By the help of following 5 points, you can calculate your LED heat sink.

Define Temperature.
Define LED parameters.
LED heat sink Calculation.
Design Verification.
Essential Remarks.

Now, we will discuss them one by one.

1. Define your expected Temperature:

First of all, define your ambient temperature. Here are the few examples of it.

Spot Light Temperature = 30 Degree.
Ceiling Down lighter = 50-55 Degree.
Automotive lighting around = 45 Degree (Only from design prospective)
TLife around = -40 up to + 85 Degree.



2. Define LED Parameters:

Here are some of the specs of LED parameters.

Take a LED cob module Citizen citilied CLL020 series.
Model # : CLL020-1203A1-303M1A2
Forward current should be around 360 mA.
Forward Voltage should be around 40.9 Vdc.
Power is approximately 14.7 W.
Luminous flux is around 1210 lm.
Maximum Case Temperature would be around Tc 100 Degree.
Maximum Junction Temperature would be around Tj 150 Degree.
Thermal Resistance should be Rj-c 2.6 Degree/W.

LED heat sink for Citizen CLL040-042

3. LED Heat Sink Calculation:

Here, we have to follow some specific formulas. We need to take care of the following items:

Individual Thermal resistance of each part.
The formula used can be = T = Pd * Rth
Here, we can calculate thermal resistance by using formula (Rj-c).
In case of recessed environment, Temperature should be 45 Degree.
The total power to dissipate should be less than total power of LED consumes.
More light the power would be, more efficient your LED module would be.
Maximum Temperature can be calculated as Tj- Ta = 135-45 = 90 Degree.
Pd= 14.7 W*80 % =11.76 W.
Heat sink with Rth value should be less than 4.65 Degree.

4. Design Verification:

Once you are done with the applying thermal pad and the heat sink, you have to verify the design. We have to keep some safety precautions prior design. Maximum Temperature limit should not be more than 100 degree centigrade. But for safety precaution we have to measure the temperature around 87-92 degree centigrade.

5. Essential Remarks:

As far as the Rth value is concerned, some manufacturers give a single thermal resistance for the heat sink. But you should be well aware of Rth of the same heat sink.

Resource Box

For more info of LED Heat Sink, pls check: http://en.ofweek.com/manufacturer/led-heat-sink

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