[time-nuts] For those that insist on using switching power supplies

[Scott Stobbe]

A basic DSO has maybe 300 uVrms noise over 100 MHz bandwidth, which is a
spectral noise floor of 30 nV/rtHz (assuming a brick-wall filter), if your
DUT is quieter than that you can always add an LNA.

On Fri, Oct 14, 2016 at 2:59 PM, Chris Albertson <albertson.chris at gmail.com>
wrote:

> On Fri, Oct 14, 2016 at 11:00 AM, Cube Central <cubecentral at gmail.com>
> wrote:
> > How would one go about testing power supplies and seeing how noisy they
> are?  I have the standard suite of tools, an oscilloscope and a little
> (dangerous) know-how.  I am just not sure what to look for or how to safely
> hook it up to test.
> >
>
> You'd ned a spectrum analyser.    You could assemble one from parts
> that are used for Software Radios.   A USB TV tunnel dongle and a
> computer and a good mixer and clean oscillator.   With hat you'd be
> able to characterize noise from DC to about 900MHz
>
> Those with more money than time would just spend the bucks to buy an SA
>
> Those who don't need numbers would just look at the DC on a scope and
> "eye ball it" and say "wow that is noisy" or "wow that looks clean"
>
> In all cases you'd want to put a realistic load on the power supply.
>  But what is that? I bet if varies a lot.
>
> And like I wrote before it may not even matter as phones don't
> directly use the 5 volt DC that these chargers produce.
> --
>
> Chris Albertson
> Redondo Beach, California
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