On Thu, Oct 13, 2016 at 6:05 AM, Van Horn, David
david.vanhorn@backcountryaccess.com wrote:

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

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@febo.com] On Behalf Of Chris Albertson
Sent: Friday, 14 October, 2016 02:29
To: Discussion of precise time and frequency measurement time-nuts@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:

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@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Hi

A spectrum analyzer and some sort of active load are generally the two pieces of gear I reach for
first when testing supplies. You need an analyzer that will cover the entire “range of interest” for
the supply or possibly multiple analyzers if that turns out to be 0.1 Hz to 6 GHz. Since noise changes
with load, whatever you do needs to be repeated at various output levels on the supply.

Bob

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/

Nick, thanks for your detailed reply.  Would you happen to have a photo of the "spring looking things?"  I am not entirely sure I have one of those included with the kit that came with the scope.
What size of capacitor would you suggest?
I happen to have the exact same dummy load that you do.  I have added on a fan for higher current/longer use.

Thanks for the help, I look forward to trying out some of the measurements that I've seen posted elsewhere ( such as this link: http://www.righto.com/2012/10/a-dozen-usb-chargers-in-lab-apple-is.html )

Cheers!

-Randal R.
	(at CubeCentral)

-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces@febo.com] On Behalf Of Nick Sayer via time-nuts
Sent: Friday, 14 October, 2016 12:17
To: Discussion of precise time and frequency measurement time-nuts@febo.com
Subject: Re: [time-nuts] For those that insist on using switching power supplies

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/

time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

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@febo.com> wrote:

I don’t have a picture, but the Internet does: http://i.stack.imgur.com/PSo3N.jpg

Well, I use mostly 0805 MLCCs on my boards, not counting the occasional polymer or electrolytic.

On Fri, Oct 14, 2016 at 11:00 AM, Cube Central cubecentral@gmail.com wrote:

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

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@gmail.com
wrote:

On Fri, 14 Oct 2016 12:00:08 -0600
"Cube Central" cubecentral@gmail.com wrote:

There are different frequency ranges one looks at when measuring
power supplies:

1. Long term stability over seconds to hours
2. Low frequency noise between 0.1Hz and 10Hz
3. Mid frequency noise between 10Hz and 20MHz
4. High frequency noise beyond 20MHz

The borders of these different ranges of noise are kind of arbitrary
and different people use different values. They are motivated by the
need of the consumer (of power) and by the limitations of different
measurement equipment.

The long term stability is what we usually call "wander" and
is mostly dominated by the thermal stability and aging of the
power supply's voltage reference and its control loop. To measure
it correctly one usually uses a high resolution DMM in the 7.5
or 8.5 digits range. One can also build a homebrew system using
a high resolution ADC (like 32bit delta-sigma converters: AD7177-2,
LTC2508-32, AD1262) and a very stable voltage reference (LTZ1000, LM399).
I'd like to refer to the volt-nuts mailinglist on how to properly
do this, as my knowledge in this area is rather limited.

The low frequency range is what we usually call the 1/f region,
although the long term stability also belongs to it. But unlike
the long term region you don't have to sacrifice a virgin to
get decent measurment data. Jim William's appnote[1] has lots of
details how to measure noise in this region. There are slightly
more modern circuits by Todd Owen/Amit Patel[2] and Gerhard Hoffmann[3].
I recently stumbled over a similar amplifier by Enrico Rubiola
and Franck Lardet-Vieudrin[4]. Both [4] and [5] explain why for
low impedance sources (like power supplies) a BJT input stage
would be a better choice than jFETs and also cover the influence
of temperature on the measurement. [6] gives some additional info
on how to design the differential input stage.
I wonder how an active offset voltage cancelation scheme for
the differential pair input stage using one of the chopper stabilized
opamps (eg LTC2057) would change the temperature dependence and long
term stability  (aka 1/f^a noise) of the circuit, but I have not seen
any measurements of a system like this yet.

