The worse case could be 20LOG(N), where N is the number of power supplies. It depends on the impedance of the source driving the 50 ohm LISN impedance. If the source impedance is high (like >500 ohms) the voltages can add linearly. If the source impedances are low (like <25 ohms) then voltage will not increase with additional power supplies. What will decrease the source impedance? Output capacitors will. If the LISN is being driven off inductors the output Z will be high.
Dave Cuthbert Micron Technology From: francesco.campede...@transport.alstom.com [mailto:francesco.campede...@transport.alstom.com] Sent: Wednesday, July 23, 2003 3:01 AM To: emc-p...@majordomo.ieee.org Subject: Additivity of Conducted Emission Hi all. Forgive me for the following (perhaps) silly question, but I'm not an expert in these topics. I need to perform conducted emission test (220Vac port) according to EN55011, on an industrial power driver (25 kHz Switch Mode Inverter). Depending upon the application, one to ten drivers can be paralelled on the same 220V line. Each driver is indipendent from the other (i.e. no sync is provided), output power and waveform can be equal or different. The switching frequency is obtained via a high frequency clock (20MHz), thus it will be very similar for all the drivers. Emission will be both Common and Differential Mode. If I measure the emission for one driver, would it be possible to derive the emission level when two or more drivers are present (at least a worst case)? If yes, how to do it? Does the noise add up linearly (so that I have to add 6 dB for two driver, 20 dB for ten in the worst case - the noise from each driver has the same frequency and phase) ? Thanks in advance Francesco ing. Francesco Campedelli R&D - HW Design ALSTOM FERROVIARIA s.p.a. via di Corticella, 75 40128 Bologna - ITALY 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: emc_p...@symbol.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
