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«A Major Qualifying Project submitted to the Faculty of WORCESTER POLYTECHNIC INSTITUTE in partial fulfillment of the requirements for the degree of ...»

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Efficient Pulse Width Modulation LED Headlight Driver

A Major Qualifying Project

submitted to the Faculty of

WORCESTER POLYTECHNIC INSTITUTE

in partial fulfillment of the requirements for the

degree of Bachelor of Science

by

Brendan Cavanagh

Nathaniel Keahi Goodale

Matthew Janiga

Date:

April 30, 2015

Stephen Bitar

John McNeill

NECAMSID/Analog Labs

Worcester Polytechnic Institute

This report represents work of WPI undergraduate students submitted to the faculty as evidence of a degree requirement. WPI routinely publishes these reports on its web site without editorial or peer review. For more information about the projects program at WPI, see http://www.wpi.edu/Academics/Projects.

TABLE OF CONTENTS

TABLE OF CONTENTS

TABLE OF FIGURES

LIST OF TABLES

PROBLEM STATEMENT

Abstract

ACKNOWLEDGMENTS

CHAPTER I: INTRODUCTION

CHAPTER II: BACKGROUND

CURRENT MARKET AND MANUFACTURERS

HEADLIGHT LIGHTING TECHNOLOGY COMPARISON

CURRENT CONSIDERATIONS AND DRAWBACKS OF LED LIGHTING

ECOLOGICAL IMPACT OF DIFFERENT BULB TYPES

POWER COMPARISON OF BULB TYPES

EXTERNAL AUTOMOTIVE LIGHTING

INTERIOR AUTOMOTIVE LIGHTING

LED NOTIFICATION APPLICATIONS

ARCHITECTURAL APPLICATIONS

CAR ELECTRICAL SYSTEM

LED HEADLIGHTS

HIGH POWER LEDS

LED DRIVER CIRCUITS

DEPARTMENT OF TRANSPORTATION HEADLIGHT REQUIREMENTS

HEADLIGHT HEAT CONSIDERATIONS

LED HEADLIGHT HEAT DISSIPATION DESIGN

CHAPTER III: PROCESS

BACKGROUND RESEARCH

FIRST CIRCUIT EVOLUTION

SECOND CIRCUIT EVOLUTION

THIRD CIRCUIT EVOLUTION

FOURTH CIRCUIT EVOLUTION

FIFTH CIRCUIT EVOLUTION

SIXTH CIRCUIT EVOLUTION

CHAPTER IV: RESULTS

CIRCUIT DISCUSSION

SPECIFICATIONS & OSCILLOSCOPE

STARTUP ISSUE

COMPARISON TO HALOGEN

EFFICIENCY AND POWER LOSSES

PRINTED CIRCUIT BOARD

LED & HEATSINK MOUNTING

CHAPTER V: FUTURE IMPROVEMENTS

CHAPTER VI: CONCLUSION

BIBLIOGRAPHY

APPENDIX A

APPENDIX B

TABLE OF FIGURES

Figure I : Bulb phase environmental impact (Lighting European Lamp Companies Federation, 2009)

Figure II : Kelvin color temperature scale (HubPages, 2011)

Figure III : Office environment color temperatures (HubPages, 2011)

Figure IV : Light level at varying distances from source (Speedster Source, 2014)

Figure V : Automobile light placement

Figure VI : Automobile power system (Firestone, 2014)

Figure VII : LED VI characteristics (Thomas & Pforr, 2009)

Figure VIII : Example LED array (Thomas & Pforr, 2009)

Figure IX : AC voltage LED array (Thomas & Pforr, 2009)

Figure X : XP-L LED typical forward voltage and current (CREE)

Figure XI : Buck converter (Diodes Incorporated, 2010)

Figure XII : Buck converter adjustable application (Diodes Incorporated, 2010)

Figure XIII : Headlamp upper beam specifications (USDoTNHTSA, 2004)

Figure XIV : Vertical & horizontal headlamp angles (Society of Automotive Engineers, 2010) 37 Figure XV : Thermal cycle testing (Society of Automotive Engineers, 2010)

Figure XVI : LED Lamp reflection for high and low beams (Koester, 2010)

Figure XVII : Lamp diagram (Koester, 2010)

Figure XVIII : Heat pipe diagram (Rice, 2004)

