[time-nuts] Super Regulator links

[Bruce Griffiths]

John Miles wrote:
> What are some of your favorite low-noise regulators?  When I made the remark
> about the uA723, I was specifically thinking of its performance compared to
> the LT1762.  With Cref=5 uF, the uA723's output noise voltage is rated at
> 2.5 uV from 100 Hz to 10 kHz.  The LT1762, which seems to be among Linear's
> quietest parts, is rated at 20 uV from 100 Hz to 100 kHz, with external
> bypassing that places most of the noise at lower frequencies.  Snake oil or
> not, that's 18 dB less noise from the 723.
>
>   
This is perhaps a result of using the apparently inherently noisier
bandgap style references which offer significant advantages (lower
minimum input voltage, lower dropout but not necessarily lower noise) in
lower voltage systems.
> There are various hacks like Wenzel's that can clean up after a noisy
> regulator
That particular circuit is only effective over the 100Hz to 10kHz range.
The brute force darlington buffered RC filter favoured by NIST is far
more effective when the  accompanying disadvantages are acceptable.
> , but if there are quieter fully-integrated solutions out there I'd
> like to hear about them.  Posted back to the list in case there are other
> views on the subject...
>
> -- john, KE5FX
>   

I havent yet come across any IC that seems to approach the performance
achievable with a 723.
The next step up without adding too much complexity is perhaps to use a
723 with a low pass filtered LM329 reference powered from its regulated
output.
To improve the ripple rejection you can add an LM317 tracking preregulator.
Beyond that a well designed discrete regulator is the only way to
improve performance.
Off course if you are building hundreds of circuits and dont want to
take the risk of occasionally striking noisy parts then you either need
to prescreen parts or buy noisier parts with guaranteed noise specs.

Lots of so called low noise regulators pop up from time to time but when
you actually read the datasheet and calculate the output noise for a 12V
supply and not the 1V or so supply to which the noise specs apply they
all seem to fall short of the 723's performance.

Bruce