conception et réalisation thermique
DESCRIPTION
Conception et réalisation thermique. Troyes, 23 février 2012. Thierry Suzanne Ingénieur d’application. Designer’s Complaint…. LEDs are specified @ single test current @ 25°C Tj. My application is different!. What is the real light output for my application?. - PowerPoint PPT PresentationTRANSCRIPT
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Conception et réalisation thermiqueConception et réalisation thermiqueTroyes, 23 février 2012
Thierry SuzanneIngénieur d’application
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Designer’s Complaint…Designer’s Complaint…
• LEDs are specified @ single test current @ 25°C Tj
• My application is different!
• What is the real light output for my application?
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LED Datasheet SpecificationsLED Datasheet Specifications
• A new trend in the data- sheet characterization of the LEDs– The LEDs are tested and binned at real world
operating conditions
Hot Binning @ 85oC
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What is LED Junction TemperatureWhat is LED Junction Temperature
LED Junction Temperature (Tj)
• Temperature directly on the LED chip/die
• What does tested and binned at 25oC or 85oC at a specific drive current of for example 700mA mean?
– The LED was driven at 700mA and light output measurements were made while the junction temperature at the LED was maintained at 85oC
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Measurement PointMeasurement Point
• Application Brief AB33 http://www.philipslumileds.com/uploads/10/AB33-pdf
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Heat GenerationHeat Generation
• LEDs are not 100% efficient power consumed is not completely converted to light
• Approximately, 30% to 50 % (depending on the technology) is converted to light and the rest is converted to heat
Heat
Radiometric Power (power converted to light)
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Heat FlowHeat Flow
• LED thermal pad does not provide enough surface to dissipate the heat
No heat in the light beam
• We add board, thermally conductive material and heat sink to transfer the heat from the LED junction to the air surrounding the LED
Thermal Pad
• Heat generated by the LED is dissipated via the thermal pad underneath the LED
• No heat in LED’s main light beam
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Effects of Heat on LEDsEffects of Heat on LEDs
• Heat affects the LEDs in 5 different ways:
– Light output– Color shift– Forward voltage shift– LED lifetime– Permanent damage
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Effects of Heat on LEDsEffects of Heat on LEDs
0%
50%
100%
150%
200%
-40 -20 0 20 40 60 80 100 120
Junction Temperature TJ [°C]
Rel
ativ
e L
igh
t O
utp
ut
(LO
P)
AmberRed GreenBlue
White
CyanRoyal Blue
Reduces Light Output
100% light output at 25oC
70C
90%
• AlInGaP: Red, Red-Orange, Amber
• InGaN: Royal-Blue, Blue, Green, Cyan, White
More sensitive to heat
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Effects of Heat on LEDsEffects of Heat on LEDs
Shifts dominant wavelength
Color K (nm/ ºC)
Amber
.09
Red
.03
Blue
.04
Green
.04
Cyan .04
*
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Effects of Heat on LEDsEffects of Heat on LEDs
Tj
0
50
100
150
200
250
300
350
400
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Forward Voltage (V)
Forw
ard
Cu
rren
t (m
A)
Red, Reddish Orange,
Amber(AlInGaP)
Royal Blue, Blue, Cyan,
Green, White (InGaN)
Vf -2.0 to -4.0mV/°C
LED Driver: Vout= 43-48V
@ 25oC Vf=3.0V
15 LEDs:
→ 15 x 3.0 = 45V
OK!!
@ 87oC Vf=2.85V
15 LEDs:
→ 15 x 2.85 = 42.75V
Not OK!!
Vf
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Effects of Heat on LEDsEffects of Heat on LEDs
(B50, L70)
What is (B50, L70)?
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Lumen Maintenance - (Bxx, Lumen Maintenance - (Bxx, Lyy)Lyy)
• Notation used to describe the average lumen maintenance characteristic of the LEDs.
