[time-nuts] Low noise power supplies?
max at maxsmusicplace.com
Fri Feb 1 14:39:14 EST 2013
Well, I stand corrected. Weren't the TM 500 instruments marketed as low
Max. K 4 O DS.
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----- Original Message -----
From: "David" <davidwhess at gmail.com>
To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
Sent: Thursday, January 31, 2013 11:10 PM
Subject: Re: [time-nuts] Low noise power supplies?
>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
>>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
>>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
>>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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