Re: Cooling a TO-220 7812 regulator

On 15/09/2024 12:28, Pimpom 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)?

I suspect that under those load conditions you will get away with it #1. I'm pretty sure the package is well able to handle that dissipation and if it can't it will fold back to thermally protect itself (in which case you will have to add a bit more heatsinking).
I once built a 78xx based PSU that was in a bright bare metal aluminium extruded box expecting it to be more than adequate heatsinking. It wasn't! The bright metal was a terrible radiator and it got hot enough to go into thermal foldback. A bit of matt black paint fixed that.
--
Martin Brown