Re: Cooling a TO-220 7812 regulator

On 16-09-2024 11:40 pm, john larkin wrote:

On Mon, 16 Sep 2024 17:46:29 -0000 (UTC), piglet
<erichpwagner@hotmail.com> wrote:
 

Pimpom <Pimpom@invalid.invalid> wrote:

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)?
>

>
You mentioned single sided board so I would be wary of just having the
regulator standing straight up anchored only by the legs. Without plated
through holes a s/s board joint cannot reliably support the weight of a
TO220 package if the unit is dropped or shaken. My preference would be to
screw it down to board if only for mechanical reasons-then the bolt
hardware and area of copper underneath provide a little bit of extra
heat-sinking it also gives more allowance against someone installing the
unit next to a furnace or somewhere hotter than 35degC

 
I think he has a 10:1 or so thermal safety margin. Most fets are rated
for 150 or 175 degC max Tj, and can stand a lot more in real life.
 
I agree about the standup vibration issue. Why not use a surface-mount
dpak?
 

I considered using the D2pak version but decided against it. One reason
is that I live in one of the most remote regions of a third world and we
have nothing like Digikey here. So I've made it a habit to use only the
most easily available parts. The D2PAK version of 78xx isn't in that
category.