CONFLICT of INTEREST NOTICE: my employer manufactures SMPS. In a "properly" laid-out SMPS, conducted emissions should not be affected in a DC/DC converter that uses Class 1 construction; but converters that float the input and/or output could see problems at both ends.
Stand-alone radiated emissions testing for a component power supply frequently (no pun intended), has significant differences from the same test performed in the end-use chassis. A noisy SMPS can be used in well-designed end-use chassis It is possible that synchronizing converters (although I have not observed this), could cause problems on units that use remote sense lines. I've often wondered why end-users spend time & money developing custom power supplies when there are many companies that offer these solutions off the shelf, that probably already meet product safety and EMC standards. luck, Brian -----Original Message----- From: Pat Lawler [ mailto:[email protected]] Sent: Wednesday, July 30, 2003 7:31 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?
