I can't speculate on the reason for the increase in leakage current; however, I suspect you have a thermal design problem with the switching circuit. I have seen an increase in conducted emissions due to a change of the switching waveform - e.g. rise and fall times and ringing - once the product has reached operating temperature. I have also seen this problem vary from unit to unit due to spurious switching noise on the waveform.
Richard Woods Sensormatic Electronics Tyco International -----Original Message----- From: [email protected] [mailto:[email protected]] Sent: Monday, December 17, 2001 10:59 AM To: [email protected] Subject: Thermal effects on EMC and Earth Leakage Group. I am interested to find out peoples opinions on a particular trend we've seen time and time again on most switch mode PSU's. It seems that once a PSU is warm its earth leakage decreases and its EMC emission performance decreases (i.e. it gets noisier). This would suggest that there is some sort of thermal effect, probabaly in the Y caps, that reduces their capacitance. Has anyone done any work in this area or can anyone explain the physics of this change. Is it as simple as expansion of the dielectric or is it more complicated than this? Any thoughts or opinions would be greatly recieved. Many thanks in advance, Duncan Hobbs ---------------------------------------------------------------------- The contents of this communication are confidential to the normal user of the email address to which it was sent. If you have received this email in error, any use, dissemination, forwarding, printing or copying of this email is strictly prohibited. If this is the case, please notify the sender and delete this message. ---------------------------------------------------------------------- ------------------------------------------- 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.
