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-------- Forwarded Message --------
Subject: Re: [PSES] power lsupply musings #1
Date: Tue, 2 Jul 2024 22:16:42 +0100
From: John Woodgate <j...@woodjohn.uk>
To: rmm.priv...@gmail.com
IEC doesn't look too promising. These are not exactly on stone tablets,
but they are old: IEC61204:1993 + AMD1:2001, IEC 61204-6: 2000. You can
preview them. go to www.iec.ch, then go to Webstore and search.
On 2024-07-02 20:01, Ralph McDiarmid wrote:
Oh boy, have I seen this, in the distant past. Today, there is likely
an IEC standard which defines how this measurement should be performed.
When I was a development engineer at a small d.c. power supply company
in the 1990s we grappled with this same issue. We eventually designed
a custom voltage probe which measured differential ripple & noise into
50 ohms with a 20 MHz bandwidth. It provided a repeatable measurement
of output noise into a stabilized impedance while rejecting
common-mode contribution. Its implementation settled most arguments
on how this measurement was done since some customers at the time were
challenging our results when we were merely using an unbalanced 10X
scope probe with any convenient oscilloscope on hand.
Any, well considered, implementation for a noise probe is probably
just as good so long as it is used consistently, and the method
disclosed to those who need to know.
Ralph
*From:*doug emcesd.com <d...@emcesd.com>
*Sent:* Monday, July 1, 2024 4:18 PM
*To:* EMC-PSTC@LISTSERV.IEEE.ORG
*Subject:* [PSES] power lsupply musings #1
Hi Everyone,
I thought I would post a bit about power supplies. Something as simple
as trying to measure ripple on the output can be very inaccurate,
overstating ripple amplitude by a lot, 100% over stated is not all
that unusual.
One problem arises from common mode noise on the output that gets into
the structure of the probe used for the measurement. Most probes have
modes resulting in display of voltages that are not actually present.
If you doubt this, just connect both terminals of a scope probe to the
low end, say ground, of a power supply output and you will often see a
significant signal that is not actually there. Whatever one measures
with a shorted probe on the ground side of the supply output is the
error in the measurement and can easily exceed the actual ripple
voltage present on the output.
Have you seen this? I cover this in detail in my presentations.
Doug
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Best wishes
John Woodgate, Rayleigh, Essex UK
Keep trying
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