Hi Doug:
I don't know your definition of "breakdown."
As a product safety engineer, a breakdown is usually an arc in air. The
temperature and duration of the arc may damage the surface of solid
insulation. You should be able to hear the arc.
Guesses:
If the 800-volt pulse is wimpy, the secondary circuits are likely to distort
the pulse shape. For a two-wire product, an energetic pulse must change the
X-capacitor to have some resistance. Even so, no operator injury is likely
as the worst that can happen is excessive primary current which, if the
circuit-breaker doesn't operate, could lead to a fire.
Or, an energetic pulse could destroy the semiconductors in the SMPS such
that 60 Hertz is applied to the HF transformer which is likely to be
destroyed, resulting in a fire, or primary voltage at the LV output.
Rich
From: doug emcesd.com <d...@emcesd.com>
Sent: Wednesday, March 5, 2025 10:44 AM
To: ri...@ieee.org; EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] major safety issue possibly affecting 20% of the
electronic devices in use
Hi Nute,
The 800 Volt pulse can be increased in amplitude easily to 3,000 Volts by a
resonance in the EMI filter possibly involving characteristics of the
transformer. Only need a "Q" of 4 to do it. That is my worry that the safety
community missed this effect which is easy to recreate in the lab. A
breakdown is happening, the only question is can it cause a permanent
problem.
Doug Smith
Sent from my iPhone
IPhone: 408-858-4528
Office: 702-570-6108
Email: d...@dsmith.org <mailto:d...@dsmith.org>
Website: http://dsmith.org
_____
From: Richard Nute <ri...@ieee.org <mailto:ri...@ieee.org> >
Sent: Tuesday, March 4, 2025 4:21:30 PM
To: doug emcesd.com <d...@emcesd.com <mailto:d...@emcesd.com> >;
EMC-PSTC@LISTSERV.IEEE.ORG <mailto:EMC-PSTC@LISTSERV.IEEE.ORG>
<EMC-PSTC@LISTSERV.IEEE.ORG <mailto:EMC-PSTC@LISTSERV.IEEE.ORG> >
Subject: RE: [PSES] major safety issue possibly affecting 20% of the
electronic devices in use
Hi Doug: In a two-wire product, the Y-caps (if any, pri-sec connected) and
xfmr pri-sec insulation are rated and tested for 3,000 volts rms. (The solid
insulation in the xfmr is probably about 8,000 volts.) I doubt that either
would be damaged
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Hi Doug:
In a two-wire product, the Y-caps (if any, pri-sec connected) and xfmr
pri-sec insulation are rated and tested for 3,000 volts rms. (The solid
insulation in the xfmr is probably about 8,000 volts.) I doubt that either
would be damaged by an 800-volt pulse applied between the output and the
primary.
Best regards,
Rich
From: doug emcesd.com <d...@emcesd.com <mailto:d...@emcesd.com> >
Sent: Tuesday, March 4, 2025 2:51 PM
To: ri...@ieee.org <mailto:ri...@ieee.org> ; EMC-PSTC@LISTSERV.IEEE.ORG
<mailto:EMC-PSTC@LISTSERV.IEEE.ORG>
Subject: RE: [PSES] major safety issue possibly affecting 20% of the
electronic devices in use
Hi Rich,
Just had a thought, if the EMI filter is doing the breakdown, there is a
chance it will eventually become a short circuit on the power leads. I have
never seen this happen before so that may point to a different mechanism.
Doug
<https://lh4.googleusercontent.com/_HuR3Ky2TF_XhFHyxnYRmiq7nHQldnMsPNYFaLG6k
b5T4y8MeCe-BDC_BscJtSFgszSSjssihHS-pjM3-jwNP8S0CwE-gN8fsRsPkojiAlmpBwb20vIVi
zS-siCUywW_jqrefbVr>
From: Richard Nute < <mailto:ri...@ieee.org> ri...@ieee.org>
Sent: Monday, March 3, 2025 14:56
To: <mailto:EMC-PSTC@LISTSERV.IEEE.ORG> EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] major safety issue possibly affecting 20% of the
electronic devices in use
Wrong attachment. Correct attachment here.
