Prepared by: Jim Young
ON Semiconductor
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EVALUATION BOARD MANUAL
Introduction
The NCL30000 is a power factor corrected LED drivercontroller. This evaluation board manual describes the setupand operation of the NCL30000LED2GEVB LED driver for230 V input. The evaluation board implements an isolatedsingle stage Critical conduction Mode (CrM) flybackconverter providing a regulated constant current to an LEDload. This board has been specifically configured to supportleading and trailing edge line dimming and has beencharacterized across a range of commercially availabledimmers. The output voltage range is suitable for nominal4 to 15 high brightness power LEDs. Protection featuresinclude open load protection, over temperature protection,and overload limiting. As shipped, the evaluation board isset up for the following parameters:
Evaluation Board Specifications
•••••••••
Input Voltage Range: 180 − 265 VacOutput Current: 350 mA $ 5%Output Voltage Range: 12 − 50 VdcOutput Power: up to 17.5 WFull Load Efficiency: >82%Power Factor: >0.93 Typical50°C Ambient OperationClass B Conducted Emissions
Compatible with Triac and Electronic Dimmers
This manual also focuses on how the board can bemodified to support alternate output currents and powerlevels. The NCL30000 datasheet contains additionalinformation on operation of the controller and LED driverapplication. Application Note AND8451 details powerstage design details and AND8448 provides specificinformation for dimming applications. Design calculationsare covered in greater detail in these documents.
The compact evaluation board is constructed withthrough-hole components on the top and surface mountcomponents on the bottom side. This board was designed tomeet safety agency requirements but has not been evaluatedfor compliance. When operating this board, observestandard safe working practices. High voltages are presenton the board and caution should be exercised when handlingor probing various points to avoid personal injury or damageto the unit.Figures 1 and 2 show the top and bottom sides of thisevaluation board. AC input connects to the terminal block inthe upper left corner. Terminals are marked “L” and “N” forLine and Neutral. The LED load connects to the terminal blockin the upper right corner. Note the board is labeled “LED+” and“LED-“. Observe polarity when connecting LED loads. Neverconnect LEDs to the driver while it is running or before theoutput capacitors discharge after removing input power. Inopen load conditions the output capacitors charge to >56 volts.Energy stored in the output capacitance can damage or shortenthe effective life of the LEDs if improperly discharged into theLEDs.
© Semiconductor Components Industries, LLC, 2010
January, 2010 − Rev. 0
1
Publication Order Number:NCL30000LED2GEVB/D
NCL30000LED2GEVB/D
Figure 1. Top Side of Board
Figure 2. Bottom Side of Board
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NCL30000LED2GEVB/D
Figure 3. Board Schematic
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NCL30000LED2GEVB/D
Board Configuration
On-time Capacitor
The evaluation board has been optimized for dimmingwith a 12 W load. Output current is regulated at 350 mAfrom 265 V rms down to a setpoint of about 200 V rms.When the input voltage is ~ 200 V rms, the control methodchanges from closed loop secondary side current control toprimary side control. As the input voltage is reduced furtherthe output current drops in a smooth fashion in response tothe lower input voltage. This response matches the driver toa dimmer thus emulating the dimming response of anincandescent bulb. The following information detailsreconfiguring the evaluation board for alternateapplications.
Table 1. Variables for Calculating Ct Capacitor
VariableLpriPoutIchargeh’VpkVctmaxNVout
Description
Transformer primary inductancePower output to LEDs
On time capacitor charge currentTransformer / secondary efficiencyDimming point peak voltageOn time capacitor peak voltageTransformer turns ratioLED load voltage (12 LEDs)
The input voltage at which dimming or reduction ofoutput current occurs is controlled by C9, power deliveredto the LED load, and parameters from the evaluation board.The approximate value of C9 is calculated by the formulabelow:
C9[
4.94@Lpri@Pout@Icharge
hȀ@V
2pk@V
Ctmax
@
ǒ
VpkN@Vout
)1
Ǔ
Values in the equation above are described in Table 1below:
Value for Evaluation Board
0.0017212275 mA0.87
200 Vrms = 282.8 Vpk4.933.8337
C9[
4.94@0.00172@12@275m
0.87@2452@4.93
@
282.8)1Ǔ+245pFǒ3.83@37In practice, the value of capacitance calculated is anapproximation of operating conditions and optimization isrequired. Empirical testing with a dimmer may be done toselect the optimum input voltage for dimming to begin. Avalue of 180 pF was selected for C9 on the evaluation boardto achieve desired results.
