Voltage Regulators query

Wynand · 23rd January 2006, 09:10 AM

If I want to use the LM317/337 to power a preamp, basically just one opamp, would I need a heatsink?

The input V will be max 35Vdc

pinkmouse · 23rd January 2006, 09:16 AM

Didn't you ask this question a while back, or am I going mad in my old age?

Dissipated power is a product of the voltage dropped and the current used. For that much voltage drop, even at low current, I would heatsink the regs. Better safe than sorry.

janneman · 23rd January 2006, 09:21 AM

Quote:

Originally posted by pinkmouse
Didn't you ask this question a while back, or am I going mad in my old age?

Dissipated power is a product of the voltage dropped and the current used. For that much voltage drop, even at low current, I would heatsink the regs. Better safe than sorry.

IOW, if the input is 35V, and the output is 15V, dropped V is 20V. With a load of say 25mA (probably less) P = 20 x 25 mW = half a watt. Maybe just a small sink would be wise, as Pinkmouse said.

Jan Didden

Wynand · 23rd January 2006, 09:27 AM

If I've asked this question before I apologize. I can't remember it though (and I don't even have old age to blame

Thanks for the explanations !!!

pinkmouse · 23rd January 2006, 09:36 AM

No problem Wynand, I'm sure I've done the same thing before!

Jan's post gives you the numbers, though I was rather hoping you'd do the maths and get a proper feel for it, then you can use it again in the future. I've found that working out simple questions like this helps a lot to get a feel for a circuit and leads to greater understanding in the long term, and as a relative newbie, I certainly need all the understanding I can get.

janneman · 23rd January 2006, 10:56 AM

Quote:

Originally posted by pinkmouse
No problem Wynand, I'm sure I've done the same thing before!

Jan's post gives you the numbers, though I was rather hoping you'd do the maths and get a proper feel for it, then you can use it again in the future. I've found that working out simple questions like this helps a lot to get a feel for a circuit and leads to greater understanding in the long term, and as a relative newbie, I certainly need all the understanding I can get.

Point taken, Al

Jan Didden

23rd January 2006, 09:10 AM	#1
Wynand diyAudio Member Join Date: Mar 2005 Location: Cape Town	Voltage Regulators query If I want to use the LM317/337 to power a preamp, basically just one opamp, would I need a heatsink? The input V will be max 35Vdc

23rd January 2006, 09:16 AM	#2
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Didn't you ask this question a while back, or am I going mad in my old age? Dissipated power is a product of the voltage dropped and the current used. For that much voltage drop, even at low current, I would heatsink the regs. Better safe than sorry. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

23rd January 2006, 09:36 AM	#5
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	No problem Wynand, I'm sure I've done the same thing before! Jan's post gives you the numbers, though I was rather hoping you'd do the maths and get a proper feel for it, then you can use it again in the future. I've found that working out simple questions like this helps a lot to get a feel for a circuit and leads to greater understanding in the long term, and as a relative newbie, I certainly need all the understanding I can get. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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23rd January 2006, 09:27 AM	#4
Wynand diyAudio Member Join Date: Mar 2005 Location: Cape Town	If I've asked this question before I apologize. I can't remember it though (and I don't even have old age to blame Thanks for the explanations !!!

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