................................................................... 48
Table 5: Efficiency at 12VDC Input, No Daughter Board at Low Power Output............ 49
Table 6: Efficiency at 230VAC Input and Daughter Board Connected ........................... 50
Table 7: Complete Efficiency Results of Device when Supplied with 12VDC ............... 76
Table 8: Complete Efficiency Results of Device when Supplied with 240VAC ............. 77 1
Chapter 1 – Introduction
1.1 Light Up The World Project
Light Up The World (LUTW) is a non-profit organisation, which is based in Canada that
aims to bring light to villages that currently have little or no access to electricity. The
chief goal of LUTW is to assist poor villagers in the developing world obtain a safe,
reliable and affordable White Light Emitting Diode (WLED) based form of home
lighting.
LUTW is achieving this goal by utilising the latest technology in solid state lighting, the
low power (1 Watt) Luxeon WLED’s. These LED’s provide enough light so that a child
can read with, thus three of these LED’s would be sufficient to light up a rural household.
The aim of this thesis is to design and implement a means of driving these LED’s in such
a way as to facilitate a means of driving 3 Luxeon LED’s in order to achieve the chief
goals of LUTW in providing light to thousands of homes in developing nations. It is
hoped that this thesis aids the efforts of LUTW.
1.2 What Is This Thesis About?
With the goals of LUTW in mind, a suitable driver for these Luxeon’s was designed and
produced such that it is capable of driving up to 3 WLED’s at the same time from a
varying power supply, with high circuit efficiency.
The design and implementation of the hardware and software to so solve the problem of
driving up to 3 Luxeon LED’s at a constant current is the main focus of this thesis.ഊ2
1.3 Overview of Document
The following report documents the procedures and methods used to design and
implement an LED driver module. A chapter-by-chapter overview is detailed below.
• Chapter 2 of this document contains background information on the Luxeon
LED’s along with detailing relevant converter theory, which is crucial in further
understanding of the design sections. An overview of currently available devices
is also contained in the section.
• Chapter 3 derives the specifications of the driver to be developed. It achieves this
by breaking down the driver into subsystems; with the specifications, both
hardware and software, of the final driver derived from the individual
requirements of each subsystem.
• Chapter 4 details how the project was originally planned, with goals and
milestones being developed. It also details how these original plans changed and
how new milestones were set and achieved.
• Chapter 5 details the hardware implementation of the driver. It starts by
describing the requirements of the hardware and how the hardware was selected
for the system noting possible component alternatives. Furthermore, this chapter
comments on the key hardware implementation decisions made.
• Chapter 6 contains the software implementation of the driver, outlining the
requirements of the software and how it is used to control the hardware of the
driver.
•
Chapter 7 details how the final implantation of the hardware and software meets
the design specifications of Chapter 3. The result of testing the final product and
the functionality of it is compared with the original specifications. The author’sഊ3
performance in completing this thesis is also reviewed, with the strengths and
weaknesses of the author evaluated, along with which additional skills were
gained in order to complete the project.
• Chapter 8 gives an outline on how this project could possibly be improved, and
suggests additions and optimizations that could be implemented into the current
design as well as into any future versions of this device.
• Chapter 9 provides a brief overview of the entire project, outlining the goals of
the project, what was actually achieved and how well it performed. This chapter
also summarises conclusions which were made previously in this report.
This report aims to provide a detailed and accurate analysis of the LED driver along with
the relevant theory associated with it. It is hoped that this report fulfills this aim and
allows for a good understanding of the driver’s design and its capability. <P>好多图片传不上来 郁闷</P><P>4
Chapter 2 – Background Information and Product
Review
This chapter includes a description of the Luxeon LED’s and their characteristics.
Relevant dc-dc converter theory is also discussed which is crucial in understanding how
the driver circuit works. A review of already available devices is also contained within
this chapter.
2.1 Luxeon Light Emitting Diodes
Luxeon LED’s are a revolutionary and energy efficient new light source, which combines
the lifetime and reliability of LED’s with the standard brightness of conventional lighting
such as incandescent and fluorescent lamps. There are three versions of the Luxeon LED
available each having a different power level. The three versions are: Luxeon (1 Watt),
Luxeon V (5-Watts), and the recently released Luxeon III (3.9-Watts).
Figure 1: Luxeon Light Emitting Diodes
Traditionally, LED light sources have been constructed using a small LED chip mounted
in an optical-grade epoxy package. However, the new Luxeon LED uses a newഊ5
packaging technology. These Luxeon LED’s use a semiconductor chip mounted on a
heat-sink slug, which provides much better thermal properties as compared to typical
LED’s. The improved thermal properties and larger chip size allow the Luxeon LED’s to
be operated at much higher currents than ordinary LED’s. Solid state light sources, such
as LED’s, exhibit self-heating characteristics when power is applied to them and this self-heating
in limits the power dissipation and drive current to around 20mA in a
conventional 5mm white LED. At 20mA, a conventional 5mm white LED generates
about 1 lumen of white light. While the Luxeon LED also exhibits self-heating, its
improved thermal properties allow it to be driven at 350mA, thereby obtaining up to 25
lumens of white light.
Luxeon LED’s also come in a variety of packages, some including heat sinks already
attached to the LED and others with a light collimator already surrounding the LED.
Figure 2 illustrates some of the packages which are available.
Figure 2: Various Luxeon Packages, from left to right; Star, Star/C, Star/O and
Emitter.
The Luxeon LED’s also have many other packaging improvements designed to increase
the light output and reliability of the package. The semiconductor chip inside the Luxeon
LED is optimised for light extraction efficiency, thermal management and current
density. In addition, the white Luxeon’s have been designed in such a way as to
eliminate several mechanisms that negatively effect the lumen output. These include:ഊ6
• A 20 times reduction in thermal resistance compared to standard 5mm LED’s.
This allows the Luxeon to be driven at currents of up to 350mA.
• Use of a different optical coupling silicone that does not yellow like optical-grade
epoxy resin.
• Use of a leadframe material that is protected from discoloration due to oxidation.
Figure 3 shows a graph comparing the relative light output between conventional 5mm
white LED’s and Luxeon LED’s. It can be seen that the Luxeon LED’s retain much of
their light output over the same amount of time compared to the conventional 5mm white
LED’s whose light output drops to around 40% its original light output over the same
time.
Figure 3 – Relative Light Output of 5mm White LED’s and Luxeon LED’s
Luxeon LED’s are also extremely rugged and have an exceptionally long lifespan. The
typical lifespan of a single Luxeon LED is up to 100,000 hours. This equates to
approximately 11 years of continuous lighting.ഊ7
One drawback on the Luxeon LED’s is that the forward voltage drop across them can
vary between different units and batches. This means that the driver required for them
has to be able to adjust the voltage accordingly, such that a constant current of 350mA is
applied to the LED regardless of which batch that the LED was produced. The typical
forward voltage drop across these LED’s varies between 2.79V – 3.99V.
2.2 DC-DC Converter Theory
Although the forward voltage drop across the Luxeon LED can vary, it is still below the
minimum input voltage of 12VDC. Thus the driver needs to produce a lower output
voltage than the input supply voltage, which is what the Buck Converter achieves.
2.2.1 Buck Converter Operation
This converter is based on switch-mode technology, which produces a lower average
output voltage with regard to the input supply voltage. This converter is classed as a
step-down converter as it “steps down” the input voltage by the use of switches whereby
a switch (BJT, MOSFET, etc) is either fully on or fully off. Since these switches are not
required to operate in their active regions, operating in the fashion of either fully on or
fully off leads to lower power dissipation in the converter circuit when compared to linear
regulators. The output voltage out of the buck converter is controlled by varying the “on”
and “off” durations of the switching component. The ratio of the switches “on” duration
to the period of switching is the duty cycle, D. Figure 4, below, shows the basic circuit
configuration, Figure 4a, and the concept of the averaging output voltage, Figure 4b.ഊ8
(a) (b)
Figure 4: Buck Converter
The buck converter essentially consists of 4 components, the switch, an inductor, a
capacitor, and a diode. The switch operates at a high frequency, upwards of 10kHz,
switching the input voltage. The inductor and capacitor act as a low-pass filter which act
to filter the high frequency switching voltage waveform and allows a dc-component, Vo,
to pass through.
