AB20-4 [LUMILEDS]
Thermal Management Considerations for SuperFlux LEDs; 热管理注意事项食人鱼LED灯
| 型号： | AB20-4 |
| 厂家： | 
LUMILEDS LIGHTING COMPANY |
| 描述： | Thermal Management Considerations for SuperFlux LEDs |
| 文件： | 总14页 (文件大小：267K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
application brief AB20ꢀ4
replaces AN1149ꢀ4
Thermal Management
Considerations for SuperFlux LEDs
Thermal management is critical in the design of LED signal lamps because temperature affects
LED performance and reliability. The following section details the effects of temperature on
LEDs. In addition, thermal measurement techniques of LED signal lamps and recommended
design practices for proper thermal management are covered.
Table of Contents
Importance of Thermal Management
for High-Power LED Assemblies
Temperature Induced Effects on LED Light Output
Change in Dominant Wavelength (Color) as a Function
Of Junction Temperature
TemperatureꢀInduced Failures of LEDs
Thermal Modeling of LED Assemblies
Thermal Resistance of LED Automotive Signal Lamps
JunctionꢀtoꢀAmbient Thermal Resistance Measurement Procedure
JunctionꢀtoꢀAmbient Thermal Resistance Measurement
Estimating JunctionꢀtoꢀAmbient Thermal Resistance
Evaluating Junction Temperature and Forward Current
Light Output and Forward Current
Derating Example Cases
2
2
2
3
4
4
5
5
6
6
7
7
Recommended Design Practices for Proper Thermal Management
PCB Design
8
8
Maximum Metallization
8
LED Spacing
9
Lamp Housing Design and Mounting of the LED Array
Circuit Design
9
10
10
10
11
11
12
Current Control
Power Dissipation
“Switching” Power Supplies
Ambient Temperature Compensation
Appendix 4A
Alternate JunctionꢀtoꢀAmbient Thermal Resistance
Measurement Procedure
12
Importance of Thermal Management
for HighꢀPower LED Assemblies
Temperature Induced Effects on LED Light Output
The junction temperature of the LED affects the
device’s luminous flux, the color of the device,
and its forward voltage. Junction temperature
can be affected by the ambient temperature
and by selfꢀheating due to electrical power
dissipation.
Typical temperature coefficients for various highꢀ
brightness LEDs are listed in Table 4.1.
The degradation of flux as a function of
increasing temperature for a typical redꢀorange,
absorbingꢀsubstrate (AS) or transparentꢀ
substrate (TS) AlInGaP LED is shown in Figure
4.1. Note, luminous flux has been normalized at
25°C.
The equation for luminous flux as a function of
temperature (°C) is given below:
Tj
ΦV (T2) = ΦV (T1)e–k
This graph shows the profound affect that
temperatures within the normal operating
guidelines can have on luminous flux. As shown,
an increase in the junction temperature of 75°C
can cause the level of luminous flux to be
reduced to oneꢀhalf of its room temperature
value. From this, it is clear that temperature
effects on luminous flux must be accounted for
in the design of a LED assembly.
∆
Where:
ΦV (T1)= luminous flux at junction temperature T1
ΦV (T2)= luminous flux at junction temperature T2
k = temperature coefficient
∆Tj = change in junction temperature (T2ꢀ T1).
Table 4.1
Temperature Coefficient for High-Brightness LED Materials.
LED Material Type
Temperature Coefficient, k
AS AlInGap, Red-Orange
AS AlInGap, Amber
TS AlInGap, Red-Orange
TS AlInGap, Amber
9.52 x 10-3
1.11 x 10-2
9.52 x 10-3
9.52 x 10-2
Figure 4.1 Luminous flux versus ambient
temperature for a typical red-orange AS/TS AlInGap
LED when operated at a constant current.
Change in Dominant Wave-length (Color) as a Function
of Junction Temperature
The junction temperature of LEDs also affects
their dominant wavelength, or perceived color.
