ostar lighting english[1]

8/8/2019 OSTAR Lighting English[1]

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May, 2006 page 1 of 15

OSTAR-LightingApplication Note

AbstractThe following application note providesinsight into the high power light sources ofthe OSTAR-Lighting LED product family.A basic overview of the construction of thelight sources, their handling and assemblyand the optical, electrical and performancecharacteristics will be given.In addition to a compilation of potential drivercircuitry for the individual design of a controlgear an overview of obtainable powersupplies of OSRAM is shown.Furthermore an approach relating to thermalrequirements will be provided in a designexample.

OSTAR-Lighting LED Light SourceThe OSTAR-Lighting LED light source wasdeveloped with an emphasis on the areas ofgeneral lighting such as:

Room Lighting

Architectural/Effect Lighting

Industrial Lighting

Radiators and Spot Lighting

Flashlights

However, it is also suitable for specialapplications such as:

Microscope Lighting

High-quality Flash Lamps

Traffic Signs

Operation Lighting in MedicalTechnology

Above all, the OSTAR-Lighting ispredestined for use in applications wherehigh luminance combined with a lowgeometric spreading of the illumination areais required. This particularly applies for

applications with additional lenses or lenssystems.

Due to its flat, compact form, the OSTAR-Lighting offers lighting manufacturers thepossibility to design and develop newillumination concepts as well as lightingdesigns or lighting systems.

In general, there are four variants of the

OSTAR

-Lighting which differ only slightlyfrom each other (Figure 1).The first two are based on a module with 4semiconductor chips; one variant isconstructed without a lens, the other with alens. The other two modules are based on aconstruction with 6 semiconductor chips,and also differentiate themselves by the useof primary optics.


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Figure 1: Modules of the OSTAR-Lighting,with and without primary optics

Construction of the OSTAR-LightingWhen designing the OSTAR-Lighting LEDlight source, special consideration was givento the thermal optimization of the module.Depending on the module type, the core ofthe module consists of four or six highlyefficient semiconductor chips mounted on aceramic substrate.For optimal heat dissipation, the ceramic is

directly mounted to the aluminum surface ofthe isolated metal core board (IMS-PCB).The hexagonal metal core board serves inheat distribution and additionally provides asignificantly large surface for a simplethermal connection to the system heat sink.The hexagonal form also permits a tightlypacked layout of multiple light sources, or asimple cluster arrangement such as a ring. Afurther advantage of the hexagonal form isthat thereby the smallest perimeter can berealized. This is especially important for theuse in flashlight applications.Because of the design and construction, thelight source itself exhibits a very low thermalresistance of RthJS = 3.6 K/W (LE W E3X).

Equipped with an ESD protection diode, theOSTAR-Lighting possesses an ESDwithstand voltage of up to 2 kV according toJESD22-A114-B.

Figure 2: OSTAR-Lighting with lens (LEWE3B)In addition, the OSTAR-Lighting carrierboard can also be furnished with anadditional NTC resistor (e.g. NTC EPCOS8502).The NTC temperature provides a goodapproximation of the average temperature ofthe underside of the board (Offset 0,25K/W= TBoard-NTC/PD). In this manner, it ispossible to implement a feedback loop for

temperature monitoring of the OSTAR-Lighting LED in the driver circuitry.

The light source consists of semiconductorchips which emit blue light and are based onthe latest highly efficient thin film technologyThinGaN.All semiconductor chips are wired in seriesin order to guarantee an equally high currentthrough all chips and to achieve a uniformbrightness across the surface.

In addition to its high efficiency, the newThinGaN technology has the decisiveadvantage that the chip is nearly a puresurface emitter.For use as a white light source, this meansthat the wavelength conversion for thecreation of white light can be carried outdirectly at the chip level.In this case, the converter material is applieddirectly to the chip surface as a chip coatingand not dissolved in the encapsulant as is


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the case with other white LEDs (volumeconversion).The advantage of the chip coating is that theconverter can be applied to the chip surfacein a homogeneous layer with uniformconcentration. This causes the convertedlight to be nearly constant across the entirechip surface.Typically, the color temperature of theOSTAR-Lighting lies in the range of 4500 to7000 K (daylight white), with a colorreproduction index (CRI) of 80.

