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LM317 thermal resistance and heatsink selection


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

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 ??


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


Well-Known Member
Most Helpful Member
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.


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

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