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LED Lighting. Muzahid Huda Bay Chips, Inc. October 17, 2009. LED Lighting. LEDs; Some basics Recent developments – more watts, more lumens Market projections Driving LEDs Example LED Driver circuits Summary. What is an LED?. - PowerPoint PPT Presentation
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LED Lighting Muzahid Huda Bay Chips, Inc. October 17, 2009
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Page 1: LED Lighting

LED Lighting

Muzahid Huda

Bay Chips, Inc.October 17, 2009

Page 2: LED Lighting

LED Lighting

• LEDs; Some basics• Recent developments – more watts, more

lumens• Market projections• Driving LEDs• Example LED Driver circuits• Summary

Page 3: LED Lighting

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

Page 4: LED Lighting

4

LED Characteristics

• “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

Page 5: LED Lighting

Wide Range of Applications

                                                      ActualSize  

We focus on “High Brightness” LEDs (HB LEDs) for Solid State Lighting

Page 6: LED Lighting

Energy ConsumptionUS Residential Lighting

• Lighting accounts for 3rd largest (11%) electrical energy consumption

• Annual US consumption for illumination was 138

Terawatt hours in 2007 US Home Electricity Usage

24%

13%

11%13%

7%

8%

6%

18%Space Heating

Water Heating

Lighting

Air Conditioning

Refrigeration

TV and PC

Washer/Dryer

Other

10% lighting efficiency improvement can cut annual CO2 emissions by 477 Metric Tons

Page 7: LED Lighting

LED Application

Video Walls

Page 8: LED Lighting

US DOE Energy Savings EstimatesLEDs 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

Page 9: LED Lighting

Styling advantage - Arrays of LEDs

Multiple LEDs arranged in arrays is one way to achieve a legal beam pattern.

Cadillac DTS

Lincoln

Courtesy: OSRAM

Page 10: LED Lighting

Recent Developments

Page 11: LED Lighting

Recent Developments

• Higher power levels– Useful for most lighting applications– 6000 lumens @ 60W available

• Improved luminous efficacy (“Efficacy”) – >>100 lumens/Watt exist

– Commercial efficacies routinely exceed 80 lm/W

Page 12: LED Lighting

Luminous Efficacy vs. LED Application

1990s 2000 2002 2004 2006 2008 2010

20 lm/W

50 lm/W

70 lm/W

100 lm/W

200 lm/W

Red Tail LightsTraffic Lights

MonochromeLCDs in Handsets

Color LCDs inHandsets

Handset Keypads

CameraFlash

Signage

Notebook LCD

Backlighting

LCD TV Backlighting

Street Lighting

MainstreamGeneral

Illumination

AutomotiveHeadlamps

AutomotiveInterior Lighting

LED Flash Lights

Page 13: LED Lighting

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.

Courtesy: Luminus

Up to 6000 lumens @ ~100 lm/W

Page 14: LED Lighting

Courtesy: Toshiba May 2008

Page 15: LED Lighting

Market Projections

Page 16: LED Lighting

LED Driver IC Market SizeLEDs 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– 2007 -2011 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

Page 17: LED Lighting

0

100

200

300

400

500

600

700

800

900

2006 2007 2008 2009 2010 2011

Personal Computing

LCD TV

General I llumination

Traffic Lights

Signage

Automotive

Consumer Portables

Mobile Handsets

Mill

ions

of

Dolla

rsLED Driver IC Market Size

HB LED applications

Page 18: LED Lighting

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

Page 19: LED Lighting

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

Page 20: LED Lighting

Place Photo Here

Incandescent Halogen LED

Light Source ComparisonLED vs. selected other technologies

Efficacy (lm/W)

7 - 20 15 - 30 50 - 100 20 – 50 (Efficiency)

Light Output (Lumens)

500 1900 3200 25 - 600

Life time (hrs)

