5 Explosion of Applications for LEDs General Illumination:ArchitecturalResidentialIndustrialPortable ConsumerOutdoor AreaProjectors & CopiersEntertainment LightingRetail DisplayMedicalEmergency/Safety LightingSigns and Channel LetteringAutomotive:HeadlightsRCLCHMSLInterior LightingInstrument PanelInfotainment BacklightingAviation, Marine, and RailCrash AvoidanceThe increasing cost of energy and concern about climate change is driving the LED market. LEDs can be used in a broad array of applications. At the same time, LED technology is undergoing rapid change and innovation. Thus there is a need to stay current with the latest developments.Mobile Devices:Display backlightingCamera flashBacklighting & Projection:InfotainmentLarge format TV displaysLaptopsPocket & Data Projectors
6 Quantifying Light From LEDs The luminosity function defines wavelengths of light which human eye is sensitive to. This is used as a metric for measuring the usable light output of light sources such as incandescent bulbs, compact fluorescent lamps and LEDs.Luminous flux is a measure of the radiation of the luminosity function from a light source. Units are in lumens.Luminous Flux(Lumens)Luminosity Function66
7 LED Color – Dominant Wavelength Sampling of color LEDsThe dominant wavelength (LambdaD) of an LED is the parameter used to specify the color. Taking a sampling of LEDs on the market, there is some variation among the color description.Sampling of LEDs in the webench library – Definition of “red” can varyOrangeBlueCyanGreenRedYellow/Amber77
8 White LEDs – Color Temperature Sampling of white LEDsIncandescent BulbDaylightWhite LEDs come in a variety of color temperatures. The color temperature correlates to what the human eye perceives from a light source as compared to an ideal black body radiator at a certain surface temperature.This slide shows how WEBENCH LED Designer categorizes themRedTintBlueTintWarm WhiteWhiteCool White88
9 Luminous Flux – Comparison Chart ApplicationBrightness (lumens)40W tungsten bulb500100W tungsten bulb1,50025W compact fluorescent55W halogen auto headlight35W high intensity discharge auto headlight3,250150W halogen projector bulb5,000150W high pressure sodium bulb16,000The high pressure sodium street lamp retails for $51.30 and has a lifetime of 30,000 hours. It contains mercury. The luminous efficacy is 107 lumens/watt.99
10 Luminous EfficacyMeasure of the efficiency of the lighting source (lumens/watt)Can be for the LED only or LED + Driver (system luminous efficacyIncreasing efficacy = lower cost10
11 Luminous Flux for LEDs Most efficient Sampling of .35A cool white LEDs:Most efficient140100 LumensFluxThe luminous flux/watt is shown for a sampling of .35A LEDs. There are some LEDs with over 100 lumens output. At 25C, it would take about 5 of these to be equivalent to a 40W tungsten filament light bulb and about 15 to be equivalent to a 100W tungsten bulb.1.2Power1111
12 WEBENCH® LED Architect Overview of the NEW Webench tool12
13 A Groundbreaking New Tool First of it’s kind on the marketSystem level approachSaves time in LED lighting system design1313
14 WEBENCH® LED Architect Overview Select LED & DriverAnalyze & OptimizeSimulateBuild ItWEBENCH LED Designer has 4 main steps1414
15 How to Access WEBENCH® LED Architect Use the entry panel onTo access WEBENCH LED Designer go to osram.national.com.151515
16 Behavior of LEDs Is Dynamic Light output increases vs currentLight output decreases vs temperatureEfficacy decreases vs currentVf increases vs currentNeed to model these behaviors to give true light outputTradeoffs:High current = more light = fewer LEDsHigh current = higher temperature = less light/shorter lifetime = bigger heat sinkHigh current = lower efficacy = no Energy Star approval
17 Can You Drive a .35A LED At .5A? And Why? LED datasheets typically rate LEDs at a nominal currentLuminous FluxEfficacy1W LED is usually .35A nominal currentLower current = higher efficacyThe LED can be driven at a higher current which increases the light output per LEDFewer LEDs may be requiredBut:Temperature goes upEfficacy goes down
18 Luminous Flux Increases With Current 125%100%.35A.5A.35A Nominal LED can be driven at .5A to get 25% more luminous flux.This reduces the number of LEDs required
19 Luminous Flux Decreases With Temperature 92%70%50C125CLuminous flux reduces to 70% of nominal at 125C.This means big heat sinks are needed
20 Heat Sinks Are Required LEDs generate a lot of heatTotal luminous efficiency of LEDs is only 4% to 22%Total visible light/input power15% of power converted to lightThermal viasLEDHeat sink85% converted to heat
21 Efficacy Decreases With Current Theoretical maximum efficacy for neutral white is 336 lumens/wattDecreased efficacy = no Energy Star certification
23 Enter LED Requirements 1) Input voltage2) Ambient temperature3) Desired light output4) LED colorThe basic requirements are shown on the LED Requirement panelAdvanced inputs
24 Advanced inputs Max Vout Parallel strings on 1 driver Max heat sink dimensionsManufacturerMax junction temperatureIf the user clicks on the advanced inputs link, the user can place limits on critical parameters. This includes the maximum Vout voltage which may be desired to be limited in order to pass safety specifications (60V is typical max). Here the user can also allow for parallel strings on one driver. This can lead to problems with current sharing and brightness between strings, however. The maximum heat sink size can be specified along with the maximum allowed junction temperature. In addition, the manufacturer and distributor can be selected.