Handling the OSTAR-LightingIn order to protect the semiconductor from

environmental influences such as moisture,the OSTAR-Lighting is equipped with aclear silicone encapsulant which has anadditional positive influence on reliability andlifetime.In addition, the silicone encapsulant permitsoperation at a higher junction temperature

(150C) in comparison to that of an epoxyresin.Due to the elastic properties of theencapsulant, however, mechanical stress tothe silicone should be minimized or avoidedas much as possible during assembling ofthe LED (see also the application note"Handling of Silicone Resin LEDs).Correspondingly, care must also be takenwith the black Globe-Top encapsulant of theconnection contacts.Excessive pressure on the Globe-Top canlead to spontaneous failure of the lightsource (damage to the contacts).In general, the use of all types of sharpobjects should be avoided in order toprevent damaging or puncturing the

encapsulant.Furthermore, it should be guaranteed thatsufficient cooling is available for the compactlight source during operation.Even at low currents, prolonged operationwithout cooling can also lead to overheating,damage or failure of the module.

Figure 3: Color groups, color temperature and spectrum of the OSTAR-Lighting


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Mounting the OSTAR-LightingFor attaching the LED light source, severalmounting methods can be used.When selecting an appropriate mountingmethod, one must generally insure that agood heat transfer is available between theOSTAR-Lighting and the heatsink and thatit is also guaranteed during operation.An insufficient or completely incorrectmounting can ultimately lead to thermal andmechanical problems during assembly.For most applications, screws shouldgenerally be used for mounting theOSTAR-Lighting light source.When mounting the LED with M3 screws(min. 3pcs, 120 displaced), a torque of 0.8Nm should be used to fasten the screws. In

order to achieve a good thermal connection,the contact pressure should typically lie inthe range of 0.35 MPa.

In addition to mounting with screws, theOSTAR-Lighting LED can also be attachedby means of gluing or clamping.When mounting with glue, care should betaken that the glue is both adhesive andthermally stable, and possesses a goodthermal conductivity.

When mounting a component to a heatsink,it should generally be kept in mind that twosolid surfaces must be brought into closephysical contact.Technical surfaces are never really flat orsmooth, however, but have a certainroughness due to microscopic edges anddepressions. When two such surfaces are joined together, contact occurs only at thesurface peaks. The depressions remainseparated and form air-filled cavities(Figure 4).

Since air is a poor conductor of heat, thesecavities should be filled with a thermallyconductive material in order to significantlyreduce the thermal resistance and increasethe heat flow between the two borderingsurfaces.

Figure 4: Heat flow with and without heatconductive materialWithout an appropriate, optimally effectiveinterface, only a limited amount of heatexchange occurs between the twocomponents, eventually leading tooverheating of the light source.

In order to improve the heat transfercapability and reduce the thermal contactresistance, several materials are suitable.Thermally conductive pastes andcompounds possess the lowest transferresistance, but require a certain amount ofcare in handling.Elastomers and foils/bands are easy toprocess, but usually require a particularcontact pressure, even with pretreatedsurfaces.The success of a particular thermal transfer

material is dependent on the quality, theprocessing of the material and thethoroughness of the design.Table 1 shows an overview of the mostcommonly used heat conductive materialsalong with their important advantages anddisadvantages.


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Description Material Advantages DisadvantagesThermallyconductive paste Typically silicone based, withheat conductive particles

ThermallyconductivecompoundsImproved thermallyconductive paste rubberyfilm after curing

Thinnest

connection withminimal pressure

High thermalconductivity

No delamination

Material discharge atthe edges

Danger ofcontamination duringmass production

Paste can escape and"creep" over time

Connections requirecuring process

Phase changematerialMaterial of polyester or

acrylic with lower glasstransition temperature, filledwith thermally conductiveparticles

