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

Cube Central cubecentral at gmail.com
Fri Oct 14 14:00:08 EDT 2016

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 at 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
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