Practical power supply noise testing
I have several supposedly low noise bench power supplies that I want to check out. They seem to work well but are quite old, so of course one wonders about the caps, etc.
Can someone suggest a practical test regime to verify power supply DC noise performance? Preferably one that doesn't require building up custom low noise amps?
Thanks!
John
I've used a pair of minicircuits phase modulators, a low noise OXCO, and a Timepod to do this.The phase modulators work best with about 9V input.The noise of my E3610A's is clearly evident as is the noise of an LM317 based regulator with unbypassed ADJ terminal.To achieve lower system noise a pair of preamps (one per phase modulator) is useful, however the noise need not exceptionally low as cross correlation lowers the effective preamp noise.
Bruce
From: John Ackermann N8UR <jra@febo.com>
To: volt-nuts@febo.com
Sent: Saturday, 2 July 2016 12:47 AM
Subject: [volt-nuts] Practical power supply noise testing
I have several supposedly low noise bench power supplies that I want to check out. They seem to work well but are quite old, so of course one wonders about the caps, etc.
Can someone suggest a practical test regime to verify power supply DC noise performance? Preferably one that doesn't require building up custom low noise amps?
Thanks!
John
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In the past when I did this, I used a high resolution digital
voltmeter like a Fluke 8505A in sample mode with a simple 10 Hz low
pass filter. I took samples for 10 seconds to get down to 0.1 Hz and
calculated the standard deviation to get RMS noise. I made a recent
post about this in connection with very low noise DC amplifiers.
To measure output ripple, I use a DSO set to line triggering.
Averaging removes all noise which is not synchronous with the AC line
frequency.
A low noise preamplifier with offset capability or a very low cutoff
frequency is still needed for lower level noise measurements. I have
a Tektronix 7A22 now but its AC coupled low pass cutoff is only
specified as better than 2 Hz and its offset capability is somewhat
limited. It works great to help with higher frequency bandpass
measurements though. A 7A13 has slightly better offset capability but
is also higher noise.
You said you want to avoid building a custom low noise amplifier
however for more sensitive measurements, even a simple operational
amplifier based design will help considerably. I always hack together
an AC coupled amplifier using a low noise JFET operational amplifier
as needed; the quality of the AC coupling capacitor is what limits low
frequency performance.
Check out Linear Technology application notes 83, 124, and 159 for
some ideas and a discussion of the AC coupling capacitor problem:
http://cds.linear.com/docs/en/application-note/an83f.pdf
http://cds.linear.com/docs/en/application-note/an124f.pdf
http://cds.linear.com/docs/en/application-note/an159fa.pdf
On Fri, 1 Jul 2016 08:47:18 -0400, you wrote:
I have several supposedly low noise bench power supplies that I want to check out. They seem to work well but are quite old, so of course one wonders about the caps, etc.
Can someone suggest a practical test regime to verify power supply DC noise performance? Preferably one that doesn't require building up custom low noise amps?
Thanks!
John
In message 2656F010-8E12-4BAD-B9AE-713CEFEE1B0A@febo.com, John Ackermann N8UR writes:
I have several supposedly low noise bench power supplies that I want to check out. They seem to work well but are quite old, so of course one wonders about the caps, etc.
Can someone suggest a practical test regime to verify power supply
DC noise performance? Preferably one that doesn't require building
up custom low noise amps?
Listen to them ?
All the "hard" noise is in the audio-range, so a series capacitor
a low-noise amp and a pair of headphones...
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Hi Poul
When testing VCOs any noise on the control voltage causes a frequency change in the output which can be characterized.
The HP/Agilent 4352 VCO tester contains a programmable DC supply with exceptionally low noise.
Instead of headphones something like the HP 4395A which has a spectrum analyzer mode with a true RBW of 1 Hz to allow
displaying root(Hz) noise levels (true I&Q detection rather than the old analog peak detection).
http://www.prc68.com/I/4395A.shtml http://www.prc68.com/I/4395A.shtml
AFAICR there were some HP app notes on measuring power supplies which may have included noise.
--
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
The lesser of evils is still evil.
-------- Original Message --------
In message 2656F010-8E12-4BAD-B9AE-713CEFEE1B0A@febo.com, John Ackermann N8UR writes:
I have several supposedly low noise bench power supplies that I want to check out. They seem to work well but are quite old, so of course one wonders about the caps, etc.
