LM317 safe operating temperature

[MarianB]

When you put the problem that way both reasons are good ones ( especially no.1 ))

 

[sbrads]

You won't damage an LM317 by using a marginal heatsink, it's rather well protected and if it gets too hot it shuts down (which will cool it). So, if the output volts hold up it's basically doing OK and an extra small fan or bigger heatsink than can achieve this is going to give a good working margin.

 

[dangus]

I've seen a 3 terminal regulator fail short circuit, which destroyed everything downstream. I believe what happened was the input voltage was too high so the regulator ran hot. So, try to keep the regulator as cool as possible.

 

[mkusan]

Hi sbrads and dangus,
thank you for your kind answers and sorry for my late reply.

As I understood it installation of bigger heat sink solved my potential problem and temperature of 50C measured on it is perfectly acceptable.

To confirm my assumptions I left CD player on play continuously for 48 hours, the thermal protection of LM317 did not come in and the voltage is rock stable at 5.09V.

My next test was not very scientific and it is not direct comparison but I was curious , so I picked the hottest component in my vintage Rotel integrated amplifier and measured temperature on its heat sink. The component in question is power regulator 2SC1826 (T-220 as well) and the temperature measured was 54C. I obviously don't expect this CD player to last for the next 33 years (Rotels age) since it was built in 1989. but it was good to know at least LM317 temperature wise it could.

Thanks
Marko