A rule that is easy to remember is the dominant
wavelength will increase one nanometer for every
10°C rise in junction temperature. In most
designs of red automotive signal lamps, this
change in color is not important because the
allowed color range is very large (approximately
90 nm). However, for some amber automotive
signal lamps, this color shift can be a concern
and should be accounted for where the allowed
color ranges are small (approximately 5 to 10 nm
depending on the regional specifications).
The equation for dominant wavelength, λd , as
a function of temperature is:
Where:
λd (T1)= dominant wavelength at junction
temperature T1
λd (T2)= dominant wavelength at junction
temperature T2
Temperature-Induced Failures of LEDs
LEDs are typically encapsulated in an optically
clear epoxy resin. At a certain elevated
epoxy encapsulant to expand and contract more
during temperature changes. This causes more
displacement of the wire bond within the LED
package, resulting in a premature wearꢀout and
breakage of the wire. Wire bond breakage results
in an open failure.
temperature, known as the glass transition
temperature, Tg, these epoxy resins transform
from a rigid, glassꢀlike solid to a rubbery
material. A dramatic change in the coefficient of
thermal expansion (CTE) is generally associated
with the Tg. The Tg is calculated as the midpoint
of the temperature range at which this change
in CTE occurs, see Figure 4.2.
To avoid catastrophic failure of LED packages,
the junction temperature, Tj , should always be
kept below the Tg of the epoxy encapsulant.
Lumileds specifies a maximum junction
temperature, Tj (max) , which is below the Tg of the
epoxy encapsulant used. For SuperFlux LEDs,
Tj (max) = 125 °C. If the Tj (max) is exceeded, the CTE
of the epoxy encapsulant will permanently and
dramatically change. A higher CTE causes the
Figure 4.2 Expansion-Temperature relationship for
clear, epoxy, LED encapsulants.
3
Thermal Modeling of LED Assemblies
Thermal Resistance of LED Automotive Signal Lamps
Assuming all the electrical power is dissipated in
Thermal resistance is associated with the
the form of heat (approximately 5ꢀtoꢀ10% of the
conduction of heat, just as electrical resistance
is associated with the conduction of electricity.
Defining resistance as the ratio of driving
potential to the corresponding transfer rate,
thermal resistance for conduction can be
power is dissipated optically), the equation for
junctionꢀtoꢀpin thermal resistance (Rθ ) of an LED
jp
can be written in the form of the equation below:
defined as shown in the equation below:
_
Where:
P = the total electrical power into the LED (If * Vf)
Where:
For LED lamp assemblies, the equation for
Rθ = thermal resistance between two points
∆T = temperature difference between those
two points
junctionꢀtoꢀambient thermal resistance, Rθ ,
ja
of an individual LED within the assembly can
be written as:
qX = rate of heat transfer between those two
points
The thermal resistance of an LED signal lamp
Where Tj = ∆Tj + Ta .
(junctionꢀtoꢀambient thermal resistance, or Rθ
)
ja
is made up of two primary components: the
thermal resistance of the LED package
As can be seen from this equation, in order to
determine Rθ of an LED within a lamp assembly,
ja
(junctionꢀtoꢀpin thermal resistance, or Rθ ) and
the rise in junction temperature, and the electrical
power into the device must be determined. The
electrical power into the LED under test can
easily be determined by multiplying its forward
current and forward voltage. The rise in junction
temperature can be determined by measuring
the change in forward voltage of the LED under
test.
jp
the thermal resistance of the lamp housing (pinꢀ
toꢀambient thermal resistance, or Rθ ). These
pa
two components of thermal resistance are in a
series configuration, therefore:
Rθ
+
Rθ
=
Rθ
ja
jp
pa
(LED emitter)
(lamp housing)
(LED signal lamp)
This is shown graphically in Figure 4.3.
Figure 4.3 Graphic representation of the components
of thermal resistance.