Easy handlingand mounting

No delamination

No curing

Contact pressurerequired

Heat pretreatmentrequired

Thermallyconductiveelastomers

Washer pads of silicone-plastic- filled with thermallyconductive particles- often strengthened withglass fibers or dielectrics

Thermallyconductive tapeDouble sided tape filled withparticles for uniform thermaland adhesive properties

No leakage ormovement

No curingrequired

Problems withdelamination

Moderate thermal

conductivity

Contact pressurerequired

Table 1: Thermal Interface Materials

Thermal ConsiderationsIn order to achieve reliability and optimalperformance for LED light sources such asthe OSTAR-Lighting, appropriate thermalmanagement is necessary.Basically, there are two principle limitationsfor the maximum allowable temperature.

First of all, the maximum allowable boardtemperature for the OSTAR-Lighting mustnot exceed 85C. Secondly, the junction

temperature must not rise above the

allowable maximum of 125C respectively150C.Both temperature limits are also specified inthe individual data sheets.

The warming of the OSTAR-Lightinggenerally results from two sources, the firstbeing external in origin (existing ambienttemperature) and the second due to internalprocesses (current-dependent powerlosses).


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This has the consequence that not alloperating conditions are suitable or allowedfor a particular ambient temperature.The maximum allowable current for DCoperation and various pulse modes ofoperation for two temperatures (TA =25Cand TA = 85C) are specified in the data

sheets.For all cases in between, the maximumoperating conditions can be estimated byinterpolation of the curves.

Influence of Junction TemperatureBasically, the maximum allowable junctiontemperature should not be exceeded, as thiscan lead to irreversible damage to the LED

and spontaneous failures.Due to underlying physicalinterdependencies associated with thefunctioning of light emitting diodes, a changein the junction temperature TJ within theallowable temperature range has an effecton several LED parameters.As a result, the forward voltage, luminousflux, color coordinates and lifetime of LEDsare influenced by the junction temperature.

Depending on the given requirements, this

can ultimately have an effect on theapplication.

Influence on Forward Voltage Vf andLuminous Flux vFor LEDs, an increase in junctiontemperature leads to a decrease in forwardvoltage VF (Figure 5), as well as a reductionin luminous flux v (Figure 6).

The resulting changes are reversible. Thatis, the original default values return when thetemperature change is reversed.

For the application, this means that thelower the junction temperature Tj is, thegreater the light output will be.

Figure 5: Relative forward voltage in relationto junction temperature (e.g. OSTAR LE WE2x)

Figure 6: Relative luminous flux in relation tojunction temperature (e.g. OSTAR LE WE2x)


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Color CoordinatesThe influence on the color coordinates dueto a change in junction temperature showsitself as a reversible shift in the defaultvalues.The magnitude of the shift can be calculatedfrom the respective temperature coefficients(Table 2).An increase in temperature to 40C, forexample, results in a shift in the x-colorcoordinate of -0.004, and a shift in the y-color coordinate of -0.008.The shift results in a change in appearanceand thus can have an influence on theapplication, depending on the givenrequirements.

Temperature coefficient [10-/K]TCx

If= 700mA, -10


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OSTAR-Lighting

LED LE W E2A / LE W E2B (4-Chip) LE W E3A / LE W E3B (6-Chip)If 350 mA 700 mA 1 A 350 mA 700 mA 1 Av(typ.) 124lm / 175lm 200lm / 280lm 240lm / 336lm 186lm / 260lm 300lm / 420lm 360lm / 504lmIv(typ.) 40cd / 44cd 64cd/ 70cd 77cd / 84cd 60cd / 65cd 95cd / 104cd 114cd / 125cdTable 3: Optical characteristics of the OSTAR-Lighting

Due to the physical properties of thesemiconductor diode, the brightness of thelight source does not increase or decreaselinearly with respect to forward current.

The result is that the forward current mustbe significantly increased in order to doublethe luminous flux, for example. This effectcan also be seen in the following diagram(Figure 8).

Figure 8: Relative luminous flux in relation toforward current IF (e.g. OSTAR LE W E3x)

For general lighting applications, thephotometric value of illuminance Ev (units oflx = lm/m) is also commonly used.The illuminance describes the luminous fluxfor a particular area at a given distance(Figure 9).

