Application Note 02_01 TELUX

Application Note 02_01 TELUX
Vishay Semiconductors
Specification, Thermal management and design-in
1. Introduction
The performance and reliability of TELUX® LED are
mainly determined by a proper thermal management
of the complete lamp system. The thermal management is a critical part in the design in of high power
LEDs
The following application note details the product
specification in the corresponding data sheets for the
different TELUX® series .
Thermal management of optical systems with LEDs
and the influence of temperature on electrical and
optical parameters are covered.
2. Data sheet informations
The data sheet presents the performance of the
TELUX® LED in tables and diagrams.
16 012
The type name contains ,,brightness series; colour
and emission angle plus customer specific information’s.
TLWR7600
customer specific details
emission angle: 6 = 60q full angle
9 = 90q full angle
Series. 7,8,9 describing different brightness series
Colour: R = red, Y = yellow,......
Company internal device description
16883
Figure 1. Description of Type Name
2.1 Structure of the datasheet:
Colour emission angle and Chip technology are
described in the first table. For luminous flux, wavelengths and forward voltage a special grouping is
done. This grouping scheme can be found in the general part of our data book. The grouping system is
compatible to the systems used by main competitors.
( Figure 2 )
The paragraphs Description, Features and Applications are giving a general introduction about the
design, technology, features and applications of the
device.
Document Number 81071
Rev. 1.1, 06-Aug.-02
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Application Note 02_01 TELUX
Vishay Semiconductors
16884
Figure 2. TELUX® grouping scheme for luminous flux , forward voltage and wavelengths for red.
100
90
70
60
50
40
30
20
10
0
0
25
50
75
100
125
Total Included Angle (Degrees)
16005
Figure 3. Percentage Total Luminous Flux vs. Total Included Angle
for 60 ° emission angle
100
3. Non thermal characteristics of the
TELUX® LED
90
% Total Luminous Flux
3.1. Emission characteristic of the TELUX® LED
The angle of half is the typical criteria of the different
TELUX® type versions.The luminous flux vs. angular
displacement and the percentage of the luminous flux
covered by different angles are describing the light
emission in detail.
This typical emission characteristic is a nearly temperature independent feature of the LED.
Typical charts are in Fig. 3 - 6. The 60 degree type is
showing a typical double peak while the 90 degree
version is showing a more sharp peak
80
% Total Luminous Flux
The second table "Absolute maximum rating" is very
important for the thermal properties of the TELUX®.
The reverse voltage, the max. DC forward and surge
current, the maximum power dissipation and junction
temperature, operation and storage temperature
range, solder temperature and the thermal resistance
(junction/ambient & junction pin) are listed in this
table.
The last table " Optical and electrical characteristics"
contains the optical parameters and the corresponding electrical parameters of the lamp. The optical
parameters as well as the electrical parameters are
more or less a function of the temperature.
The data sheet contains also graphs illustrating the
operational conditions. The relevant graphs for the
thermal management are described below.
80
70
60
50
40
30
20
10
0
0
16201
25
50
75
100
125
Total Included Angle (Degrees)
Figure 4. Percentage Total Luminous Flux vs. Total Included Angle
for 90 ° emission angle
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Document Number 81071
Rev. 1.1, 06-Aug.-02
Application Note 02_01 TELUX
Vishay Semiconductors
0q
10q
4. Thermal limitations of
the TELUX LED
20q
Iv rel – Relative Luminous Intensity
30q
40q
1.0
0.9
50q
0.8
60q
70q
0.7
80q
0.6
0.4
0.2
0
0.2
0.4
0.6
16876
Figure 5. Rel. Luminous Intensity vs. Angular Displacement
for 60 ° emission angle
0°
10°
20°
Iv rel – Relative Luminous Intensity
30°
40°
The junction temperature mainly affects the luminous flux, the wavelengths and the forward voltage of
the TELUX® LED. The junction temperature itself will
be affected by ambient temperature and self heating
due to electrical power dissipation. Approximately
only 5 to 10 % of the power is dissipated optically, the
main portion is heating up the device.
