It seems to me that you would not care if only some small fraction of the surge potential coupled from primary to secondary for a short period of time especially if it is common mode, but that what you don't want to have happen is a differential dc level shift. Therefore I would mount the power supply so that its primary power input was in my test chamber, but the dc output was in my control room, and the penetration was either shielded or filtered or both. The filtering would not be dc-to-light. it would be what was necessary to knock down a 50 or 100 Ohm source impedance signal to negligible levels, because that would represent the radiation coupling around the supply. And the filter time constant would be on the order of the surge duration (small feedthrough cap penetrations). Anything I see differentially after that can betaken to be the power supply behavior under stress.
> From: [email protected] > Date: Thu, 18 May 2006 10:03:03 -0400 > To: [email protected], [email protected] > Subject: Re:Burst and surge tests > > Ian, > > This is a very good question. > > Not that long ago we were qualifying a power supply that would shut down and > restart each time it saw the Surge pulse during the 4-5 test. We told the PSU > manufacturer that their product fails Surge but they came back and told us > that, > according to the standard, as long as the power supply returned to normal > operation when the test was complete, it passes. > > As anyone would know, the immunity tests are system tests and if the power > supply shut down causing your electronics to reset and causing a loss of data > then the system would FAIL. > > So, we have specified that the output of power supplies must not cause our > electronics to malfunction during the 4-4 or 4-5 tests. We specify that the DC > output of a power supply can not go "out of spec" during these tests. It is > very > hard to verify this because the transients caused during the test will couple > into the measuring device, such as a scope or meter. If someone has a good > method to test this I would be very interested in hearing how. If you filter > out > the transients then you maybe blinding yourself to what's really happening on > the dc output. > > Brian > > ____________________Reply Separator____________________ > Subject: Burst and surge tests > Author: [email protected] > Date: 5/18/2006 9:46 AM > > Dear Group, > > I have a question regarding the likely behaviour of ac to dc switch mode > power supplies during fast transient burst tests to EN 61000-4-4 and surge > tests to EN 61000-4-5. > > For a manufacturer to claim conformity to these standards are any > constraints placed on the behaviour of the dc output voltage during the > tests? I am particularly interested in the likely change in DC voltage > output as the appropriate burst/surges are applied to the ac input. > > Many thanks in anticipation of your replies. > > Best regards > > Ian Unwin > Lead Engineer > Servomex Group Limited > > > ********************************************* > *Register now at www.servomex.com/zap.html * > *for an opportunity to win a great prize * > *in our monthly draw. * > ********************************************* > ________________________________________________________________________ > This email has been scanned for all viruses by the MessageLabs SkyScan > service. This electronic message contains information from Servomex which may > be privileged or confidential. The information is intended to be for the use > of the individual(s) or entity named above. If you are not the intended > recipient be aware that any disclosure, copying, distribution or use of the > contents of this information is prohibited. 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