Pat, I deal with MOSFET and IGBT offline switchers running at some fairly high power levels and switching frequencies. I've found that operating these switchers in quadrature (or some other angle) helps considerably. In my applications, the generation of RF emissions is in pulse edges of the transistor. If pulse edges desgined to intentionally occur at different points in time, then the emissions are less than what they would have been when perfectly synchronous.
I've also found that when several inverters are running asynchronous to one another, the increase in emissions is approximately the root-sum-square (RSS) of each noise source (in uV, not dBuV). If the inverters are exactly sycnhronous then I expect you would get something close to the sum of the noise sources. Regards, -doug Douglas E. Powell Corporate Compliance Dept. Advanced Energy Industries, Inc. Fort Collins, CO 80535 USA From: Pat Lawler [mailto:pat.law...@verizon.net] Sent: Wednesday, July 30, 2003 8:31 AM To: EMC-PSTC Subject: Synchronizing DC-DC converters to reduce emissions? We are designing a switching power supply for a customer that has multiple outputs. Due to the tight regulation requirements, all outputs have their own PWM modulators and control loops. The customer feels the RF emissions (as measured by CISPR 11) will be reduced by synchronizing the frequencies of all the converters. I think synchronizing the PWM sections will make the total power supply emissions as high as possible (emissions are coherent?). 1) What has been your experience with controlling noise from multiple switching power supplies? Is synchronizing a good idea? 2) If the supplies are synchronized, would a phase shift between converters (avoiding simultaneous switching of all converters) help? Thanks, --- _______________________________________________________________ This message, including any attachments, may contain information that is confidential and proprietary information of Advanced Energy Industries, Inc. The dissemination, distribution, use or copying of this message or any of its attachments is strictly prohibited without the express written consent of Advanced Energy Industries, Inc. 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
