Suppose the time delay is the result of propagation through the series L and
shunt Cs of the SMPS EMC filter acting as a transmission line. Then assume
that the following rectifier is forced into conduction to a low impedance
( by the large amplitude even if it does not happen naturally), so
mis-terminating the filter/transmission line,and reflecting the incident
pulse back thru the filter/transmission line and out into the world again.
That would provide a mechanism that doesn't involve any very unusual
mechanisms.
An easy check would be to apply magnets to saturate the EMC filter cores and
so shorten the electrical length of the filter/transmission line.
Richard Marshall
MA, CEng., FIEE, FInst.P, FIET
Richard Marshall Laboratories
30 Ox Lane, Harpenden, Herts.
AL5 4HE UK
Phone +44 (0)1582 460815 www.design-emc.co.uk
Member of the EMC Industry Association
----- Original Message -----
From: "Brian Oconnell" <[email protected]>
To: <[email protected]>
Sent: Wednesday, November 05, 2014 7:40 PM
Subject: Re: [PSES] New electrical phenomenon reproduced tonight!
My usual caveat - am an EMC amateur. If the transient is propagated in
serial fashion then 're-emitted' (as theorized by Mr Woodgate) with
similar characteristics as test pulse, do not see how the typical control
loop would see the disturbance, other than a resultant OV lock-out.
Oscillations on the PFC FET could result if the transient energy were
coupled to a hi-z gate drive circuit, but, at least logically, it would
seem that the main controller would just lock or skip pulses until the
disturbance energy is gone.
Observed this 10 years past during variations of EFT and surge test
configurations while playing with floating and ground-referenced mains on
an open-frame SMPS, where the chassis could be ground pin-reference or
floated. Observed again last year while testing another factory's class II
p/s where my GRP was not correctly placed.
Response of given model SMPS to ESD/EFT/Surge can vary somewhat, where the
difference is the end-use installation. EMC testing of an COMPONENT p/s is
problematic and mfr's test data may not be representative of performance
in your box. This may become a recurring and noticeable problem as SMPS go
to higher switching frequencies to increase efficiency and decrease size
per industry demands.
Perhaps TC108 can consider looking at this for the glorious coming of
IEC62368-1, as there are power supplies being developed now that operate
up to 30MHz.
Brian
-----Original Message-----
From: CR [mailto:[email protected]]
Sent: Wednesday, November 05, 2014 7:16 AM
To: [email protected]
Subject: Re: [PSES] New electrical phenomenon reproduced tonight!
I suspect the effect seen with SMPS' is due to transients forcing
operation outside the designed stability region of their controllers.
If so, this would not be a new EM effect, but a common immunity problem.
Cortland Richmond
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