4.1. Dominant wavelengths
The dominant wavelength is a linear function of the
junction temperature and can be described by the following equation:
λd(Tj) = λd(Tjo) + TCλd * ΔTj (1)
The coefficient TCλd is a material specific parameter
and listed in fig. 7
λd(Tj) = dominant wavelength as a function of temperature
λd(Tj0) = dominant wavelength at a certain temperature T0
ΔTj = temperature difference (Tj - Tj0)
1.0
0.9
50°
0.8
60°
70°
0.7
80°
0.6
0.4
16877
0.2
0
0.2
0.4
Angular Displacement
0.6
Figure 6. Rel. Luminous Intensity vs. Angular Displacement
for 90 ° Emission Angle
ld
16885
Figure 7. Temperature Coefficient of λd
4.2. Luminous flux
The luminous flux is an exponential function of the of
the junction temperature and can be described as:
φv(Tj) = φv(Tj0) * e-kΔT (2)
φv(Tj) = luminous flux as a function of temperature
φv(Tj0) = luminous flux at a certain temperature T0
Document Number 81071
Rev. 1.1, 06-Aug.-02
k = material specific parameter (typical 1,1 * 10-2 for
AS AlInGaP red)
ΔT = temperature difference (Tj - Tj0)
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Application Note 02_01 TELUX
Vishay Semiconductors
For application the φv(Ta) is measured (Fig. 8 and
Fig. 9). In generally the junction temperature is determined by Ta + ΔT from electrical power dissipation.
The calibration is done after a stabilisation of the
parameter, to eliminate short time effects.
FVrel– Relative Luminous Flux
1.8
IF = 50 mA
1.6
1.4
True Green
1.2
1.0
0.8
16889
Blue
Blue Green
0.6
0.4
Figure 10. Forward Voltage
0.2
0.0
–40 –20
0
20
40
60
80
100
Tamb – Ambient Temperature ( qC )
16879
100
90
I F – Forward Current ( mA )
Figure 8. Luminous Flux as a Function of Tamb for InGaN
FVrel– Relative Luminous Flux
2.0
Yellow
1.6
1.4
1.2
Red,
Softorange
1.0
0.8
16880
0.6
Yellow
70
Red
Yellow
60
50
40
30
20
10
0
1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5
VF – Forward Voltage ( V )
Figure 11. Forward Current vs. Forward Voltage for AlInGaP
0.4
0.2
0.0
–40
16878
IF = 70 mA
1.8
80
–20
0
20
40
60
80
100
Tamb – Ambient Temperature ( °C )
100
90
4.3. Forward voltage.
The forward voltage is a function of current and junction temperature( Fig.10 - 12). For the specification at
max. current at 25 °C, the junction temperature is
defined by the thermal resistance (Rthja = 200 K/W).
This will be described in the next chapter and in combination with the thermal resistance it is a function of
Tamb, due to linear shift by a selfheating effect of
ΔT = Rthja * P. ( Fig. 14 )
I F – Forward Current ( mA )
Figure 9. Luminous Flux as a Function of Tamb for AlInGaP
80
Blue Green
True Green
70
60
50
40
Blue
30
20
10
0
2.5
16881
3.0
3.5
4.0
4.5
5.0
VF – Forward Voltage ( V )
5.5
Figure 12. Forward Current vs. Forward Voltage for InGaN
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Document Number 81071
Rev. 1.1, 06-Aug.-02
Application Note 02_01 TELUX
Vishay Semiconductors
16882
IF = 20 mA
Red
Yellow
1.1
1.0
VF – Forward Voltage
V Frel– Relative Forward Voltage
1.2
Blue
Blue
Green True
Green
0.9
0.8
–40 –20
0
20
40
60
80
Tamb – Ambient Temperature ( qC )
100
16894
2.9
2.8
2.7
2.6
2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
1.7
–40
AlInGaP red
IF = 70 mA
Gr.2
Gr.1
Gr.0
–20
0
20
40
60
80
100
Tamb – Ambient Temperature ( C )
Figure 13. Forward Voltage vs. Ambient Temperature for AlInGaP
und InGaN
Figure 15. Forward Voltage against Tamb for Different VFGroups
In a first approximation from Fig. 13 a linear temp.
coefficient for Vf can be defined in the temperature
range above - 25 °C. ( Fig. 13 )
This temp. coefficient is only typical for one Vf group
because the Vf(T) is also a function of the Vf group
itself as shown in Fig. 15 for AlInGaP red.
4.4. Thermal resistance
Similar to electrical resistance, which is associated to
the conduction of electricity, the thermal resistance is
associated to the conduction of heat. Defining resistance as the ratio of driving potential to the corresponding transfer rate, the thermal resistance for
conduction can be defined as:
Rth = ΔT/qx (3)
where ΔT = temperature difference between the
2 points, qx = rate of heat transfer between those 2
points.
