High Brightness LED Driver Solutions for General Lighting. Created by Bernie Weir

Transcription

1 High Brightness LED Driver Solutions for General Lighting Created by Bernie Weir

2 World of Lighting ~ 20-22% of electrical energy is used for lighting of which 40% is for incandescent lighting, this represents 2000 TWh/year Residential 28% Industrial 16% Streetlighting 8% Restaurants, Retail and Services 48% >70% of the Energy Usage is Outside of the Residential Market Source: OSRAM 2

3 LED Technology Forecast and Impact US DOE January

4 Chromaticity LED Optical Characteristics Some defined box in the white area on or near the Black Body Locus Bin sizes (x, y coordinates) varies by supplier Brightness (luminus flux) All the light output into a sphere Factors in human sensitivity to light of different wavelengths 4

5 Challenges of Driving LEDs All are White LEDs Nichia Rigel NJSW036AT Forward voltage varies by color, current & temperature Color point shifts with current and temperature, more pronounced with Red and Amber 5

6 Operating Relationship Electrical, Optical & Thermal 1 2 Luxeon Rebel White OSRAM Platinum Dragon 3) Higher power raises Tj, reduces flux (light out) 1) Increasing drive current, increases flux 3 2) Higher current, increases Vf & power Seoul Semiconductor Z1 6

7 Thermal Path is Critical to LED Lifetime 5mm LED Lighting-class LED No Thermal path Thermal path 5mm lamps have almost no thermal path Rth >350 ºC/W typical Chip (T J ) and phosphor can essentially cook themselves Lighting-class LEDs are designed for high temp operation Rth <10 ºC/W typical Lamp can stay within data sheet parameters with good thermal design 7

8 LED Lifetime 110% 100% Lumen Output (%) 90% 80% 70% 60% 100 W Incandescent 5mm LED 42W CFL 50 W Tungsten Halide 400 W Metal Halide 25 W T8 Fluorescent Lighting-class LED 50% 40% Operating Time (k hrs) Courtesy LRC, Rensselaer Polytechnic Institute All conventional light sources dim over time, even LEDs Standard light sources fail (open filament etc) Properly designed LEDs dim gracefully End of life is based on Lumen Maintenance (L70) which is a function of operating temperature 8

9 Application Drives LED Selection What is the area/pattern to be lit? Linear strip or path Spot Area Optics considerations (narrow or wide beam) Diffuser Reflector Lens Reflector Lens Thermal density and heat removal Size and lit appearance 9

10 LED Packaging Trends Smaller size Multi-high power chips Multi-small chips Phosphor coatings methods Higher wattage packages Deposited silicone primary lens systems 10

11 Arrangement of LEDs Driving single strings of LEDs is highly preferred as it provides ideal current matching independent of forward voltage variation, Vout floats Users do configure LEDs in Parallel/Series combinations Requires matched LED forward voltages If an LED fails open, the other LEDs may be overdriven Cross connecting and multiple parallel techniques try to mitigate the risk of a fault Series Parallel Series-Parallel Cross connect If a LED fails open, only 1 LED will be have 2x the drive current 11

12 Example of a Low Current Driver Features Constant current as AC voltage increases No delay in turn on after LED threshold voltage is reached Bright LEDs at low voltages LEDs protected from voltage surge New family of simple 2 terminal Constant Current Regulators (CCR) 20, 25, and 35 ma current SOT123 and SOT223 packages 45 V maximum operation NSI V RMS, TP1-156 V P-P 115 Vac 25 ma 100 Ω 30 LEDs TP2 - LEDs 108 V, 52% On Current probe 25 ma 12

13 LED Driver Basics AC Mains Non-Isolated or Isolated Power Conversion Driver LED(s) The main function of a driver is to limit the current regardless of input and output conditions across a range of operating conditions Ac-Dc power conversion and driver regulation can be merged together into a single driver or separated into two stages The arrangement of LEDs and the luminaire specifications dictate the fundamental driver requirements Isolated solutions means there is no physical electrical connection between the AC line voltage and the LEDs 13

14 Driver Operation Constant Voltage and Constant Current Regions Range of current and/or voltage regulation is driver/design specific Driver constant current behavior may not have a textbook relationship Constant Voltage Constant Current Some drivers are designed for constant power so LED forward voltage determines current Output is voltage Regulated or clamped across a range of current Output can be designed to have tight current limited The output voltage depends on the LED forward voltage 14

