1. Muzahid Huda Bay Chips, Inc. October 17, 2009
LED Lighting
Muzahid Huda
Bay Chips, Inc.
October 17, 2009

2. LED Lighting LEDs; Some basics
Recent developments – more watts, more lumens
Market projections
Driving LEDs
Example LED Driver circuits
Summary

3. What is an LED?
Light Emitting Diodes or LEDs can come in many different shapes and packages. But one thing each of these has in common is that it is a Semiconductor based material that Emits Light
Courtesy: OSRAM

4. LED Characteristics “Pure” light source Why all the excitement?4
“Pure” light source
LEDs emit a narrow spectrum light when forward biased
Why all the excitement?
Resistant to shock and vibration
Saturated colors – don’t need filters
Small size enables new applications and designs
Fully dimmable without color variations (PWM)
Cold start capable (-40°C) – For outdoor, industrial, automotive
Fast response (< 40ns)
Long Life

5. Wide Range of Applications
                                                       Actual Size  
We focus on “High Brightness” LEDs (HB LEDs) for Solid State Lighting

6. Energy Consumption US Residential Lighting
Lighting accounts for 3rd largest (11%) electrical energy consumption
Annual US consumption for illumination was 138 Terawatt hours in 2007
10% lighting efficiency improvement can cut annual CO2 emissions by 477 Metric Tons

7. LED Application Video Walls

8. US DOE Energy Savings Estimates LEDs Magazine Oct ‘08
Switch to LEDs could save $22B in electric costs
Colored-light applications:
Traffic signals and pedestrian crossings; decorative lights; exit signs; signage
Indoor applications:
Recessed downlights; refrigerated display cases; retail displays; task lights; office undershelf lights; under-cabinet lights
Outdoor white-light applications:
Street and area lights; step, path, and porch lights

9. Styling advantage - Arrays of LEDs
Cadillac DTS
Lincoln
Multiple LEDs arranged in arrays is one way to achieve a legal beam pattern.
Courtesy: OSRAM

10. Recent Developments

11. Recent Developments Higher power levels
Useful for most lighting applications
W available
Improved luminous efficacy (“Efficacy”)
>>100 lumens/Watt exist
Commercial efficacies routinely exceed 80 lm/W

12. Notebook LCD Backlighting
Luminous Efficacy
vs. LED Application
Mainstream
General Illumination
200 lm/W
Automotive
Headlamps
Street Lighting
LED Flash Lights
LCD TV Backlighting
100 lm/W
Automotive
Interior Lighting
Notebook LCD Backlighting
70 lm/W
Camera
Flash
Signage
50 lm/W
Color LCDs in
Handsets
Handset Keypads
Monochrome
LCDs in Handsets
20 lm/W
Red Tail Lights
Traffic Lights
1990s
2000
2002
2004
2006
2008
2010

13. LED Development Trends
Japanese Philosophy:
Not the increase in power handling capacity per die per se, but the efficacy that is more important to improve
US Philosophy:
Focused more on increasing power handling capacity
Highest wattage LEDs available from Luminus, Inc.
Up to 6000 ~100 lm/W
Courtesy: Luminus

14. Courtesy: Toshiba May 2008

15. Market Projections

16. LED Driver IC Market Size LEDs Magazine Oct ‘08
HB LED driver IC market to exceed $1.9 billion in 2011
Growth driven by general illumination, signs and displays, and automotive applications
Compound Annual Growth Rate (CAGR) of 38%
The $865 million market for driver ICs in 2006 was dominated by mobile phone applications
Mobile phone share will drop from 77% in 2006 to 50% in 2011
LED driver ICs for laptop display backlight applications will see revenue increase

17. LED Driver IC Market Size HB LED applications
Millions of Dollars So

18. Applications Issues and Challenges - LEDs
Energy Efficiency
Needed to “measure up” to current fluorescent technology
Photometry & Color
Different applications need different light distributions & color temperatures
Thermal Management
Light output & lumen degradation
Reliability issues due to heat
Lumen Maintenance & Life
Lumens depreciate over time
Life test parameters to specify lifetime

19. Applications Issues and Challenges - Electronics
Energy Efficiency
Drivers that operate at optimum efficiency
Efficiency measurement techniques
Performance and Functionality
Size and cost
Conducted and radiated EMI
Harsh environments eg. Surge, lightning, load dump, cold start
String compatibility
Thermal Management
Wide temperature range and high humidity
Reliability & Life
Lifetime of passive components: capacitors, magnetics