Rich
From: Richard Nute < <mailto:ri...@ieee.org> ri...@ieee.org>
Sent: Sunday, March 2, 2025 3:35 PM
To: <mailto:EMC-PSTC@LISTSERV.IEEE.ORG> EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] major safety issue possibly affecting 20% of the
electronic devices in use
Hi Doug:
Thinking about your findings, one of the specific explanations or
accountings for the change in power supply response may be something like
this. Consider the attached "schematic" of a typical two-wire direct
plug-in power supply. Your test set-up is to apply an 800-volt pulse to one
pole of the output while connecting one or both poles of the primary to
ground. The pulse then appears (divides) across the secondary circuit, the
transformer, and the primary circuit. You monitor the current waveform from
the pulse generator to the power supply. (The 138 k resistances in my
schematic represent the worst-case -- lowest impedance at 60 Hertz --
Y-capacitors.) The pulses after the initial pulse are from the power
supply. (What is the output impedance of the pulse generator after it
outputs the pulse?)
We don't know what circuits and components are in the boxes, "rect & reg"
and "smps." However, we can guess that the "rect & reg" box has a series
transistor and several capacitors. And, the 138 k resistors are in
actuality capacitors. Capacitors will be charged (over-charged?) to some
extent by the pulse. These will discharge, generating pulses back to the
source. The semiconductors in the circuit will probably be deteriorated by
the 800-volt pulse such that subsequent applications of the 800-volt pulse
will have different impedances. And, it will take some time for the
semiconductors to react to the pulse. Resistors subject to overvoltage may
also be damaged. However, the 238 k (minimum at 60 Hz) Y-capacitors will
not be subject to a voltage exceeding their ratings (at least 1,500 volts
rms). Likewise, the transformer insulation will not be subjected to
insulation damage voltage. (Note that the transformer doesn't act as a
transformer for the 800-volt pulse.)
My conjecture analysis (above) continues to be that the "protective
separation" has not been damaged by the 800-volt pulse. The secondary
events are due to discharge of the components in the power supply.
Best regards,
Rich
From: doug emcesd.com < <mailto:d...@emcesd.com> d...@emcesd.com>
Sent: Saturday, March 1, 2025 11:38 AM
To: <mailto:ri...@ieee.org> ri...@ieee.org;
<mailto:EMC-PSTC@LISTSERV.IEEE.ORG> EMC-PSTC@LISTSERV.IEEE.ORG
Subject: RE: [PSES] major safety issue possibly affecting 20% of the
electronic devices in use
Hi Rich,
I forgot to adequately answer your question of why I tested the supply
unpowered.
I always try to get at the simplest configuration that elicits the effect.
In this case I made the first discovery of the effect on the power cable of
a small router that I was debugging for ESD issues. The power supply of the
router was a small AC plug variety.
After a few minutes I realized that I could get the effect with the power
supply laying on the table not connected to anything, just the ESD gun
connected across the mains and output of the supply. The removal of the AC
power enabled much more control over the test setup and led to information
about the issue than would not have been possible with the mains connected.
For instance, the total path on the table of the ESD gun and router
connections was about two meters. The observed multiple ESD responses of the
power supply from a single ESD event were mostly in the hundreds of
nanoseconds in separation, too long for the path on the table but what I
would expect for a resonant circuit to break over a barrier. BUT, close
examination of the train of pulses generated by the power supply found some
cable discharge events (I can tell they are cable discharge events by the
waveshape) whose characteristics are just what I would expect from the
discharge of a 2 meter cable!!! I would never have been able to make that
observation with the power cable connected. So. the barrier was affected not
only by internal resonances in the power supply but breakdowns appear to be
happening via cable discharge as well!
I always whittle the test setup down the simplest one I can that exhibits
the desired response.
My philosophy carries over as well to debugging high frequency immunity
tests such as ESD, EFT, radiated immunity, and conducted immunity. In those
tests, my approach is to make all the mechanisms at play in causing the
problem (and there are often multiple mechanisms that interact with each
other) orthogonal to each other, meaning independent, so I can fix one at a
time and know how much of the problem was due to each mechanism. This is not
done on the standard test setup but on an engineering bench using techniques
I developed over the years. Some of these are described on my website and
more are in my courses (like the one at the end of this month), in more
detail.
Debugging an immunity problem using the standards-based test, like applying
ESD while trying to find the ESD problem, generally is very time consuming
and usually does not lead to understanding of the mechanisms. People try to
do this and often find something that works, but they rarely understand the
total effect of what was done and that can lead to more problems in the
field later on. This approach is like throwing darts at the wall with the
target covered by a sheet.
Design of experiments is extremely important but sometimes ignored in the
engineering world.
Doug
<https://lh4.googleusercontent.com/_HuR3Ky2TF_XhFHyxnYRmiq7nHQldnMsPNYFaLG6k
b5T4y8MeCe-BDC_BscJtSFgszSSjssihHS-pjM3-jwNP8S0CwE-gN8fsRsPkojiAlmpBwb20vIVi
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