4
Junction-to-Ambient Thermal Resistance Measurement Procedure
Step 4: Assemble the modified PCB into the lamp housing
A simple method for measuring the Rθja of a lamp
assembly is possible by assuming the Rθjp of the device
under test (DUT) is of a typical value. By making this
assumption, only the pin-to-ambient thermal resistance,
Rθpa , needs to be measured to calculate the Rθja of the
lamp (Rθja = Rθjp + Rθpa). This simplified procedure for
measuring Rθja is described below:
such that the thermocouple wires are extending
outside the lamp.
Step 5: Energize the entire lamp assembly at the design
voltage for a minimum of 30 minutes. This will allow
the lamp assembly to thermally stabilize.
Step 6: Measure the pin temperature of the DUT along with
the ambient temperature in the room.
Step 1: Assume the Rθjp of the LED emitter is that shown
in the data sheet (typical Rθja for HPWA-xx00 =
155 °C/W, and for HPWT-xx00 = 125 °C/W).
Step 7: Calculate the Rθpa of the lamp assembly using the
following equation:
Step 2: Pick one LED within the assembly to be used as
the DUT. The hottest LED in the assembly should
be chosen, for example an LED in the middle of
the assembly and next to a resistor.
Tp - Ta
Rθpa
=
P
Where the power, P, into the DUT is calculated by
multiplying the heating/design current by its
corresponding forward voltage.
Step 3: Solder a small thermocouple (approximately 0.25
mm in diameter) onto one of the cathode leads of
the DUT near the top surface of the PCB. Large
thermocouples, which can alter the thermal
Step 8: Calculate the Rθja of the lamp assembly by adding
the Rθjp of the emitter from Step 1 to Rθpa from
Step 7.
properties of the DUT, should be avoided.
Junction-to-Ambient Thermal Resistance Measurement
These sections give detailed instructions on
how to perform thermal resistance
not available. An alternate method for measuring
thermal resistance is provided in Appendix 4A.
This method monitors the change in forward
voltage of the LED to determine the change in
junction temperature and thermal resistance.
This method requires an elaborate test setup and
precise measurements. This technique is
commonly used by Lumileds Lighting.
measurements on LED assemblies. The first
method described in the box above, Junctionꢀ
toꢀAmbient Thermal Resistance Measurement
Procedure, allows for simple measurements to
be made on lamp assemblies without an
elaborate test setup. The second method
presented, Estimating JunctionꢀtoꢀAmbient
Thermal Resistance, eliminates the need for
measured thermal resistance. This type of
estimation is ideal for early evaluations, where
an actual prototype and/or test equipment is
Lumileds will evaluate the thermal resistance of
LED assemblies and signal lamps upon request.
Please contact your local applications engineer
for information.
5
Table 4.2
Typical Rθ Values for the Classes of LED Lamp Assemblies
ja
Typical Rθ (°C/W)
LED Lamp Classification
ja
Class 1
Class 2
Class 3
Class 4
325
400
500
650
Estimating Junction-to-Ambient Thermal Resistance
The procedures described in Junction-to-Ambient Thermal
Resistance Measurement Procedure are accurate
methods for determining the Rθja of an LED within a
plastic lamp assembly. However, in some cases, the time
and/or equipment may not be available to perform such
testing. In these cases, an educated estimate may be the
best method available. Lumileds has developed some
basic classifications of LED lamp assemblies and
corresponding Rθja estimates. Below is an explanation
of the different classes, and the Rθja estimates.
Class 3: Multiple rows, or an x-y arrangement, of LEDs with
the current-limiting resistors/ drive circuitry located
off of the PCB, either in the wire harness assembly
or on a separate PCB.
Class 4: Multiple rows, or an x-y arrangement, of LEDs with
the current-limiting resistors/ drive circuitry located
on the same PCB as the LEDs. This is the most
common situation for LED rear combination lamp
applications.
Table 4.2: lists the typical Rθja values for each class of LED
lamp assembly listed above. These are only
estimates and should not be used for detailed,
worst-case analyses.