The mid frequency range is mostly influenced by the telecom
noise requirements, which for historical reasons cover the 10Hz
to 20MHz range. It is probably the easiest region to measure
with homebrewn instruments. A decently fast ADC with a low
noise voltage reference (like the LTC6655) are all you need.
Depending on how accurately you want to measure the noise, it makes
sense to further split this range into a lower range up to ~500kHz
and an upper range above 500kHz. The reason is that there are today
several high resolution ADCs available that support sampling rates of
up to 1Msps (and some beyond),eg:
AD7982, 18bit 1Msps
AD7984, 18bit 1.33Msps
AD7960, 18bit 5Msps
LTC2386-18, 18bit 10Msps
LTC2378-20, 20bit 1Msps
LTC2368-24, 24bit 1Msps
These would allow to accurately measure the noise range that is
IMHO most interesting for most applications. Interesting because
a lot of applications are insensitive to noise below 1Hz or even
below 10Hz and noise above several 100kHz becomes easy to filter
out using inductors, ferrit beads and ceramic capacitors. When
choosing an ADC for this range make sure you check the actual
SNR/SFDR performance as it a higher output resolution not necessarily
corresponds to the actual performance delivered. This becomes
especially pronounced when going higher with the sampling rate
to cover the higher noise frequency ranges. Beyond 5-10Msps 16bit
is the best you can get and conversly the SNR is limited to
something around 90dB-95dB.

The high frequency noise, I mentioned above 20MHz, but probably
the limit is more in the 1-10MHz range, is where radiation
becomes interesting. Ie with increasing frequency it becomes
harder and harder to "isolate" electronics against noise
and it becomes necessary to shield it with metal plates.
This range is important for the switched power supplies that
started this thread. These supplies have usually switching
frequencies between a couple of 10kHz to low 100kHz for high
power and AC/DC supplies and goes up to a few MHz for the low
power (where low power is relative and can be several W) low
voltage DC/DC supplies. And as these supplies are switching hard
they produce lots of harmonics. A badly designed supply can easily
produce very noticable spikes at 100MHz. Measuring this type of
noise is probably easiest with a good digital oscilloscope with
a sufficiently high analog bandwidth and sampling rate. Alternatively
specturm analysers are a good choice too. Going homebrew in this
range is kind of difficult, as high resolution ADCs max out around
100-125Msps, with the odd exception of LTC2107 that gives 16bit up
to 210Msps (and still an 80dB SNR). Ie the maximum achievable
bandwidth is 40-90MHz for single ADC configurations. But interfacing
these high-speed ADCs requires an FPGA and thus considerable effort.
An alternative approach is to build a spectrum analyser like setup
with a tunable oscillator and a down-mixer. The problem here would
then be to get a flat frequency response and the required calibration.
Another approach is to use an SDR system with a low lower frequency
limit, but this also requires to kind of calibrate it as these are
not ment for power measurements and thus their frequency response
is not really flat. But they give at least a good indication whether
you have any spikes that stick far out.

One thing I haven't mentioned yet is that you will need to have some
form of load that can be switched. Power supply noise is highly dependent
on the current flow, especially for switched power supplies. But
because the load will also create noise, you probably want to just
have a bank of relay switched power resistors. In case you want to
measure the response on load switches, you should replace the relays
by power transistors (otherwise the bouncing of the relay will
confound the measurement).

		Attila Kinali

[1] "775 Nanovolt Noise Measurement for A Low Noise Voltage Reference",
by Jim williams, Linear AN124, 2009
http://www.linear.com/docs/28585

[2] "Measuring 2nV/sqrt(Hz) Noise and 120dB Supply Rejection
on Linear Regulators", by Todd Owen and Amit Patel, Linear AN159, 2016
http://www.linear.com/docs/47682

[3] "A 220 pV/sqrt(Hz) low noise preamplifier", by Gerhard Hoffman, 2014
http://www.hoffmann-hochfrequenz.de/downloads/lono.pdf

[4] "Low Flicker-Noise DC amplifier for 50Ω Sources", by Enrico Rubiola
and Franck Lardet-Vieudrin, 2004
http://rubiola.org/pdf-articles/journal/2004rsi(rubiola)low-flicker-dc-amplifier.pdf
http://arxiv.org/abs/physics/0503012

[5] "Some Considerations for the Construction of Low-Noise Amplifiers in
Very Low Frequency Region", by Sikula, Hashiguchi, Ohki, Tacano. 2004
http://dx.doi.org/10.1007/1-4020-2170-4_27

[6] "Some Tips on Making a FETching Discrete Amplifier", by George Alexandrov
and Nathan Carter, Analog Dialog 47-10, 2013
http://www.analog.com/library/analogdialogue/archives/47-10/discrete_amplifier.html

--
Malek's Law:
Any simple idea will be worded in the most complicated way.