[time-nuts] Low noise power supplies?

David davidwhess at gmail.com
Fri Feb 1 00:10:53 EST 2013

I have seen it used in a couple of Tektronix TM500 instruments but the
purpose may have been to generate a lower voltage power supply rail
instead of noise reduction.  Tektronix often added LC sections on
their switching power supply outputs and distributed smaller LC
sections to prevent coupling between different circuits.

On Thu, 31 Jan 2013 22:12:42 -0600, "Max Robinson"
<max at maxsmusicplace.com> wrote:

>You haven't seen it used because it doesn't work very well.  It appeared in 
>a few pieces of Heathkit equipment but I don't think HP or Tek used it at 
>all.  Any AC component of base to collector voltage has a small but definite 
>effect on Vbe which transfers voltage in the reverse direction from 
>collector to emitter even though the base is held at AC ground.  A three 
>terminal regulator does a better job of suppressing ripple from a power 
>Regulators use a zener diode as the reference and there are circuits in 
>which a zener is used as a noise source.  What does that tell you?  The 
>quietest power supply is an analog regulator followed by one or more RC 
>filter sections.  The inductor in an LC filter is likely to pick up more hum 
>and noise than it filters out.  My presumption is that a low noise power 
>supply is likely to be providing a small amount of power to the load and 
>load regulation is probably not a problem.

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