Class 1: Single row of LEDs with the current-limiting
resistors/drive circuitry located off of the PCB,
either in the wire harness assembly or on a
separate PCB.
Class 2: Single row of LEDs with the current-limiting
resistors/drive circuitry located on the same PCB
as the LEDs. This is the most common situation
for LED CHMSL assemblies.
Evaluation Junction Temperature and Forward Current
The primary concern when evaluating the
thermal characteristics of an LED assembly
is to ensure that the junction temperature of
the LEDs is kept below the specified maximum
value (125 °C for SuperFlux LEDs). There are
three factors which determine junction
Tj = (Rθ . PLED) + Ta
ja
Tj = (Rθ . If LED . Vf LED) + Ta
ja
Typical values for Ta(max) are shown in Table 4.3.
To determine the worstꢀcase, highest junction
temperature, this equation becomes:
temperature: 1) ambient temperature, 2) Rθ ,
ja
and 3) power into the LED. Below is a sample
junction temperature calculation, which
illustrates how these three factors interact:
Tj max = (Rθ . PLED max ) + Ta max
ja
Tjmax = (Rθ . If max . Vf max ) + Ta max
ja
Tjmax ≤ 125°C
6
Lumileds plots these curves for different values
referred to as the derating curves. The derating
curves for HPWTꢀxx00 devices, are shown in
Figure 4.4. Derating curves for HPWAxx00
devices are provided in the SuperFlux LED
Technical Data Sheet. Refer to sideꢀbar Derating
Example Cases for further explanation.
of Rθ along with their intersection with the
ja
maximum drive current of 70 mA, and their
intersection with the maximum ambient
temperature of 100 °C and includes this graph
in all LED data sheets. This graph is typically
Light Output and Forward Current
The relationship between light output and
decrease as forward current is increased. For
forward current for different thermal resistances
is shown in Figure 4.5. For LED assemblies with
assemblies with high Rθ , a great deal of heating
ja
occurs resulting in high junction temperatures.
In these cases, the effects of increasing junction
temperature can offset the effects of increasing
forward current. Proper thermal management
and drive current selection is critical to
low thermal resistances (Rθ = 200 °C/W), the
ja
relative flux increases almost proportionally to
the forward current. However, for LED
assemblies with high thermal resistances
(Rθ = 600 °C/W), the relative flux can actually
maximizing the performance of LEDs.
ja
Derating Example Cases
Case 1—Class 1 LED CHMSL
From Table 4.2 the thermal resistance can be estimated
as Rθja = 650 °C/W. Using Figure 4.4, the maximum
allowable forward current through each LED is 30 mA at
Ta(max) = 75 °C.
Consider an LED CHMSL application using 12 HPWTꢀ
MH00 LEDs in a row, with a current limiting resistor in the
wire connector. The auto manufacturer has specified a
maximum ambient temperature of 75 °C.
As can be seen from these simplified sample cases, the
Rθja has a major impact on junction temperature, and thus
maximum allowable forward current. The different
applications using the same LED have a difference in
maximum forward current of nearly 2:1.
From Table 4.2 the thermal resistance can be estimated
as Rθja = 325 °C/W. Using Figure 4.4, the maximum
allowable forward current through each LED is 55 mA
at Ta (max) = 75 °C.
Case 2—Class 4 LED Rear Combination Lamp (RCL)
Consider an LED RCL application using 36 HPWTMH00
LEDs in a 6x6 pattern, with the drive circuitry on the same
PCB as the LEDs. The auto manufacturer has specified a
maximum ambient temperature of 75 °C.
A more detailed determination of maximum forward current is
presented in Application Brief 20ꢀ3 Electrical Design
Considerations for SuperFlux LEDs.
7
Recommended Design Practices for
Proper Thermal Management
PCB Design
Proper PCB design can reduce the Rθ of a
cathode leads of the LEDs are ideal. Very little
heat is conducted through the anode leads of
the LED, so additional metallization surrounding
these leads does not help.
ja
LED lamp assembly, and thus reduce the
junction temperature of the LEDs. Listed below
are some recommended practices for the
design of LED PCBs.
