4
\$\begingroup\$

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
\$\endgroup\$
8
\$\begingroup\$

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.

\$\endgroup\$
  • \$\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\$ – Connor Wolf Nov 19 '10 at 0:39
  • 1
    \$\begingroup\$ Hey, I've seen heat-sinked TO-92. \$\endgroup\$ – markrages Nov 19 '10 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 '10 at 4:59
8
\$\begingroup\$

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.

\$\endgroup\$
  • \$\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 '11 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\$ – Nick Alexeev Oct 27 '13 at 20:34
1
\$\begingroup\$

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

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.