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LM317 thermal resistance and heatsink selection

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Elerion, Jul 11, 2018.

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  1. Elerion

    Elerion Member

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    Looking for thermal resistance in the LM317 datasheet from TI, I found something which doesn't make any sense to me.

    http://www.ti.com/lit/ds/symlink/lm317.pdf
    Page 4

    There're two TO220 packages, which seem differ in the thickness of the tab.
    One of them is 4.2 ºC/W junction-case, which is close to the typical 5ºC/W assumed by many people. But the other one is just 0.1 ºC/W ??

    :eek:

    Can it be that LOW ?
    I think that either I'm missing something, either there's a mistake in those figures.
    Anyone knows?
    Thanks
     
  2. crutschow

    crutschow Well-Known Member Most Helpful Member

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    Yes, that thermal-resistance value does seem to be abnormally low.
    I suspect a typo.
    For example this regulator (page 2) shows a thermal resistance of 3°C/W for that package.
    I would use the value for the LM317 KCT package.
     
    • Agree Agree x 1
  3. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    I thought going to the LM337 data might give more information. No help.
     
  4. dave miyares

    Dave New Member

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  5. Elerion

    Elerion Member

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    The onsemi datasheet shows 5ºC/W.
    This is the figure I'm using.
    Strange that TI datasheet is wrong for this classic IC.
     
  6. crutschow

    crutschow Well-Known Member Most Helpful Member

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    Typos get into even the best written documents.
     
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