15 Basic Configurations In a integral configuration, the power conversion and constant current driver are all within the light fixture Tight coupling of LED light source to the driver Optimum efficiency Simplifies installation In a distributed configuration, the ac-dc power conversion is separate from driver (s) Modular applications like track and cove lighting Simplifies safety considerations Increases flexibility 15

16 Offline LED Applications by Power Level Based on Today s LED Performance Low Power 1-12 W Under-cabinet lighting Desk Lamps Accent Appliances A lamp Bulb Replacement Medium Power 8-40 W Down Lighting Spot Light (PAR38) Equivalent Decorative Light Fixtures Bollards Ceiling Fans Freezer and Refrigerator Lights High Efficiency LED Supplies (ballasts) (24 V/ 48 V) High Power >40 W Area Lighting Street Lights Fluorescent Lights HID Replacement High Efficiency LED Supplies (ballasts) (24 V/ 48 V) 16

17 Factors to Consider Output Power Range of LED forward voltage Current target, maximum LED arrangement Power Source 115 Vac, Universal (US/EU), Industrial 208/277 Vac or other Low Voltage Lighting (landscape, track etc) Solar / Battery Functional Requirements Dimming PWM, 0-10 V, Triac, Wireless, DALI, Proprietary, Other Analog, Digital, or multi-level dimming Lighting Control occupancy, motion, timer Additional Requirements Efficiency Power Factor Size Cost Fault handling (short circuit, open circuit, overload, over temperature Standards Safety (UL,CSA,VDE) Energy Star Reliability Other Considerations Mechanical connections Installation Repair / Replacement Lifecycle Logistics 17

18 Isolated Topology by Power Range Increasing power & Power Density Flyback is the best choice for Low power and LLC is best choice for highest efficiency LLC HB resonant topology flyback 18

19 Offline LED Specific Standards ENERGYSTAR SSL Specification (Version 1.1-2/2009) Luminaire based limits, product specific requirements including power factor No off state power requirement rules out standard wall plug adapters, exception are devices with smart controls, standby < 0.5 W in those cases Electromagnetic & RFI per FCC 47 CFR Part 15/18 IEC (5/2006) - Requirements for DC or AC supplied electronic control gear for LED Modules include: Maximum SELV operating output voltage <= 25V rms (35.3 Vdc) Proper /Safe operation under various fault conditions: No LEDs testing and 2x the rated LEDs or modules Output short circuited No smoke emission or flammability under malfunction ANSI C82.xxx LED Driver specification in development Safety UL, CSA etc - UL1310 (Class 2) / UL / UL1012 See appendix for more information 19

20 Basic Offline Topology Discrete or Analog (NCP4300A) implementation Flyback Controller or converter depending on power 20

21 20 W+ Universal NCP1351 Controllers Discrete Regulator Simple Secondary Control Variable Frequency PWM Controller External HV FET Example based on NCP W Universal input (DN06040) Can support 350 ma to 1 A, design set for 700 ma, 33 Vdc 21

22 NCP1351 LED Demo Board Performance Efficiency across V f and Line (Iout = 700 ma nom) 90% 80% 70% 60% Efficiency (%) 50% 40% 30% 20% 10% 125 x 37 x 35 mm 115 Vac 230 Vac 0% LED Voltage (Vdc) 22

23 Range of Low Power LED Driver Demo Boards Pout based on Vac input range Integrated HV FET Pout (W) NCP1013LED NCP1014LEDGT NCP1028LED NCP1351LED 23

24 Non-isolated Offline Buck Configuration Peak current controlled topology operating in deep continuous conduction Why: Option to eliminate need for large electrolytic output capacitor Simple control scheme with good current regulation Can take advantage of the ON Semiconductor DSS capability to power driver directly from the line Circuit should be optimized for the number of LEDs 24

25 25 Inverted Peak Current Control Buck

26 Regulate Peak Control Valley Continuous Conduction Mode Current is always flowing through the inductor L = (VIN,MAX VOUT) * (VOUT / VIN,MAX) * (1/fs) *(1/ (%Ripple * Iout)) Must respect minimum on-time (LEB + Tpd + MOSFET turn-off time) 26

27 Example: NCP1216 PCC Buck Circuit 115 Vac Iout = 500 ma (nom) NCP1216 is directly powered from the ac mains simplifying startup and operation Efficiency is a function of output power (current, # LEDs), external component selection (FET, inductor, rectifier) and switching frequency Dimmable through opto-coupler for safety isolation DN06050 Design Note available demonstrates performance including EMI filtering 27