25 Step 1: Choose The Ideal LED Solution LEDs and heat sink required to give the desired light outputThe user is presented with a variety of LED + heat sink choices. These are all configured to meet the user’s light output requirement. Based on the optimization knob setting, the software calculates the number of LEDs required at the optimal LED current, and then selects a heat sink. The cost of the heat sink and LEDs, luminous efficacy and heat sink footprint are calculated and displayed in a table and graph. In addition, a thumbnail view of the LEDs arrayed on the heat sink is provided.
26 Detailed LED Performance Click on the details button to get LED performanceWhy does the flux go down with increasing current?
27 Visualize the LED choices What is best for the goals? 100Bubble size = costFootprint of HS (cm2)A graph is provided which shows the heat sink footprint vs luminous efficacy. The bubble size is the cost of the LEDs and heat sink. In this way, the user can quickly visualize the best solution. The user can click and drag the mouse to zoom in and get more details. The best results are in the lower right corner with small bubble size.706478Efficacy (lumens/watt)
28 Optimize the LED Solution Optimization knob1 = Smallest footprint2 = Lowest cost3 = Balanced4 = Higher efficacy5 = Highest efficacyBy turning the optimization knob, the user can change the design goals from a balanced design (3), low cost (2), small footprint (1) and high efficiency/luminous efficacy (4, 5). For each knob setting the software calculates different LED and heat sink solutions to best achieve the design goals.
29 Example Range of LED Options for 1300 Lumens 25cm25.2C/W77L/W$44.45Heat SinkSizeEfficacyCostOptimization12 LEDs258cm23.1C/W63L/W$30.558 LEDs51144cm2.69C/W97L/W$74.1613LEDsTemp115C114C48CHere are several options for a system of 1300 lumens at different optimization knob settings. This includes the LEDs and heat sink but not the driver.The first option is at knob setting 1 which targets low footprint. This has the lowest footprint, but also the relatively low efficacy high temperature and high price.Knob setting 2 gives the lowest price, but the efficacy drops and the size goes up. The temperature remains high.Option 5 has the highest luminous efficacy and the lowest temperature which will lead to better reliability, but also has the highest cost and the largest footprint.Thus we can see there are tradeoffs to be made for each important parameter.Note: The costs are for low volumes and should be used for relative comparisons.Osram Oslon LUW CP7PKTLP5C8E29
30 Hands On Exercise Source: 24 – 32V Light output: 2000 lumens Design Problem:Goals:Source: 24 – 32VLight output: 2000 lumensNeutral white LEDMaximum string voltage: 60VNo parallel LEDs on a single driver allowedWhat is the LED and heat sink combination with the:Smallest footprintHighest luminous efficacyLowest costNote the following:LED manufacturerLED part number# LEDsHeat sink thetaSALED current303030
31 LED Arrays – Parallel vs Serial In order to get the desired amount of light, LEDs must be combined.Parallel:Keeps total Vf low – good for buck driver topologyBut Vf of each LED may not be the same, so some LEDs may get higher current/brightness/temperatureSeries:No problem with differences in current and thus brightness/But, Vf adds up. If exceeds VinMin, then need to use Boost topology driverSince multiple LEDs are normally required to get the desired amount of light, the LED array must be determined. There are advantages and disadvantages in both parallel and series arrangement of the LEDs.3131
