LM317 safe operating temperature

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I replaced 7805 regulator in my CD player with a small pcb with LM317 (TO-220) on it. I am measuring 80C/176F with an ambient temperature of 26C/78F. Obviously those temperatures were measured with the top off, so I can imagine when the lid is closed they are even higher.

I did not use the original heat sink on which 7805 was mounted to, that was not possible without further modification which is what I am trying to avoid obviously:D.

Data sheet mentions 125C/257F as max. operating temp, but since max. and optimal is not necessarily the same thing I would like to hear your advices.
 
The heat sink you used is smaller than the original one? i'm asking this because LM317 supports about 0,5A more than 7805 so in theory it should stay cooler...What is the voltage that powers the 317's stabiliser?

That is NOT how things work!

The temp rise, other things being equal, is a function of actual dissipation (V across x I through).

Nothing to do with what it WILL support.

If you use a smaller heatsink it will get hotter. Personally, I do not like anything getting too hot to touch comfortably. 80degC is!
 
Maybe i didn't make myself clear, as LM317 ( T220 device ) supports more current ( 1,5A as to 1A for 7805 ) it also supports more Pd, that is why i sayd it should stay cooler ( maybe a poor choice of words ), but i think it is clear what i ment.

On the other hand, i did NOT recomanded a smaller heat sink, i've just asked if he used such thing... if so than it is not ok, but we need to know the voltage that powers the stabiliser cus if it is possible to lower it down ( No more than Vout+3 or 4V ) than the Pd would be smaller so the device would stay cooler.
 
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Just another Moderator
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I guess the other question that should be asked is safe for the device or safe for it's surroundings :) cooler means less stress on nearby components and also less likelyhood of developing dry joints.

Long legs, and a decent distance from other components should allow a higher operating temp, than mounted close to the board and close to other components.

Tony.
 
I guess the other question that should be asked is safe for the device or safe for it's surroundings :) cooler means less stress on nearby components and also less likelyhood of developing dry joints.

Long legs, and a decent distance from other components should allow a higher operating temp, than mounted close to the board and close to other components.

Tony.

Hi Tony,
the board is rather empty around this regulator, except for one film cap.

I thought about extending the legs of the regulator but was not sure about its caveats, higher resistance comes to mind. And I do not have enough knowledge to determine whether extra couple of cm would have any significant impact on the regulation.

Thanks
Marko
 
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The datasheet recommends connecting direct to the case of the regulator for resistance reasons. See this except from the national datasheet.

So yes lead length could make a difference depending on the implementation details :)

Tony.
 

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Congrats on the succes ;)

As i see you could even try fitting a small cooler inside, to ventilate the device and that way you will have no more worryes about the temperature, but the worm air has to be able to escape the case.


Hi MarianB,
I am afraid that the small vent would be noisy, and the silent one would be expensive:D. I could be wrong but I have a feeling that this setup is even more cool than with the old LM7805 in place, at least judging by the lid temperature (finger testing not exact numbers here).

What I am contemplating now;) is a separate regulator for either SAA7220 or TDA1543. Any thoughts on that?

Thanks
Marko
 
As i understand, both SAA7220 and TDA1543 requires 5V and a small current so maybe a 7805? it could even do without any heatsink if supply voltage for it is at about 9V.

You are absolutely correct, all these chips were powered from just one LM7805 which I now substituted with LM317. My plan was to use same inbuilt transformer which gives as already stated 9.47V and I now have one LM7805 spare:). Only question is it worthwhile doing this?

Thanks
Marko
 
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