• Lumen maintenance for SSL devices is typically defined in terms of the percentage of initial light output remaining after a specific period of time.
• (Bxx, Lyy)– Bxx: percentage of LEDs, on average– Lyy: percentage of light output remaining
• Example – (B50, L70) at 50000hours:– On average, the light output of 50% (B50) of the LEDs
within the system will drop to lower than 70% (L70) of their initial light output after 50000hours.
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Effects of Heat on LEDsEffects of Heat on LEDs
Reduces operating life
~50.0%
~155k
~165k
~175k
(B50, L70)
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Effects of Heat on LEDsEffects of Heat on LEDs
May cause severe damage
Thermal management is critical
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Basic cooling considerationsBasic cooling considerations
• Conduction:– The transfer of heat energy
through a substance or from one substance to another due to temperature difference
Radiation
ConductionConvection• Convection:
– The process in which hot air rises and cool air delves down. Hot air will cool down as it flows through the cooler air mass until it reaches equilibrium.
• Radiation:– The transfer of heat via
electromagnetic waves through space
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Thermal ManagementThermal Management
• It is critical to extract the heat away from the LED module and transfer it to ambient
• This can be done using the principles of conduction, convection and radiation
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Heat SinksHeat Sinks
Efficiency of heat sinks depends mainly on:
– Surface area• The larger the surface area,
the more heat dissipated
– Structure or shape• Proper structure increases
turbulent airflow which creates a more efficient heat sink
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Heat SinksHeat Sinks
– Material• Use of materials with better thermal conductivity
gives a more efficient heat sink– Ex. cooper 401 W/m-K vs. aluminum 235 W/m-
K
Laminar Flow Turbulent Flow
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Thermal Resistance RThermal Resistance RTHTH
• Thermal resistance describes how much that material resists the flow of heat through it
— Units: oC/W or oK/W
• It changes with the material type, thickness, surface area, and power (number of LEDs)
• We want this number to be as low as possible to make sure heat flows easily from one point to another
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Thermal Resistance RThermal Resistance RTHTH
LED thermal resistance: RTH
junction to slug
Board thermal resistance: RTH
board
Thermal interface material thermal resistance: RTH thermal interface
Heat sink thermal resistance: RTH heatsink
RRTHTH = R TH board+ R TH thermal interface + R TH heat sink+R TH junction to slug
+
+
+
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Thermal Conductivity (k)Thermal Conductivity (k)
Thermal Conductivity Units are in W/mK.
• The measure of a material’s ability to conduct heat (W/mK)
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Case Study Case Study
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Scenarios:
Scenario A: Passive Cooling
• Open Frame
• Closed Fixture
Scenario B: Active Cooling
• Open Frame
• Closed Fixture
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QLED – QLED – Thermal SimulationThermal Simulation
• FLS has jointly developed with Qfinsoft, QLED, a thermal design and simulation software
• In parallel, FLS has launched a thermal design and simulation service to assist customers
• 4 FLS Engineers are assigned to carry out this service
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What is QLED?What is QLED?
• FLS jointly developed QLED with Qfinsoft • QLED is a thermal design and simulation
software developed for modeling LUXEON LED lighting systems
• The accuracy of the LED models and their behavior were endorsed by Philips Lumileds
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What is QLED?What is QLED?
QLED is a virtual environment which allows customers to create different models.
