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Old 9th October 2005, 04:56 PM   #1
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Default Very low noise 7805?

Just wonder if anybody used the ST series of 7805, esp the precision 1A type L7805AC where the spec states 10uV from 10hz to 100khz, plus low output impendance of 0.017ohm. This is much better than even the lt317, lt1085.
It would be great if this is true as I can use it as I can use it as a simple drop in.
I will have to find it first however.
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Old 9th October 2005, 05:31 PM   #2
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Ops, forgot to paste the link to the datasheet.

http://www.st.com/stonline/products/...44/l7805ac.pdf
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Old 9th October 2005, 05:39 PM   #3
Mad_K is offline Mad_K  Norway
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eN is 10uV/Vo. That makes it 50uV @ 5V. The TS7805 is 40uV by comparison..
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Old 10th October 2005, 02:35 AM   #4
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My mistake, thanks for pointing that out.
Same as other 7805 type.
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Old 10th October 2005, 10:56 AM   #5
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Quote:
Originally posted by ChuckT
My mistake, thanks for pointing that out.
Same as other 7805 type.

Assumed noise is flat, that would give 158 nV/SqrrtHz

Usually (!) some LF nose is still present beuound 10 Hz so I'd expect more LF noise and some 100 nV/SqrrtHz.

78/79 regs are extremely non linear in output impedance behaviour, avoid them, they act as mixers.

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Old 10th October 2005, 11:22 AM   #6
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Quote:
Originally posted by Guido Tent
[snip]78/79 regs are extremely non linear in output impedance behaviour, avoid them, they act as mixers.

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Guido,

If I want to avoid 317-type regs to limit the number of components, what 3-pin regs would you recommend for +/- 15V applications? If any ..

Jan Didden
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Old 10th October 2005, 12:11 PM   #7
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Quote:
Originally posted by janneman


Guido,

If I want to avoid 317-type regs to limit the number of components, what 3-pin regs would you recommend for +/- 15V applications? If any ..

Jan Didden

Hi Jan

Well, yes, if any....

In that range, the LT1086 would be nice, but that one hasn't got a counterpart which thus calls for 2 floating supplies tied together.

There is a number of tricks to make such 3 pin regs sound better. One of them is loading them such that their output stage delivers more current (hence becomes more linear). Still, they were never designed with audio in mind.

Currently, Tentlabs is designing a discrete regulator that subsitutes 78/79 style regs. Keep watching the webspace......

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Old 10th October 2005, 12:50 PM   #8
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Quote:
Originally posted by Guido Tent
[snip]Currently, Tentlabs is designing a discrete regulator that subsitutes 78/79 style regs. Keep watching the webspace......

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Thanks Guido, but take it easy, I've done that already ..

Jan Didden
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Old 10th October 2005, 01:10 PM   #9
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Quote:
Originally posted by janneman



Thanks Guido, but take it easy, I've done that already ..

Jan Didden

Hi Jan

I know

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Old 10th October 2005, 02:54 PM   #10
Zombie is offline Zombie  Sweden
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Hi Guido and Jan!
Are your regulators a drop-in? Just pull the 7xxx out and the discrete in?
Cheers
Tom
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