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I do guess it will require but I have never used a heat sink before, so I am not sure.

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Depends a bit, 5W on a naked TO220 is pushing it in the absence of airflow, and I would probably screw the thing down to some suitable bit of metal if it was to be sustained for more then a few seconds.

What does your parts datasheet say about Tjmax, Rjc and naked package thermal resistance to ambient? How hot is your ambient? Can you mount the thing right down near the board and use a honking great copper pour?

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  • \$\begingroup\$ st.com/resource/en/datasheet/tip41c.pdf Actually, I could not find those values, if you don't mind, please have a look. \$\endgroup\$ – muyustan Nov 30 '19 at 14:22
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    \$\begingroup\$ Well it gives a max junction temp of 150c, and 65 watts PD at 25 degrees case temp, so Rjc is clearly (150 - 25)/65 = ~2C/W, so at 5W the junction will be ~10 degrees above case temperature, which puts the limiting case temperature at 150-10 = 140C. Assume say 40 degrees ambient and you have 100 degrees between the device case and ambient air before you overheat the junction. The TO220 package without heatsink is something like 70C/W to ambient so 1W would probably be ok, 5W will kill it. \$\endgroup\$ – Dan Mills Nov 30 '19 at 14:36
  • \$\begingroup\$ Note that those parts are clearly intended for switching service as they give no SOA curve and second breakdown is mentioned nowhere, so they should only be used in switching applications, and there are usually better parts for that these days (A modern mosfet could do the same switching duty without even getting warm). \$\endgroup\$ – Dan Mills Nov 30 '19 at 14:38
  • \$\begingroup\$ I was planning to use it for an audio amplification application. It also puts audio amplification at the first page of datasheet. I am confused now. \$\endgroup\$ – muyustan Nov 30 '19 at 15:10
  • \$\begingroup\$ Odd, maybe I am missing something but I didnt notice any sort of SOA plot. They are pretty much prehistoric parts at this point, there are FAR better things to use in an audio amp, if something only doing a few watts is even worth doing as a discrete design these days. \$\endgroup\$ – Dan Mills Nov 30 '19 at 15:14

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