Modifying this evaluation board for alternate LEDconfigurations and power levels is straight forward. Usingthe equation above, enter the target LED power, LEDvoltage, and the target AC input voltage below whichdimming should occur. Select a capacitor somewhat below
the value returned by the approximate formula. Performanceshould be evaluated using the desired dimmers. Checkoperation by noting the conduction angle below which LEDcurrent reduces. Increasing the value of capacitor C9 lowersthe conduction angle where dimming occurs. Performancecan be optimized by selecting the value of C9.
Figure 4 below is the bottom side of the evaluation board.Component locations are circled indicating those values thatare most likely to be changed to optimize for a differentpower level.
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NCL30000LED2GEVB/D
Figure 4. Bottom Side PCB Component Locations
Output Current Setup
A particular driver application may require LED currentother than 350 mA. Output current is controlled by R29located in Figure 4. The following formula is used to set theoutput current.
R29+0.07Iout
Dissipation for current sense resistor R29 is defined by theformula below.
PR29+0.07R29Table 2. Winding Configuration
Winding Configuration
Series (default)
Parallel
H1FL1FL1
H2 2 The secondary windings of power transformer T1 areconnected in series to support the 50 V / 350 mA outputrating of the evaluation board. Applications below 25 V orgreater than 450 mA output should have the transformersecondary windings configured in parallel. This helpsmaintain proper primary bias voltage and enhances currentcarrying capability of the transformer. Table 2 shows how toconfigure the transformer flying leads in the PCB holes forseries and parallel configuration. Figure 5 is the top side ofthe circuit board highlighting the wire holes H1 − H6. H3FL2 H4FL3 H5 H6FL4FL4 http://onsemi.com 5 NCL30000LED2GEVB/D Figure 5. PCB Holes for Transformer Leads As built, the evaluation board is suitable for 17.5 Wmaximum. The transformer secondary windings willsupport up to 1 A of LED current with secondary windingsconfigured in parallel. A 300 V output rectifier was selected for applications upto 50 Vdc output and 265 V ac input. Lower voltagerectifiers are recommended for applications below 50 Vdc.A lower forward voltage drop output rectifier will improveefficiency. Selecting a rectifier with a higher current ratingtypically provides lower forward drop at the currents ofinterest. A 3 A rectifier was selected for the evaluation boardto provide low forward drop. Any change to the outputrectifier requires verifying the maximum voltage rating isnot exceeded. Output Capacitor requires two 1,000 mF capacitors in parallel to provide 30%ripple. Primary Current Limit Maximum current in the switching FET Q3 is establishedby R20. The demo board components have been designed tosupport up to 17.5 W output at 180 V rms input. Note C9 hasbeen preconfigured for 180 pF which limits the maximumpower. If the application requires alternate power level orinput voltage, the value of R20 can be adjusted. Lowerpower or high input line voltage applications my benefitfrom a higher value resistance which providescycle−by−cycle current monitoring in the event of a fault.The formula below provides an estimated value for R20which includes a 25% tolerance for components and start upconditions. R20+ Open Load Protection 0.51.25@Ipri The evaluation board regulates constant current andtherefore the output voltage is determined by the LED loadcharacteristics at the set current level. Energy storage tomaintain high power factor and low output ripple currentrequires relatively large output filter capacitors. The LEDload can be modeled as a constant voltage source with someseries impedance. In essence, the ripple current in the LEDsis controlled by the series impedance coupling the constantvoltage nature of the filter capacitance and constant voltagecharacteristic of the LEDs in a complex relationship. Two 470 mF capacitors connected in parallel provideabout 30% or 105 mA peak-to-peak ripple for a 350 mAaverage LED current. Increasing the output capacitancereduces the ripple current and conversely decreasingcapacitance will increase the ripple. Applications requiringaverage output currents other than 350 mA can be scaled tothis value. For example an application requiring 700 mA The evaluation board includes a circuit to protect theoutput capacitors in the event of open load conditions. Theoutput voltage will be limited when zener diode D12exceeds the zener voltage plus ~0.7 V. D12 is presently 56 Vwhich means the maximum output will be approximately56.7 V. D12 can be changed to protect output capacitors ofdifferent voltage rating. Select D12 zener voltage to matchopen load requirements. The location of D12 is shown inFigure 4. Typical Performance Data Figure 6 below displays the relationship between inputvoltage and LED current for a 12 LED, 13 W load. Higher http://onsemi.com 6 NCL30000LED2GEVB/D input voltages allow the secondary side control loop toregulate 350 mA output current at 37 V nominal load. Notethe inflection point where reduction in current begins as the 350315280245LED Current (mA)2101751401057035030507090110130150170Input Voltage (Vac) 190210230250LED CurrentEfficiencyinput voltage is reduced below 200 Vac. This is the dimminginception point. 