LM317 safe operating temperature - Page 3

MarianB · 29th June 2012, 08:21 AM

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

))

sbrads · 29th June 2012, 09:34 PM

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 · 1st July 2012, 05:35 AM

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 · 2nd July 2012, 07:09 AM

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

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29th June 2012, 08:21 AM	#21
MarianB diyAudio Member Join Date: Jul 2011 Location: Romania	When you put the problem that way both reasons are good ones ( especially no.1 ))

29th June 2012, 09:34 PM	#22
sbrads diyAudio Member Join Date: Jun 2005 Location: Kent, UK	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.

1st July 2012, 05:35 AM	#23
dangus diyAudio Member Join Date: May 2004 Location: Vancouver Island	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.

2nd July 2012, 07:09 AM	#24
mkusan diyAudio Member Join Date: Jan 2011 Location: Zagreb	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