The diode acts as a pathway for the inductor current whilst the switch is off, allowing the
energy stored in the inductor to be transferred to the load. When the switch is on, the
diode is reverse biased and the input provides energy to the load and to the inductor.
(a) (b)
Figure 5: Circuit diagram when the switch is: (a) on; (b) off
The buck converter can operate in either Continuous Conduction Mode (CCM) or in
Discontinuous Conduction Mode (DCM). The difference between the 2 modes being that
in CCM, the current flowing through the inductor is continuous, and only flows in one
direction and the current in the inductor never reaches zero, whereas in DCM it does not.
The driver is to be designed such that the converter is operating in CCM.ഊ9
2.2.2 Continuous Conduction Mode
In CCM, the output voltage is related to the input voltage and duty cycle by the equation:
Vo = DVd (2.1)
The inductor current ripple, ∆IL, is given by:
L o s I = V/L (1 - D) T ∆(2.2)
And the voltage ripple at the output is given by:
L s I T Vo = 8C
∆∆(2.3)
These equations will come into effect in component choosing later in Chapter 4.
2.2.3 Converter Control
As the mentioned in 2.2.1, the output voltage is determined by the duty cycle of the
switches. Variation in the switching frequency makes it difficult for the filter
components to filter the ripple in the output voltage and current waveforms, thus a
constant switching frequency is desired. The duty cycle then needs to be varied with a
constant switching frequency and the method of doing this is called Pulse Width
Modulation (PWM) switching.
There are several methods of generating a PWM signal, both analogue and digital
methods are available. Analogue methods include Voltage Mode Control and Current
Mode Control. Digital methods are implemented through the use of micro-controllersഊ10
(MCU) and Digital Signal Processing (DSP) chips. The method of control implemented
into the final design was chosen to be digital through the use of a MCU. This is further
discussed in Chapter 4 and 5.
2.3 Currently Available Products
There are a number of commercially available products which have been designed to
drive Luxeon LED’s, with many of them capable driving multiple LED’s. This section
examines examines these products concluding an a summary of the features and
limitations of these devices.
2.3.1 Xitanium LED Drivers
The Xitanium Drivers, available from Luxeon Star (<a href="http://www.luxeonstar.com" target="_blank" >http://www.luxeonstar.com</A>) is a
driver module comes in 2 versions. One of which is capable of powering up to 8 series
connected 1-Watt Luxeon LED’s, while the other version is designed to power between
6-12 series connected 5-Watt Luxeon LED’s. Both these versions operate from an input
supply of 120VAC.
Figure 6: Xitanium Driver Module ഊ11
2.3.2 Lumidrives Series
LumiDrives Ltd. (<a href="http://www.lumidrives.com" target="_blank" >http://www.lumidrives.com</A>) have developed a number of driver
modules for the Luxeon LED’s.
Microdriver: This driver comes in 2 versions, the Microdriver3 and the Microdriver9.
The Microdriver3 is a mains input 230VAC driver which can power up to 3 LED’s. This
version is not dimmable. The other version, the Microdriver9, is also operates from
230VAC and can power between 4 to 9 Luxeon LED’s. This version can provide
dimmable lighting.
Figure 7: Microdriver3/9 LED Driver Module
Microl: This driver also comes in 2 version, the MicrolV3 and the MicrolV9. Similar to
the Microdriver, they can power up to 3 Luxeon LED’s (V3) or 4 -9 (V9). Both these
drivers operate from a 12-24V AC or DC input supply.ഊ12
Figure 8: MicrolV3/9 LED Driver Module
2.3.3 LED Dynamics
LED Dynamics (<a href="http://www.leddynamics.com" target="_blank" >http://www.leddynamics.com</A>) also developed some driver modules for
Luxeon LED’s.
MicroPuck: This driver was designed to power a single 1W Luxeon LED from two
1.5V batteries.
PowerPuck: This driver comes in 2 versions, one version only capable or powering 1-2
1-Watt Luxeon LEDs and the other version capable of powering 1 5-Watt Luxeon or four
1-Watt Luxeons. Both versions of this driver operate from an input voltage of 12VDC.
Figure 9: PowerPuck Luxeon LED Driver ഊ13
2.3.4 Table of Feature Comparisons of Luxeon LED Drivers
Number of Luxeon LED’s that
can be powered
Power
Supply
Luxeon V
Capable?
1-Watt LED’s 5-Watt LED’s
Xitanium 120VAC Yes 1-8 6-12
Microdriver3 230VAC No 1-3 N/A
Microdriver9 230VAC No 4-9 N/A
MicrolV3 12VAC/DC No 1-3 N/A
MicrolV9 12VAC/DC No 4-9 N/A
MicroPuck 3VDC No 1 N/A
PowerPuck 350mA 12VDC No 1-2 N/A
PowerPuck 700mA 12VDC Yes 1-4 1
Table 1: Comparison of Luxeon LED Drivers
2.4 Summary
This chapter has presented a review of currently available Luxeon LED Drivers, an
overview of the Luxeon LED’s and their characteristics, and also presented relevant dc-dc
converter theory. Chapter 3 will derive the specifications of the thesis project.</P> <P>14
Chapter 3 – Product Specifications
Having examined existing products and their characteristics, a set of design specifications
for the final product which meets the requirements of the project needs to be derived.
The final product specifications are derived by separating the original device into smaller
subsystems and derive design specifications of these subsystems. Successful fulfillment
of these product specifications will result in a fully functional and useful product.
3.1 Separating the Device into Subsystems
The final product must be able to drive three Luxeon LED’s from either 12VDC or
230VAC. This is the original design criteria that the driver must conform to. Any failure
in satisfying this requirement will result in a non-functional and incomplete product.
The device can be separated into five main subsystems, each of whom can then be
classed into two categories, software or hardware. Figure 10 illustrates the five main
subsystems and the interactions between subsystems, with Table 2, classifying the
subsystems into hardware or software categories.
Subsystem Contains
(Hardware/Software)
Power Supply Hardware
Controller Hardware and Software
Power Electronics Hardware
Luxeon LED’s Hardware
User Input/Output Hardware
Table 2: Product Subsystems Classification</P><P>15
3.2 Hardware Specifications
All the subsystems in the device contain some hardware and the hardware requirement of
each subsystem is detailed below.
3.2.1 Power Supply
The original design criteria state that the device must be able to operate from either
12VDC or from 230VAC. The hardware for the power supply must be able to ensure
safe operation of the device, especially when it is implemented at 230VAC.ഊ16
3.2.2 Controller
The controller requires a number of input/output pins and be able to control and adjust
the power electronics subsystem. It must also be fast enough to carry out all these tasks
with ease and have enough memory such that it is able to store the control program.
Enough memory for the controller is also crucial for instances where swap space is
needed when carrying out calculations and instructions.
3.2.3 Power Electronics
The power electronics subsystem is the bulk of the device as it allows the Luxeon LED’s
to be powered efficiently and effectively. As the driver needs to be a buck converter,
controlled by PWM switching, one of the key requirements of entire buck converter is
that it needs to be able to operate at the switching frequency without undue negative
effects. Negative effects include the switches not being able to operate at the desired
frequency, the inductors unable to tolerate the drive currents or the capacitors not
withstanding the voltages ripples.
3.2.4 Luxeon LED’s
The requirements of this subsystem directly impact onto the power electronics subsystem
as that system needs to be able to power these LED’s. The Luxeon LED requirement
specifications are for a voltage of between 2.79V – 3.99V and a current of 350mA.