Figure 9: Definition of illuminance EvWhen directly comparing illuminance valuesof illuminants and LEDs, the distance atwhich the value was specified should betaken into account, since illuminance isindirectly proportional to the square of thedistance.

2

)(

r

IrE vv =

(Photometric Distance Law)

This mean, for example, that when thedistance is doubled, the illuminance isreduced by a factor of four (Table 4).


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OSTAR-Lighting

LE W E2A LE W E2B LE W E3A LE W E3BModul4-Chip 6-Chip

Evat 0,5m 265 lx 280 lx 380 lx 416 lxEvat 1m 64 lx 70 lx 95 lx 104 lxEvat 1.5m 28 lx 31 lx 42 lx 46 lxEvat 2m 16 lx 18 lx 24 lx 26 lxTable 4: Illuminance of the OSTAR-Lighting@ IF = 700 mAFor better visualization, one can refer to aso-called illuminance diagram (Figure 10) for

the respective illuminant. This describes theilluminance for a particular area atpredefined distances.

Here it should be noted, that the measuredor specified illuminance only represents thebrightness for the center of the LED orillumination field.

In practice, this means that the exactbrightness curve in the area is dependent onthe radiation characteristics of the light

source or LED. The exact curve can bedetermined with the help of the respectivespecific radiation characteristics.

The radiation characteristics of the variousOSTAR-Lighting light sources vary due tothe attached lens.Figure 11 shows the radiation characteristics

of the LED without a lens; Figure 12 showsthe characteristics with primary optics.

Figure 11: Radiation characteristics ofOSTAR-Lighting without lens (LE W ExA)

Figure 12: Radiation characteristics ofOSTAR-Lighting with lens (LE W ExB)Generally, the illuminance can beadditionally influenced through the use ofappropriate secondary optics.Secondary optics with a 30 radiation angle,adapted to the radiation characteristics ofthe OSTAR-Lighting, would increase theilluminance by about a factor of 3, forexample.

Figure 10: Illuminance of the OSTAR-Lighting LED light sources @ IF = 700 mA


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May, 2006 page 10 of 15

Electrical Performance and Operationof the OSTAR-LightingIn addition to optimized optical performance,the new ThinGaN technology exhibitsimproved electrical characteristics in

comparison to those of customary standardchip technology. These improvements haveled to a significantly reduced forward voltageand higher allowable currents, for example.Table 5 shows the electrical characteristicsof the OSTAR-Lighting light source.

Like all white LEDs which create white lightfrom a blue LED with phosphor conversion,the OSTAR-Lighting exhibits a dependencyof the color coordinates on the forwardcurrent applied (Figure 13).

The result is that a change in the forwardcurrent also causes a shift in the x-y colorcoordinates. Relative to the default colorcoordinates for the grouping current (IF =700mA), a reduction in current leads to aslight shift in the yellow direction; anincrease leads to a shift in the blue direction.

In the application, this can ultimately mean amodified appearance. Particular attentionmust be dedicated to this parameter whendimming the OSTAR-Lighting light source

(see also the application note "DimmingInGaN).Since the OSTAR-Lighting LED light sourceshould be driven with constant current, it isrecommended that when selecting ordeveloping an appropriate power supplyunit, that pulse width modulation (PWM)functionality is present.

Figure 13: Color coordinate change inrelation to forward current IF (e.g. OSTARLE W E3x)The PWM function offers the distinctadvantage that when dimming, the colorcoordinates remain constant since thecurrent level remains constant and only the

pulse duration varies.

Table 6 gives a compilation of possibledriver components for the individual designof a control gear for the OSTAR-LightingLED light sources. Additionally, therespective number of OSTAR-LightingLEDs per component depending on outputvoltage and maximum operating current islisted.

