heatsinks for LM317/337? think chunk or thin with larger surface area?

[dentaku]

Which heatsink would be better for an LM317/337?
The thick chunk or the thin one with the larger surface area?
I'd probably cut the part that sticks out at the right of the thin one so it's the same width all the way.

I'm assuming larger surface area is better than larger mass in this case?

[Simon]

well depends on how much heat you want to dump and your ambient. Many heatsinks are made to mechanically suit their enclosure. A small chunky heatsink will be good for absorbing occasional bursts on power as they can "store" it and then release it over time whereas for continuos dissipation you need surface area, you want reasonable thickness near the device so that heat is moved away quickly. I had a heatsink once with a thick centre that thinned out as it went from centre to outer edges.

[dentaku]

well depends on how much heat you want to dump and your ambient. Many heatsinks are made to mechanically suit their enclosure. A small chunky heatsink will be good for absorbing occasional bursts on power as they can "store" it and then release it over time whereas for continuos dissipation you need surface area, you want reasonable thickness near the device so that heat is moved away quickly. I had a heatsink once with a thick centre that thinned out as it went from centre to outer edges.

Well, my power supply ( +/- 20V down to around +/- 1.25-ish V ) will have a wide open back with the heatsinks sticking out so I guess the finned ones would be best because I don't want to store the heat inside the enclosure.

[mariush]

Use this page to figure out how many C/w should the heatsink have for you extreme cases (ex 20v in, 1.25v out , 500mA or something like that) : http://www.ef-uk.net/data/heatsinking.htm

 I'd guess the small heatsink is about 25-25 C/W and the larger one is probably about 15-20 c/w but the second one is better used with a fan blowing over the surface.

note also that lm317 , lm337 .. at least some of them ... can only dissipate about 15 watts ... so no 24 in , 3v out @ 1A .. just too many watts dissipated in the regulator.

Digikey has a huge inventory of heatsinks http://www.digikey.com/product-search/en/fans-thermal-management/thermal-heat-sinks/1179752   pick to-220 , to-247 etc and look at the "thermal resistance at convection or natural column and then at the pictures of the heatsink to get an idea about how large a heatsink without fan would have to be.

[dentaku]

I just weighed them and the finned one actually weighs much more than I imagined. It's quite a bit heavier than the thick one plus it will stick out the back of the enclosure much further so that's what I'm going to use.