The thermal resistance of LED lamp where the LED is
mounted on a PCB as illustrated in Fig. 16 can be
divided into 2 parts.
Type
TC VFńmVńK
TLWR
* 4.5 (70 mA)
TLWY
* 4.1 (70 mA)
TLWB
* 6.2 (50 mA)
TLWTG
* 4.7 (50 mA)
TLWBG
* 5.6 (50 mA)
RthJP
16893
RthPa
Figure 14. Temperature Coefficient of VF
Ta
16887
Figure 16. Components of Thermal Resistance
1. thermal resistance of the LED package (junction to
pin thermal resistance or Rthjp)
Document Number 81071
Rev. 1.1, 06-Aug.-02
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Application Note 02_01 TELUX
Vishay Semiconductors
230
The thermal resistance junction to pin Rthjp is 90 K/W.
The optical and electrical Parameters are specified
based on a cathode heat sink of 70 mm2. The thermal
resistance junction to ambient for 70 mm2 heat sink
on cathode side (both pins are connected) Rthja is 200
K/W.
From equation (5)
Rthja = (Tjmax-Tamax) /Pmax
with Pmax = Vfmax x Imax
Tjmax = Rthja * Vfmax * Imax (6)
From this equation the derating diagram forward current via temperature for Rthja = 200 K/W can be calculated. The charts for TELUX AlInGaP and InGaN are
shown below in Figure 18 and 19.
100
red
I F - Forward Current (mA)
2. thermal resistance of the lamp housing (pin to
ambient thermal resistance or Rthpa).These two components are adding up to the thermal resistance junction to ambient
Rthja = Rthjp + Rthpa (4)
Based on the assumption that the electrical power is
dissipated mainly as heat, the junction to pin thermal
resistance of an LED can be defined in the following
equation:
Rthja = ( Tj - Ta)/P = ((ΔTj + Ta) - Ta)/P = ΔTj/P (5)
where Tj = ΔTj + Ta
The electrical power can easily be determined by multiplying forward current and forward voltage. The rise
in junction temperature can be determined by measuring the change in forward voltage of the LED.
There are different possibilities to measure the thermal resistance "junction to ambient". A simple method
is to assume that Rthjp for the tested device is known
from data sheet. Solder a very thin thermocouple on
one cathode pin of the hottest LED in your PCB. The
solder point should be close to the surface. After measuring the pin temperature, the ambient temperature
and the power, the Rthpa can be calculated as: Rthpa=
(Tp-Ta)/P. With equation (4) the thermal resistance
junction to ambient can be calculated. The thermal
resistance junction to ambient vs. cathode padsize is
shown in Figure 17, Tj = Tak + Rthjp * P. The anode
pad is not contributing to heat dissipation.
80
60
40
20
RthJA= 200 K/W
0
0
15983
20
40
60
80
100
Tamb - Ambient Temperature (°C)
120
Figure 18. Forward Current vs. Ambient Temperature
2
Padsize 8 mm
per Anode Pin
220
60
200
190
180
170
160
0
16009
50
100 150 200 250
Cathode Padsize mm2
300
Figure 17. Thermal Resistance Junction Ambient vs. Cathode
Padsize
4.5. Maximum power, maximum current and maximum junction temperature
The maximum junction temperature is limited mainly
by the chip
Actual: Tjmax = 125 °C for TELUX with AlInGaP chip
Tjmax = 100 °C for TELUX with InGaN chip
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IF - Forward Current (mA)
RthJA in K/W
210
50
40
30
20
10
RthJA = 200 K/W
0
0
16067
20
40
60
80
100
120
Tamb - Ambient Temperature (°C)
Figure 19. Forward Current vs. Ambient Temperature for InGaN
4.6. Ambient Temperature and thermal resistance
of the enclosure
The LED’s on the PCB are often mounted into an
enclosure as shown in Fig. 20. It is very important to
realise that the ambient temperature is the temperaDocument Number 81071
Rev. 1.1, 06-Aug.-02
Application Note 02_01 TELUX
Vishay Semiconductors
ture of the air surrounding the LED. This means that
the real ambient temperature inside the enclosure is
higher than the temperature outside the enclosure
due to heat generated by the LED, the other electronic parts and in some applications extremely by the
sun illumination.
