High Brightness LED Driver Solutions for General Lighting Created by Bernie Weir 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 LED Technology Forecast and Impact US DOE January 2009 3 LED Optical Characteristics • Chromaticity • 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 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 Operating Relationship Electrical, Optical & Thermal 1 2 Luxeon Rebel White 3) Higher 1) Increasing drive power raises Tj, current, increases flux reduces flux (light out) 2) Higher current, increases Vf & power 6 OSRAM Platinum Dragon 3 Seoul Semiconductor Z1 Thermal Path is Critical to LED Lifetime 5mm LED Lighting-class LED No Thermal path Thermal path • • • 7 5mm lamps have almost no thermal path Rth >350 ºC/W typical Chip (TJ) 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 LED Lifetime 110% Lumen Output (%) 100% 90% 100 W Incandescent 5mm LED 42W CFL 50 W Tungsten Halide 400 W Metal Halide 25 W T8 Fluorescent Lighting-class LED 80% 70% 60% 50% 40% 0 10 20 30 40 50 60 Operating Time (k hrs) • 70 80 90 100 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 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 • Thermal density and heat removal • Size and lit appearance 9 Lens LED Packaging Trends • • • • • • 10 Smaller size Multi-high power chips Multi-small chips Phosphor coatings methods Higher wattage packages Deposited silicone primary lens systems 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 If a LED fails open, only 1 LED will be have 2x the drive current Parallel Series-Parallel 11 Cross connect 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 NSI45025 New family of simple 2 terminal Constant Current Regulators (CCR) • 20, 25, and 35 mA current • SOT123 and SOT223 packages • 45 V maximum operation 110 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 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 Driver Operation Constant Voltage 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 • Some drivers are designed for constant power so LED forward voltage determines current Constant Current • Output is voltage Regulated or clamped across a range of current 14 •Output can be designed to have tight current limited •The output voltage depends on the LED forward voltage Basic Configurations • In a integral configuration, the power conversion and constant current driver are all within the light fixture • In a distributed configuration, the ac-dc power conversion is separate from driver (s) – – – – 15 Tight coupling of LED light source to the driver Optimum efficiency Simplifies installation – – Modular applications like track and cove lighting Simplifies safety considerations Increases flexibility Offline LED Applications by Power Level Based on Today’s LED Performance • Low Power – 1-12 W • Medium Power – 8-40 W • • • • • • Under-cabinet lighting Desk Lamps Accent Appliances A lamp Bulb Replacement • • • • • • • 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) • Area Lighting – – – High Power – >40 W • 16 Street Lights Fluorescent Lights HID Replacement High Efficiency LED Supplies (ballasts) (24 V/ 48 V) Factors to Consider • Output Power – Range of LED forward voltage – Current – target, maximum – LED arrangement • • – – – – – Efficiency Power Factor Size Cost Fault handling (short circuit, open circuit, overload, over temperature – Standards – Safety (UL,CSA,VDE) – Energy Star – Reliability 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 17 Additional Requirements • Other Considerations – – – – – Mechanical connections Installation Repair / Replacement Lifecycle Logistics Isolated Topology by Power Range re c In g n i as p e w o r& P e w o e D r ity s n LLC HB resonant topology Flyback is the best choice for Low power and LLC is best choice for highest efficiency flyback 18 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 61347-2-13 (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 60950 / UL1012 – See appendix for more information 19 Basic Offline Topology Discrete or Analog (NCP4300A) implementation Flyback Controller or converter depending on power 20 20 W+ Universal NCP1351 Controllers Simple Secondary Control Discrete Regulator Variable Frequency PWM Controller External HV FET •Example based on NCP1351 20 W Universal input (DN06040) •Can support 350 mA to 1 A, design set for 700 mA, 33 Vdc 21 NCP1351 LED Demo Board Performance Efficiency across Vf and Line (Iout = 700 mA nom) 90% 80% 70% Efficiency (%) 60% 50% 40% 30% 115 Vac 230 Vac 20% 125 x 37 x 35 mm 10% 0% 0 5 10 15 LED Voltage (Vdc) 22 20 25 30 Range of Low Power LED Driver Demo Boards Pout based on 90-265 Vac input range 25 Integrated HV FET Pout (W) 20 15 10 5 0 23 NCP1013LED NCP1014LEDGT NCP1028LED NCP1351LED 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 Inverted Peak Current Control Buck 25 Regulate Peak – Control Valley • Continuous Conduction Mode – Current is always flowing through the inductor 26 • L = (VIN,MAX – VOUT) * (VOUT / VIN,MAX) * (1/fs) *(1/ (%Ripple * Iout)) • Must respect minimum on-time (LEB + Tpd + MOSFET turn-off time) 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 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 200-400 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 D1 AC1 Q1 STD1NK60 MRA4003T3G C1 100nF 230Vac C2 1uF 400Vdc D2 MMSD4148T1 10k 1/2W AC2 1R 1W 1 0.4 2.2uF 400Vdc 2 6 4 5 LED 0.35 LED Current (A) 1mH C5 8 3 NCP1200 C3 0.3 1uF 16Vdc R2 U1 C4 NCP1200 - 40kHz 205 215 225 235 Input Voltage (Vac) 245 255 265 10uF 25Vdc 18k 1/4W R3 0.25 28 2R2 1/4W L1 R4 R1 0.2 195 R5 2k 1/4W D3 MURA160T3 Tapped Inductor Approach Extends Duty Ratio, Increase Iout 29 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 > 0.95+ 30 Class C Limits This class applies to lighting equipment exceeding 25 W Harmonic Order n 2 3 5 7 9 11 < n <= 39 λ is the circuit power factor Maximum Value expressed as a percentage of the fundamental input current 2 30*λ 10 7 5 3 The standard equates to a THD<35% (PF around 0.94). In practice, lighting equipment suppliers may target THD<20%. 31 Improving Power Factor for Flyback Circuits • Traditional Flyback converters have a PF of ~0.5-0.55 • Improving this to > 0.7 for low power applications does not require new topologies, just circuit optimization 1u – Passive technique (Valley-Fill) – ONSEMI “haversine” flyback optimization – Critical Conduction Mode Flyback VF := 0 D6 VF := 0 D4 D1 VF := 0 VF := 0 1 D7 C2 D5 VF := 0 D2 VF := 0 VF := 0 1k R2 1u C1 • For high power applications like street lights, a dedicated PFC boost stage is normally used 32 D3 NCP1014GTG Demo Board J1-1 1 R1 4R7 Line D1 C1 D3 D2 L1 2.7mH MRA4007 + TESTPOINT D4 C3 R2 1.5nF 47K E1 1 100nF MRA4007 J1-2 MRA4007 MRA4007 C2 220nF 1 D7 MURS320T3 R6 1R8 R7 1R8 J2-1 