Figure XIX : First Circuit Evolution Schematic

Figure XX : Transient Analysis of Circuit I

Figure XXI : Second Circuit Evolution Schematic

Figure XXII : Third Evolution Schematic

Figure XXIII : Transient Analysis Circuit III

Figure XXIV : Fourth Circuit Evolution Diagram

Figure XXV : IC Comparison Chart

Figure XXVI : IC Application Circuit

Figure XXVII : Breadboard IC Circuit

Figure XXVIII : IC Breakout Board

Figure XXIX : Sixth Circuit Evolution

Figure XXX: Final Circuit Schematic

Figure XXXI: Normal Operation CH1 (input voltage), CH2 (gate voltage), CH3 (load voltage) 61 Figure XXXII: Startup Delay Capture

Figure XXXIII: PCB Layout

Figure XXXIV: PCB Rev 01

Figure XXXV: LED Mount & Heatsink

Figure XXXVI: LED Headlight Operational

LIST OF TABLES

Table 1 : Bulb lifespans (autoevolution, 2014)

Table 2 : Bulb type lumens and power usage

Table 3 : Headlamp lower beam specifications (Society of Automotive Engineers, 2010)......... 36 Table 4: Design Specifications

Table 5: Halogen v. LED

PROBLEM STATEMENT

Automotive headlight technology has lagged behind other technological adoptions used in vehicles. Most automotive headlights are essentially the same as they have been for the past five decades, utilizing incandescent halogen bulbs. This technology converts almost 90% of its energy into heat rather than light, and has a shorter life time compared to the alternatives available today. LED headlights are emerging in the marketplace on high end vehicles and aftermarket conversion kits. However, incandescent bulbs hold the majority of market share since they are made in large quantities, cheap and quick to manufacture, and offer satisfactory lighting characteristics. LED headlight technology is attractive since it boasts higher efficiency, resulting in higher MPG, extends the range of electric vehicles, longer lifespan than traditional bulbs, and provides more effective luminescence. These headlamps require a proper LED driving circuit, ease of installation, provide sufficient light to illuminate the road, maintain price comparable with that of traditional incandescent halogen bulbs. Unlike typical bulbs, LEDs do not radiate significant amounts of heat, leading to potential ice accumulation on the headlight cover glass. This paper concentrates on the use of pulse-width modulation for increased lumen output with greatly reduced power consumption.





ABSTRACT

LED headlights can provide better luminescence and less power consumption when compared to traditional halogen headlights. The adoption of LEDs in automobiles has been slow as the technology is more expensive than halogen bulbs, more complex to integrate, and younger. As such, an efficient, simplistic, and easy to use illumination driver was developed to spur on the widespread adoption of LED use in automobile lighting. The circuit developed is capable of providing the necessary illumination for a fraction of the energy input required by traditional lighting.

ACKNOWLEDGMENTS

We would like to thank Professor Bitar, our main advisor, for all the help and guidance he provided throughout the year. His help was instrumental in the development of this project as and the successful completion of the circuit. We would also like to thank our co-advisor Professor McNeill as well as our sponsor NECAMSID. A special thanks to Bob and Bill from the ECE shop for their willingness to provide us with materials and help us fashion components.

CHAPTER I: INTRODUCTION

The desire for energy efficiency has spurred on a new drive in industry to produce products that consume as few resources as possible to operate. Traditional lighting techniques such as halogen bulbs have been the focus of some of these efficiency improvements. Almost 90% of the energy consumed by a halogen bulb is converted into heat rather than visible light (autoevolution, 2014). In the home, U.S. power companies have started to phase out incandescent lights in favor of CFLs (Compact Florescent Lights) and LED lighting (Light Emitting Diodes). Not only has the home seen pushes for improved lighting efficiency but so hasn't the automotive industry. As gas prices increase and the consumers’ desire for greater MPG increases with it, automakers have taken to improving the efficiency of their illumination systems. By switching to LED lighting for a car’s headlights, interior lights, running lights, indicators, etc. auto manufacturers can reduce energy consumption and advertise a higher MPG as well as boast environmentally friendly improvements. Currently, the integration of LED bulbs into headlights is typically seen only in electric vehicles and high end cars. However, recently announced cars such as 2015 Ford F150 will be the first pickup truck to offer a full forward LED illumination system. Currently, halogen bulbs and Xenon HID’s have the majority of market share, but as LED technology and ease of integration improve they will begin to take a greater portion of the market.

