The EUT does not generate rf emissions in the sense of generating rf energy. It draws rf current from the bus in addition to the current at the power frequency. The job of the EMI filter is to force the rf current draw to remain within the EUT. It does that by providing local energy storage (caps) and inductors to make the caps the most attractive source of energy to draw on. By keeping the flow of rf current in the equipment most radiated emissions should be decreased, at least compared to having rf currents flow down several meters of power conductor.
on 12/3/01 12:59 PM, Muriel Bittencourt de Liz at [email protected] wrote: > > > Hello Group, > > I have a "long-time" question, concerning the energy issues in a EMI powerline > filter. > > I'll put a case, and ask the question after. > > This is the case: > > - When trying to minimize the conducted emissions from a electrical equipment > / circuit, one of the things to do is to put a EMI filter at the power > entrance. This filter can be from a manufacturer (ready filter) or you can > make one (with common mode inductors, capacitors, inductors). > > This are the questions (they arearelated, i.e., complete each other): > > - What, physically speaking, happens to the EMI energy that leaves the > equipment when I add a filter??? When there is no filter, I understand that > the energy goes to the mains?? Does the filter reflect the EMI energy, keeping > it "arrested" inside the equipment? > > - Thinking under the light of the principle of energy conservation, what > happens to the EMI energy when I add a filter?? It cannot be lost... > > - ... And, supposing that the energy keeps arrested inside the equipment, > isn't it worse for radiated emissions?? i.e., it can increase the level of > radiated emissions?? > > Thanks in advance for your attention. > > Regards, > > Muriel Bittencourt de Liz > Ph.D. Student > Interest Areas: EMC for power electronics, RF measures, EM interference > Federal University at Santa Catarina State > Florianópolis, Santa Catarina, Brazil > > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: [email protected] > Dave Heald [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > No longer online until our new server is brought online and the old messages > are imported into the new server. > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