OSTAR-Lighting

Module LE W E2A / LE W E2B (4-Chip) LE W E3A / LE W E3B (6-Chip)If 350mA 700 mA 1.0 A 350mA 700 mA 1.0 AUf(typ.) 13 V 15.2 V 16.2 V 19.5 V 22 V 24.5 VUf(max.) 14.5 V 17.2 V 19.8 V 22 V 25.8 V 29.8 V

Table 5: Electrical characteristics of the OSTAR-Lighting light sources


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January, 2006 page 11 of 15

Table 7 shows an overview of the obtainablepower supplies of OSRAM for driving theOSTAR-Lighting LED light sources.

In Figure 14 examples of a driver circuit forOSTAR-Lighting light sources are shownby means of power supplies from OSRAM.

Driver -IC# OSTAR @ If = 700mAManufacturer Type Voltage Current(max.) 4 Chips 6 Chips

LM3478 Vin = 3 - 240V(DC/DC) Vout = 1.24 - 36V I = 1A 2x 1x

LM5000 Vin = 3.1 - 40V(DC/DC) Vout = 3.1 - 80V I = 2A 4x 3x

LM5010 Vin = 8 75V(DC/DC) Vout = 2.5 - 60V I = 1A 3x 2x

LM5021 Vin = 90 270V (max. 80% duty cycle)

National

(AC/DC) Vout

= 12 - 270V I = 1A 15x 10x

VIPer 22A Vin = 90 - 265V(AC/DC) Vout = 5 - 18V I = 700 mA 1x ---

VIPer 53A Vin = 82 - 265V(AC/DC) Vout = 5 - 40V I = 1 A 2x 1x

L6562 (L6565) Vin = 82 - 265V(AC/DC) Vout = 12 - 270V I = 1 A 15x 10xL4976D Vin = 8 - 55V(DC/DC) Vout = 0.5 - 50V I = 1 A 2x 1x

L5970D Vin = 4.4 - 36V(DC/DC) Vout = 0.5 - 35V I = 1 A 2x 1x

L6902D Vin = 8 - 36V

STMicroelectronics

(DC/DC) Vout = 1.2 - 34V I = 1 A 1x 1x

TPS40200 Vin: 4.5 52VDC/DC Vout: 0.7-46V I = 3A 2x 1x

TPS5430 Vin:5.5-36VDC/DC Vout: 4.75 - 31V I = 3A 1x 1x

UCC3813 Vin: 85 265V

Texas Instruments

AC/DC Vout: 4 - 400V I = 1A 23x 15xHV9910 V

in= 8 - 450V

(AC or DC) Vout < Vin I = 2 A 24x 16x

HV9931 Vin = 8 - 450V(AC or DC) Vout > 3V I = 1 A 12x 8x

HV9930 Vin = 8 - 200V(DC/DC) Vin < Vout < Vin I = 1 A 12x 8x

HV9911 Vin = 9 - 250V

Supertex

(DC/DC) Vout > Vin I = 2 A 24x 16xTable 6: Compilation of driver components for driving the OSTAR-Lighting light sources


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May, 2006 page 12 of 15

Operating / Control Devices# OSTAR @ If = 700mATyp Voltage Current (max.) 4 Chips 6 Chips

OT 9/100-120/350E Vin = 100 - 120V(AC/DC) Vout= 1.8 - 25V I = 350mA 1x 1x

OT 9/200-240/350 Vin = 200 - 240V(AC/DC) Vout= 1.8 - 25V I = 350mA 1x 1x

OT 9/10-24/350 DIM Vin = 10 - 24V(DC/DC) Vout= 0 24.5V I = 350mA 1x 1x

OT 35/200-240/700 Vin = 200 240V(AC/DC) Vout 50V I = 700mA 3x 2x

OT 18/200-240/700DIM Vin = 200 - 240V(AC/DC) Vout 25V I = 700mA 1x 1x

Table 7: Operating and Control Devices of OSRAM (product family OPTOTRONIC)

Figure 14: Examples of a driver circuit with power supplies from OSRAM


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May, 2006 page 13 of 15

Design ExampleIn the following example, a hanging lampwith three OSTAR-Lighting LEDs serves toillustrate the procedures related to the

thermal requirements.