LEDs are far more efficient than traditional bulbs at generating light. Unlike halogen/incandescent bulbs, most of the energy is converted directly into light rather than waste heat. One reason LED headlights can be vastly more efficiency is by using pulse width modulation (PWM) to control the amount of light emitted. PWM works by turning the LED on and off at a frequency faster than the eye can see. PWM uses something called a duty cycle. Duty cycle determines what percentage of the time the power should be off. A 50% duty cycle would mean 50% of the time the power is on and 50% of the time the power is off. If an LED were driven with a constant voltage and then switched to a 50% duty cycle PWM driver, its efficiency would double. This is because 50% of the time the LED would technically be off. However, the frequency is such that the human eye cannot perceive this flickering. This is how a computer monitor operates, the screen is actually refreshing 60 times per second but we would never be able to notice it with the naked eye. By finding the correct frequency and duty cycle, the brightness and increased power efficiency can be achieved. Another aspect traditional halogen bulbs suffer in is dimming applications. When dimming a traditional bulb, an adjustable resistor is put in series with the bulb to vary the voltage over the bulb, this in turn adjusts the amount of light emitted. Thus dimming a traditional bulb does not reduce the expended energy. However, dimming an LED works as intended, a more dim light will use less power and PWM can be used to do this.

The team’s focus on automobile headlights is due to the unique nature of cars versus a stationary object plugged into an outlet. Cars consume electrical energy from the battery which consumes gasoline from the tank. Anything that drains more power from the battery will cause more gasoline consumption to allow the car to charge itself. Headlights are massive consumers of this energy from the battery. Halogen headlights draw upward of 50 watts per bulb. This power draw can be dramatically reduced by using LED bulbs which only take around 15W per bulb. Another advantage to LED bulbs is their longevity, as they last tens of thousands of hours compared to the average of only one thousand hours for halogen headlights.

Tesla, Toyota, and Audi are leaders in the field of integrating LED headlights, being some of the early adopters of the technology. LEDs were first adopted by Audi in a high profile manor because of their form factor and unique look. As LEDs are small, and arrays can be used to generate the required light, they can be made in various shapes and sizes. This appealed to the auto manufacturers as it allowed them to mold custom light housings into their vehicles. The LEDs also proved to be brighter and easier to mold into the desired light pattern for headlights than halogen bulbs used in the past. Along with the advantages of light brightness and design manipulation qualities of LEDs, Tesla and Toyota integrated LEDs to save on battery power.

Now this battery could be preserved thus increasing MPG and extending the range of the vehicle or allowing additional features. Tesla and Audi are of course high end automakers, however we have seen slow adoption of LEDs into a more reasonable line of automobiles. Most hybrid or electric vehicles use LEDs as electrical power consumption is even more important than before.

They are also being installed by end users in order to give them the lumen output they want or improve their cars efficiency.

There are several manufactures that are currently producing high power LED drivers that are able to power LEDs for headlights in vehicles. Allegro, TI, Rohm, and LT all produce these chips. However, with the exception of Allegro, the chips are far more complicated than they need to be, with multiple uses and setup configurations possible with each chip. This over complexity and feature recycling leads to inefficiency, higher price, more failure points, and more a complex understanding required. The aim of this project team was to develop a simple high power LED driver for headlights using pulse width modulation. If an easy to understand, effective, cheap, but extremely efficient driver could be developed, it might help ease the integration of LED’s into all applications, specifically headlights.

CHAPTER II: BACKGROUND

As of 2014 the market for light emitting diode (LED) lighting in both the automotive and household industries is rapidly growing to incorporate increasingly efficient and effective products and techniques. In 2011 the LED market as a whole grew by 10%, while the use of LED’s in the lighting sector grew by an astonishing 44% (LEDs Magazine, 2011). With this it is clear there is demand for practical, energy efficient, LED lighting options within the automotive industry. According to some, there is an expected compound annual growth rate (CAGR) of 34% for LED headlights alone, as the automotive industry reaches towards converting all front-end lighting to either Xenon high intensity discharge lamps (HID) or LEDs in a motion to reduce costs and increase MPG (miles per gallon) (LEDs Magazine, 2011). The automotive industry is going through a transitional period where manufacturers are slowly incorporating LED headlights into cars by creating headlight hybrids. The low beam of the car is reserved for the LEDs as they are more reliable, longer lasting, and more energy efficient. Whereas the high beams are implemented with halogen lamps or Xenon HIDs for increased brightness and distance. Currently, LEDs are produced by several major manufacturers like General Electric (GE), Philips, Osram Sylvania, and Cree.



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