[time-nuts] Low noise voltage regulators

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Feb 25 01:08:18 UTC 2010

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.


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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