To
Ta
5. PCB design
Proper PCB design can reduce the Rthja of a lamp
assembly and finally this will lower the junction temperature of the LED chip.The Thermal resistance
"junction to ambient" as a function of cathode pad size
is shown in Fig 17. Since the most of the electrical
power in the LED is dissipated as heat, the LED’s
should be spaced as far as packaging and optical
constrains will allow. 10 mm and 15 mm are ideal in x,
y and it is helpful to design large metal pads to keep
the temperature on the PCB on a low level.
Resistors and other electronic parts which contribute
to the heat should be distributed on the PCB at largest
possible distance from the LED’s. For thermal management as well as for current control it is better to
use more than only one resistor to achieve a better
distribution of the generated heat.
16886
16888
Figure 20. Thermal Resistance of the Enclosure
Following the definition of the thermal resistance in
equation (5), the thermal resistance of the enclosure
can be written as below:
Rthao = (Ta - To)/PT
(7)
where:Rthao = thermal resistance of the enclosure
Ta = temperature inside the enclosure closest to the
LED
To = temperature outside the enclosure
PT = power consumption of all devices inside the
enclosure
The junction temperature can be estimated as:
Tj = To + (PLED x Rthja) + ΔTD + PTRthao
(8)
where: ΔTD = temperature evaluation due to power
density of the PCB
Document Number 81071
Rev. 1.1, 06-Aug.-02
large cathode pad
min. anode pad
resistor
Figure 21. PBC Design with Proper Metallization and Device
Placement
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Application Note 02_01 TELUX
Vishay Semiconductors
6. Soldering
Solder-method recommendation
The TELUX LED is not released for reflow soldering
16891
Figure 22. Soldering Conditions
- Double wave profile
As per CECC00802 (5s peak)
- Hand soldering
260 °C for 5 sec 2 mm from body of the device
300
5s
Lead Temperature
250
235 °C ... 260 °C
second
wave
first wave
Temperature (°C)
200
full line: typical
dotted line: process limits
wave
ca. 200 K/s
ca. 2 K/s
150
100 °C ... 130 °C
100
ca. 5 K/s
2 K/s
50
forced cooling
0
0
50
100
150
200
250
Time (s)
948626
Figure 23. Double Wave Solder Profile
• Most critical part of the profile is the preheating. It is
recommended to keep the preheating temperature on
a maximum level of 100 °C for 30 sec. As defined in
the "Absolute maximum ratings" for the product.
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Document Number 81071
Rev. 1.1, 06-Aug.-02
Application Note 02_01 TELUX
Vishay Semiconductors
Ozone Depleting Substances Policy Statement
It is the policy of Vishay Semiconductor GmbH to
1. Meet all present and future national and international statutory requirements.
2. Regularly and continuously improve the performance of our products, processes, distribution and
operatingsystems with respect to their impact on the health and safety of our employees and the public, as
well as their impact on the environment.
It is particular concern to control or eliminate releases of those substances into the atmosphere which are
known as ozone depleting substances (ODSs).
The Montreal Protocol (1987) and its London Amendments (1990) intend to severely restrict the use of ODSs
and forbid their use within the next ten years. Various national and international initiatives are pressing for an
earlier ban on these substances.
Vishay Semiconductor GmbH has been able to use its policy of continuous improvements to eliminate the use
of ODSs listed in the following documents.
1. Annex A, B and list of transitional substances of the Montreal Protocol and the London Amendments
respectively
2. Class I and II ozone depleting substances in the Clean Air Act Amendments of 1990 by the Environmental
Protection Agency (EPA) in the USA
3. Council Decision 88/540/EEC and 91/690/EEC Annex A, B and C (transitional substances) respectively.
Vishay Semiconductor GmbH can certify that our semiconductors are not manufactured with ozone depleting
substances and do not contain such substances.
We reserve the right to make changes to improve technical design
and may do so without further notice.
Parameters can vary in different applications. All operating parameters must be validated for each
customer application by the customer. Should the buyer use Vishay Semiconductors products for any
unintended or unauthorized application, the buyer shall indemnify Vishay Semiconductors against all
claims, costs, damages, and expenses, arising out of, directly or indirectly, any claim of personal
damage, injury or death associated with such unintended or unauthorized use.
Vishay Semiconductor GmbH, P.O.B. 3535, D-74025 Heilbronn, Germany
Telephone: 49 (0)7131 67 2831, Fax number: 49 (0)7131 67 2423
Document Number 81071
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Application Note 02_01 TELUX
Vishay Semiconductors
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Document Number 81071
Rev. 1.1, 06-Aug.-02