[time-nuts] Low noise voltage regulators

WB6BNQ wb6bnq at cox.net
Thu Feb 25 01:33:18 UTC 2010


Bruce,

Why not just use a diode in place of the 2M3904 circuit ?  Seems like it would do the same
thing with less parts.

Also, would not the Texas Instruments TL-431 be a better choice as it has a lower noise spec
them the LM329 part.  In addition, with its adjustable nature, the TL-431 would be adjusted
to make sure the single diode (in place of the 2N3904 circuit) is shut off when the TL-431
comes up to speed.

Obviously, this would be best with intended output voltages above the reference level.

Bill....WB6BNQ


Bruce Griffiths wrote:

> I meant something like the attached circuit schematic for an LM723 based
> 15V regulator.
> The circuit can be easily extended to use an external pass transistor
> where more current is needed.
>
> The LM329 is biased from the regulator output which improves the
> reference line rejection.
> The 723's internal reference is used only during startup.
> The 2N3904 disconnects the internal reference when the LM329 terminal
> voltage exceeds about 5.4V.
> Some optimisation of the circuit may be required.
>
> Bruce
>
> Arnold Tibus wrote:
> > Hi,
> >
> > NS gives some informations about improvements in their AN-173.pdf
> > http://www.national.com/ds.cgi/LM/LM117.pdf
> > Audio freaks are discussing it in
> > http://www.diyaudio.com/forums/solid-state/28978-improving-lm3x7-regulator-circuit.html
> > Is that what you are looking for?
> >
> > 73
> > Arnold
> >
> >
> > On Thu, 25 Feb 2010 11:22:02 +1300, Bruce Griffiths wrote:
> >
> >
> >> You can improve the performance of the LM723 if one substitutes an LM329
> >> for the internal reference biased from the regulator output.
> >> The trick is to use the internal reference for startup and decouple it
> >> with a diode or similar once the LM329 achieves its nominal output.
> >>
> >
> >> Currently, there appear to be 2 variants of the LM723 one (made by
> >> National) that uses a noisy bandgap reference and another variant that
> >> actually uses a quieter zener reference.
> >>
> >
> >> Bruce
> >>
> >
> >> Brooke Clarke wrote:
> >>
> >>> Hi neville:
> >>>
> >>> My old Gibbs rack mount 5 MHz standard used the LM723 linear
> >>> regulator.  I believe it's one of the lowest noise regulators you can
> >>> use.
> >>> http://www.national.com/mpf/LM/LM723.html#Overview
> >>>
> >>> Have Fun,
> >>>
> >>> Brooke Clarke
> >>> http://www.PRC68.com
> >>>
> >>>
> >>> Neville Michie wrote:
> >>>
> >>>> Hi,
> >>>> I remember a reference, probably by Bruce, that LEDS provide a low
> >>>> noise voltage reference.
> >>>> I am proposing to build a voltage regulator for a thermally
> >>>> controlled LPRO rubidium oscillator,
> >>>> with the voltage regulator being mounted on the 0.5 inch thick
> >>>> aluminium heat sink plate.
> >>>> The LEDS would also be mounted on the plate, which has controlled
> >>>> temperature.
> >>>> The LPRO has internal voltage regulation, and by running it at ~40C
> >>>> and 18Volts, the thermal
> >>>> flux within the unit is minimised as is the power demand.
> >>>> What I want to know is if a LM317 running on a stack of LEDs driven
> >>>> by the LM317 output
> >>>> would provide a low noise power source? What would be better?
> >>>>
> >>>> cheers, Neville Michie
> >>>>
> >>>>
> >
> >
> >
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