32 Driving The LED – Switching Regulator Topology Buck (Step Down):SimpleLowest current requirementsRequires high input voltage (VinMin > Vled)Boost (Step Up):Well known topologyRequires high current (Vin*In = Vout*Iout/Efficiency)Ex: Vin: 5V, Vout: 14V, Iout: .35A, Eff: 90%,Requires Iin of 1.1ABuck/BoostMore complicated/expensive but needed if VinMin < Vout < VinMax (Battery)LEDs are DC devices and require an LED driver to maintain constant current. When using a switching regulator, which topology can be used depends on the input voltage and LED array voltage and current. WEBENCH shows different topologies and the tradeoffs that each one brings.3232
33 Step 2: View LED + Driver Solutions Complete solutions including:LED arrayHeat sinkDriver(s)On the select driver page, the user is presented with a listing of suitable LED driver solutions for the selected LED array. These include different arrangements of the LEDs in series and parallel strings. As a result, there may be several different topologies each with different numbers of drivers. For example, let’s take a case where the input voltage is 24V with 10 LEDs each having 3V forward voltage drop and a drive current of .5A. To drive 10 of these LEDs, they can be put in a single series string of 10 which would result in a total of 30V and .5A, which might require a boost topology. Or they could be arranged into 2 parallel strings of 5 which gives at total of 15V which would enable a buck topology. But this would require 2 drivers if parallel strings on a driver were not desired (this is the default case in WEBENCH and it can be modified in the advanced inputs panel).
34 Example Range of Driver Topology Options for 1300 Lumens, Vin = 14-22V Boost88cm269L/W$37.14Driver+ArrayTotalSizeEfficacyCostTopologyBuck91cm267L/W$41.62Buck/94cm260L/W$43.79#LEDs1 x 93 x 32 x 5Osram Oslon LUW CP7PKTLP5C8EHere are several options for a system of 1300 lumens using a DC input of 14-22V. This highlights the differences between the three topologies. The numbers are for the entire system including the LEDs, heat sink and driver.Thus we can see there are tradeoffs to be made for each important parameter. The costs are for low volumes and should be used for relative comparisons.34
35 LED System tradeoffs 106 Footprint of HS+driver (cm2) Buck Boost The user is presented with a graph of the footprint, efficacy and price for various LED/heat sink/driver options. In this case, the boost drivers tend to be the most efficient and have the smallest footprint. The buck options require more drivers and so they end up being more expensive than the single boost driver. In other applications, the result may be different.865969System efficacy (lumens/watt)
36 LEDs Dominate the Design FootprintSizeCost9 LEDs + HS82cm2$34.24DriverHere is a closer look at one of the LED/heat sink/driver combinations. The LED and heat sink dominate the numbers.6cm2$2.901300 Lumens, Optimization 3, Boost Driver
37 Create and View Design Design Dashboard: LED System summary LED array LED / heat sink displayChartsOptimization GraphsBill of Materials GraphsSimulationCustom Design ReportPrototypingThe user can utilize the full capabilities of WEBENCH Designer. In addition, on the left side of the WEBENCH page is a listing of system level parameters, a block diagram schematic of the LED and driver array and a representation of the LEDs on the heat sink. If there are multiple drivers of the same type, changing the design in WEBENCH Designer for one driver will automatically change it for all the drivers.
