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LED LIGHTING

shejir pally
Prodigy 30 points
Other Parts Discussed in Thread: LM3421

Hi,

I am new to this community and i am little exited... I am designing a LED lighting with LM3421 using 24 suel LEDs(0.3W,25 lm/each). The LEDs will be driving in 90mA (almost 90%) with an input of 12 to 24V DC. What should be the minimum distance i have to keep in between LEDs for heat desippation in the PCB? 

  • 0
    Mastermind 7395 points

    Well... that is more a question to be asked to the LED manufacturer. What is the LED part name? Do they have any recomendation for layout, with considerations for thermal management?

     

    ... and welcome to the community :)

  • 0 in reply to Avi Chami1
    Prodigy 30 points

    Hi Albert,

    Thank you very much for your reply,

    I am using suel STW8Q14BE LED, I am planning to have 12+12 (total 24 LEDs)such LEDs in two rows in a 1 feet tube light.Which is a .3 W LED will be driven at 90mA. Hope you can help me to by suggesting the minimum distance to be kept between each LEDs. 

  • 0 in reply to shejir pally
    Mastermind 7395 points

    The thermal resistance of the device acc. the datasheet is 100°C/W. At 0.3W power consumption, the LEDs should be hotter in approx. 30°C more than the ambient temperature. It doesn't seem that you are stressing the device, you can also check the graph showing forward current vs. ambient temperature, at 90mA you are OK even at 85°C ambient.

    However, the vicinity of other LEDs will produce a hot area around them that is higher than ambient temperature. Personally I don't have experience in building strings of devices like you are going to do. If I were you I would arrange a jig with 4-5 devices, and measure their temperature while varying their distance, and also testing how neighbor devices lit, affect the temperature of the LED. 

    It is also important to define what will be the final product operating temperature. WIll it be up to 50°? 60°? 70°? Your definition will dictate the worst case for the temperature tests.

  • 0 in reply to Avi Chami1
    Prodigy 30 points

    Ok,Thats a great idea to check it practically with some jig. Thank you very much for your advise and i will update you with the results. I have ordered for the components. Thank you once again. 

  • 0 in reply to shejir pally
    Mastermind 7395 points

    No problem! :)

    Best of luck with your tests

  • 0 in reply to Avi Chami1
    Prodigy 10 points

    Albert:

    The proper arrangement of LED emitters involves more than thermal management. Optics is also important.

    Placing LED emitters close together emulates a point source of light. Placing them far apart emulates an diffuse source of light which also dissipates heat better, but is more expensive and takes up more room.

    For a proper optical effect, user preferences must also be considered. If an user dislikes glare, a diffuse illumination should be tried. However, if space is limited (such as within a light bulb), only a compact emitter arrangement is possible.

  • 0 in reply to Mau Pham
    Mastermind 7395 points

    Mau,

    Shajir question was about thermal management. Undoubtely there are many other questions for arranging LEDs: optics considerations as you mentioned, but also color combining and geometric appearance... and many more. I only answered Shajir question which was very specific and technical.

    BTW, I have seen LED strings in many configurations, from very close up to very far apart.