From: firstname.lastname@example.org (carltons)
Subject: Re: Split power supply for LM723 - safe?
References: <3DDF5FD3.4AB82A49@worldonline.fr> <3DDFB011.829BB7B6@worldonline.fr>
User-Agent: NewsWatcher-X 2.2.3b2
NNTP-Posting-Date: Sat, 23 Nov 2002 20:57:07 GMT
Date: Sat, 23 Nov 2002 20:57:08 GMT
In article <3DDFB011.829BB7B6@worldonline.fr>, "A.Iakovlev"
> carltons wrote:
> > Why the 723? There are many very good, low power, low noise, regulators
> > now available. The 723 was a beautiful design in 1970, but this is 2002!
> Yes, the 723 is an old thing, but it still widely available and it is quite
> > BTW, what is your application and what are your other design constraints?
> The application is low noise power for digital audio circuits : S/PDIF
> receiver/PLL and the DAC. The space is not a premium; I need DIP/SOIC parts ;
> need 5.0V and 5.5V output.
> I have researched quite a number of LDO etc. modern regulators but haven't
> found anything offering 2.5 uV noise (100Hz - 10KHz ; well up to 30uV would
> still be ok), low overshoot on load variations, available in adjustable
> version, in DIP/SOIC and not expensive. ADP3303 looks good but its adjustable
> version (ADP3303A) is available only in TSSOP.
Most audio circuits, digital or analog, have good power supply rejection
and don't need a perfectly clean supply. I would worry more about other
sources of noise such as input coupling from outside noise sources, etc.
and that warrants good shielding and good grounding techniques.
BTW, I would question whether or not the 723 could be as good as you think
it may be. The old designs had pretty good noise performance, but the
error amp can't have that kind of noise performance, I don't believe,
unless you're thinking in terms of uV/sqrt hz. Regardless, the audio amps
that you'll be using will reject this supply noise by 50 db or more I'm