These LED’s also need to be protected from voltage and current surges, so protection
circuitry will have to be integrated into the design.ഊ17
3.2.5 User Input/Output
A means of inputting user requests into the device and giving the user adequate feedback
on operation is required for easy usage of the product. Typically, user input can be
implemented through the use of switches and buttons, with feedback given to the user
through the means of coloured LED’s and signal sounds.
3.3 Software Specifications
The hardware design relies on a reliable and effective software design. The software is
required to control the device and adjust control of the device accordingly depending on
user inputs and feedback signals from the hardware. It may also be desirable if the user
can be given feedback from the device on possible errors or states that the software may
encounter. The program can be considered to consist of three main subsystems. The first
subsystem will need to check for and interpret user input into the system as to what is
required of the device. The second subsystem is the main control loop which will
calculate and carry out control functions of the hardware, such that the desire of the user
is met. The last subsystem will give feedback to the user on possible errors or states that
the device is in.
3.3.1 Software Subsystems
1. Check for and interpret user input
2. Carry out control functions of the hardware.
3. Indicate to the user of errors/states of the device.ഊ3.4 Summary
This chapter has separated the final device into smaller subsystems and has also
developed a number of specifications for each of these subsystems. Chapter 4 will detail
the project plan and schedule.</P> 19
Chapter 4 – Implementation Plan and Schedule
This chapter details how this project was planned, and how work was executed. A series
of product goals were developed and a project schedule was detailed in the Progress
Report which was submitted in Week 7 of the project.
4.1 Project Goals
In order to reach the final goal of the project, that is, to fulfill all product specifications
which have been detailed in the previous chapter. The Progress Report contained a
number of project goals and these goals included:
1. Design a constant current source to power the Luxeon LED’s.
2. Design a pulsed current source to power the Luxeon LED’s.
3. Evaluate constant current and pulsed current designs and choose the best design.
4. Adapt the chosen design to 12VDC.
5. Adapt the chosen design to 230VAC.
6. Test and evaluate 12VDC and 230VAC designs.
7. Enhance product.
Upon revision of these goals as the project progressed and more was understood about
the project and how it would be completed, it became clear that a new set of goals had
been developed. These revised goals included are the final goals which have all been met
in the completion of this project.ഊ20
1. Design a step-down converter suitable for driving the Luxeon LED’s, operating
from 12VDC.
2. Design an adapter which will step-down 230VAC to 12VDC to facilitate the
operation of the device at 230VAC.
3. Test and evaluate the designs.
4. Enhance the product.
These revised goals allowed for a much simpler approach to the project.
4.2 Project Schedule
Along with the project goals which was submitted in the Progress Report, a set schedule
was planned in order to maintain the project. A number of project milestones were
developed and their proposed dates included:
1. Finish constant current design, 26 th April.
2. Finish pulsed current design, 30 th June.
3. Choose design, 17 th July.
4. Working 12VDC device, 14 th August.
5. Working 230VAC device, 18 th September.
6. Fully working designs, 9 th October.ഊ21
It was the intention of completing these tasks by their set dates, however due to the
project goals being revised a new set of goals having been developed, some of these
original project milestones became unnecessary. With the revised goals in mind and
which milestones were still relevant with respect to the revised goals, these project
milestones were met.
1. Completed step-down converter design, operating from 12VDC, 11 th August.
2. Completed 230VAC adapter design, 23 rd September.
3. Tested and evaluated product, 16 th October.
4. Enhanced product, 16 th October.
It can be seen that the relevant milestones were completed after their set dates, this can be
attributed to a substantial amount of research been undertaken earlier on in the project.
This research facilitated the rapid completion of product design, construction and testing
later on in the project.
4.3 Planned Method of Implementation
It was originally planned that the device would drive all three LED’s individually,
allowing for individual power management on each LED along with the ability to turn on
or off each LED and allow for individual dimming on each Luxeon. This however came
to grief as it was discovered that the chosen micro-controller had difficulty in performing
this task with numerous problems occurring and a lot of time being spent trying to rectify
these problems. It became apparent that this problem could not be rectified in time and it
was decided that the LED’s could not be driven individually as originally planned. This
meant that the Luxeon’s now had to be driven in series or in parallel. It was chosen to be
powered in series as the designed circuit could easily facilitate the means of doing so.ഊTrying to drive the LED’s in parallel would mean major changes in the device and it was
not practical to do such major changes.
4.3 Summary
This chapter has detailed how the project was originally planned and how these plans
changed and adapted as the project progressed. Chapter 5 will discuss the hardware
implementation, such that it will meet the specifications which were stated in chapter 3. 23
Chapter 5 – Hardware Implementation
This chapter includes the details of how the hardware was implemented within this thesis.
With the hardware specification already derived in the chapter 3, components to satisfy
the criteria are selected with possible component alternatives also noted.
5.1 Power Supply
A key device specification is that it has to operate from 12VDC or from 230VAC. This
specification was satisfied by first designing the device to be operated exclusively from
12VDC and then designing an adapter that will produce 12VDC from 230VAC. This
section details how this plan was implemented.
5.1.1 Operation from 12V
As the device was to be a step-down converter, much of the converter circuitry could be
easily run off the 12V supply rail as the output of the converter was approximately 10V,
easily achieved by a buck converter. The micro-controller (MCU), however, was limited
to a 2.7V – 5.5V operating range and a suitable regulator was required to supply 5V to
the micro-controller. A switch-mode step down regulator chip was chosen to perform the
task of supplying 5V to the MCU with the component being the LM2594HV-5, available
from National Semiconductors.ഊ24
Figure 11: 12V to 5V step-down converter to power the MCU
Alternative components that could have been used include using the standard 7805 linear
regulator or other switch-mode regulators such as the LM2574HV-5, LM2671-5. The
LM2594HV-5 chip was chosen because of the high efficiency and low component count
of the circuit required, only 2 more components than a linear regulator. It was also
chosen above the other switch-mode regulators for two reasons; it has a high input
voltage (maximum of 60V) as designated by the “HV” tag in the product number which
the LM2671-5 does not, and it has a higher switching frequency than the LM2574HV-5
which allows for a smaller inductor.
Figure 12: LM2594HV-5 Step-Down Converterഊ25
5.1.2 Operation from 230VAC
The 230VAC to 12VDC adapter was originally planned as a high-voltage step-down
flyback converter using the Power Integration TOPSWITCH-GX series of switch-mode
regulators. However, due to time restrictions and difficulty in obtaining these switch-mode
regulators, the adapter design was simplified down to using a standard step-down
transform. The adapter that was obtained was a 230VAC/12VAC 12VA rated
transformer, with the secondary side comprising of two 12V windings rated at 410mA
each. This transformer was used in conjunction with a full bridge diode rectifier in order
to regulate 230VAC into approximately 15VDC.
Figure 13: 230VAC to 12VDC Adapter Schematic
Figure 14: 230VAC to 12VDC Adapterഊ26
5.2 Micro-Controller
There are a number of micro-controller chips that could have been chosen which would
have satisfied the required specifications, and the chip that was chosen was the
ATmega8L from Atmel. Some of the key features of this MCU were the six analogue-to-digital
(ADC) channels, twenty-three input/output (I/O) pins and three PWM channels
with a frequency of up to 31.25 kHz, which would allow for individual LED power
management. Other features of this chip are that it operates up to 8MHz, low power
consumption and a supply voltage requirement of 2.7V – 5.5V. The plastic dual in-line
package (PDIP) version was chosen as it is easily implemented into circuit boards and
testing boards as opposed to the MicroLeadFrame (MLF) version. Possible alternative
MCU’s are the ATmega8535, AT90S8535 or the ATmega16.
Figure 15: Pin Configuration of the ATmega8Lഊ27
Figure 16: ATmega8L Micro-Controller
5.3 Power Electronics
The bulk of the device, being the power electronics is comprised of three buck
converters, each being a ‘channel’ as each channel is being controlled by one of the
PWM channels from the MCU. Each buck converter channel comprises of a P-channel
MOSFET acting as the switch, an inductor, a fast recovery diode and a capacitor. An
NPN BJT acts as the gate driver/buffer between the MCU and the MOSFET. Extra
components include pull-up and pull-down resistors for the BJT and MOSFET as well as
a small capacitor used to boost the switching of the BJT.
