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

lists at lazygranch.com lists at lazygranch.com
Thu Nov 24 14:25:46 EST 2011


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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