Peter, Thanks for the paper (you sent me directly). It indeed shows that EMC is most of the time about the unspecified, here in spice models. The spice model presented still does not include any environmental parasitics... Knowledge and experience provide us EMC-consultant with an consistent view on what in reality happens, in addition to what the designer tries to accomplish with his design.
All designers (but the RF specialists) overlook the third connection to any circuit , the real earth ! (sometimes represented by a conductive enclosure) Regards, Ing. Gert Gremmen ce-test, qualified testing bv Van: Pete Perkins [mailto:[email protected]] Verzonden: Monday, December 22, 2008 1:42 AM Aan: Gert Gremmen; [email protected]; 'Richard Nute'; 'John Woodgate' Onderwerp: FW: Thevenin equivalent circuit for SMPS emission sources - issues Gentlemen, Attached is the GDT modeling paper mentioned in the PSNet post. I appreciate your insights and comments in all of this. Br, Pete Peter E Perkins, PE Principal Product Safety Engineer Tigard, Ore 97281-3427 503/452-1201 fone/fax [email protected] From: Pete Perkins [mailto:[email protected]] Sent: Sunday, December 21, 2008 4:29 PM To: 'John Woodgate'; '[email protected]' Subject: RE: Thevenin equivalent circuit for SMPS emission sources - issues John & PSNet, The development of good models for components & circuits has been underway for more than 100 years. Simplification has been applied from the beginning because of the additional work involved in solving the needed equations as the complexity increased. Thanx to the use of modern digital computers it continues to get surprisingly easy to handle complex models for components or circuits. Sometimes we're surprised as to how much complexity needs to be included to better model the device to analyze the effects seen. For instance, in the Nov 2008 IEEE Transactions on Electromagnetic Compatibility there is a short letter 'Gas Discharge Tube Modeling with PSpice' by Zola (Univ of Buenos Aires). This describes a simple model for use on PSpice programs run on desktops. This model uses a double transistor along with 4 other elements to describe the performance for one polarity with the elements inverted for the opposite polarity. The bibliography contains a dozen references to similar models and modeling techniques going back 15 years considered in developing this model. My point is that developing the correct model to apply in any situation is not trivial. A simple model, if it describes the effects seen, is the best. If it doesn't exactly fit the situation then more complexity needs to be added. From my experience models are improved by adding in 'stray' elements which have been left out for the last simplification. The modeling of the FET in a SMPS may be adequate for using that device in an operating circuit (I'm especially sure that it is if the model has been developed by the manufacturer to help sell these devices - as are the devices available in the SPICE that I use). But, this may not be adequate for issues outside the box which have not been considered in the development of this model. The model is an electrical equivalent of the physical silicon and will be a simplification in many ways. It is not a direct simulation of the silicon physics operation. Moving from one type of model to another is conceptually straightforward but may lead to difficulties if the first model doesn't properly take all of the details into account. How many ways can we describe a circuit with an input and an output? The matrix models include [A B C D], [H1 H2 H3 H4] parameters and maybe almost a dozen more it seems. All describe the same circuit but each view provides a different insight into the innards and their operation. This doesn't mean that we shouldn't try to get a better understanding of the physics in detail and include that in the modeling. It is best if the addition of elements for understanding are based upon the physics of the device or upon the usual measurements which show the need for additional elements. So I am primarily looking at the measured data rather than trying to develop a model to explain it. I appreciate the others who are chasing these model details; we need as much help as we can get to understand this. Well, way too much for one quick post... Br, Pete Peter E Perkins, PE Principal Product Safety Engineer Tigard, Ore 97281-3427 503/452-1201 fone/fax [email protected] - 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 <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/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]>
