[time-nuts] low noise voltage regulation, again

Bob Camp lists at cq.nu
Thu Feb 18 12:09:45 UTC 2010


Cleaning up a switcher is going to require you to take out the radiated as well as the conducted crud. You also will have ground loop issues all over the place. 

Much easier to just start with a linear supply in the first place. There are oceans full of them out there on the auction sites. 

Since the LPRO has a pretty conventional regulator inside it, cleaning up the external supply will only get you so far. More or less Input noise / isolation < output noise and you are done. 

I have no idea what the TBolt has on the supplies. I'm pretty sure the OCXO has a regulator much like the TBolt does. 


On Feb 17, 2010, at 10:57 PM, Scott Burris wrote:

> I'm finally thinking about building some real power supplies for my Thunderbolts
> and LPRO-101, and that got me thinking about the topic of low noise power
> supplies again.
> I think Dr. Bruce and I exchanged some messages about this a year or two ago,
> when I was looking at "RF regulators" and the conclusion seemed to be that
> the ancient ua723 was still the low noise champ.  Is that still the case, or
> are there better modern regulators?
> I was thinking of doing strictly linear regulators, but then I read this
> note at Wenzel:
> http://www.wenzel.com/documents/finesse.html
> I think of this as the "short out the noise before anyone sees it" approach.
> Do you think the circuit of figure 4 can clean up the output of a switching regulator
> down to 20nv?  I assume this was written as a post cleanup of a linear regulator.
> Alternatively, what do you think about these Maxim circuit ideas which claim
> 7nv and 6nv:
> http://www.maxim-ic.com/app-notes/index.mvp/id/3656
> http://www.edn.com/contents/images/608157.pdf
> Is it better to apply cleanup circuits like this to average regulators or
> go back to something derived from the 723 or its kin?
> Just casting about for ideas about what I should be experimenting with.
> Scott
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