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Thoughts on DIY LED (4)

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  • Thoughts on DIY LED (4)

    Now, let's talk about heat dissipation. What a nightmare!

    I won't bring you into funky calculations, but I'll lay the basic priciples for you to understand the data sheets that come with LEDs and heat sinks.

    As I stated before, there are but two things to kill a LED. Electrical current and heat. Let's talk about heat.

    A LED is a solid state device. As a matter of fact, it is a P-N junction made-out of doped (no pun intended) sillicon. No more nor less than the transistors in your 80W sound system. As a matter of fact, exactly the same principles of heat dissipation apply to the both of them. In that respect, to me, it's nothing more than a transistor (though it is not).

    The junction has a fusion point beyond which it will vaporize. This is a knowned value tested in the manufacturer's lab. And here begins the never-ending-chain.

    I am talking about a chain because it's one hell of a chain. Every step of the chain is calculated in degres/Watt, but the ugly thing is that you have to read it backwards. Let me explain.

    Each step of the chain is interpreted as a resistor in a series circuit and you have to keep adding on-and-on while always keeping in mind the disspated power. OK, I've lost you.

    Let's put our clothes back-on, take a shower and start all over again.

    Imagine that the junction will fuse @ 250. Now we get into the chain. The manufacturer will give us the thermal resistance in between the junction and the device body. That, we cannot change. But here begins the real fun. Our thermal paste or glue has it's own thermal resistance and our heat sink also. But that's not all. The room temperature has to be taken into accouct also. And if it was not enough, the work of the fans take part in the equation.

    So, it is 28 in the room. The heat sink raises to 80 without fans, but maintains @ 35 with the fans running. It is the temperature of the heat sink that you have to take account for. So, let's say the fans run and the sink is at 35. You then have to multiply the thermal resistance of the compound in between the device and the sink by the power and add this number of degrees to the total. Then again, the device to junction thermal resitance multiplied by the power and you end-up with 210 degrees. She will survive.

    But crank the power to the device or raise the room temperature and she might fry. Not easy, he?

    As I said before, keep it luke warm and no more...

    Please contribute. I long for your expertise as well.

    So long...

  • #2
    I find you annoying for some reason lol


    • rouelibre
      rouelibre commented
      Editing a comment
      It is your very right. Maybe you are not the soldering iron type? Have a nice day.

  • #3
    Although the technical aspect loses me all of this could prove very handy. I have an electrical friend who could use this to help us build some lights. Thanks again.


    • #4
      I dont care if this is useful to others, my point is thats all he came here to do. Only 10 post and all about this LED stuff and thats its nothing else. Just a flyby poster thinking they're helping out.