Pat, I agree with you and would avoid syncronization. Another consideration is using pulse position modulation rather than pulse width modulation. PWM only changes the ratio of odd to even harmonics of the switching frequency while PPS spreads the peak energy and may lower the emission peak within the CISPR bandwidth.
Brent DeWitt From: [email protected] [mailto:[email protected]]On Behalf Of Pat Lawler 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 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: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] 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
