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Old 23rd January 2006, 09:10 AM   #1
Wynand is offline Wynand  South Africa
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Default 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
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Old 23rd January 2006, 09:16 AM   #2
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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.
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Old 23rd January 2006, 09:21 AM   #3
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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.

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Old 23rd January 2006, 09:27 AM   #4
Wynand is offline Wynand  South Africa
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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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Old 23rd January 2006, 09:36 AM   #5
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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.
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Old 23rd January 2006, 10:56 AM   #6
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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

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