1 Neutral 1 D5 J2-2 + T1A FL1 C9 1000uF R8 10R R9 10R 1 4 Reduce bulk cap to improve power factor LED Anode 1 MURA160 Fly Leads D6 T1B 3 FL2 C8 R10 C10 10K 10nF J2-5 + 1 1000uF MMBD914LT1 LED Cathode T1C 2 J2-6 1 1 E2 Output capacitance Increased Q1 BC857 100 D8 24V 1 VCC DRAIN FB 3.3K GND 3 2 4 NCP1014 R4 R13 10K 200 R5 Q2 BC846 C6 47uF U2 R14 R15 2 2.2uF 3 C5 1 4 2.2K 100nF 1K U1 R3 C4 R12 Off board Reduce cap to increase dynamic self supply frequency for improved EMI - TESTPOINT - TESTPOINT R11 820 1K D9 5.1V C7 2.2nF Optional dimming components Slow loop response to improve power factor 33 8mm Primary-Secondary Boundary 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 Demo: NCP1014GTG Portable Desk Lamp Desk Lamp NCP1014 LED Driver with PF Correction 35 35 W Halogen 4 LED Cree MC-E Multichip Array Magnetic Transformer Light Source Pin (W) @ 120 Vac Illuminance (Lux)* Power Factor Halogen (35 W bulb) 41.7 W 744 0.961 Quad LED 10.9 W 795 0.857 Summary of Results * Illuminance measures at 0.5 m Achieving High Power Factor and Low Distortion High voltage dc node NCP1652 PFC Controller Secondary side control is not draw for simplicity 36 Area Lighting Considerations Dimming Control NCP1652 PWM Power Supply AC PFC Isolated DC-DC DC Output LED Module w/ CCR PWM LED Lamp w/CCR PWM Two Stage Modular Approach AC-DC + Constant Current Stages LED Lamp w/CCR • Light output varies significantly – – 37 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 NCP1652 48 V Fixed Output Schematic Ideal for Fixed Voltage Area Lighting F1 2.5A C1 C2 0.47 "X" 0.47 "X" MRA4007T C3 0.1uF 400V R7 R6 365K 365K D5 R9 R10 R11 30.1K 332K 365K R2 560K 0.5W R3 36K 3W D10 C4 22uF 400V D11 R4 27K 100 MMSD MURS120T 4148T C6 6 470uF D7 1 35V MURS R5 160T + C11 4.7uF 25V C12 470pF 2.2K R16 C13 33nF 100K 1nF 6 0 ohm 7 8 10 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 BU10-1012R2B 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. 38 C23 0.1 D8 11 100, 63V MUR860 3.3K 1/4W Z4 (24V) MMSZ5252B SFH615A-4 U2 R22 10K 9 MMSD 4148T 4 1 3 2 R27 1K R28 R29 102K C26 R21 R18 C15 C16 C17 C18 Z3 MMSZ 5248B Notes: 100, 1/2W 1nF R26 2.7K 3.3 ohm 11 R17 39K C24 R23 R25 C14 10nF + R24 C19 C20 C21 C22 Q1 SPP11N80C3 12 MMSZ 5245B L3 3.3uH R31 0.1 13 D9 8 C8 16 15 14 NC Z2 8.6K C10 R14 R13 7.32K 680pF C9 R15 680uF, 63V x 3 100 49.9K R12 (6:1) 100nF 2 400V C5 100uF 35v NCP1652 U1 T1 C7 5 R8 2K 1/2W 1 2 3 4 5 D6 0.1 0.1 1nF R19 76.8K Z1 0.1uF 1M 0.5W MRA4007T R1 1.5KE440A AC In D1 - D4 1N5406 x 4 L2 L1 24K 10 R20 0.10 ohm 0.5W 1uF U3 TL431A C25 0.1 C27 2.2nF "Y" NCP1652 90 Watt LED Supply 48V, 2A Out, 90-265VAC Input R30 5.6K 48V 2A _ NCP1652 Efficiency Results Configuration: 48 V / 2 A 94 92 Efficiency (%) 90 88 86 115 V ac 230 V ac 84 82 80 10% 20% 30% 40% 50% 60% % of Full Load 39 70% 80% 90% 100% Modifying Secondary Side for CC/CV Operation Efficiency Vf = 45 Vdc 40 NCL30000 CRM Isolated Flyback • Low Power (5-20 W) also need high power factor – LED Drivers/Ballasts – Downlights / Spot Lights / Outdoor Lighting • Key Objectives – – – – – • 41 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 NCL30000 Basic Application Diagram AC Line Input Dout EMI FILTER Cin RSU Ra D1 Cv Rb Rx 8 VCC RL OUT2 R1 RZCD 7 + IN2+ 5 IN2- 6 - Rt NCL30000 1 MFP NCS1002 Vcc 8 Q1 OUT1 - IN1- 2 C1 R2 2 COMP DRV 7 3 CT GND 6 1 + IN1+ 3 Ccomp GND Cc 4 CS ZCD Ry 4 5 Ctim COUT Rc RCS 42 RLED 