# Best package for heat sinking?

I'm buying a LM317 and it comes in 3 different packages. Which is the best for attaching a heat sink? The options are:

• TO-3
• TO-220
• TO-92

LM317 in TO-92 only does 100mA, wheras the TO-3 and TO-220 are both 1.5A - so it depends on how much current you need!

"Best for attaching a heat sink" - hard to say. It's easy to attach a TO-220 to a heatsink, just a hole and thermal compound (or one of the clip on ones). You can also just attach them to the PCB for a bit of extra cooling.

T0-3 can have a lower thermal resistance to the heatsink, but generally are more awkward to mount.

TO-92 isn't really possible to attach to a heatsink.

• There are different varieties of LM317, some good for 1A, some for 1.5A. Also, if you're dropping a lot of voltage in the reg, you need to derate it a bit. – Connor Wolf Nov 19 '10 at 0:39
• Hey, I've seen heat-sinked TO-92. – markrages Nov 19 '10 at 3:26
• There is a heat sink for almost everything online. now at radio shack, you are out of luck. We have used heat sinks on some weird packages at work. – Kortuk Nov 19 '10 at 4:59

Linear publishes this information

$\theta_{JA}$:

TO-3: 35°C/W

TO-92: 160°C/W

TO-220: 50°C/W

So the TO-3 wins in $\theta_{JA}$, which implies that it would be able to transfer the most heat to a heatsink as well. Never seen a TO-92 attached to a heatsink, i would thing it would require a lot of support to try to do so.

In terms of physical attachment, the TO-220 and TO-3 are about the same, just a different type of heatsink is needed. TO-3 would take up more space in most applications.

Several other companies publish similar charts but a quick google-fu didn't turn one up for national, send em an e-mail, I'm sure they have the data somewhere.

• Lowest $\theta_{JA}$ doesn't necessarily mean lowest $\theta_{JHs}$! Imagine a TO-220 with a 1cm body height. This will have a better $\theta_{JA}$, but the $\theta_{JHs}$ would be the same. – stevenvh Jul 24 '11 at 12:46
• TO-3 packages are often mounted on the enclosure, or on a heat sink exposed outside of the case. Example. – Nick Alexeev Oct 27 '13 at 20:34

TO-220 would be the easiest/best for attaching a heatsink in your application, I'd suspect