Re: Cooling a TO-220 7812 regulator

On a sunny day (Sun, 15 Sep 2024 16:58:01 +0530) it happened Pimpom
<Pimpom@invalid.invalid> wrote in <5xzFO.64422$lZG8.30677@fx09.ams1>:

I'm going to use a standard 7812 TO-220 regulator on a single-sided 1 oz
board with the dissipation varying as below:
>
- Idle at 120-150mW
- 0.5W for 1-5 minutes at irregular intervals
- Up to 4W for 1 second at the start of each 0.5W phase
>
The interval between the 1-5-minute periods is variable and may be 1 to
10 minutes.
>
The ground pin is soldered to ~2 sq.in. of copper on the PCB.
>
Options:
1) As described. No extra heatsinking.
2) Mount it on a small Al heatsink.
3) Place the regulator horizontally on the underside and bolt it to the
copper.
>
Tamb = ~35ºC max
>
Do you think option 1) is enough? Or should I go for 2) or 3)?

Rth to ambient is about 50 IIRC
so 4 W long enough makes a 200 degrees rise..
.5W makes a 32 degrees rise.
But the thing will thermal limit
That limit may affect whatever it is you power from it.
I always used cheap small heatsinks with the thing standing up,
no need to warm the PCB whith maybe sensitive stuff on it
If you have an  alu housing an need more power screw it against that, pehaps with a Mica insulator
 https://panteltje.nl/pub/8052AH_BASIC_computer/8052AH_BASIC_computer_inside_img_1727.jpg

If all else fails, biiger heatsink, this is the biggest one I have :
 https://panteltje.nl/pub/big_heatsink_IMG_6292.JPG
:-)