Voltage Regulator - 5V (COM-00107)

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@Pixmusix looks like you beat me to it as i was formatting my equations :stuck_out_tongue: I’ll post for posterity anyway.
Dave Jones has a great EEVBlog video from forever ago that goes deep on calculating temperature rise and thermal resistance. Thinking about heat flow like an electrical circuit is a game changer and how it’s really done in engineering.

in any case, let’s do a worked example with data assuming the TO220 is in free air - so we’ll use the junction-to-ambient value for thermal resistance:

R_{thj-amb} = 50°C/W \\ V_{in} = 18V \\ V_{out} = 5V \\ I = 0.1 A

Power dissipated is

P = (V_{in} - V_{out} ) I = (18-5) \times 0.1 = 1.3W

So temperature of the junction is

T_{rise} = P \times R_{thj-amb} = 1.3 \times 50 = 65°C

The junction will be 65°C above ambient which is pretty hot!
If you bond the package to a heatsink you can add the R_{thj-case} resistance with whatever thermal resistance data you have on the heatsink which will be much lower.

Actually works pretty well :sweat_smile: Too hot to touch for me is tuned to about 50°C (plus minus 10 :stuck_out_tongue: ) which is super good enough for maker projects

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