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

[Scott Stobbe]

It is also wise to measure the noise floor of the test setup as fully
connected as possible. For one of those usb charger cubes, you can use a
power bar with a power switch (which will only switch the hot line on/off,
earth and neutral are permanently connected, one would hope). You will see
a lot of other noise sources before you even power up your DUT.

On Fri, Oct 14, 2016 at 2:16 PM, Nick Sayer via time-nuts <
time-nuts at febo.com> wrote:

> Set your scope for AC coupling. Set your scope probe for 1x rather than
> 10x. Use the absolutely shortest scope grounding you can. That’s what those
> spring looking things that came with it are for. I typically use the spring
> gizmo and probe on an SMD cap. The ground wire with an alligator clip will
> just pick up far more noise than you’ll be measuring. This is how I was
> able to measure the noise and ripple of the SC189Z switcher feeding the
> OCXO in my GPSDO. I got measurements of ~4 mV P-P that way. Be careful you
> don’t get the probe and ground reversed - your scope won’t likely have an
> isolated ground from your DUT and that would therefore be bad.
>
> You’re going to want to check the supply’s performance under load. For
> that, you’ll may want to get yourself a dummy load. I got one from Tindie
> for testing my Pi Power design: https://www.tindie.com/
> products/arachnidlabs/reload-2/
>
>
>
> > On 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.
> >
> > Thanks in advance for any tips!
> >
> >       -Randal R.
> >               (at CubeCentral)
> >
> > -----Original Message-----
> > From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Chris
> Albertson
> > Sent: Friday, 14 October, 2016 02:29
> > To: Discussion of precise time and frequency measurement <
> time-nuts at febo.com>
> > Subject: Re: [time-nuts] For those that insist on using switching power
> supplies
> >
> > On Thu, Oct 13, 2016 at 6:05 AM, Van Horn, David <david.vanhorn@
> backcountryaccess.com> wrote:
> >> To be fair here, phone chargers have almost no requirement to be quiet
> other than conducted and radiated emissions limits.
> >> It's charging a battery.
> >
> > Not only that but,  the 5 volts comping out of the larger is almost
> certainly the input to another DC/DC power supply and NOT used directly.
> > You can't charge a Lithium battery with the 5 volts the charger outputs.
> >
> > If you don't know about LiPo batteries, they need a constant current
> power source and then as they get close to charged the charger switches to
> constant voltage (VERY roughly) at about 4V per cell.
> >
> > I have a project right here on my desk as I type.  I'm using the output
> of a generic USB hub.  The circuit is  a cap from 5V to GND and
> > then a low dropout regulator to get 3.3 volts.    I don't care to much
> > if there is huge ripple on the 5.0 volts coming in as long as it stays
> above the LDO limit.
> >
> > Also it looks like they tested the USB chargers with no load.  A typical
> load might have a say, 0.01uf cap to short the noise to ground.  So in use
> the power might be better?
> >
> > It was no surprise the counterfeit chargers were horrible.  The
> manufacturers are by definition of "counterfeit" being dishonest slim
> balls. Why would he care about anything other then that he can fool
> > some people into buying his product.   There are third party chargers
> > that are not trying to copy a well known brand, these are usually much
> better
> >
> >
> > --
> >
> > Chris Albertson
> > Redondo Beach, California
> > _______________________________________________
> > time-nuts mailing list -- time-nuts at febo.com To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > and follow the instructions there.
> >
> > _______________________________________________
> > time-nuts mailing list -- time-nuts at febo.com
> > To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
> > and follow the instructions there.
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
> and follow the instructions there.
>