Figure 17: A Single Buck Converter Channelഊ28
5.3.1 MOSFET and BJT Selection
A P-channel MOSFET was chosen as this would allow high-side switching, that is,
switching on the high voltage side (with respect to ground) of the converter. This
allowed the simple current sensing and software implementation. The MTP2955V was
chosen as it was already ‘on-hand’ and thus allowed for rapid circuit experimentation.
The MOSFET is rated to 12A and has a Vgs max of 25V. This would allow this converter
to operate at much higher loads (more LED’s) if needed. A number of P-channel
MOSFETS could be used in place of this particular one.
The NPN BJT could also be any generic switching NPN transistor and the MPS651 was
chosen as it, like the MTP2955V, was already ‘on-hand’. This BJT has a switching
frequency of up to 65 kHz, when used in conjunction with a boost capacitor and resistor
as per Figure 14. Alternatives to this BJT would be any small signal NPN transistor with
a switching frequency of greater that 32 kHz. The BC546-549 series is a better
alternative as it has a much higher switching frequency.
5.3.1.1 Switch Operation
The P-channel MOSFET acts as a switch in the buck converter operates in the following
process, when a high signal is generated from the PWM channel on the MCU, it turns on
the BJT. While this BJT is on, it’s collector pin becomes low (approximately 0.3V), and
as it is connected to the gate on the MOSFET, the MOSFET also turns on which allows
current to flow through it as it is acting as a switch. The resistor, R4 in the diagram, act
as a pull up resistor for the gate of the MOSFET and also as a collector current limiting
resistor for the BJT. Resistor R13 acts as a current limiting resistor into the base of the
BJT such that it does not draw an excessive amount of current out of the MCU such that
it does not damage it. Resistor R5 also aids in the BJT base current limiting process and
it also acts as a pull-down resistor on the BJT. Capacitor C8 aids in the switching of the
BJT as it speeds the switching characteristics of the BJT.ഊ29
5.3.2 Inductor Selection
The inductor value was chosen at 390µH as it was the largest value inductance with the
current rating of 450mA which is suitable for the Luxeon LED’s. This inductor was also
chosen as it was a through-hole type inductor. The maximum current ripple in the
inductor occurs when only one LED is connected to the output of the buck converter
channel, and when using equation (2.2)
L o s I = V/L (1 - D) T ∆
o V =3.5V, L = 390µH, D = 29.16% and s T = 31.25µs
When using the above values with equation (2.2) the current ripple is calculated to be
198mA which equates to a maximum current of approximately 450mA. Another suitable
inductor value is 330µH, and when using equation (2.2) again, the current ripple is
calculated to be 235mA and the maximum current equates to 467mA.
5.3.3 Capacitor Selection
The capacitor was chosen to be 220uH as it was large enough to ensure that there was
little voltage ripple seen at the load. The voltage ripple was calculated using equation
(2.3)
L s I T Vo = 8C
∆∆
L I ∆= 198mA, s T = 31.25µs and C = 220µF
When using the above values into equation (2.3) the output voltage ripple is calculated to
be 0.0035V.ഊ30
Alternative capacitors could be used, ensuring that the capacitance is large enough to
ensure a small output voltage ripple.
5.3.4 Diode Selection
The 1N4937 ultra-fast recovery diode was chosen as it was easily sourced and had a
reverse recovery time of less than the switch on time. The reverse recovery time is
necessary to be less than the switch on time, as to ensure low power losses in the circuit.
Alternative components would be any schottky diode with a current rating greater than
500mA and a voltage rating of greater than 25V. Typical schottky diodes include the
80SQ045N and MBR1060-MBR10100.
Figure 18: Three Buck Converter Channels
5.4 Luxeon LED’s
In order to give current feedback to the MCU, it was necessary to place a 1 Ω resistor in
series with the Luxeon LED’s. The voltage across that resistor is then measured by an
ADC pin on the MCU which then calculates the amount of current flowing through the
Luxeon LED. A 1 Ω resistor was chosen as smaller values led to instability within the
control of the circuit, particularly when the Luxeon LED’s were chosen to be run at theഊ31
low output power level, and values larger than 1 Ω led to higher power losses across it
and a lower circuit efficiency.
As the Luxeon LED’s were already given, the only other hardware that was required for
them was protection circuitry against voltage and current surges. Current surge
protection was implemented through the use of a 500mA fast blow fuse. Voltage
protection was implemented by the use of an 18V zener diode and another BJT. The
voltage protection works in the following method; if the voltage becomes greater than the
zener voltage, the diode allows current to flow through it, this current then turns on the
BJT as the diode is connected to the base of the BJT. This BJT has it’s collector is also
connected to the output voltage rail and when it turns on, it allows a surge current to flow
through it, which activates the current surge protection and blows the fuse.
Figure 19: Voltage and Current Protection Circuitryഊ32
Figure 20: Fuse Housing with Zener Diode and BJT
5.5 User Input/Output
To facilitate a means of allowing user input and output (I/O) into the controller, and to
provide some feedback on driver operation, a smaller ‘daughter’ board was designed for
this specific purpose. This daughter board connected exclusively to Port D on the MCU,
and provided for six input lines and 2 output lines. The input lines were connected to
three switches, each of the switches being able to set two input pins on the MCU to either
high or low voltage levels. The output lines connected to small LED’s and another LED
is present to indicate whether the device is on or off. The daughter board is then
connected to the main circuit board through a 10-wire ribbon cable. The schematic for
the daughter board is attached in Appendix A.ഊ33
Figure 21: Daughter Board for User Input and Output
5.6 Schematics and Printed Circuit Board Design
The schematics and printed circuit board design (PCB) were developed using the
specialized software, Protel 99 SE. The schematics for the device are available in
Appendix A, and the PCB diagrams are available in Appendix B.
5.6.1 PCB Layout Considerations
As the bulk of the device is made up of three switch-mode converters, the placement of
components is important. The high speed, switching paths within the buck converter
must be kept as sort as possible such that inductances caused by the switching do not
cause problems within the circuit and lead to lower efficiency.
With this consideration in mind, the PCB was designed such that the buck converter
components were kept as close together as possible. The three buck converter channels
placed in parallel to each other and also placed, in conjunction with the MCU, such that
the PWM signal tracks from the MCU were also kept reasonably close and that there wasഊ34
a minimum number of vias along those signal paths. Smaller switches were also placed
in the PWM signal path, such that it would allow in-system programming (ISP) of the
MCU. These switches were needed as a PWM pin on the MCU was also a programming
pin. The switch would then allow the power electronics subsystem to become isolated
from the MCU during programming. If the power electronics subsystem was not isolated
during programming, the switches in the buck converter would turn on, and high currents
and voltages would occur at the load as the buck converter is no longer controlled. Along
with the PWM isolation switches, another 10 pin socket is needed for the programming
connection. With ISP available, software upgrades to the device is possible with great
ease.
Figure 22: Isolation Switches and Programming Connection
Another consideration is that the track widths on the PCB for the power electronics must
be wide enough to carry the current to and from the Luxeon LED’s. The track widths
within the power electronics sections were set to 1.5mm, while the rest of the circuitry
having 0.7mm track widths.ഊFigure 23: Final PCB
5.7 Summary
This chapter has detailed how the device hardware was implemented. The selection of
major components and possible alternatives were also contained within this chapter. The
next chapter details how the device software was implemented. 36
Chapter 6 – Software Implementation
This chapter discusses how the software for this thesis was implemented into the device.
The process undertaken to reach a software solution which meets the specifications which
were outlined in Chapter 3 is described in this Chapter.
6.1 Software Development
The software for the LED driver was developed with the aid of CodeVisionAVR, which
is a program that allows the user to write and compile C programs for the Atmel AVR
range of micro-controllers. It also allows for in-system programming thus making an
ideal software development tool.
