Application Note

Light Emitting DiodeHow to Calculate the Junction Temperature
for the Nichia 193 Series LEDs

Table of Contents
1. Overview .......................................................................... 2
2. Applicable Part Numbers ................................................. 2
3. TMP Measurement ............................................................. 3
4. How to Calculate the Junction Temperature (TJ) ............. 3
5. Calculation Example of the Junction Temperature (TJ) ... 4
6. Considerations and Suggestions when Using aThermocouple................................................................... 4
7. TMP Measurement Considerations .................................... 5
8. Summary .......................................................................... 6

The “Nichia 193” collectively refers to Nichia part numbers listed in the table in Section 2
Applicable Part Numbers. These Nichia part numbers within this document are merely Nichia’s partnumbers for those Nichia products and are not related nor bear resemblance to any other company’s
product that might bear a trademark.
This document contains tentative information, Nichia may change the contents without notice.
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Application Note
1. Overview

Light Emitting DiodeWhen designing applications using LEDs, it is necessary to consider the heat generated from theLEDs during operation. The junction temperature (TJ) of the LED is an important aspect to beconsidered in selecting the operating conditions of the application. If the absolute maximum rating
TJ is exceeded even for a short period of time, it may cause an adverse effect on the performance ofthe LED; in the worst case, it could cause the LED not to illuminate. Note that the LED must beoperated to ensure that the absolute maximum rating TJ is not exceeded. To prevent the TJ fromexceeding the absolute maximum rating TJ, it is necessary to know how high the TJ will be whenthe LED is operated in the conditions/environments in which the LED will actually be used.
This application note provides how to estimate the TJ by measuring the temperature at themeasurement point Nichia specifies with a thermocouple.

2. Applicable Part Numbers
This application note applies to the LEDs listed in Table 1.
Table 1. Applicable Part Numbers
Series Name
Part Number

Nichia 193 Series
NCSW193F

NC2W193F

NC3W193F

NC4W193F

NC5W193F

11.8×8.0×1.7

11.8×8.0×1.7

11.8×8.0×1.7

11.8×8.0×1.7

11.8×8.0×1.7

ExampleAppearance

OutlineDimensions(mm)This document contains tentative information, Nichia may change the contents without notice.
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Application Note
3. TMP Measurement
The TJ estimation can be calculated by measuring the temperature of the LED (TMP) at themeasurement point Nichia specifies once the LED has been attached to a PCB. The measuring
current should be the maximum operating current (IF) that will be applied to the LED under theconditions in which the LED will actually be used. See Figure 1 for the TMP measurement point.
To measure the TMP, solder the temperature sensing part on the tip of the thermocouple onto the dieheatsink of the LED as shown in Figure 1.
TMP Measurement Point

LED

Cathode MarkTMP Measurement Point
SolderLED
SolderLight Emitting Diode

Thermocouple
Thermocouple

PCB

Solder

PCB

SolderAn NC5W193F LED is shown as an example;
the TMP measurement point is the same for all
the LEDs in this series.

Figure 1. TMP Measurement Point

4. How to Calculate the Junction Temperature (TJ)
When the product using the LED is operated, the TJ can be calculated with Equation 1 below.
Equation 1: TJ = TMP + RθJMP × W
TJ: Junction Temperature (˚C)
TMP: Measurement Point Temperature (˚C)
RθJMP: Thermal Resistance from the Chip to the TMP Measurement Point (˚C/W)
W: Input Power (IF × VF) (W)IF=Forward Current (A), VF=Forward Voltage (V)The RθJMP value may be different depending on the part number. For the RθJMP value of each partnumber, refer to the annex: Thermal Resistance Values of the Nichia 193 Series LEDs. For the LEDs
whose RθJMP values are not listed in this annex, contact a local Nichia sales representative.

This document contains tentative information, Nichia may change the contents without notice.
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Application Note
5. Calculation Example of the Junction Temperature (TJ)
This section provides an example of the TJ calculation using the measured TMP.
Example: The NC3W193F LED is operated at an input power of 9.75W.
The measured TMP is 60˚C.