100%90%80%70%60%50%40%30%20%10%0%270EfficiencyFigure 6. Line Regulation and Efficiency for 13 W Load Efficiency performance is shown in Figure 6 as well. Notethe efficiency remains above 70% until the output currentdrops below 70 mA. The output voltage is about 34 Vmeaning the delivered power is about 2.4 W or less than20% of the full power. As the current delivered is reduced,the fixed losses for startup and biasing begin to dominate theefficiency curve resulting in a steep drop off of efficiency.Harmonic content characterizes the waveshape of theinput current waveform. Odd order harmonics of thefundamental distort the input waveform resulting innon−sinusoidal shape. International standard IEC61000−3−2 Class C places limits on input current harmonicsfor lighting equipment. A category for devices drawing notmore than 25 W applies to this reference design.Performance of this demonstration board with a 12 W LEDload at 230 Vac, 50 Hz input and applicable limits are shownin Table 3. Table 3. INPUT CURRENT HARMONIC CONTENT Harmonic 35 Value11.02%5.16% Limit86%61% Power factor and input current Total Harmonic Distortion(THD) are performance factors receiving considerableattention from utility companies and government agencies.Figure 7 below displays performance of the evaluationboard. The EMI filter was designed for a 17.5 W load. Thefilter can be optimized for higher power factor inapplications requiring less power. http://onsemi.com 7 NCL30000LED2GEVB/D 2019181716151413121110 THDPower Factor0.980.970.960.950.940.930.920.910.90.890.88270 Power Factor (PF)Percent Input Current THD (%)180195210 225 Input Voltage (Vac) 240255 Figure 7. Power Factor and THD The evaluation board was tested with a variety ofcommercial dimmers. Figure 8 shows the dimmingperformance with several triac and electronic dimmers.Dimming control range varies by manufacturer, but a range 385350315280245LED Current (mA)2101751401057035002040of greater than 10:1 was consistently demonstrated. Notethat minimum conduction angle and therefore LED currentis controlled by the design of the triac or electronic dimmerselected. Lutron LLSM−502Clipsal KB31RD400MK SX8501Clipsal 32V500Alombard 741021Legrande CelianeClipsal 32E450UDClipsal 32E450LM6080100Conduction Angle (degrees) 120140160Figure 8. Performance of Evaluation Board with Various Line Dimmers http://onsemi.com 8 NCL30000LED2GEVB/D Table 4 lists commercial dimmers successfully tested with the evaluation board. The load is 12 LEDs (Vf = 37 Vdc) andnominal current is set for 350 mA. Table 4. DIMMER COMPATIBILITY CHART ManufacturerAlombardClipsalClipsalClipsalClipsalLegrandeLutronMK Dimmer Model741021KB31RD40032E450LM32E450UD32V500999.58LLSM−502SX8501 Minimum Conduction Angle (degrees) 20.738.210.630.89.21827.441.8 Current at Minimum Conduction Angle (mA) 7.255.2129.5023.825.774 Conclusion The NCL30000LED2GEVB is a versatile dimmer-compatible LED driver. This board provides rapidassessment of capabilities and serves as a basis for LEDdriver solutions. Smooth flicker-free dimming performanceis demonstrated with a wide variety of commerciallyavailable dimmers. Full 350 mA LED current is provided atmaximum dimmer setting. High power factor and high efficiency provide a cost effective solution for a dimmercompatible LED driver. Additional Application Information and Tools The NCL30000LED2GEVB evaluation board,NCL30000 datasheet, AND8451 Power Stage DesignGuidelines, MicrosoftR ExcelR Design Spreadsheet, andAND8448 TRIAC Dimming application note are availableat www.onsemi.com. Microsoft and Excel are registered trademarks of Microsoft Corporation. ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further noticeto any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liabilityarising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages.“Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. Alloperating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rightsnor the rights of others. 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