6.1.1 Software Basics
The first task that was taken was to make an ordinary LED flash. This relatively simple
task was achieved by toggling an I/O pin on the MCU to either high or low. Although
this task may seem trivial, it ensured that the basics of simple programming and using
CodeVisionAVR and the Mega8L MCU were learnt.
6.1.2 Generating PWM Signals
The next task that was undertaken was to generate a PWM signal out of the MCU. This
task was completed by using the code generation wizard within CodeVisionAVR, aptly
named CodeWizardAVR. This allowed for simple enabling of PWM outputs. To enable
PWM signals, Timer 1 and Timer 2 need to be enabled, with the system clock selected as
the clock source and also set to 8 MHz as the crystal oscillator on the MCU is 8 MHz.
The next option to select was the mode of the timer, and to generate PWM signals, thereഊ37
are two options; Phase Correct PWM or Fast PWM. Fast PWM was chosen as it will
generate a PWM signal at 31.25 kHz, whist Phase Correct PWM produces PWM signals
at 16.16 kHz. At 16.16 kHz, the switching of the MOSFET’s in the circuit could be
heard as a constant ringing tone, thus Fast PWM was chosen to avoid this annoyance.
Non-inverted PWM signals were also chosen, but inverted PWM could also be used, it
would only be a matter of slightly altering the control code later on in order to produce
the same results. Figure 23, below, shows the CodeWizardAVR window within
CodeVisionAVR.
Figure 24: CodeWizardAVR Window Showing PWM Options
With the option to enable PWM generation set, the next step needed to generate PWM
signals is to set the value of the duty. This is done by setting a value to the PWM
registers, the registers being; OCR1A, OCR1B and OCR2. These registers correspond to
the pins as marked in Figure 15. The duty cycle of the PWM then corresponds to aഊ38
percentage, represented as a hex number, of 256 (FF). For example, a 50% duty cycle
corresponds to the value 80 in hex (50% of 256 is 128 which equals 80 in hex.).
6.1.3 Enabling Analogue to Digital Conversion
Enabling the ADC is needed for use in the control functions of the device. Using the
ADC is also made simpler by using CodeWizardAVR. As the voltage across the 1 Ω
sense resistor is small, a smaller reference voltage is more ideal as this will enable more
accuracy when measuring the voltage across that sense resistor. Enabling ADC on the
MCU is achieved by ticking the ADC Enabled selection in CodeWizardAVR, and then
select the voltage reference as the voltage across the AREF pin. CodeWizardAVR also
gives an option for the ADC speed, and in this case it was chosen to be the fastest
available, that being 125 kHz.
Figure 25: CodeWizardAVR Window Showing ADC Optionsഊ39
6.2 Software Design
Once the basics of using CodeVisionAVR and the MCU had been learnt, the design of
the software was fairly straight forward. From the software specifications from Chapter
3, all three of the software subsystems can be integrated into a main software flowchart
diagram. Figure 25 shows the software flowchart that was designed in order to satisfy the
requirements of the software specifications.ഊ40
Figure 26: Main Software Flowchart Diagram
The main module of the software is an infinite loop. The task of checking for user input
is performed every time the loop is enacted. Once it has detected that there is user desire
to turn on the Luxeon LED’s, it then reads user input again to decide whether or not the
No
Start
Initialise
Start Main
Loop
Read user
input
Turn on
LED’s?
High Power
Setting?
Yes
Initialise Low
Power Mode
Initialise High
Power Mode
Read user
inputഊ41
user wishes to use the LED’s in high power or low power. After it has decided which
mode of operation it is required to be in, it then initialises that mode of operation.
The high power and low power modes of operation work in the same manner, the only
difference being the set point level across the sense resistor that it is trying to maintain.
Figure 26 shows the software flowchart for the power mode control.
Figure 27: Power Mode Control Flowchart Diagram
The power mode control subsystem is also an infinite loop. It operates by reading the
ADC channel and then increasing or decreasing the duty cycle of the PWM channel that
corresponds to the buck converter channel that the ADC pin is connected to. This way it
is constantly adjusting the circuit such that it is always running at the power mode that it
is set to.
Start
Read ADC
Is ADC higher
than setpoint?
Increase PWM
duty cycle
No
Decrease PWM
duty cycle
Yesഊ42
6.3 Final Code
The final code which is implemented into the device, is available in Appendix C.
6.4 Summary
This chapter has detailed the software implementation into the Luxeon LED driver.
Chapter 7 moves on and evaluates the final product against the specifications which were
derived in Chapter 3. 43
Chapter 7 – Product Evaluation
The objective of this thesis was to design a driver which can drive up to three Luxeon
LED’s from both 12VDC and 230VAC. The LED’s also needed to be protected from
voltage surges and be run at the optimum current of 350mA.
The device which was designed and implemented fulfills these criteria. It can drive up to
three LED’s in series at their optimum current of 350mA, and also protects them from
both voltage and current surges. It is designed to be run from 12VDC and, with an
adapter, from 230VAC. On this basis, the product has met the required specifications.
This chapter is more in-depth examination of the quality of the final product by
comparing it to the derived design specifications in Chapter 3. This chapter also analyses
the performance of the author as an engineer.
7.1 Evaluation of the device Against the Specifications of
Chapter 3
This section evaluates the device against the derived product specifications of Chapter 3.
Both a brief and detailed evaluation has been completed.
7.1.1 Quick Checklist of Device Against the Specifications
Briefly reiterating the specifications of Chapter 3, the device must:
Be able to operate from 12VDC and 230VAC
Protect the Luxeon LED’s from voltage and current surges
Provide a means of user input and output.ഊ44
Power the LED’s from their optimal current of 350mA, regardless of the variable
forward voltage across the LED’s.
The switch-mode step-down converter able to operate at the PWM switching
frequency signal from the MCU.
Be controlled by a MCU which is fast enough and has enough memory to carry
out all required tasks.
7.1.2 Detailed Checklist of the Device Against the Specifications
The device must be able to operate from 12VDC or 230VAC.
The final product is able to operate from 12VDC and 230VAC. The device was designed
to be powered from 12VDC, and it satisfies the 230VAC requirement by the means of a
step-down adapter which converts 230VAC to 12VDC. The device also goes to exceed
the requirement of being able to be run from 12VDC by it being able to operate from a
variable DC input voltage, up to a maximum of 25VDC.
Protect the Luxeon LED’s from voltage and current surges.
The Luxeon LED’s are protected from voltage and current surges by a combination of
fuses, zener diodes and BJT’s. The entire device is also protected from such voltage and
current surges by using another combination of fuses and zener diodes on the input
supply of the device.ഊ45
Provide a means of user input and output.
User input into the device has been implemented by the use of a three three-pole
switches, each of which can toggle two I/O pins on the MCU to either high or low
voltages. User output from the device has been implemented by the use of 3 small
LED’s, one of which displays whether the device is powered or not and another one
which flashes three times upon start-up or reset. The last LED has not been used for any
specific purpose at this point in time. This specification has been exceeded as the means
of user input and output into the device can be changed by designing another daughter
board which can connect to the same connector on the device.
Power the LED’s at their optimum current of 350mA, regardless of the variable
forward voltage across the LED’s.
The device drives the LED’s at their optimum current of 350mA regardless of the
forward voltage across the LED’s as it calculates the current flowing through them by
measuring the voltage across a series sense resistor. As the voltage across the resistor
will be constant at 350mA, the device aims to achieve at providing a constant voltage
across the sense resistor (and hence a constant current) by constantly increasing and
decreasing the switching frequency of the buck converter.
The switch-mode step-down converter able to operate at the PWM switching
frequency signal from the MCU.
