Application Note

Light Emitting Diode

Thermal Design Guide for the Nichia
NVSU119C(U375, U385, U395, U405) LEDs

Table of contents
1. Overview .......................................................................2
2. TJ Measurement Method ..............................................2
3. TS Measurement Point ..................................................2
4. Heat Dissipation Configuration and TJ Measurement
Results ...............................................................................3
5. Design Considerations ..................................................5
6. Applications...................................................................5
7. Summary .......................................................................7The Nichia part numbers NVSU119C within this document are merely Nichia’s part numbers for these
Nichia products and are not related nor bear any resemblance to any other company’s product that mightbear a trademark.
This document contains tentative information, Nichia may change the contents without notice.
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May 31, 2022

Application Note
1. Overview
The light output of LEDs decreases due to the effect of heat generation. When LEDs are operated above
the maximum LED junction temperature (TJMAX), the reliability will drop significantly. In order to use theNVSU119C LED with high performance and high reliability, it is important to design the heat dissipation
so that the junction temperature TJ does not exceed 125°C for the TJMAX for U375 and U385 ranks and130°C for the TJMAX for U395 and U405 ranks.
This application note covers the effect on the TJ when a board with one LED is driven with two different
heat dissipation configurations and the TJ of a board with multiple LEDs. This information can be used asa reference for thermal design.

Light Emitting Diode2. TJ Measurement Method
The following equation can be used to calculate the TJ.
TJ = TS + RθJS × W
TJ: LED Junction Temperature (℃)
TS: Soldering Temperature (℃)
RθJS : Thermal Resistance from Junction to TS Measurement Point (℃/W)
W: Input Power (W) = IF(A)×VF(V)The specifications of the NVSU119C are as follows:
NVSU119C
SymbolCondition

RθJS (℃/W)
VF (V)

IF=700mA

U375
Typ
3.4
3.4

U385
Max
3.8-

Typ
2.6
3.35

U395
Max
3.1
-

Typ
2.6
3.3

U405
Max
3.1-

Typ
2.4
3.1

Max
3.1
-

Absolute Maximum Ratings (TS=25℃):
IFMAX (mA)
IFPMAX (mA)
Topr (℃)
TJMAX (℃)

1400
2000
-10～85125(U375, U385), 130(U395, U405)

IF : Forward Current (mA)
IFP : Pulse Forward Current (mA)IFP conditions : pulse width ≤10ms and duty cycle ≤10%
Topr : Operating Temperature (℃)
Figure 1. TS vs Allowable Forward Current

3. TS Measurement PointTs Point

Cathode Mark

Figure 2. TS Measurement point
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Application Note
4. Heat Dissipation Configuration and TJ Measurement Results
The TJ was confirmed when one LED was mounted on the board and it was driven with two different
heat dissipation configurations.
Heat dissipation configuration 4-1, One LED on the board + Heatsink A
The specification of the board is as follows:
Copper foil
0.105

Thickness(mm)Insulation layer
0.120

Copper base
1.5

Outline dimensions(mm)
30 × 30Light Emitting Diode

The thermal conductivity of the copper foil and copper base is 390W/m⋅K and that of the insulation layer
is 4.5W/m⋅K.

Figure 3. Structure of the board + LED

Picture 1. Board appearance

The specification of heatsink A is as follows:
Heatsink A
Material

Size(mm)

Al50 × 38 × t25

FinThickness of thebase Material(mm)5Number of fins

Size(mm)Arrangement8

1 × 388×1

Thermalresistance
(℃/W)
5.70

Thermal conductivity of thermal grease is 5.3W/m⋅K.
The results of the evaluation with heatsink A are shown below:
TA (℃)Part number

Wavelength Rank
U375
U385

25

NVSU119C
U395
U405

IF (A)
0.7
1.4
0.7
1.4
0.7
1.4
0.7
1.4

VF (V)
3.4
3.5
3.33.4
3.3
3.4
3.1
3.2

W (W)
2.4
4.9
2.3
4.8
2.3
4.8
2.2
4.5

TS (℃)
40
55
39
52
39
53
3749

TJ (℃)
49
74
46
67
46
68
4463

With heat dissipation configuration 4-1 using the U375 rank, there was enough margin to not exceed theTJMAX even when 1.4A was applied. The shorter the wavelength, the tighter the heat dissipation, theresults for the other wavelengths showed even greater margins for the heat dissipation.
Nichia performed another evaluation where the size of the heatsink was increased.
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Application NoteBoard
Thermal grease
Heatsink A
Picture 2. Evaluated light source 4-1

Heat dissipation configuration 4-2, One LED on the board + Heatsink B

Light Emitting DiodeThe specification of heatsink B is as follows:
Heatsink B
Material

Size(mm)

Al53 × 53 × t35

FinThickness of thebase Material(mm)4Number of fins

Size(mm)Arrangement64

0.8 × 913 × 5

Thermalresistance(℃/W)
4.25

Thermal conductivity of thermal grease is 5.3W/m⋅K.
The results of the evaluation with heatsink B are shown below:
TA (℃)Part number