Maximum Metallization
Conventional PCB design involves connecting
various points on the board with traces of
sufficient width to handle the current load. This
process is usually visualized as adding traces to
a blank PCB. For LED PCBs, this process
should be reversed—visualized as removing
metal only where needed to form the electrical
circuit. Large metal pads surrounding the
Figure 4.4 Graph of HPWT-xxOO Derating Curves.
Table 4.3
Typical Ta (max) Values for Automotive Signal Lamps
Typical Ta (max) (°C)
Application
Exterior-mounted signal lamp
Interior-mounted CHMSL
Interior, head-liner mounted CHMSL
70
80
90
Figure 4.5 Relative Luminous Flux vs. Forward
Current.
Figure 4.6 LED CHMSL PCB with proper
metallization and component placement.
8
The resistors should be located in a remote
portion of the PCB (away from the LEDs), on a
separate PCB, or in the wire harness if possible.
If this is not possible, the resistors should be
distributed evenly along the PCB to distribute
the heat generated. In addition, the traces from
resistors to metallized areas surrounding
cathode leads on the LEDs should be
minimized to prevent resistors from heating
adjacent LEDs. This can be accomplished by
thinning down these traces, or by having
metallized areas contacting the LEDs and
resistors only contact the anode leads of the
LED. A portion of an LED CHMSL PCB depicting
the design concepts discussed is shown in
Figure 4.6.
LED Spacing
Most of the electrical power in an LED is
dissipated as heat. Tighter LED spacing
provides a smaller area for heat dissipation,
resulting in higher PCB temperatures and thus
higher junction temperatures. The LEDs should
be spaced as far apart as packaging and
optical constraints will allow. Most CHMSL
applications use only a single row of LEDs at
spacing greater than 15 mm which is ideal, as
opposed to many amber turn signal applications
which use a tightly spaced (less than 10 mm) xꢀy
array of LEDs.
Lamp Housing Design and Mounting of the LED Array
LED lamp housings should be designed to
provide a conductive path from the backside of
the PCB to the lamp housing. This is typically
accomplished by mounting the backside of the
PCB directly to the lamp housing such that they
are contacting one another across the entire
length of the PCB. This mounting scheme can
be improved by applying a thermally conductive
pad between the PCB and the lamp housing.
The thermally conductive pad conforms to the
features on the backside of the PCB and
PCB along its top and bottom edges to slots in
the side of the lamp housing. Again, the area for
conduction into the lamp housing is reduced to
the contact areas of the slots, which reduces the
effectiveness of conduction.
If the PCB is mounted in such a way that
conduction to the lamp housing is not effective
(trapped air is a very poor conductor of heat),
then allowances for convective cooling should be
made. The most common technique to take
advantage of natural convection is to put holes in
the top and bottom side of the lamp housing to
allow for vertical air flow over the PCB. However,
where the lamp housing must be sealed for
environmental reasons, this type of approach is
impractical.
provides a larger contact area for conduction.
Often the PCB is mounted to the lamp housing
on top of raised bosses. In this case, the area
for conduction into the lamp housing is reduced
to the contact area on the top side of the
bosses, greatly reducing its effectiveness.
Another common configuration mounts the
9
Circuit Design
Circuit design can help control the junction
temperature of the LEDs in two important ways:
1) minimize fluctuations in the drive current
(power input), and 2) dissipate a minimum
amount of heat, or dissipate heat in such a
way as to minimize its effect on the LEDs.
Figure 4.7 Schematic of a current control circuit for
LED automotive lamp applications.
Current Control
An ideal drive circuit will provide the same
current to the LEDs even as ambient
temperatures and battery voltages vary.
Inexpensive, simple current control circuits
can be designed to accomplish this task.
A schematic of such a circuit is shown in
Figure 4.7.