400 – 10000 200-1500 1000 - 2500 >50,000

CCT (K) 2500 - 3000 3000-3300 4150 2700 - 10000

HID

Page 21: LED Lighting

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

Page 22: LED Lighting

Life of Vehicle PerformanceCourtesy: OSRAM

Page 23: LED Lighting

Driving LEDs

Page 24: LED Lighting

Buck Mode LED DriverMR-16 Lamp

Typical input voltage is 12V rms (AC)Typical output power is 1W to 3W

Page 25: LED Lighting

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

Practical ConsiderationsLED Binning

The human eye can detect a brightness difference when the intensity ratio is > 2:1

Page 26: LED Lighting

Luminous Intensity Binning

Lot2 Lot3Lot1

1090 mcd480 mcd

Intensity range in production at rated current:

Bin2

560 mcd 710 mcd 900 mcd 1120 mcd

Bin3 Bin4Bin1

450 mcd

Conceptual description; Actual binning limits may vary

Intensity BinningExample

Page 27: LED Lighting

LED DriversGeneral 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

Page 28: LED Lighting

LED Configurations

1) Series

2) Parallel(1) 3) Parallel(2)

Can be constant current sources

1

11

2 3

1 Voltage variations 2 Vf variations; Current hogging

3 Current stress when one or more strings fail

Page 29: LED Lighting

LED Configurations

1) Series

2) Parallel(1) 3) Parallel(2)

1

1 No current variations due to voltage 2 Vf variations; Current hogging

3 Current stress when one or more strings fail

1

2 3

1

Page 30: LED Lighting

Resistor Drive

0

0.1

0.2

0.3

0.4

0.5

9 12 16

Input Voltage Vi

LE

D C

urr

en

t Io

Vf=3.0V

Vf=3.4V

Vf=4.0VVi

Io

Vf

Power loss

Varying current

Changing brightness

Impossible to automatically adjust

for binning

0

2

4

6

8

9 12 16

Input Voltage Vi

Res

isto

r P

ower

D

issi

patio

n Ploss @ Vf =3.0V

Ploss @Vf =3.4V

Ploss @ Vf =4.0V

Page 31: LED Lighting

LED DriversCommon Topologies

• Choice of topology depends on many factors– Input and output voltage range– Efficiency– Cost– Flexibility of use– Reliability

•Flyback•Forward•Resonant•Buck

*Often need PFC

•Buck•Boost•Buck-Boost•SEPIC•Flyback•Forward

LED DriverLED Driver

Linear Switch Mode

DC/DC AC/DC

Page 32: LED Lighting

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

Page 33: LED Lighting

Linear LED Driver

• Simple– 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

Page 34: LED Lighting

Constant Current DriveLinear Current Source

Linear Current Source; LED Current Regulation

0

0.1

0.2

0.3

0.4

9 12 16

Input Voltage Vi

LE

D C

urr

ent

Io

Vf = 3.0V

Vi = 3.4V

Vf = 4.0V

Linear Current Source Dissipation

0

2

4

6

9 12 16

Input VoltageVi

Line

ar C

urre

nt

Sou

rce

Dis

sipa

tion

Vf = 3.0V

Vf = 3.4V

Vf = 4.0V

Vi

Io

Vf

Power loss

Constant current

Constant brightness

Can integrate adjustments for

binning

Linear Control

Page 35: LED Lighting

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

Page 36: LED Lighting

Switch-mode Driver Topologies

= Duty cycle

Boost

Is2 = ILED

Is1

VLED/Vi = 1/(1-)Vi

Buck

Is = ILED

VLED/Vi = Vi

Buck BoostIs1

Is2 = ILED

VLED/Vi = /(1-)Vi

• VLED > Vi• No output short protection• Non-isolated• Two current sense resistors (two control loops)

• VLED > Vi, = Vi, or < Vi• No output short protection• Non-isolated• Two current sense resistors (two control loops)

• VLED < Vi; Vi can vary• No output cap needed in CCM operation• Simple, low cost• Synchronous for high efficiency

Page 37: LED Lighting

Constant Current DriveSwitch-mode Current Source

Vi

Io

Vf

Power loss (Small)

