Between several hundred microfarads of storage capacity and the EMI filter, that doesn't seem terribly likely but it can't be completely discounted so it makes sense as a rationale.
> From: "Eric Petitpierre" <[email protected]> > Reply-To: <[email protected]> > Date: Thu, 6 Oct 2005 12:06:40 -0400 > To: "'Ken Javor'" <[email protected]>, > <[email protected]> > Cc: <[email protected]> > Subject: RE: Conducted emission testing for FCC & CE. > > Ken, > > Your logic would hold if all of the USB device energy was broadband at the > same level. > Since power supplies typically do not have a flat transfer curve, it may be > resonant to > some of the USB device frequencies. Then you have a low impedance path > straight through > to the power cord. > > Regards, > Eric Petitpierre > Cornet Technology > Springfield, VA > > -----Original Message----- > From: [email protected] [mailto:[email protected]]On Behalf Of Ken Javor > Sent: Thursday, October 06, 2005 10:35 AM > To: [email protected] > Cc: [email protected] > Subject: Re: Conducted emission testing for FCC & CE. > > > No answer here, I'm just trying to get educated on the premise behind the > original question. > > The modification prompting the requirement for conducted emission testing is > the addition a USB device powered from the PC USB host. I assume this > device consumes on the order of 1 Watt of power. The incremental increase > in load on the power supply is therefore on the order of 1%. > > The dB increase in power supply differential mode conduced emissions is > therefore > > 10*log (1.01) = 0.04 dB > > This is well within the uncertainty range. > > Are my assumptions incorrect or what crucial information am I missing that > drives the need for requalifying ac mains conducted emissions? > > I (perhaps naively) thought that this modification would have required a > radiated emissions rescan because of the new USB interface and cable, or > perhaps conducted emissions testing on the USB cable utilizing an absorbing > clamp. > > It is not at all obvious to me how the addition of the USB interface > necessitates a mains conducted emission test. > >> From: "Robert A. Macy" <[email protected]> >> Date: Thu, 06 Oct 2005 07:52:47 -0700 >> To: [email protected] >> Cc: [email protected] >> Subject: Re: Conducted emission testing for FCC & CE. >> >> It is my opinion that you must test conducted emissions at >> both AC input conditions, and archive those test results. >> >> >> The mechanisms for conducted emissions can vary greatly >> whether you're at 110/60 or 230/50. Better test. A good >> Power Supply will minimally exhibit that effect, but who >> knows if you have that one. >> >> Radiated is *very* unlikely to vary due to the AC mains, >> however it can still change at the low end, but I've not >> seen that happen much. >> >> Why balking at doing such a simple, short test? >> >> - Robert - >> >> On Thu, 6 Oct 2005 08:46:33 +0530 >> [email protected] wrote: >>> Dear Experts, >>> Our product is a USB device connected to the PC >>> USB host and >>> operates at 5 volts D.C supply provided by the host >>> system. Both FCC & CE >>> insists that conducted emission testing is required for >>> this kind of >>> devices, with emissions measured at the a.c input side. >>> Is it necessary to >>> run 2 tests, one with a 230 volts 50 Hz a.c supply (for >>> CE) and the other >>> with 110 volts 60 Hz a.c supply (for FCC)? >>> >>> >>> Sincerely >>> >>> K.Balasubramanian >>> Project Leader - Hardware. >>> >>> - >> >> - >> ---------------------------------------------------------------- >> This message is from the IEEE Product Safety Engineering Society >> emc-pstc discussion list. Website: http://www.ieee-pses.org/ >> >> To post a message to the list, send your e-mail to [email protected] >> >> Instructions: http://listserv.ieee.org/listserv/request/user-guide.html >> >> List rules: http://www.ieee-pses.org/listrules.html >> >> For help, send mail to the list administrators: >> >> Scott Douglas [email protected] >> Mike Cantwell [email protected] >> >> For policy questions, send mail to: >> >> Jim Bacher: [email protected] >> David Heald: [email protected] >> >> All emc-pstc postings are archived and searchable on the web at: >> >> http://www.ieeecommunities.org/emc-pstc >> > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society > emc-pstc discussion list. Website: http://www.ieee-pses.org/ > > To post a message to the list, send your e-mail to [email protected] > > Instructions: http://listserv.ieee.org/listserv/request/user-guide.html > > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > > Scott Douglas [email protected] > Mike Cantwell [email protected] > > For policy questions, send mail to: > > Jim Bacher: [email protected] > David Heald: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > > http://www.ieeecommunities.org/emc-pstc > - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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