28 Considerations for 230 Vac Applications Driving small strings of LEDs at high voltages results in extremely narrow duty cycles Switching controllers have leading edge blank circuit of ns before current is sensed Switching frequency must be reduced for proper operation and input voltage is kept to a minimum with a half wave rectified input circuit AC1 D1 MRA4003T3G Q1 STD1NK60 R5 L1 C1 C2 100nF 230Vac 1uF 400Vdc D2 MMSD4148T1 2R2 1/4W 1mH 0.4 AC2 R1 1R 1W R4 10k 1/2W C5 2.2uF 400Vdc 3 6 LED Current (A) C3 1uF 16Vdc R2 18k 1/4W 4 5 NCP1200 U1 C4 NCP kHz 10uF 25Vdc LED 0.25 R3 2k 1/4W D3 MURA160T Input Voltage (Vac) 28

29 29 Tapped Inductor Approach Extends Duty Ratio, Increase Iout

30 Power Factor Requirements for Offline LED Drivers IEC (EU) requirements dictate THD performance for Lighting (over 25 W), other international standards apply depending on the region US DOE ENERGY STAR includes mandatory PFC for Solid State Lighting regardless of the power level. This is a voluntary standard and applies to a specific set of products such as down lights, under cabinet lights and desk lamps for example >0.7 for residential applications >0.9 for commercial applications While not absolutely mandated in the for lighting in all countries, it may be required based on the application: Utilities drive major commercial uses to have high PF at the facility level Moreover when utilities owns/service the streetlight it is in their interest to have good power factor, typically >

31 Class C Limits This class applies to lighting equipment exceeding 25 W Harmonic Order n < n <= 39 λ is the circuit power factor Maximum Value expressed as a percentage of the fundamental input current 2 30*λ The standard equates to a THD<35% (PF around 0.94). In practice, lighting equipment suppliers may target THD<20%. 31

32 Improving Power Factor for Flyback Circuits Traditional Flyback converters have a PF of ~ Improving this to > 0.7 for low power applications does not require new topologies, just circuit optimization 1u C2 Passive technique (Valley-Fill) ONSEMI haversine flyback optimization Critical Conduction Mode Flyback D6 1 D7 VF := 0 D4 VF := 0 D5 VF := 0 VF := 0 D2 D1 VF := 0 VF := 0 1k R2 VF := 0 D3 1u C1 For high power applications like street lights, a dedicated PFC boost stage is normally used 32

33 NCP1014GTG Demo Board J1-1 1 R1 4R7 Line D1 D2 L1 2.7mH J1-2 1 Neutral C1 100nF MRA4007 D3 MRA4007 MRA4007 D4 MRA4007 C2 220nF C3 1.5nF D5 MURA160 R2 47K T1A 1 D7 FL1 MURS320T3 + C9 1000uF R6 R7 R8 1R8 1R8 10R + TESTPOINT E1 J2-1 1 J LED Anode Reduce bulk cap to improve power factor D6 MMBD914LT1 4 3 T1C 2 T1B Fly Leads FL2 C uF R9 10R R10 10K C10 10nF J2-5 1 J2-6 1 LED Cathode Reduce cap to increase dynamic self supply frequency for improved EMI R3 3.3K 1 U1 3 VCC DRAIN 2 FB GND 4 Output capacitance Increased Q1 BC857 R D8 24V R12 1K E2 - TESTPOINT - TESTPOINT NCP1014 R4 200 R5 2.2K Q2 BC846 R13 10K Off board C4 100nF C5 2.2uF C6 47uF U2 3 4 C7 2.2nF R R15 1K D9 5.1V Slow loop response to improve power factor 8mm Primary-Secondary Boundary Optional dimming components 33

34 Performance of Haversine Flyback DN06051 design note illustrates how to modifying the NCP1014 for higher PF > 0.8 using the haversine flyback optimization which easily meets US Residential Energystar Requirements 34

35 Demo: NCP1014GTG Portable Desk Lamp Desk Lamp 35 W Halogen Magnetic Transformer Light Source Pin 120 Vac Illuminance (Lux)* Power Factor Halogen (35 W bulb) 41.7 W Quad LED 10.9 W NCP1014 LED Driver with PF Correction 4 LED Cree MC-E Multichip Array Summary of Results * Illuminance measures at 0.5 m 35

36 Achieving High Power Factor and Low Distortion High voltage dc node NCP1652 PFC Controller Secondary side control is not draw for simplicity 36