Light Emitting DiodeThe RθJMP value of the NC3W193F LED is 1.8˚C/W (refer to the annex: Thermal Resistance Valuesof the Nichia 193 Series LEDs).
Using Equation 1 (TJ = TMP + RθJMP × W), the following calculation is obtained:
TJ = 60(˚C) + 1.8(˚C/W) × 9.75(W) = 77.6(˚C)

6. Considerations and Suggestions when Using a Thermocouple
It is recommended to use a thermocouple with wires that are as thin as possible. If the wires are too
thick, they may create thermal paths causing measurement errors.
If the temperature sensing part of the thermocouple is too large and/or is not located at the tip of thethermocouple, the temperature sensing part may not contact the TMP measurement point; if thetemperature sensing part is attached too far away from the TMP measurement point and/or in contact
with a place that is not the TMP measurement point, it may affect the measurement accuracy. See
Figure 2.

Correct

Incorrect

Temperature
Sensing Part

Temperature
Sensing Part

The wires are thin.
The temperature sensing part contacts theTMP measurement point.

The wires are thick.
The temperature sensing part is too large.

Figure 2. Examples of Correct/Incorrect Thermocouples(Before soldering to the die heatsink)

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Application Note

Light Emitting Diode

The temperature sensing part of a thermocouple is at the base of the bonding/contacting area of thewires. Figure 3 (b) shows a thermocouple twisted near the base. With this type of thermocouple,
perform the temperature measurement at the base of the twisted part, not at the tip of thethermocouple. With a thermocouple whose temperature sensing part is not at the tip, the TMP
measurement may be lower than the actual TMP even when the tip is in contact with the TMP
measurement point; ensure that the temperature sensing part is attached to contact the TMP
measurement point.
Correct

Incorrect

Incorrect

（a）

（b）

（c）

Temperature
Sensing Part
Temperature
Sensing Part

Temperature
Sensing Part

Figure 3. Temperature Sensing Part of Thermocouples

7. TMP Measurement Considerations
Even under the same operating conditions, the TJ of the LED may vary depending on the heatdissipation conditions around the LED. The TMP should be measured once the saturation temperature
at the junction has been reached while ensuring that the LED is incorporated in the chosen
application at the finished product level and in a manner that takes into consideration theconditions/environments in which the LED will actually be used, oriented the way it will actually
be used, and the LED is operated at the maximum possible ambient temperature after aging.
Taking into consideration the possibility of measurement variations it is recommended that theevaluation is performed with more than one LED. The more measurements that are used in theevaluation, the easier it will be to judge the accuracy of the TMP measurement.

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Application Note
8. Summary

Light Emitting DiodeIn this application note, Nichia has provided how to calculate the estimated value of the T J for theLED mounted on a PCB using the thermal resistance RθJMP and the measured TMP. To estimate theTJ more accurately, perform the evaluation as per the precautions/suggestions provided herein
regarding how to attach the thermocouple to the die heatsink of the LED and the TMP measurement
conditions/environments.
Additionally, ensure that the chosen design has a sufficient margin to not exceed the absolute
maximum rating TJ by taking into consideration the heat dissipating conditions (i.e. the material,design, etc. of the components used with the LED, mounting conditions of the LED, etc.) and thevariation of the heat dissipation performance of each individual component.

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Aug. 25, 2022Application NoteDisclaimer
This application note is a controlled document of Nichia Corporation (Nichia) published to provide
technical information/data for reference purposes only. By using this application note, the user
agrees to the following:・ This application note has been prepared solely for reference on the subject matters incorporated
within it and Nichia makes no guarantee that customers will see the same results for their chosen
application.

Light Emitting Diode・ The information/data contained herein are only typical examples of performances and/orapplications for the product. Nichia does not provide any guarantees or grant any license underor immunity from any intellectual property rights or other rights held by Nichia or third parties.
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NICHIA CORPORATION
http://www.nichia.co.jpThis document contains tentative information, Nichia may change the contents without notice.
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