20. Light Source Comparison LED vs. selected other technologies
Incandescent
Halogen
HID
LED
Efficacy (lm/W)
7 - 20
20 – 50 (Efficiency)
Light Output (Lumens)
500
1900
3200
Life time (hrs)
400 – 10000
>50,000
CCT (K)
4150
Place Photo Here

21. Forward Lighting 2007 saw the launch of the first LED headlamps.
LEDs match the color temperature of HID as well as create stylistic brand recognition.
Courtesy: OSRAM

22. Life of Vehicle Performance Courtesy: OSRAM

23. Driving LEDs

24. Buck Mode LED Driver MR-16 Lamp
Typical input voltage is 12V rms (AC)
Typical output power is 1W to 3W

25. Practical Considerations LED Binning
What is Binning? / Why is it required?
Upon completion of assembly, LED’s are measured for brightness, color, and forward voltage
They are placed into “bins” according to each characteristic
Types of Binning
Intensity Binning
Color Binning
Forward Voltage Binning
The human eye can detect a brightness difference when the intensity ratio is > 2:1

26. Intensity Binning Example
Luminous Intensity Binning
Intensity range in production at rated current:
Lot2
Lot3
Lot1
1090 mcd
480 mcd
Bin2
560 mcd
710 mcd
900 mcd
1120 mcd
Bin3
Bin4
Bin1
450 mcd
Conceptual description; Actual binning limits may vary

27. LED Drivers General Considerations
LEDs are current driven devices
LED Drivers must deliver a constant current to the LED or LED string(s)
Power supply voltage may fluctuate
The driver must regulate its output current even if the input fluctuates

28. LED Configurations 1 3 2 1 1 1 2 1) Series 3
Can be constant current sources 1 3 2 1 1
2) Parallel(1) ) Parallel(2) 1
Voltage variations 2
Vf variations; Current hogging
1) Series 3
Current stress when one or more strings fail

29. LED Configurations 1 1 2 3 1 1 2 1) Series 3
2) Parallel(1) ) Parallel(2) 1
No current variations due to voltage 2
Vf variations; Current hogging
1) Series 3
Current stress when one or more strings fail

30. Impossible to automatically adjust for binning
Resistor Drive
Power loss
Varying current Io Vi
Changing brightness Vf
Impossible to automatically adjust for binning

31. LED Drivers Common Topologies
Choice of topology depends on many factors
Input and output voltage range
Efficiency
Cost
Flexibility of use
Reliability
LED Driver
Linear
Switch Mode
DC/DC
AC/DC
Buck
Boost
Buck-Boost
SEPIC
Flyback
Forward
Flyback
Forward
Resonant
Buck
*Often need PFC

32. DC/DC LED Drivers Drive LEDs from DC power source
AC/DC conversion usually occurs independently upstream
“Simple” to implement
LEDs are DC devices (Unidirectional current)
Two Types
Linear Drivers
Switch Mode DC/DC Drivers

33. Linear LED Driver Simple Constant LED Current
Low parts count
Constant LED Current
Output voltage is lower than input voltage
Not very efficient
V_OUT must be close to V_IN to maximize efficiency
Needs good heat management
Pass transistor dissipates heat
I_s
I_LED +
V_FDBK -
Error Amp
V_REF
V_IN
V_OUT
PD = I_LED X (V_IN – V_OUT)
DIM
TMP EN

34. Constant Current Drive Linear Current Source
Power loss
Constant current Io Vi
Constant brightness Vf
Can integrate adjustments for binning
Linear Control

35. Switch Mode DC/DC Driver
Most use inductors for energy storage and delivery
Switch Capacitor types use capacitors for energy storage
Energy (Current) ramps up in inductor during switch “ON” period
Energy (Current) delivered to LED string(s) during switch “OFF” period
Switching frequency is usually >20kHz
Avoids audible noise
Commonly in the 100’s of kHz range

36. Switch-mode Driver Topologies
Boost
Is2 = ILED
Is1
VLED/Vi = 1/(1-d) Vi
Buck
Is = ILED
VLED/Vi = d Vi
VLED > Vi
No output short protection
Non-isolated
Two current sense resistors (two control loops)
Buck Boost
Is1
Is2 = ILED
VLED/Vi = d/(1-d) Vi
VLED < Vi; Vi can vary
No output cap needed in CCM operation
Simple, low cost
Synchronous for high efficiency
VLED > Vi, = Vi, or < Vi
No output short protection
Non-isolated
Two current sense resistors (two control loops)
d = Duty cycle

37. Constant Current Drive Switch-mode Current Source
Power loss (Small)
Constant current Io Vi
Constant brightness Vf
Can integrate adjustments for binning
Switch-mode Control