Current control circuits are often too expensive
and unnecessary for LED CHMSL applications.
The most common LED CHMSL drive circuit
consists of a current limiting resistor(s) and a
silicon diode for reverse voltage protection in
series with the LEDs. In this circuit design,
the input current into the LEDs varies as the
battery voltage changes. The current control
characteristics of this type of circuit improve
as larger resistor/s are used with fewer LEDs
in series. However, circuits with fewer LEDs in
series will have greater heat generation in the
drive circuit. Figure 4.8 graphs the forward
current provided to the LEDs vs. the input
battery voltage for resistor circuits with three,
four, and five LEDs in series.
Figure 4.8 LED forward current vs. battery voltage
for circuits of two, three, four and five LEDs in
series with a current limiting resistor.
Power Dissipation
If the LED drive circuit is in a remote location
relative to the LEDs (in the wire harness or on a
separate PCB), then the power dissipated by the
drive circuit does not affect the junction
temperature of the LEDs. Drive circuit heating
is a concern when the drive circuit is on the same
PCB as the LEDs. Drive circuit power dissipation,
and thus heat generation is inversely proportional
to the number of LEDs in series. Circuits with
fewer LEDs in series will have greater heat
generation in the drive circuit.
For most automotive applications in which the
battery voltage is approximately 13 V, Lumileds
recommends configuring four LEDs in series. Four
LEDs in series is a good compromise between
forward current control, heat generation, and
minimum turnꢀon voltage for the LED array.
For more information on picking the optimum
design current, and LED drive circuit for your
application, please reference Application Brief
20ꢀ3 Electrical Design Considerations for
SuperFlux LEDs.
10
Ambient Temperature Compensation
Drive circuitry can be designed which
compensates for increasing ambient temperature
by decreasing the forward current to the LED
array. This allows the lamp designer to drive the
LED array at a higher forward current by reducing
the amount of current derating.
Temperature compensation is achieved by
incorporating temperature sensitive components
into the drive circuitry, such as positive
temperature coefficient (PTC) resistors. An
example of the resistance vs. temperature
characteristics of a PTC resistor is shown in
Figure 4.10.
Figure 4.9 LED driver module for automotive
lighting applications.
“Switching” Power Supplies
Current sources, which operate efficiently over a
wide range on input voltages, can be designed
using pulseꢀwidth modulation (PWM) circuitry.
Such circuits have the advantage of low heat
dissipation, and large input voltage compliance.
This type of power supply is traditionally used in
applications where electrical efficiency and heat
dissipation are of critical importance, such as a
laptop computer. Due to their widespread
adoption in other applications, the cost of
components has decreased, and their
availability has increased, making this an
interesting alternative for driving LED arrays.
A block diagram of a simple switching current
source is shown in Figure 4.9.
Figure 4.10 Resistance-Temperature curve for
PTC resistor.
The PWM module varies the pulse width based
on the input and feedback voltages. The
feedback voltage is proportional to the current
through the LED array, where voltage is
measured directly above a small fixed
resistance connected to ground. The filter
circuitry is used to smooth out the output
voltage of the PWM / transistor switch. With
minor modifications, this type of circuit can be
used to drive multiple LED arrays and a variety
of drive circuits.
It can be seen that the resistance of such a device
radically increases when the body temperature of
the PTC resistor reaches the switching
temperature. By designing a drive circuit such that
the switching temperature occurs at a
temperature less than Ta(max), full current derating
is not necessary.
Consider the case in which the switching
temperature of the PTC resistor is achieved at an
11
ambient temperature of 50 °C at the maximum
input voltage. The forward current at Ta < 50 °C
is 55 mA, and due to the increase in resistance
the forward current at Ta > 50 °C is 30 mA. In
such a case, the maximum junction
temperature will be achieved at 50 °C,
therefore, 50 °C can be used as Ta(max) in the
current derating calculations.
Figure 4.11 Current control circuit using
temperature compensation.
An example of a current control circuit using
temperature compensation is shown in
Figure 4.11.