The switch-mode step-down converter is able to operate at the maximum PWM switching
frequency signal from the MCU, that being 31.25 kHz. Upon testing of the buck
converter, it is seen that the maximum frequency that it can operate from is
approximately 60 kHz.ഊ46
Be controlled by a MCU which is fast enough and has enough memory to carry
out all required tasks
The MCU in the device, being an Atmel ATmega8L running at a clock frequency of 8
MHz is fast enough to carry out all required tasks. This MCU also has enough memory
to store the main program and enough memory for swap space information. A feature of
the MCU is that it is able to be reprogrammed whilst still in the system, so that if a better
way of using the current hardware, or if a different daughter board is designed, new
software can be easily programmed into the MCU.
Figure 28: Final Product
7.2 Device Efficiency
The efficiency of the device in powering the Luxeon LED’s has been calculated by
measuring the input power and then measuring the power which is being delivered to the
Luxeon LED’s. Measuring the actual efficiency of converting input power to actual light
output power has not been conducted as it would require specialist equipment that is not
available at this point in time. In terms of general light output from the system, each
Luxeon LED has been measured with a simple light meter and has been found to outputഊ47
approximately 150 Lux, or 15 Candela. All three LED’s then combine to produce around
450 Lux, which is enough light for reading and studying activities 1 .
A number of tests have been conducted in order to determine the efficiency of the device.
The differences between tests included: whether the daughter board was connected or
not, high output power or low output power, or if the device was powered from 12VDC
or 230VAC. With regard to testing from 230VAC, the full input power was unable to be
determined without using complex testing procedures, so the input power into the device
was measured as the output power from the adapter. The efficiency of the 230VAC to
12VDC adapter has not been calculated.
The following is a list of tables and graphs and the manner in which the device was
tested. Table 3 and Figure 27 are the results when the device was tested from an input
supply of 12VDC, with the daughter board connected. Table 4 and Figure 28 are the
results when the device was tested from an input supply of 12VDC, without the daughter
board and the LED power setting at high power. Table 5 and Figure 29 are results when
the device was tested from an input supply of 12VDC, without the daughter board and the
LED power setting at low power. And, Table 6 and Figure 30 represent the efficiency
results when the device is powered from 230VAC, with the daughter board attached.
Complete detailed tables and figures are available in Appendix D.
LED Configuration and Power Setting P in P out Efficiency (%)
Single LED, Low Power Setting 0.720 0.252 34.94
Single LED, High Power Setting 2.256 1.187 52.60
Dual LED\'s, Low Power Setting 0.996 0.546 54.87
Dual LED\'s, High Power Setting 3.060 2.128 69.54
Three LED\'s, Low Power Setting 1.308 0.836 63.89
Three LED\'s, High Power Setting 4.320 3.567 82.56
Table 3: Efficiency at 12VDC Input and Daughter Board Connected
1 Approximately 500 Lux is recommended for reading and studying tasks. Source: School Lighting Design
Guide.ഊ48
34.94%
52.60% 54.87%
69.54%
63.89%
82.56%
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
Efficiency (%)
Single LED,
Low Power
Setting
Single LED,
High Power
Setting
Dual LED\'s,
Low Power
Setting
Dual LED\'s,
High Power
Setting
Three LED\'s,
Low Power
Setting
Three LED\'s,
High Power
Setting
LED Configuration
Figure 29: Efficiency at 12VDC Input and Daughter Board Connected
LED Configuration P in P out (total) Efficiency (%)
Single LED, Single Channel 1.710 1.069 62.50
Dual LEDs, Dual Channels 3.150 2.144 68.06
Dual LEDs, Single Channel 2.745 2.174 79.19
Three LEDs, Dual Channels (2 in series on one channel + 1) 4.230 3.119 73.73
Three LEDs, Single Channel 3.624 3.146 86.80
Table 4: Efficiency at 12VDC Input, No Daughter Board Connected at High Power
Outputഊ49
62.50%
68.06%
79.19%
73.73%
86.80%
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
Efficiency (%)
Single LED, Single
Channel
Dual LEDs, Dual
Channels
Dual LEDs, Single
Channel
Three LEDs, Dual
Channels (2 in
series on one
channel + 1 on
another channel)
Three LEDs, Single
Channel
LED Configuration
Figure 30: Efficiency at 12VDC Input, No Daughter Board Connected at High
Power Output
LED Configuration P in P out (2) P out (total) Efficiency (%)
Single LED, Single Channel 0.540 0.000 0.252 46.59
Dual LEDs, Dual Channels 0.873 0.243 0.485 55.51
Dual LEDs, Single Channel 0.804 0.000 0.496 61.63
Three LEDs, Dual Channels (2 in series on one channel + 1) 1.152 0.243 0.713 61.87
Three LEDs, Single Channel 1.044 0.000 0.712 68.20
Table 5: Efficiency at 12VDC Input, No Daughter Board at Low Power Outputഊ50
46.59%
55.51%
61.63% 61.87%
68.20%
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
Efficiency (%)
Single LED, Single
Channel
Dual LEDs, Dual
Channels
Dual LEDs, Single
Channel
Three LEDs, Dual
Channels (2 in series
on one channel + 1 on
another channel)
Three LEDs, Single
Channel
LED Configuration
Figure 31: Efficiency at 12VDC Input, No Daughter Board Connected at Low
Power Output
LED Configuration and Power Setting P in P out Efficiency
Three LED\'s, High Power 4.364 3.197 73.25
Three LED\'s, Low Power 1.374 0.788 57.30
Dual LED\'s, High Power 3.208 2.248 70.08
Dual LED\'s, Low Power 1.094 0.526 48.10
Single LED, High Power 2.818 1.183 41.99
Single LED, Low Power 0.814 0.270 33.21
Table 6: Efficiency at 230VAC Input and Daughter Board Connectedഊ51
73.25%
57.30%
70.08%
48.10%
41.99%
33.21%
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
Efficiency(%)
Three LED\'s, High
Power
Three LED\'s, Low
Power
Dual LED\'s, High Power
Dual LED\'s, Low Power
Single LED, High Power
Single LED, Low Power
LED Configuration
Figure 32: Efficiency at 230VAC Input and Daughter Board Connected
It can be seen that the device operates at the highest efficiency when it is driving three
Luxeon LED’s. It is seen that the highest efficiency, at 87%, was achieved when three
LED’s were being driven from an input supply of 12VDC and there was no daughter
board connected to the device. It is also seen that the lowest efficiency, at 33%, was
observed when the device was being operated from a 230VAC input supply and driving
only a single Luxeon LED.ഊ7.3 Evaluation of the Author’s Performance as an Engineer
One of the biggest personal challenges that can be undertaken at university is the
development of a thesis project. It is a journey which can offer great insights into an
individual’s engineering strengths and weaknesses. One of the major weaknesses of the
author was time management as it was seen that the author grossly underestimated the
amount of time needed for this project and, as such, spent an awful amount of time
towards the end on the project in order to complete it. This is a weakness that the author
is now aware of and as such, can better plan any future projects of this nature. The author
also did have the wrong approach into tackling this problem (trying to drive each LED
individually) and it was fortunate that this method did not work as the device was found
to be highly inefficient when powering only single LED’s. For the most part of the
project, the author did work with direction and undertook all of the necessary tasks which
were needed in order to complete this project.
Whilst completing this project, the author has learnt a number of things. He has learnt
how to identify possible problems within circuits and when constructing PCB’s and how
to minimize these errors. He has become proficient in the use of the development
software, in particular, Protel 99SE and CodeVisionAVR.
The most important lesson that has been learnt by the author is that planning is the most
important step when undertaking any project. Planning coupled with proper time
management and good engineering skills will produce quality solutions to given
problems. 请翻译整理一下，不要光发些鸟语，毕竟坛子里的兄弟不都是这方面的高手。 55
Chapter 9 – Conclusion
9.1 What was set to Achieve?
The aim of this thesis was to design a device which could drive up to three Luxeon
LED’s from an input supply of either 12VDC or 230VAC. This would help to achieve
the goals of LUTW and it’s aim in providing people in developing countries with access
to clean and efficient lighting.