38. Topologies vs. Applications Guidelines
DESIGN BASE BY POWER RANGE
AC or DC IN
Architecture
Power Range
Applications
DC IN
Buck
0.5W - 2W
Luminaires, LED Bulbs, Down Light, Linear Lamps, Bar Lamps, Decorative
3W - 6W
8W - 12W
15W - 20W
25W - 40W
50W - 65W
Boost
LED Bulbs, FL Replacement, Down Light, Linear Lamps, Bar Lamps
Buck-Boost
Garage lighting, Emergency, Automotive
Cuk
Forward, Flyback
Panels, Down Light, Linear, Bar
Resonant
50W -100W
Street lamp, Flood Light, Search Light, Marine Lihts
100W – 250W
250W – 400W

39. Example LED Driver Circuits

40. Buck-Boost LED Driver (DC/DC) Example
Versatile Topology:
For fixed input voltage, automatically
adjusts output voltage to accommodate
long or short string of LEDs.
Conversely, if input voltage varies widely
above and below LED string voltage, the
Driver automatically adjusts duty ratio to
maintain constant output voltage.
Useful for automotive lighting:
9V battery voltage can vary from over 14V
down to 6V.

41. Buck-Boost LED Driver (DC/DC) AnalysisVi Vo
Ion
Q1: ON/OFF VD
VLED + -
Continuous Mode operation
Q1 is ON:
Vi = Ldi/dt = L*IP/Ton
3. Q1 is OFF:
Vi – Vo = Vi – (VLED +Vi) = -VLED = -Ldi/dt = -L*Ip/Toff
4. Combining:
VLED / Vi = Ton / Toff = Ton / (T – Ton) Note: T = Ton + Toff = 1/f
= (Ton/T) / ((T – Ton)/T)
= d / (1 – d) d = duty ratio
5. When:
d < 0.5: VLED / Vi > Voltage buck mode
d = 0.5: VLED / Vi = Pass through mode
d > 0.5: VLED / Vi > Voltage boost mode
6. Operating mode depends on:
Sum of all the LED forward voltages (no. of LEDs) R4
Ton Toff
Current
Ion Ioff
IDC t VD
VD = VLED + Vi IP
Pi = Po/n where n = efficiency
Po = VLED * {IDC * (1-d) + IP * (1-d)/2}
Set Ip using sense resistor R4

42. Resistor vs. Linear vs. Switch-mode Comparing LED Driver Schemes
PROS
Simple
Simple; No inductor
Very efficient
Lowest parts cost
Low cost
No. of LEDs not limited by Vi
No EMI
Constant Io
Other functions are discrete
Integrated (Dim, programming)
Integrated functions (Dim, programming)
CONS
Low efficiency
Complex
Io varies with Vi and LED Vf
Thermals
No. of LEDs limited by Vi
Adjust R in production
Need to suppress EMI

43. Off-Line LED Drivers Drive LEDs directly from AC power
Replaces standard light bulbs/lamps
Needs AC to DC conversion
Bridge rectifier at input
Often needs input/output isolation
Flyback, forward or resonant mode converters
Resonant converters offer highest efficiency
Often need Power Factor Correction
Front end PFC reduces overall efficiency
Efficiency = nPFC X nCONV
Example: Efficiency = 0.93 X 0.92 = 85.6%
Courtesy: Power Integrations

44. LED Dimming PWM Dimming ILED Analog Dimming
TON1 T
TON2
PWM
Dimming
Analog
Lower brightness
Higher brightness
ILED
PWM Dimming
LED current is pulsed
Peak value of current is constant
No color shift
Analog Dimming
LED current is varied
May cause color shift
Some drivers have an on-board ramp generator
An external analog voltage compared to the ramp provides PWM signal to dim the LED
This is called Analog Controlled PWM Dimming
Analog Controlled Dimming
PWM
Ramp
Signal t
Analog voltage

45. 14W LED Driver Wide Input/Output voltage Range

46. 3W to 24W LED Driver Operates from 6V to 30V
Driver IC
AC/DC in,
DIM Input
Inductor
Power Switch
LED +
LED –
GND
DIM and Fault Protection Switch

47. Summary
Solid-State Lighting continues to evolve with certain expectations:
Greatly increased lifetime = Lower Maintenance Costs $$$
Uses a fraction of the power compared to traditional light– Greater Energy-Efficiency = Lower Energy Costs $$$
LED lighting market is growing at 38%
Many technical challenges need to be overcome – These are many areas of opportunity to work on