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LED Lighting

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?.

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LED Lighting

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

  6. Energy ConsumptionUS 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 cancut annual CO2 emissions by 477 Metric Tons

  7. LED ApplicationVideo Walls

  8. 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

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

  10. Recent Developments

  11. 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

  12. 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 lumens @ ~100 lm/W Courtesy: Luminus

  14. Courtesy: Toshiba May 2008

  15. Market Projections

  16. 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

  17. LED Driver IC Market SizeHB LED applications Millions of Dollars

  18. ApplicationsIssues 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. ApplicationsIssues 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 ComparisonLED vs. selected other technologies Halogen LED Incandescent HID 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 PerformanceCourtesy: OSRAM

  23. Driving LEDs

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

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

  27. 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

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

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

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

  31. LED Driver Switch Mode Linear LED DriversCommon Topologies • Choice of topology depends on many factors • Input and output voltage range • Efficiency • Cost • Flexibility of use • Reliability 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. PD = I_LED X (V_IN – V_OUT) DIM TMP EN V_OUT I_LED Error Amp + V_REF V_IN I_s + V_FDBK - 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

  34. Vf Constant Current DriveLinear Current Source Power loss Constant current Io Vi Constant brightness 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. Vi VLED/Vi = 1/(1-d) VLED/Vi = d Vi Is2= ILED Is = ILED Is1 Is1 Boost Buck VLED/Vi = d/(1-d) Vi Is2 = ILED Buck Boost Switch-mode Driver Topologies • VLED < Vi; Vi can vary • No output cap needed in CCM operation • Simple, low cost • Synchronous for high efficiency • 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) d = Duty cycle

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

  38. Topologies vs. ApplicationsGuidelines

  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. - Vi VLED Ion + Vo VD Q1: ON/OFF IP Current Ion Ioff t IDC VD = VLED + Vi VD Ton Toff Buck-Boost LED Driver (DC/DC)Analysis • 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 > 1 Voltage buck mode • d = 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) R4 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-modeComparing LED Driver Schemes

  43. Courtesy: Power Integrations 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%

  44. Lower brightness Higher brightness ILED PWM Dimming Analog Dimming Higher brightness TON2 T TON1 T ILED PWM Ramp Signal 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 Analog Controlled Dimming Analog voltage

  45. 14W LED DriverWide Input/Output voltage Range

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

  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

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