I didn't see the post to which Cortland is responding, but if I had I would have said that power supply noise is of two types, narrowband and broadband. The narrowband fundamental and harmonics from the switched mode power supply (SMPS) are (generally*) fixed in frequency and amplitude, and are quite repeatable unless the load on the secondary side of that power supply is changing drastically. If the SMPS operates off a dc bus, that is all the noise there is. If it operates off an ac bus, then there are rectification harmonics, which are broadband and "chaotic" in the sense that they are not at fixed frequencies, but the envelope will be well-defined and they are differential mode, so the filter design for that is straightforward.
I can always tell a commercial design that has been adapted for military use by the telltale conducted emission signature which is well-behaved above the commercial limit start frequency of 150 kHz but balloons up at the lower frequencies required by the mil limit which starts at 10 kHz, so we see the unfiltered rectification harmonics decreasing in amplitude as they approach 150 kHz. * Some power supply designs (Vicor is one) change switching frequency as load changes instead of duty cycle, so if the load is changing the switching frequency changes with it. Designing a filter for a power supply like that would have to involve filtering for both light and heavy loads. I have no direct experience with such designs. Ken Javor Phone: (256) 650-5261 > From: Cortland Richmond <k...@earthlink.net> > Reply-To: <k...@earthlink.net> > Date: Thu, 31 Mar 2016 14:48:48 -0400 > To: <EMC-PSTC@LISTSERV.IEEE.ORG> > Subject: Re: [PSES] Commom mode current vs. differential mode current and LISN > > On 3/29/2016 5:59 PM, Elliott Martinson wrote: >> But noise is chaotic, and subsequent measurements of the L conductor >> only won¹t even be exactly the same. The phase relationships of >> different noise signals from different sources in the device are >> constantly changing depending on when the measurement was made as well. > > It's not "noise," though, in the classical sense -- and it can be > distinguished by frequency and (in the time domain) by waveform. For one > examples see my photo at > https://www.flickr.com/photos/101461001@N06/25883518240/in/dateposted-public/ > f > > > I had been called out of retirement on contract, and brought in my own > o'scope, since the lab's equipment was all in use. The ringing waveform > was the signal from a LISN (into 50 Ohms) and the waveform below it was > taken with a suitably insulated scope probe near the SMPS causing the > problem. > > Cortland Richmond > > - > ---------------------------------------------------------------- > This message is from the IEEE Product Safety Engineering Society emc-pstc > discussion list. To post a message to the list, send your e-mail to > <emc-p...@ieee.org> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used > formats), large files, etc. > > Website: http://www.ieee-pses.org/ > Instructions: http://www.ieee-pses.org/list.html (including how to > unsubscribe) > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <sdoug...@ieee.org> > Mike Cantwell <mcantw...@ieee.org> > > For policy questions, send mail to: > Jim Bacher: <j.bac...@ieee.org> > David Heald: <dhe...@gmail.com> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