37 Area Lighting Considerations Dimming Control AC NCP1652 Power Supply PFC Isolated DC-DC DC Output PWM LED Module w/ CCR PWM LED Lamp w/ccr Two Stage Modular Approach AC-DC + Constant Current Stages PWM LED Lamp w/ccr Light output varies significantly Poll Height and Spacing Type of Traffic Flow (residential, city center) Significant range of power and light levels required for area lighting One basic design can be scaled up or down in light output by adding LED light bars With a modular approach light bars are field upgradeable 37

38 NCP V Fixed Output Schematic F1 2.5A Ideal for Fixed Voltage Area Lighting AC In R1 1M 0.5W L1 C "X" L2 C "X" R7 365K D1 - D4 1N5406 x 4 C3 0.1uF 400V R6 Z1 R9 R10 R K 365K 332K 365K 1.5KE440A MRA4007T D5 C4 22uF 400V R2 560K 0.5W D10 MRA4007T C5 100uF 35v R4 100 R8 R5 2K 1/2W 100 D11 MMSD 4148T R3 36K 3W D6 C7 100nF 400V 5 MURS120T C uF D7 35V 1 MURS 160T T1 (6:1) R24 100, 1/2W C19 C20 C21 C22 D8 MUR860 1nF 680uF, 63V x 3 L3 3.3uH C23 100, 63V C V 2A _ Notes: C9 680pF R12 27K C10 1nF R K + C11 4.7uF 25V R14 8.6K C12 470pF R15 2.2K C13 33nF R16 100K NCP U NC Z2 MMSZ 5245B C14 10nF D9 MMSD 4148T R17 39K C8 R18 C15 C16 C17 C nF Z3 49.9K MMSZ 5248B uF R ohm R25 0 ohm R K R22 10K R21 Q1 10 R ohm 0.5W SPP11N80C3 SFH615A-4 U2 4 1 C U3 TL431A 2.2nF "Y" R26 2.7K R28 24K R27 1K C26 1uF R31 3.3K 1/4W Z4 (24V) MMSZ5252B C R29 102K R30 5.6K 1. Crossed schematic lines are not connected. 2. Heavy lines indicate power traces/planes. 3. Z2/D9 is for optional OVP (not used). 4. L1 is Coilcraft BU R2B or equivalent. 5. L2 is Coilcraft P3221-AL or equivalent. 6. L3 is Coilcraft RFB0807-3R3L or equivalent. 7. Q1 and Q2 will require small heatsinks. NCP Watt LED Supply 48V, 2A Out, VAC Input 38

39 NCP1652 Efficiency Results Configuration: 48 V / 2 A Efficiency (%) V ac 230 V ac % 20% 30% 40% 50% 60% 70% 80% 90% 100% % of Full Load 39

40 Modifying Secondary Side for CC/CV Operation Efficiency V f = 45 Vdc 40

41 NCL30000 CRM Isolated Flyback Low Power (5-20 W) also need high power factor LED Drivers/Ballasts Downlights / Spot Lights / Outdoor Lighting Key Objectives Directly drive LEDs with tight constant current output regulation High Power Factor >0.9, IEC Class C Harmonic Content Greater than 80% efficiency at low power levels 5-15 W Pout, 83% typical Scale-able to handle a range of power LEDs and current levels Can support existing dimming solutions (TRIAC and Trailing Edge) Design approach to achieve high power factor in a single stage uses a critical conduction mode (CrM) fixed on-time flyback topology 41

42 NCL30000 Basic Application Diagram AC Line Input EMI FILTER D out C in R SU R a D 1 C v R b R x 8 R L OUT2 VCC IN R 1 R ZCD 7 - IN2-6 R t 1 NCL30000 MFP Vcc 8 Q1 NCS1002 IN1- - OUT1 2 R 2 2 COMP DRV 7 C 1 1 IN C comp 3 4 C T CS GND ZCD 6 5 C c GND 4 R y C tim C OUT R CS R c R LED 42

43 Theory of Operation Fixed on-time control results in sinusoidal input current in phase Key Requirements Input capacitance must be very low Control bandwidth must be low (<20 Hz) to maintain constant on-time over a line cycle Secondary feedback controls on-time based on line and load 43

44 NCL30000 Demo Requirements Intended to supply 350 ma and drive a wide range of LEDs (4-15) LED driver applications. Component selections to support 700 ma or higher output current Reference design is targeting <20 W with this transformer, board can also support larger transformer for higher power Scalable solution for different power levels 115 Vac Version Vac 230 Vac Version Vac Vac Extended universal included 277 Vac - no Triac control For Triac Dimming, on time has to be adjusted for a specific number of LEDs to achieve best dimming performance. Default is 12 LEDs Robust Protection Open LED, Shorted Output, Overload 44

