Very low noise 7805?

ChuckT · 9th October 2005, 05:56 PM

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.

ChuckT · 9th October 2005, 06:31 PM

Ops, forgot to paste the link to the datasheet.

http://www.st.com/stonline/products/...44/l7805ac.pdf

Mad_K · 9th October 2005, 06:39 PM

eN is 10uV/Vo. That makes it 50uV @ 5V. The TS7805 is 40uV by comparison..

ChuckT · 10th October 2005, 03:35 AM

My mistake, thanks for pointing that out.
Same as other 7805 type.

Guido Tent · 10th October 2005, 11:56 AM

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.

best

janneman · 10th October 2005, 12:22 PM

Quote:

Originally posted by Guido Tent
[snip]78/79 regs are extremely non linear in output impedance behaviour, avoid them, they act as mixers.

best

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

Guido Tent · 10th October 2005, 01:11 PM

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......

best

janneman · 10th October 2005, 01:50 PM

Quote:

Originally posted by Guido Tent
[snip]Currently, Tentlabs is designing a discrete regulator that subsitutes 78/79 style regs. Keep watching the webspace......

best

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

..

Jan Didden

Guido Tent · 10th October 2005, 02:10 PM

Quote:

Originally posted by janneman

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

Jan Didden

Hi Jan

I know

best

Zombie · 10th October 2005, 03:54 PM

Hi Guido and Jan!
Are your regulators a drop-in? Just pull the 7xxx out and the discrete in?
Cheers
Tom

9th October 2005, 05:56 PM	#1
ChuckT diyAudio Member Join Date: Nov 2002 Location: HK	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.

9th October 2005, 06:39 PM	#3
Mad_K diyAudio Member Join Date: Sep 2002 Location: Norway	eN is 10uV/Vo. That makes it 50uV @ 5V. The TS7805 is 40uV by comparison.. __________________ Mads K

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9th October 2005, 06:31 PM	#2
ChuckT diyAudio Member Join Date: Nov 2002 Location: HK	Ops, forgot to paste the link to the datasheet. http://www.st.com/stonline/products/...44/l7805ac.pdf

10th October 2005, 03:35 AM	#4
ChuckT diyAudio Member Join Date: Nov 2002 Location: HK	My mistake, thanks for pointing that out. Same as other 7805 type.

10th October 2005, 03:54 PM	#10
Zombie diyAudio Member Join Date: Feb 2003 Location: At home	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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