Hi Eric: > Up to now we always performed the heating test of the purchased SMPS: we > measured the temperature of the critical components on the smps itself to > see if they remain under the safe limit. > We are now having a problem with a particular power supply. The 600 W power > supply is a fully closed metal box with cooling fans on the front. When we > open it and add thermocouples on the PFC part of the power supply, the PFC > fails. > This is probably due to the fact that we are coupling in some wrong signals > on a feedback circuit. We tried it several times with the same result: > failure of the PFC part of the SMPS. > My question is: is the heating test really necessary? Yes. When the power supply is installed in the end-product, the end-product may affect the air flow and will definitely affect the radiated heat. Consequently, the temperatures measured during the power supply evaluation -- even though in 50 C envirionment -- may not be the same when the power supply is installed in the end-product. If the PFC shuts down as a result of attaching the thermocouples, then you are attaching them to the wrong parts and/or routing the TC wire too near sensitive circuits. (Clearly, thermocouples were attached during the power supply evaluation -- and the PFC did not shut down!) As a general rule, for the purposes of safety measurements, thermocouples should not be attached to live parts. Most safety standards are concerned with the temperature of insulations, not of the parts. Of course, measuring the parts in contact with inusulation gives a worst-case measurement of insulation temperature. I suggest you ask for advice from the PS supplier as to where to attach thermocouples to reproduce the measurements reported in the CB. Best regards, Rich This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ieee-pses.org/ 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