For example, models can range from:
A single LED on a heat sinkto
Multiple LEDs on a custom made board within an enclosed space or casing with active cooling
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Benefits of Using QLEDBenefits of Using QLED
1. It minimizes the number of design cycles, reduces development costs, and decreases time to market
Concept Prototype Testing Product
QLEDConcept ProductPrototype Testing
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2. Simple user interface
Benefits of Using QLEDBenefits of Using QLED
Main Toolbar
Simulation Manager
3D Toolbar
Message WindowComponent Toolbar
3D Model View
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Key FeaturesKey Features
• Provides very fast simulation results, with most simulations taking only minutes
• Offers an easy to use library system for material selection
• Includes a powerful, yet easy to use design optimizer
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QLED CapabilitiesQLED Capabilities
• Simulation modes include:
– Steady state: DC current (constant ON)
– Transient: Pulse or strobe LEDs
– Parameterized Trials
– Optimization
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Scenario AScenario A
Passive cooling
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Fortimo DLM 1100lm Fortimo DLM 1100lm Thermal path basic solutionThermal path basic solution
• Temperatures:– 1 = test point Tc– 2 = heat sink @ module
side– 3 = ambient
• Resistances:– R1 = LED DLM path 1-2– R2 = heat sink path 2-3
13
2
3
2
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Fortimo DLM 1100lm Fortimo DLM 1100lm Thermal ResistancesThermal Resistances
Rth
c-hs
Rth
hs-am
b
Rth
hs-am
bTc
Ths
Tamb
0.2 K/WSide view
Top view
1
3
2
3
3
12
12
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Fortimo DLM 1100lm Fortimo DLM 1100lm Thermal Thermal resistance of heat sinkresistance of heat sink
• Example of standard heat sink:• Needed 4.214 K/W (max)• Heat sink: Aavid Thermalloy
– Length @ 4.01 K/W = 35 mm – Width= 76.2 mm, height= 38.1 mm, #fins= 8
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Thermal Simulation – Open FrameThermal Simulation – Open Frame
• Ambient = 35oC• Tc ≈ 62oC• Matches the theoretical calculations
LEDs junction temp.
Tc
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Thermal Simulation – Closed Thermal Simulation – Closed FixtureFixture
• Tc = 90oC• Exceed the max.
Tc• Thermal design
must be modified
• Fully enclosed can (air tight)• No vents for air to go in and
out• Steel Fixture
Tc
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Solutions? – larger heat sinkSolutions? – larger heat sink
• Larger heat sinks:– Tripled the heat
sink height
• Tc ≈ 73oC• We still need to
lower Tc to 65oC Tc
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Solutions? – larger heat sinkSolutions? – larger heat sink
• Fins extended to touch the fixture
• Tc ≈ 59oCTc
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Solutions? – vented fixtureSolutions? – vented fixture
• Vents on upper and lower sections of the fixture• Tc ≈ 82oC• Even with larger heat sinks, it may be difficult to reduce
Tc
Tc
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Scenario BScenario B
Active Cooling
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Nuventix – Open FrameNuventix – Open Frame
• Each setting has a thermal resistance depending on the performance setting
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Nuventix – Open FrameNuventix – Open Frame
• At the standard setting and ambient temperature = 35oC, Tc ≈ 44.7oC
• Tc = P x Rth(hs-ambient)
+ Tambient
• Tc = 13 x 0.75 + 35 = 44.75oC
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Nuventix – Closed FixtureNuventix – Closed Fixture
• Experimental testing
• SynJet to be modeled in QLED
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© Future Electronics Inc. Confidential and Proprietary Making LED Lighting Solutions Simple TM
© Future Electronics Inc. Confidential and Proprietary Making LED Lighting Solutions Simple TM
© Future Electronics Inc. Confidential and Proprietary Making LED Lighting Solutions Simple TM
© Future Electronics Inc. Confidential and Proprietary Making LED Lighting Solutions Simple TM
© Future Electronics Inc. Confidential and Proprietary Making LED Lighting Solutions Simple TM
© Future Electronics Inc. Confidential and Proprietary Making LED Lighting Solutions Simple TM
© Future Electronics Inc. Confidential and Proprietary Making LED Lighting Solutions Simple TM
© Future Electronics Inc. Confidential and Proprietary Making LED Lighting Solutions Simple TM
© Future Electronics Inc. Confidential and Proprietary Making LED Lighting Solutions Simple TM
© Future Electronics Inc. Confidential and Proprietary Making LED Lighting Solutions Simple TM