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 • 43 Secondary feedback controls on-time based on line and load 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 - 90-130 Vac – 230 Vac Version 180-265 Vac – 90 – 305 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 NCL30000 Demo Board Dual transformer footprints for 15 W / 30 W Designs 45 Efficiency and Current Regulation versus Load NCL30000 115 Vac Demo Board 370 86% 84% Efficiency -> 350 82% 340 80% 330 78% 320 76% 310 74% 300 72% 0 10 20 30 LED Forward Voltage (Vdc) 46 40 50 60 Efficiency (%) LED Current (mA) 360 Power Factor and Harmonic Distortion Input Current THD (%) 13 0.99 12 0.98 11 0.97 10 0.96 9 0.95 8 0.94 7 0.93 THD Power Factor 6 5 0.92 0.91 4 90 95 100 105 110 115 Input Voltage (Vac) 47 1 120 125 130 0.9 135 Power Factor (PF) NCL30000 115 Vac Demo Board 14 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 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 Efficiency and Current Regulation versus Load NCL30000 115 Vac Demo Board 60 Constant Power Region 50 LED Voltage (Vdc) 40 LED Power Dimming Point Constant Current Region 30 20 10 Short Protection Region 0 0 100 200 300 400 LED Current (mA) 50 500 600 700 800 NCL30000 350 mA Isolated Flyback 400 90% 350 80% 300 70% 250 60% 200 50% 150 40% 100 30% 50 20% 0 20 30 40 50 60 70 80 Input Voltage (Vac) 51 90 100 110 120 130 10% 140 Efficiency LED Current (mA) 115 Vac / 12 LED / Triac Dimming Version NCL30000 350 mA Isolated Flyback 115 Vac Line Dimming Control - 12 LEDs in Series 400 350 LED Current (mA) 300 250 200 Leviton Sureslide Leviton Electronic 150 Cooper Aspire Lutron Skylark Leviton Illumittech 100 Lutron Digital Fade Leviton Rotary GE DI 61 50 Lutron Toggler 0 0 20 40 60 80 100 Conduction Angles (degrees) 52 120 140 160 180 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 Power Factor and Harmonic Distortion 1.00 13 0.99 12 0.98 11 0.97 10 0.96 9 0.95 0.94 8 THD Power Factor 7 0.93 6 90 115 140 165 190 215 Input Voltage (Vac) 54 240 265 290 0.92 315 Power Factor Input Current THD NCL30000 90-305 Vac Demo Board 14 Efficiency and Current Regulation versus Load NCL30000 90-305 Vac Demo Board (Vout = 12 LEDs, 37 Vdc) 400 86% 84% Efficiency -> 375 82% 350 78% 76% 74% 325 72% 300 90 110 130 150 170 190 210 Input Line Voltage (V ac) 55 230 250 270 290 70% 310 Efficiency (%) Iout (mA) 80% EMI Performance NCL30000 Demo Board (90-305 Vac Version) 56 Isolated High PF Efficiency/Solutions CRM + Resonant Half Bridge Efficiency 90% CCM single stage NCP1652/NCL30001* (PWM dimmable) 85% NCL30000 CRM Flyback Output Current 0.3-3 A Universal Input 80% 25 57 50 75 Output Power 100 * Available Dec 2009 100-200 W CRM/LLC High Power Streetlight Supply NCP1397 58 50k hours of LED life is great but …. Occasionally there can be failures Caused by. . . Some Application Are. . . 9LED infant mortality 9 Mission Critical 9Assembly Partial Defects 9 Safety Dependent 9Transients 9 Difficult Access 59 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 LED Lighting Must be Approached as a System 61 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 For More Information • View the extensive portfolio of power management products from ON Semiconductor at www.onsemi.com • View reference designs, design notes, and other material supporting the design of highly efficient power supplies at www.onsemi.com/powersupplies 63