9.2 What was Achieved?
The final device managed to achieve the following results:
Operates from either 12-25VDC or from 230VAC with the adapter.
Protects the Luxeon LED’s from voltage and current surges. The device is also
protected from voltage and current surges.
User input and output has been achieved by using switches and small signaling
LED’s.
The Luxeon LED’s are driven at their optimal current of 350mA, regardless of the
variable forward voltage across the LED’s. The Luxeon LED’s can also be driven
at a lower current of 100mA.
A switch-mode step-down converter that is able to operate at the PWM switching
frequency signal from the MCU. The maximum switching frequency that the
buck converter can operate at is 60 kHz.ഊ56
The device is controlled by an Atmel ATmega8L which is fast enough and has
enough memory to carry out all required tasks.
Provides a means of upgrading the onboard software, along with provision for a
changeable daughter board.
The entire design has a very high power efficiency.
It can be seen from the above points, that the device has fulfilled the requirements and
specifications that was placed upon it and has also gone some way in having additional
features that would serve it as an excellent device.
This device demonstrates that engineering is an interesting and exciting field which can
help to benefit countless people in other parts of the world.ഊ57
Bibliography
1. Light Up The World, <a href="http://www.lutw.org/" target="_blank" >http://www.lutw.org/</A>, Accessed 20 September, 2003.
2. Lumens, Footcandles, Candlepower, Measuring Light Output,
<a href="http://www.theledlight.com/lumens.html" target="_blank" >http://www.theledlight.com/lumens.html</A>, Accessed 14 March 2003.
3. Metric to Imperial Conversion, <a href="http://metric.fsworld.co.uk" target="_blank" >http://metric.fsworld.co.uk</A>, Accessed 14 March
2003.
4. Speleogroup, LED Caving Lamps, <a href="http://www.speleogroup.org" target="_blank" >http://www.speleogroup.org</A>, Accessed 29 June
2003.
5. Luxeon Technical Datasheet DS23 “Luxeon Star”, Lumileds Lighting
<a href="http://www.lumileds.com" target="_blank" >http://www.lumileds.com</A>, 2002.
6. Luxeon Technical Datasheet DS25 “Luxeon Emitter”, Lumileds Lighting
<a href="http://www.lumileds.com" target="_blank" >http://www.lumileds.com</A>, 2002.
7. Luxeon Application Brief AB 07 “Lumen Maintenance of White Luxeon Power
Light Sources”, Lumileds Lighting <a href="http://www.lumileds.com" target="_blank" >http://www.lumileds.com</A>, 2002.
8. Luxeon Star, “Xitanium Drivers”, <a href="http://www.luxeonstar.com/xitanium-driver" target="_blank" >http://www.luxeonstar.com/xitanium-driver</A>.
html, Accessed September 16, 2003.
9. Mohan, Underland and Robbins, “Power Electronics: Converters, Applications
and Design”, Wiley and Sons INC, 1995
10. R.W Erickson, “Fundamentals of Power Electronics”, Kluewer Academic
Publishers, 1999.ഊ58
11. LM2594/LM2594HV Datasheet “Simple Switcher Power Converter”, National
Semiconductor, 1999. <a href="http://www.national.com" target="_blank" >http://www.national.com</A>
12. “Atmel AVR ATmega8 Datasheet”, 2486J-AVR-02/03 ed: Atmel Corporation,
2003.
13. HP Infotech. CodvisionAVR. 2003 (v1.23.8.c),
<a href="http://www.hpinfotech.ro/html/cvavr.htm" target="_blank" >http://www.hpinfotech.ro/html/cvavr.htm</A>
14. John F. Wakerly, “Digital Design”, Prentic Hall, 2001.ഊReferences
Luxeon Technical Datasheet DS23 “Luxeon Star”, pages 1-3, and Technical
Datasheet DS25 “Luxeon Emitter”, page 1.
<a href="http://www.lumileds.com" target="_blank" >http://www.lumileds.com</A>
Luxeon Application Brief AB 07 “Lumen Maintenance of White Luxeon Power
Light Sources”, page 4.
<a href="http://www.lumileds.com" target="_blank" >http://www.lumileds.com</A>
Mohan, Underland and Robbins, “Power Electronics: Converters, Applications
and Design”, page 165.
Mohan, Underland and Robbins, “Power Electronics: Converters, Applications
and Design”, page 166.
Luxeon Star, “Xitanium Drivers”, accessed September 16, 2003.
<a href="http://www.luxeonstar.com/xitanium-driver.html" target="_blank" >http://www.luxeonstar.com/xitanium-driver.html</A>
LumiDrives, “Microdriver™ 3 LED Power Driver”, accessed October 04, 2003.
<a href="http://www.lumidrives.com/content/products/microdriver3.htm" target="_blank" >http://www.lumidrives.com/content/products/microdriver3.htm</A>
LumiDrives, “MicroV9™ Low Voltage LED Power Driver”, accessed October
04, 2003. <a href="http://www.lumidrives.com/content/products/microlv9.htm" target="_blank" >http://www.lumidrives.com/content/products/microlv9.htm</A>
LED Supply, “PowerPuck 12V 5W 700mA LED Drive Module”, accessed
October 04, 2003. <a href="http://www.ledsupply.com/02008a.html" target="_blank" >http://www.ledsupply.com/02008a.html</A> 另外还有原理图，pcb等，详细的框图，没办法搞上来，有需要的朋友跟帖，或发pm给我qq（非要我在线才能传）号或邮箱（现在邮箱不一定收的到） 69
Appendix C – Software Code
/*********************************************
This program was produced by the
CodeWizardAVR V1.23.8c Evaluation
Automatic Program Generator
© Copyright 1998-2003 HP InfoTech s.r.l.
<a href="http://www.hpinfotech.ro" target="_blank" >http://www.hpinfotech.ro</A>
<a href="mailte-mail:office@hpinfotech.ro" target="_blank" >e-mail:office@hpinfotech.ro</A>
Project :
Version :
Date : 19/09/2003
Author : Freeware, for non-commercial use only
Company :
Comments:
Chip type : ATmega8L
Program type : Application
Clock frequency : 8.000000 MHz
Memory model : Small
External SRAM size : 0
Data Stack size : 256
*********************************************/
#include <mega8.h>
#include <delay.h>
// The set point (as a percentage)
#define FULL_POWER_SET_POINT 35
#define HALF_POWER_SET_POINT 10
// The maximum PWM values for each channel
#define MAX_CHANNEL1 0xFF
#define MAX_CHANNEL2 0xFF
#define MAX_CHANNEL3 0xFF
// Controls for the set point
<a>file://volatile</A> long set_point = FULL_POWER_SET_POINT;
<a>file://int</A> full = 1;
// External Interrupt 0 service routine
interrupt void ext_int0_isr(void)ഊ70
{
/*if (full)
{
set_point = HALF_POWER_SET_POINT;
full = 0;
}
else
{
set_point = FULL_POWER_SET_POINT;
full = 1;
}*/
}
#define ADC_VREF_TYPE 0x00
// Read the AD conversion result
unsigned int read_adc(unsigned char adc_input)
{
ADMUX=adc_input|ADC_VREF_TYPE;
// Start the AD conversion
ADCSRA|=0x40;
// Wait for the AD conversion to complete
while ((ADCSRA & 0x10)==0);
ADCSRA|=0x10;
return ADCW;
}
// Declare your global variables here
void main(void)
{
// Variables used to store the channel readings
/*int channel1;
int channel2;
int channel3; */
// Used to store the calculated set point value
<a>file://int</A> set_point_check;
// Input/Output Ports initialization
// Port B initialization
// Func0=In Func1=Out Func2=Out Func3=Out Func4=In Func5=In Func6=In Func7=In
// State0=T State1=0 State2=0 State3=0 State4=T State5=T State6=T State7=T
PORTB=0x00;
DDRB=0x0E;
// Port C initialization
// Func0=In Func1=In Func2=In Func3=In Func4=In Func5=In Func6=Inഊ71
// State0=T State1=T State2=T State3=T State4=T State5=T State6=T
PORTC=0x00;
DDRC=0x00;
// Port D initialization
// Func0=In Func1=In Func2=In Func3=In Func4=In Func5=In Func6=In Func7=In
// State0=T State1=T State2=T State3=T State4=T State5=T State6=T State7=T
PORTD=0x00;
DDRD=0xC0;
// Timer/Counter 0 initialization
// Clock source: System Clock
// Clock value: Timer 0 Stopped
TCCR0=0x00;
TCNT0=0x00;
// Timer/Counter 1 initialization
// Clock source: System Clock
// Clock value: 8000.000 kHz
// Mode: Fast PWM top=00FFh
// OC1A output: Non-Inv.
