Re: Cooling a TO-220 7812 regulator

On Mon, 16 Sep 2024 01:11:45 +0530, Pimpom <Pimpom@invalid.invalid>
wrote:

On 16-09-2024 12:25 am, john larkin wrote:

On Sun, 15 Sep 2024 23:03:09 +0530, Pimpom <Pimpom@invalid.invalid>
wrote:
 

>

Thanks for the input. Calculating heatsink requirement for continuous
dissipation is one thing. Short bursts are another.

 
You can estimate the mass and specific heat of a fet and do the math.
It's even easier to test one. You could do that quickly.
 
Given a TO-220 gadget, it would be nice to know the temp rise per
joule dumped into it. Maybe I'll measure that.
 
First google hit:
 
https://www.avrfreaks.net/s/topic/a5C3l000000UNfNEAW/t104767
 
"A TO-220 package has a thermal capacitance of 0.54(J/C) and thermal
resistance of about 62(C/W) without a heatsink."
 
Based on that, 4 watts for 1 second works out to about 8C rise. The
PCB will help a little.
 

That's good to know. Even if those data are a bit off, it still leaves
plenty of headroom for a safe operation including hotspots on the chip.
>
BTW I think it was you who mentioned Saturn PCB Toolkit in a thread
several years ago. I've been using it since then. It's a useful tool.
>
There was a time when they seemed to have blocked downloads from outside
the US. They didn't actually say so and it took me some time to figure
it out. I managed to get around that with a VPN. I'm using v8.39 now.

Saturn is great, but the current version defaults to a hideous color
scheme, which fortunately can be fixed.