45 NCL30000 Demo Board Dual transformer footprints for 15 W / 30 W Designs 45

46 Efficiency and Current Regulation versus Load 370 NCL Vac Demo Board 86% 360 Efficiency -> 84% % LED Current (ma) % 78% Efficiency (%) % % % LED Forward Voltage (Vdc) 46

47 Power Factor and Harmonic Distortion 14 NCL Vac Demo Board Input Current THD (%) Power Factor (PF) THD Power Factor Input Voltage (Vac) 47

48 Line Dimmable LED Drivers Triac dimmers (leading edge, phase cut) are intended for resistive loads and tend to behave badly when connected to an electronic transformer Some manufacturers have specialized dimmers for electronic transformers such as low voltage track lighting Moreover for commercial applications there are also transistor based dimmers that have falling edge control (three wire connection) Triac dimming is common in residential a nd retail application 48

49 Matching LED Driver to Dimmer A typical switch mode power supply feedback system will attempt to maintain constant output over a wide range of input voltage by increasing duty cycle or in this case on time For line dimming, LED current should reduce proportionately to reduction of the RMS input voltage The maximum on time is set to limit the power at the nominal LED string power During dimming, the controller will not be able to increase on time, so natural dimming of the LED occurs in a predictable manner 49

50 Efficiency and Current Regulation versus Load 60 NCL Vac Demo Board 50 Constant Power Region LED Voltage (Vdc) LED Power Dimming Point Constant Current Region Short Protection Region LED Current (ma) 50

51 NCL ma Isolated Flyback 115 Vac / 12 LED / Triac Dimming Version % % % LED Current (ma) % 50% 40% Efficiency % 50 20% 0 10% Input Voltage (Vac) 51

52 NCL ma Isolated Flyback 115 Vac Line Dimming Control - 12 LEDs in Series LED Current (ma) Leviton Sureslide Leviton Electronic Cooper Aspire Lutron Skylark Leviton Illumittech Lutron Digital Fade Leviton Rotary GE DI 61 Lutron Toggler Conduction Angles (degrees) 52

53 Comments on Triac and Transistor Dimming As illustrated, dimming range is highly dependent on the characteristics of the wall dimmer Triac dimmers were originally designed for incandescent lamps and presented a much higher load (4-5x higher) than a LED replacement down-light Unfortunately each manufacturer has different dimmer characteristics As LED lighting enters the mainstream we would expect dimmer manufacturers to start optimizing their products to LEDs 53

54 14 Power Factor and Harmonic Distortion NCL Vac Demo Board Input Current THD Power Factor 8 7 THD Power Factor Input Voltage (Vac) 54

55 Efficiency and Current Regulation versus Load NCL Vac Demo Board (Vout = 12 LEDs, 37 Vdc) % 84% 375 Efficiency -> 82% 80% Iout (ma) % Efficiency (%) 76% % 72% % Input Line Voltage (V ac) 55

56 56 EMI Performance NCL30000 Demo Board ( Vac Version)

57 Isolated High PF Efficiency/Solutions 90% CRM + Resonant Half Bridge Efficiency 85% 80% NCL30000 CRM Flyback CCM single stage NCP1652/NCL30001* (PWM dimmable) Output Current A Universal Input Output Power * Available Dec

58 W CRM/LLC High Power Streetlight Supply NCP

59 50k hours of LED life is great but. Occasionally there can be failures Caused by... LED infant mortality Assembly Partial Defects Transients Some Application Are... Mission Critical Safety Dependent Difficult Access 59

60 NUD4700 LED Shunt Protection Current Source Protects operation in the event of an open LED fault Supports up to 1 A with proper heat sinking NUD4700 in PowerMite Package 60

61 LED Lighting Must be Approached as a System 61

62 Conclusion Offline LED power solutions continue to evolve in a rapid manner as new LEDs are introduced Variety of offline solutions depending on power level, features, and performance ON Semiconductor has a complete portfolio of PFC and PWM controllers and converters to address range of LED power applications Visit the ON Semiconductor website to see what new reference designs are being introduced optimized for specific AC line powered LED applications 62

63 For More Information View the extensive portfolio of power management products from ON Semiconductor at View reference designs, design notes, and other material supporting the design of highly efficient power supplies at 63