// OC1B output: Non-Inv.
// Noise Canceler: Off
// Input Capture on Falling Edge
TCCR1A=0x00;
TCCR1B=0x00;
TCNT1H=0x00;
TCNT1L=0x00;
OCR1AH=0x00;
OCR1AL=0x00;
OCR1BH=0x00;
OCR1BL=0x00;
// Timer/Counter 2 initialization
// Clock source: System Clock
// Clock value: 8000.000 kHz
// Mode: Fast PWM top=FFh
// OC2 output: Non-Inverted PWM
ASSR=0x00;
TCCR2=0x00;
TCNT2=0x00;
OCR2=0x00;
// External Interrupt(s) initialization
// INT0: On
// INT0 Mode: Falling Edge
// INT1: Offഊ72
GICR|=0x40;
MCUCR=0x02;
GIFR=0x40;
// Timer(s)/Counter(s) Interrupt(s) initialization
TIMSK=0x00;
// Analog Comparator initialization
// Analog Comparator: Off
// Analog Comparator Input Capture by Timer/Counter 1: Off
// Analog Comparator Output: Off
ACSR=0x80;
SFIOR=0x00;
// ADC initialization
// ADC Clock frequency: 125.000 kHz
// ADC Voltage Reference: AREF pin
// ADC High Speed Mode: Off
// ADC Auto Trigger Source: None
ADMUX=ADC_VREF_TYPE;
ADCSRA=0x86;
SFIOR&=0xEF;
// Global enable interrupts
#asm("sei")
PORTD.6=1;
delay_ms (200);
PORTD.6=0;
delay_ms (200);
PORTD.6=1;
delay_ms (200);
PORTD.6=0;
delay_ms (200);
PORTD.6=1;
delay_ms (200);
PORTD.6=0;
delay_ms (200);
while (1)
{
<a>file://set_point_check</A> = 1024*set_point/100;
<a>file://channel1</A> = read_adc(0);
if (PIND.3)
{ഊ73
TCCR1A=0xA1;
if (read_adc(0) < (1024*FULL_POWER_SET_POINT/100))
{
++OCR1A;
}
else if (read_adc(0) > (1024*FULL_POWER_SET_POINT/100))
{
--OCR1A;
}
}
else if (PIND.2)
{
TCCR1A=0xA1;
if (read_adc(0) < (1024*HALF_POWER_SET_POINT/100))
{
++OCR1A;
}
else if (read_adc(0) > (1024*HALF_POWER_SET_POINT/100))
{
--OCR1A;
}
}
else
{
TCCR1A=0x00;
OCR1A = 0x00;
}
<a>file://channel2</A> = read_adc(1);
/*if (read_adc(1) < (1024*35/100))
{
<a>file://if</A> (OCR1B < MAX_CHANNEL2) // Don\'t overflow
++OCR1B;
}
else if (read_adc(1) > (1024*35/100))
{
<a>file://if</A> (OCR1B > 1) // Don\'t overflow
--OCR1B;
}*/
<a>file://channel3</A> = read_adc(2);
if (PIND.5 == 1)
{
TCCR2=0x69;
if (read_adc(2) < (1024*FULL_POWER_SET_POINT/100))
{
++OCR2;ഊ}
else if (read_adc(2) > (1024*FULL_POWER_SET_POINT/100))
{
--OCR2;
}
}
else if (PIND.4 == 1)
{
TCCR2=0x69;
if (read_adc(2) < (1024*HALF_POWER_SET_POINT/100))
{
++OCR2;
}
else if (read_adc(2) > (1024*HALF_POWER_SET_POINT/100))
{
--OCR2;
}
}
else
{
TCCR2=0x00;
OCR2 = 0x00;
}
};
} 75
Appendix D – Efficiency Resultsഊ76
LED Configuration and Power Setting
V in
(Volts)
I in
(Amps)
P in
(Watts)
V out
(Volts)
I out
(Amps)
P out
(Watts)
Efficiency (%)
1 LED, Low Power Setting 12 0.060 0.720 2.96 0.085 0.252 34.94
1 LED, High Power Setting 12 0.188 2.256 3.49 0.340 1.187 52.60
2 LED\'s, Low Power Setting 12 0.083 0.996 5.94 0.092 0.546 54.87
2 LED\'s, High Power Setting 12 0.255 3.060 6.65 0.320 2.128 69.54
3 LED\'s, Low Power Setting 12 0.109 1.308 8.89 0.094 0.836 63.89
3 LED\'s, High Power Setting 12 0.360 4.320 10.49 0.340 3.567 82.56
High Power Setting, No Daughter Board
LED Configuration
V in
(Volts)
I in
(Amps)
P in
(Watts)
V out (1)
(Volts)
I out (1)
(Amps)
P out (1)
(Watts)
V out (2)
(Volts)
I out (2)
(Amps)
1 LED, Single Channel 9 0.190 1.710 3.34 0.320 1.069
2 LEDs, Dual Channels 9 0.350 3.150 3.36 0.320 1.075 3.340 0.320
2 LEDs, Single Channel 9 0.305 2.745 6.73 0.323 2.174
3 LEDs, Dual Channels (2 on one channel + 1) 9 0.470 4.230 6.73 0.310 2.086 3.330 0.310
3 LEDs, Single Channel 12 0.302 3.624 10.05 0.313 3.146
Low Power Setting, No Daughter Board
LED Configuration
V in
(Volts)
I in
(Amps)
P in
(Watts)
V out (1)
(Volts)
I out (1)
(Amps)
P out (1)
(Watts)
V out (2)
(Volts)
I out (2)
(Amps)
1 LED, Single Channel 12 0.045 0.540 2.96 0.085 0.252
2 LEDs, Dual Channels 9 0.097 0.873 2.95 0.082 0.242 2.96 0.082
2 LEDs, Single Channel 12 0.067 0.804 5.97 0.083 0.496
3 LEDs, Dual Channels (2 on one channel + 1) 12 0.096 1.152 5.95 0.079 0.470 2.96 0.082
3 LEDs, Single Channel 12 0.087 1.044 8.9 0.080 0.712
Table 7: Complete Efficiency Results of Device when Supplied with 12VDCഊLED Configuration and Power
Setting V in I in P in V out I out P out Efficiency
Three LED\'s, High Power 14.17 0.308 4.364 9.99 0.320 3.197 73.25
Three LED\'s, Low Power 16.17 0.085 1.374 8.95 0.088 0.788 57.30
Dual LED\'s, High Power 14.85 0.216 3.208 6.71 0.335 2.248 70.08
Dual LED\'s, Low Power 16.33 0.067 1.094 5.98 0.088 0.526 48.10
Single LED, High Power 15.07 0.187 2.818 3.43 0.345 1.183 41.99
Single LED, Low Power 16.61 0.049 0.814 2.97 0.091 0.270 33.21
Table 8: Complete Efficiency Results of Device when Supplied with 240VAC <P>鸟语不好，麻烦有看的鸟语的解释下</P> <P>没有图很遗憾，能否给我发一份，谢谢！</P><P><a href="mailtlymex@vip.sina.com" target="_blank" >lymex@vip.sina.com</A></P> <P>这里不是英文论坛，估计没有人会完整看完的，建议译成中文再发上来。</P>