Have I understood correctly, that after 100 000 of the 800 V pulse test,
the EUTs failed the normal hi-pot test? This is not a test on newly-made
products, to which IEC safety standards are applicable. Of course, the
tests in such standards can be applied to products that have seen
service, but failures are to be expected.
On 2025-02-27 21:32, doug emcesd.com wrote:
Hi Rich,
If there is a true air gap not involving other material then I agree
with you. Then the only problem is with medical as those cross gap
discharges are essentially ESD events and will cause response from
tissues.
If the “air” gap is on a circuit board then we have a problem. If I
breakdown a gap on a board with a million discharges (a number easy to
reach in a month in the field with EFT plus the following multiple
discharges that follows each pulse) I think there is danger of forming
a conductive path on the board, decades ago we called these “carbon
tracks.”
I have observed these since I started designing and building high
voltage circuits in 1963 (it’s a wonder that I did not electrocute
myself back then).
The little supply that generated some of the data for the paper used
to have this effect only below 3,000 Volt pulses with the "sweet" spot
at 800 Volts. But now it will exhibit this behavior above 3,000 Volts
as well so something has changed in the supply.
I have confirmed this effect at three locations using different ESD
guns, different scopes, and different power supplies.
Doug Smith
Sent from my iPhone
IPhone: 408-858-4528
Office: 702-570-6108
Email: [email protected]
Website: http://dsmith.org
------------------------------------------------------------------------
*From:* Richard Nute <[email protected]>
*Sent:* Thursday, February 27, 2025 11:27:30 AM
*To:* doug emcesd.com <[email protected]>
*Cc:* 'Pete Perkins' <[email protected]>; [email protected]
<[email protected]>
*Subject:* RE: major safety issue possibly affecting 20% of the
electronic devices in use
Hi Doug: Thanks for your response and especially your paper. Thanks to
Figure 1, I am no longer alarmed by a possible breakdown of insulation
between primary and secondary. In Figure 1, I see the set-up:
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Hi Doug:
Thanks for your response and especially your paper.
Thanks to Figure 1, I am no longer alarmed by a possible breakdown of
insulation between primary and secondary. In Figure 1, I see the set-up:
Pulse generator -> cable -> probe -> cable -> power supply -> ground
Within the power supply:
Secondary circuits -> solid insulation, air insulation, EMI
capacitance, transformer winding inductance -> primary circuit
From a safety point of view, I see a complex capacitance coupling
current (and possible inductive effects of the transformer windings)
to the primary circuit. But, I don’t perceive any dielectric damage.
Thanks again,
Rich
Ps: I would expect a difference in the current waveforms between
Figures 1 and 2 configurations.
*From:*doug emcesd.com <[email protected]>
*Sent:* Wednesday, February 26, 2025 8:27 PM
*To:* [email protected]
*Cc:* 'Pete Perkins' <[email protected]>; [email protected]
*Subject:* Re: major safety issue possibly affecting 20% of the
electronic devices in use
Hi Rich and the group,
Accidentally hit send on the last one.
Here is a link to the paper:
https://emcesd.com/pdf/An_Unusual_Source_of_Multiple_ESD_Events_in_Electronic_Equipment_final.pdf
<https://urldefense.proofpoint.com/v2/url?u=https-3A__emcesd.com_pdf_An-5FUnusual-5FSource-5Fof-5FMultiple-5FESD-5FEvents-5Fin-5FElectronic-5FEquipment-5Ffinal.pdf&d=DwMFAg&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=c9NR2mGfldry-2pM9Bbuww&m=tP4ynwqzldJBFpq8iMilqEevrzZeqxneKUW-xaGcWoqbmd9pw8D2X6uhVIqHLn3Y&s=RaBr8PHRC7w6R7th2YG58KCbStWnsaXTOYaftCWCVLo&e=>
I think resonance in the EMI filter with a Q of 5 could do it. I was
in the lab today and determined the effect is due to the long tail on
ESD and EFT events, not the fast rise time. I got some very good scope
shots of the phenomenon today. In the past I have observed the effect
in both small two wire supplies and even in a 1.5 kW supple in a
semiconductor fab.
I did not realize the safety implications when I wrote that paper.
Later on and I started to think how that phenomenon could happen is
when the light bulb went off in my brain.
I plan to build a suitable pulser with no moving parts to wear out to
see if I can induce damage. I can build such a pulser in about an
hour with parts I have laying around. It will produce pulses with a
few ns rise time and a 300-500 ns fall time with an amplitude of 1200
Volts or so, a very easy thing for me to assemble. An ESD gun will
work but with a lot wear on the HV relay to make 100,000 pulses.
Doug Smith
Sent from my iPhone
IPhone: 408-858-4528
Office: 702-570-6108
Email: [email protected]
Website: http://dsmith.org
<https://urldefense.proofpoint.com/v2/url?u=http-3A__dsmith.org&d=DwMFAg&c=euGZstcaTDllvimEN8b7jXrwqOf-v5A_CdpgnVfiiMM&r=c9NR2mGfldry-2pM9Bbuww&m=tP4ynwqzldJBFpq8iMilqEevrzZeqxneKUW-xaGcWoqbmd9pw8D2X6uhVIqHLn3Y&s=1i3LVauSapb-sFcpt0k7VIs85Bqx1xUSa1qeYh-4fXE&e=>
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