Constant current

Constant brightness

Can integrate adjustments for

binning

Switch-mode Control

Switch-mode Source Power Dissipation

0

0.05

0.1

0.15

9 12 16

Input Voltage Vi

Curr

ent S

ourc

e Di

ssip

atio

n Vf = 3.0V

Vf = 3.4V

Vf = 4.0V

Page 38: LED Lighting

Topologies vs. ApplicationsGuidelines

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

8W - 12W

LED Bulbs, FL Replacement, Down Light, Linear Lamps, Bar Lamps

15W - 20W

25W - 40W

50W - 65W

Buck-Boost

8W - 12W

Garage lighting, Emergency, Automotive

15W - 20W

25W - 40W

Cuk

8W - 12W

Garage lighting, Emergency, Automotive

15W - 20W

25W - 40W

Forward, Flyback 25W - 40W

Panels, Down Light, Linear, Bar50W - 65W

AC or DC IN Resonant

50W -100W

Street lamp, Flood Light, Search Light, Marine Lihts

100W – 250W

250W – 400W

Page 39: LED Lighting

Example LED Driver Circuits

Page 40: LED Lighting

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 widelyabove and below LED string voltage, theDriver automatically adjusts duty ratio tomaintain constant output voltage.

Useful for automotive lighting:

9V battery voltage can vary from over 14Vdown to 6V.

Page 41: LED Lighting

Buck-Boost LED Driver (DC/DC)Analysis

1. Continuous Mode operation

2. 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 > 1 Voltage buck moded = 0.5: VLED / Vi = 1 Pass through mode d > 0.5: VLED / Vi > 1 Voltage boost mode

6. Operating mode depends on: Sum of all the LED forward voltages (no. of LEDs)

Ton Toff

Cu

rre

nt

Ion Ioff

IDC t

VD

VD = VLED + Vi

IP

Vi

Vo

Ion

Q1: ON/OFF

VD

VLED

+

-

Pi = Po/ where = efficiency

Po = VLED * {IDC * (1-d) + IP * (1-d)/2}Set Ip using sense resistor R4

R4

Page 42: LED Lighting

Resistor vs. Linear vs. Switch-modeComparing LED Driver Schemes

Linear Current Source Efficiency

0

0.2

0.4

0.6

9 12 16

Input Voltage Vi

Ele

ctri

cal

Eff

icie

ncy Vf = 3.0V

Vf = 3.4V

Vf = 4.0V

Switch Mode Current Source Efficiency

0.90.920.940.96

9 12 16

Input Voltage Vi

Ele

ctri

cal

Eff

icie

ncy

Vf = 3.0V

Vf = 3.4V

Vf = 4.0V

RESISTOR LINEAR SWITCH MODE

PROS Simple Simple; No inductor

Very efficient

Lowest parts cost

Low cost No. of LEDs not limited by Vi

No EMI No EMI

Constant Io Constant Io

Other functions are discrete

Integrated (Dim, programming)

Integrated functions (Dim, programming)

CONS Low efficiency Low efficiency

Complex

Io varies with Vi and LED Vf

Thermals

No. of LEDs limited by Vi

No. of LEDs limited by Vi

Adjust R in production

Need to suppress EMI

Resistor Drive Eficiency

0

0.2

0.4

0.6

9 12 16

Input Voltage Vi

Ele

ctri

cal

Eff

icie

ncy Vf = 3.0V

Vf = 3.4V

Vf = 4.0V

Page 43: LED Lighting

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 = PFC X CONV

– Example: Efficiency = 0.93 X 0.92 = 85.6%

Courtesy: Power Integrations

Page 44: LED Lighting

PWM

RampSignal

t

LED Dimming

• 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

TON1

T

TON2

T

PWMDimming

AnalogDimming

Lower brightness

Higher brightness

ILED

ILED

Higher brightness

Analog voltage

Analog Controlled DimmingAnalog Controlled Dimming

Page 45: LED Lighting

14W LED DriverWide Input/Output voltage Range

Page 46: LED Lighting

3W to 24W LED DriverOperates from 6V to 30V

Driver IC

AC/DC in,DIM Input

Inductor

Power Switch

LED +LED –GND

DIM and Fault Protection Switch

Page 47: LED Lighting

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


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