38 Hands On Exercise Source: 24 – 32V Light output: 2000 lumens Design Problem:Goals:Source: 24 – 32VLight output: 2000 lumensNeutral white LEDMaximum string voltage: 60VNo parallel LEDs on a single driver allowedWhat is the system (including the LEDs, heat sink and driver) with the:Smallest footprintHighest luminous efficacyLowest cost(Note the LED array and driver topology used)383838
39 Creating A Custom LED Array Click on custom LED button
40 Custom LED Array Configuration Manually change the array, heat sink, LED currentThis will change the calculated light output
42 Hands On Exercise Customer wants more light: Source: 24 – 32V Design Problem:Goals:Customer wants more light:Source: 24 – 32VLight output: 2000 lumensNeutral white LEDMaximum string voltage: 60VNo parallel LEDs on a single driver allowedUse the custom LED array to increase the light output to 2500 lumensWhat is the LED and heat sink combination?Note the following:1) Footprint2) Luminous efficacy3) Cost4) LED manufacturer5) LED part number6) # LEDs7) Heat sink thetaSA8) LED current424242
43 Optimization – Efficiency vs Footprint Left side:Higher frequencySmaller footprintRight side:Lower frequencyLower resistanceHere is a summary of optimizations done on a buck controller design. In general, at a high optimization number, the frequency is lower, which causes lower AC switching losses. However, it also requires more inductance to limit the ripple current. This results in a larger inductor due to the higher number of turns required and larger overall footprint. At the lower optimization settings, the opposite is true. Higher frequency requires less inductance and thus, results in smaller inductors and lower overall footprint.There are additional factors being weighted in the selection process including parasitic resistance (ESR, DCR), component cost and availability.43
44 Optimization – Power Dissipation As freq is decreased:FET Pdiss improvesL Pdiss may get worseHigher L is requiredto maintain VoutPPL = V*dt/diAt the higher optimization numbers with lower frequency, the AC switching losses decrease so the power dissipation of the M1 and M2 FETs decreases dramatically. However the requirement for larger inductance to keep the Vout ripple low usually results in higher inductor power dissipation due to more turns/more wire/higher DCR. This partially offsets the effect of lower switching losses.Lower frequency
45 Optimization SummaryTo get high efficiencyDecrease frequency to reduce AC lossesChoose components with low resistanceTo get small footprintIncrease frequency to reduce inductor sizeChoose components with small footprintCostThese parameters are at odds with each other and need to be balanced for a designer’s needsTools are available to visualize tradeoffs and make it easier to get to the best solution for your design requirements
46 Hands On Exercise Source: 14-22V -Light output: 2500 lumens Design Problem:Goals:Source: 14-22V-Light output: 2500 lumens-Neutral white LED-No limit on maximum string voltage-No parallel LEDs on a single driver allowedUse an LM3429 controllerSee if you can find a FET that costs less.For the original FET and the replacement FET, what is the:FET costFET temperaturePdissGate chargeRdsOnOverall design efficiency464646
47 Why Do Electrical Simulation? Design has already been configured for stable operation, but:May want to verify operation under dynamic conditionsMay want to further optimize the design for your requirements:Improve transient responseMinimize output rippleImprove loop stability
48 Simulation Controls Select sim type and start sim After sim is completeSelect waveforms hereWaveform viewer
49 Simulation Waveform Viewer Advanced controlsRight click to delete a waveformClick and drag to zoom
50 Model Verification: Sim vs Bench LED CurrentSwitch VoltageWhen creating Spice models, it is very important to verify the results against bench data. This can be a time consuming process.Spice model verification involves taking bench data at various operating points and comparing to simulationInductor Current
51 Example: Effect of Output Cap Vin: 24-32VLight output: 650 lumensLED: 5 x Cree MX6AWT-A D51ILED: 0.497A (target)LM3402What are the advantages/disadvantages of having:1) Standard output cap?2) No output cap?3) Smaller value output cap?Use the WEBENCH Advanced Options to check this
58 Example: Effect of PWM Dimming Frequency Vin: 24-32VLight output: 650 lumensLED: 5 x Cree MX6AWT-A D51ILED: .497A (target)LM3402Compare default 2kHz dimming frequency to 4kHzHow will this affect the circuit behavior?
64 Hands On Exercise Create a design using the following: Design Problem:Goals:Create a design using the following:Source Voltage: 24 – 32VLight output: 650 lumensCool WhiteOptimization 3LED: 5 x Cree MX6AWT-A D51LM3402Run a line transient simulation1) Using the default input transient range of 24V – 32V, what is the LED current overshoot and undershoot?2) Change the input transient to 26V to 30V. What is the LED curent overshoot and undershoot?646464
65 Summary WEBENCH LED Architect: Considers LED and heat sink properties LED parameters are dynamic:Environment must be taken into accountWEBENCH LED Architect: Considers LED and heat sink propertiesComputes LED ArrayProvides driver configuration/topology based on size, cost, efficiencyWEBENCH Design Tools save you time65
66 Also FPGA Power Architect: Thank You!Try WEBENCH® LED Architect yourself :Also FPGA Power Architect:66