Wavelength Rank
U375
U385

25

NVSU119C
U395
U405

IF (A)
0.7
1.4
0.7
1.4
0.7
1.4
0.7
1.4

VF (V)
3.4
3.5
3.3
3.4
3.3
3.4
3.1
3.2

W (W)
2.4
4.9
2.3
4.8
2.3
4.8
2.2
4.5

TS (℃)
3851
36
48
36
47
3445

TJ (℃)
4770
4363
4362
4159

Board
Thermal grease
Heatsink B
Picture 3. Evaluated light source 4-2

By increasing the size of the heatsink from A to B, the heat dissipation performance was improved andthe TJ was further lowered.

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Application Note
5. Design Considerations

Light Emitting Diode

The performance of naturally air-cooled heatsinks varies depending on the orientation of the fins of theheatsink. Since the TS will increase when warm air accumulates, it is important that the air movement isnot obstructed. At Nichia, the fins are placed to face vertically to allow warm air to escape from the top(See Figure 4).
When designing the system, pay attention to the orientation of the fins when installing the heatsink.

Picture 5.
Picture 4.
Fins facing down
Fins facing vertical(Nichia uses this orientation) (This orientation obstructs the air flow)

Figure 4.
Image of the heat path when finsare facing vertical

6. Applications
When multiple LEDs are mounted, the heat dissipation will be more severe. For reference, the TJ of aboard with 144 NVSU119C(U385) LEDs cooled by a heatsink with a fan is shown below. This
information can be used as a reference for thermal design.
Heat dissipation configuration 6-1, 144 LEDs on the board + Heatsink with fan (heatsink C withfan attached)
The specification of the board is as follows:
Copper foil
0.035

Thickness(mm)Insulation layer
0.120

Copper base
1.5

Outline dimensions(mm)
25.3 × 45

LED mounting
pitch (mm)4.2

The thermal conductivity of the copper foil and copper base is 390W/m⋅K and that of the insulation layer
is 11.1W/m⋅K.

Picture 6. Board appearance

Figure 5. Structure of the board + LED

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Application Note

Light Emitting DiodeGrease

Figure 6. Evaluated light source 6-1

Picture 7. Appearance (Surface)

Figure 7. Light source(6 x 6pcs. LEDs on one board x 4 boards)

Picture 8. Appearance (Back)

The specification of heatsink C is as follows:
Heatsink C
Material

Size(mm)

Al

150 × 63.5 × t52

FinThickness of thebase Material(mm)15

Number of fins

Size(mm)Arrangement33

150 × 0.7

1 × 33The specification of the fan is as follows:Size(mm)
60 × 60 × t38

FanVolume flow3(m /min)
2.15

Static pressure
(Pa)
617

The results of the evaluation with heatsink C are shown below:
TA (℃)Part number

Wavelength Rank

25

NVSU119C

U385

IF (A)
0.5
0.7
1.0

VF (V)
2.3
2.5
2.9

W (W)
1.2
1.8
2.9

TS (℃)4552
64

TJ (℃)
495773

With heat dissipation configuration 6-1, there was enough margin to not exceed the TJMAX even when
1.0A was applied.

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Application Note7. Summary
On a board with one LED, there was sufficient margin to stay under the TJMAX, even with an air-coolingheat dissipation configuration using only a heatsink. Additionally, a larger heatsink size resulted in aneven lower TJ.
When multiple LEDs are mounted with a high density, forced air cooling with a heatsink and a fan wassufficient to cool the LEDs. When high-density mounting using multiple LEDs, heat interference occurs
between adjacent LEDs, resulting in poor heat dissipation. Make sure that the pitch width is sufficient,increase the heatsink size, or attach a fan to the heatsink, etc. and check that it is sufficiently cooled beforeuse.

Light Emitting DiodeThe absolute maximum ratings for the NVSU119C LED per the Nichia specification:
IF=1.4A, TJMAX=125℃(U375, U385), 130℃(U395, U405)
Nichia will not guarantee the LEDs if used above these ratings.

This document contains tentative information, Nichia may change the contents without notice.
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Application Note

Light Emitting DiodeDisclaimer
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 tothe 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 chosenapplication.
 The information/data contained herein are only typical examples of performances and/or applications
for the product. Nichia does not provide any guarantees or grant any license under or immunity fromany intellectual property rights or other rights held by Nichia or third parties.
 Nichia makes no representation or warranty, express or implied, as to the accuracy, completeness orusefulness of any information contained herein. In addition, Nichia shall not be liable for any
damages or losses arising out of exploiting, using, or downloading or otherwise this document, or any
other acts associated with this document.
 The content of this application note may be changed without any prior or subsequent notice.
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NICHIA CORPORATION
http://www.nichia.co.jp

This document contains tentative information, Nichia may change the contents without notice.
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