Can someone suggest a practical test regime to verify power supply
DC noise performance? Preferably one that doesn't require building
up custom low noise amps?
Listen to them ?
All the "hard" noise is in the audio-range, so a series capacitor
a low-noise amp and a pair of headphones...
In message 5776E31D.7090404@pacific.net, Brooke Clarke writes:
Instead of headphones something like the HP 4395A [...]
Well, there is a slight difference in price there, isn't there ? :-)
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Its certainly a good way to quickly check if anythings drastically wrong and one could even compare them with a known source such as an LM317 based regulator with no ADJ pin bypass. If one can hear the noise then its possible that a sound card could make some meaningful measurements of the headphone amp output.
John, do you have any specs for the supplies?It would be nice to know the likely best case output noise level.
To measure the ripple of most supplies I usually just connect my USB scope (dc coupled) to the supply output.This certainly works (with my 14 bit scope at least) with E3610A/E3611A series supplies. For lower ripple supplies I use AC coupling.
The 100Hz (in my case) ripple shows up nicely in the FFT.
Bruce
From: Poul-Henning Kamp <phk@phk.freebsd.dk>
To: Discussion of precise voltage measurement volt-nuts@febo.com; Brooke Clarke brooke@pacific.net
Sent: Saturday, 2 July 2016 11:28 AM
Subject: Re: [volt-nuts] Practical power supply noise testing
In message 5776E31D.7090404@pacific.net, Brooke Clarke writes:
Instead of headphones something like the HP 4395A [...]
Well, there is a slight difference in price there, isn't there ? :-)
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Hi John,
A simple check is to measure the output with an HP 3400A or HP3400B. These are true RMS meters (AC coupled) with 10 Hz to 10 MHz BW and capability to handle VERY high crest factors and still give an accurate readings. They go down to 1 mV FULL-SCALE which should be sensitive enough for checking bench supplies.
Best regards,
mitch
-----Original Message-----
From: volt-nuts [mailto:volt-nuts-bounces@febo.com] On Behalf Of John Ackermann N8UR
Sent: Friday, July 01, 2016 8:47 AM
To: volt-nuts@febo.com
Subject: [volt-nuts] Practical power supply noise testing
I have several supposedly low noise bench power supplies that I want to check out. They seem to work well but are quite old, so of course one wonders about the caps, etc.
Can someone suggest a practical test regime to verify power supply DC noise performance? Preferably one that doesn't require building up custom low noise amps?
Thanks!
John
volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.
If you are looking for sub 10 Hz noise you could just null bridge two of
them with an ordinary multimeter.
On Fri, Jul 1, 2016 at 8:47 AM, John Ackermann N8UR jra@febo.com wrote:
I have several supposedly low noise bench power supplies that I want to
check out. They seem to work well but are quite old, so of course one
wonders about the caps, etc.
Can someone suggest a practical test regime to verify power supply DC
noise performance? Preferably one that doesn't require building up custom
low noise amps?
Thanks!
John
volt-nuts mailing list -- volt-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.
Hi Bruce -- that's a really neat idea, particularly since the supplies I
want to test are used for phase test measurements!
I'm curious though about a pair of modulators. I'd think that you would
split the reference output, insert the modulator into one side of the
line, and then measure the noise increase when putting power on the
modulator input. Not sure where the second modulator would be used.
Thanks,
John
On 07/01/2016 09:14 AM, Bruce Griffiths wrote:
I've used a pair of minicircuits phase modulators, a low noise OXCO, and a Timepod to do this.The phase modulators work best with about 9V input.The noise of my E3610A's is clearly evident as is the noise of an LM317 based regulator with unbypassed ADJ terminal.To achieve lower system noise a pair of preamps (one per phase modulator) is useful, however the noise need not exceptionally low as cross correlation lowers the effective preamp noise.
Bruce
From: John Ackermann N8UR <jra@febo.com>
To: volt-nuts@febo.com
Sent: Saturday, 2 July 2016 12:47 AM
Subject: [volt-nuts] Practical power supply noise testing
I have several supposedly low noise bench power supplies that I want to check out. They seem to work well but are quite old, so of course one wonders about the caps, etc.
Can someone suggest a practical test regime to verify power supply DC noise performance? Preferably one that doesn't require building up custom low noise amps?
Thanks!
John
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.
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