Appendix 4A
Alternate Junction-to-Ambient Thermal Resistance
Measurement Procedure
Step 1: Pick one LED within the assembly
to be used as the DUT. The hottest LED in the
assembly should be chosen, for example an
LED in the middle of the assembly and next to
a resistor.
wires to one cathode lead and to one anode lead
of an LED, which is of the same type as the DUT.
Next solder the other end of these wires directly
to the PCB in such a way as to have this dummy
LED take the place of the DUT in the circuit.
Step 2: Electrically isolate the DUT from the rest
of the circuit by cutting the appropriate Copper
traces on the printed circuit board (PCB).
Step 5: Assemble the modified PCB into the lamp
housing such that the dummy LED and the DUT
wires are extending outside the lamp.
Step 3: Solder long thin wires onto one cathode
lead and one anode lead of the DUT. These
wires should be long enough to extend outside
the lamp housing once it is reassembled
Step 6: Measure the initial Vf of the DUT at a very
low test current. This test current should be low
enough such that it causes a minimum amount
of heating (1 mA is recommended).
because they will be used to apply the heating
current and to measure the ∆Vf of the DUT.
Step 7: Energize the entire lamp assembly at the
design voltage, and DUT at the design current for
the individual LEDs for a minimum of 30 minutes.
This will allow the lamp assembly to thermally
stabilize.
Step 4: Complete the original circuit of the PCB
assembly by attaching a dummy LED onto the
PCB to take the place of the isolated DUT. This
can be accomplished by soldering long, thin
12
Step 8: Measure the Vf of the DUT at the
heating current (Vf heating).
Step 11: Calculate the power, P, into the DUT by
multiplying the heating/design current by its
corresponding Vf heating as determined in Step 8.
Step 9: Turn off all power to the lamp, and
immediately (≤ 10 ms) reꢀmeasure the Vf of
the DUT at the test current selected in 6).
Step 12: Calculate Rθ using the values of ∆Tj and
ja
P calculated in Steps 10 and 11. Lumileds can
Step 10: Calculate the ∆Tj of the DUT by
dividing the ∆ Vf (∆Vf = Vf (Step 6) ꢀ Vf (Step 9)) by
the appropriate factor in Table 4.3.
provide the Rθ measurements of LED lamp
ja
assemblies as described above as a service to its
LED customers.
Table 4.3
Ratios of the change in forward voltage vs. the change
in junction temperature for high-brightness led materials
∆ Vf /∆ Tj ( mV / °C)
LED Material Type
AS AlInGap
TS AlInGap
-2.0
-2.0
13
Company Information
Lumileds is a worldꢀclass supplier of Light Emitting Diodes (LEDs) producing
billions of LEDs annually. Lumileds is a fully integrated supplier, producing
core LED material in all three base colors (Red, Green, Blue)
and White. Lumileds has R&D development centers in San Jose,
California and Best, The Netherlands. Production capabilities in
San Jose, California and Malaysia.
Lumileds is pioneering the highꢀflux LED technology and bridging the gap
between solid state LED technology and the lighting world. Lumileds is
absolutely dedicated to bringing the best and brightest LED technology to
enable new applications and markets in the Lighting world.
LUMILEDS
www.luxeon.com
www.lumileds.com
For technical assistance or the
location of your nearest Lumileds
sales office, call:
Worldwide:
+1 408-435-6044
US Toll free: 877-298-9455
Europe: +31 499 339 439
Asia: +65 6248 4759
Fax: 408-435-6855
Email us at info@lumileds.com
2002 Lumileds Lighting. All rights reserved. Lumileds Lighting is a joint venture between Agilent Technologies and Philips
Lighting. Luxeon is a trademark of Lumileds Lighting, LLC. Product specifications are subject to change without notice.
Lumileds Lighting, LLC
370 West Trimble Road
San Jose, CA 95131
Publication No. AB20ꢀ4 (Sept2002)
14
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