[time-nuts] Low noise power supplies for time nuts circuitry

Azelio Boriani azelio.boriani at screen.it
Thu Nov 24 21:09:27 UTC 2011


The -12V in the TBolt is not used for the serial port. the HIN232 of the
TBolt goes from the +5V only, it generates the + and - by the usual
switched capacitor technique common to other RS232 interfaces (ADM232,
MAX3221 and so on). The -12V powers the LT1014 quad precision opamp that I
presume handles the EFC, so care must be taken about the -12 although the
PSRR of the opamp comes to the rescue.

On Thu, Nov 24, 2011 at 8:25 PM, <lists at lazygranch.com> wrote:

> When you design a regulator, lots of gain is not a criteria in the error
> amp. (Who needs microvolt accuracy?) High gain generally means two gain
> stages, which in turn makes it difficult to compensate when driving
> reactive loads. Thus most op amps are generally a bad idea for an error amp
> in a regulator.
>
> Noise needs to be defined. Generally it means broadband noise. But if your
> regulator is on the verge of oscillation when the load current or line
> voltage changes, who cares if the broadband noise is low?
>
> This thread is starting to baffle me. Simply dig up a low noise regulator
> chip. LTC comes to mind. Or troll the net for audiophile shunt designs if
> you are going to roll your own.
>
> What you see done in design often is dubious. Just because it is built,
> doesn't mean it is good. (Hey, there are doctors that give bad medical
> advice.) You need to evaluate existing designs for your application.
>
> It pays to read the datasheet religiously. Some of these high accuracy
> regulators can't handle low ESR caps on the output.
> -----Original Message-----
> From: Joe Gwinn <joegwinn at comcast.net>
> Sender: time-nuts-bounces at febo.com
> Date: Thu, 24 Nov 2011 10:14:35
> To: <time-nuts at febo.com>
> Reply-To: Discussion of precise time and frequency measurement
>         <time-nuts at febo.com>
> Subject: Re: [time-nuts] Low noise power supplies for time nuts circuitry
>
> At 2:28 PM +0000 11/24/11, time-nuts-request at febo.com wrote:
> >Message: 3
> >Date: Thu, 24 Nov 2011 13:22:38 +0100
> >From: Attila Kinali <attila at kinali.ch>
> >To: Discussion of precise time and frequency measurement
> >       <time-nuts at febo.com>
> >Subject: Re: [time-nuts] Low noise power supplies for time nuts
> >       circuitry
> >Message-ID: <20111124132238.0c810b78.attila at kinali.ch>
> >Content-Type: text/plain; charset=US-ASCII
> >
> >On Wed, 23 Nov 2011 04:50:49 -0800
> >Chuck Forsberg WA7KGX N2469R <caf at omen.com> wrote:
> >
> >>  How well would a pair of cascaded 3 terminal regulators do - say a 7815
> >>  feeding a 7812.
> >
> >78xx Regulators are quite noisy. You can use them to filter the
> >noise of a cheap DC/DC converter, but i wouldnt use them feed
> >high precision electronics. There are a lot better designs these days.
>
> What I see done in low-noise circuits is a low-noise opamp used as a
> linear voltage regulator to clean up the output of a 78xx or the like
> regulator.
>
> Joe Gwinn
>
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