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

3 Answers 3


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.

  • \$\begingroup\$ 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. \$\endgroup\$ Nov 19, 2010 at 0:39
  • 1
    \$\begingroup\$ Hey, I've seen heat-sinked TO-92. \$\endgroup\$
    – markrages
    Nov 19, 2010 at 3:26
  • \$\begingroup\$ 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. \$\endgroup\$
    – Kortuk
    Nov 19, 2010 at 4:59

Linear publishes this information


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.

  • \$\begingroup\$ 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. \$\endgroup\$
    – stevenvh
    Jul 24, 2011 at 12:46
  • 1
    \$\begingroup\$ TO-3 packages are often mounted on the enclosure, or on a heat sink exposed outside of the case. Example. \$\endgroup\$ Oct 27, 2013 at 20:34

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


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