The starting point for the thermalobservation is the three OSTAR-LightingLEDs (LEW E2B, 4x Chip Module with Lens)at an operating current of 700 mA and amaximum ambient temperature of TA= 25C.

With a typical brightness of 280 lm at700 mA per module, the total brightness is840 lm for the lights.

From these given values and the informationfrom the data sheet, the coolingrequirements can be found by the followingformula:

kHeatthJBthInterfaceth

ModulDiss

RRRP

Tsin,,,

,

=

where

][][6][

][][4][][

3,

2,

)()(

AIVUWP

AIVUWPTTTKT

ffXELEWModulDiss

ffXELEWModulDiss

FactorSafetymbientAunctionJ

=

=

=

withTJunction= max. junction temperature(from data sheet TJ = 125C)TAmbient= ambient temperature(TA = 25C)TSafety-Factor = safety factor(typ. 10 - 20C)Uf = forward voltage(from data sheet Uf= 3.8 V)If= forward current(IF = 700 mA)Rth,Interface = thermal resistance of the

transition material(e.g. thermally conductivepaste 0.1 K/W)

Rth,JB = thermal resistance of the OSTARLighting (from data sheet LEW E2BRth,JB = 5 K/W)Rth,Heatsink = thermal resistance of thecooling/heatsink

The thermal resistance for the requiredcooling per LED yields:

WKR

WKR

kHeatth

kHeatth

/35.3

/)51.064.10

1025125(

sin,

sin,

=

=

With the calculated value for the thermalresistance, an appropriate heatsink can beselected from a manufacturer.

Because the light fixture housing, analuminum plate, is also used for cooling inthe previous example, a second step isneeded to calculate the required coolingarea.

0426.0

)735.3

1(

1

1

sin,

sin,

mA

mR

A

AR

kHeatth

kHeatth

=

=

=

=

A = cooling area of a planar heatsink = coefficient for free convection(7 Wm-K-1)

For the lighting example with three OSTAR-Lighting LEDs, this results in a total coolingarea of about 0.1280 m (1280 cm).With a ring-formed design, a light fixture withan outside diameter of 52 cm, a width of9 cm, and a thickness of 4 mm can berealized (Figure 15).

In addition to thermal evaluation by meansof simulation or calculations, it is generallyrecommended to verify and safeguard thedesign with a prototype and thermalmeasurements.


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May, 2006 page 14 of 15

Figure 15: Design ExampleHanging lamp with 3 OSTAR-Lighting LEDlight sourcesThe power supply for the hanging lamp islocated in the ceiling fixture; the wires to theOSTAR-Lighting LEDs are integrated intothe support cables.

ConclusionDeveloped for high power operation withcurrents of up to two Amperes, the OSTAR-Lighting LED light sources achieve a

luminous flux of a few hundred to athousand lumens, depending on operationalparameters.

The OSTAR-Lighting LEDs reachbrightnesses similar to those of halogenlamps (typ. 500-700 lm) rated at 35 Watts ofpower.

Because of the high power operation,suitable thermal management is mandatoryin order to achieve and guarantee optimal

performance and reliability of the module.

When developing new lamp designs basedon the OSTAR-Lighting, it is generallyrecommended that in addition to performinga thermal simulation, the design should beverified and safeguarded with a prototypeand thermal measurements.

Appendix

Don't forget: LED Light for you is your place to be whenever you are lookingfor information or worldwide partners for your LED Lighting project.

www.ledlightforyou.com


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May, 2006 page 15 of 15

Authors: Andreas Stich, Monika Rose

About Osram Opto SemiconductorsOsram Opto Semiconductors GmbH, Regensburg, is a wholly owned subsidiary of Osram GmbH, one ofthe worlds three largest lamp manufacturers, and offers its customers a range of solutions based onsemiconductor technology for lighting, sensor and visualisation applications. The company operatesfacilities in Regensburg (Germany), San Jos (USA) and Penang (Malaysia). Further information isavailable at www.osram-os.com.All information contained in this document has been checked with the greatest care. OSRAM OptoSemiconductors GmbH can however, not be made liable for any damage that occurs in connection withthe use of these contents.

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