A company I represent has a problem with their switching power supply. A single point failure in the regulator can cause the output voltage to rise higher than the voltage ratings of the electrolytic capacitors. As a result, the capacitors are overstressed and fail in a variety of ways depending upon the capacitor venting method. Sometimes the vent will pop and thats the end of it. Other times, the capacitor will overheat and expel ethylene glycol in the form of vapor or liquid. In some cases, the conductive fluid will bridge the primary circuits to earth causing a failure of the hypot test. This is unacceptable for IEC950 compliance.
I have spoken to several power supply designers and they inform me that it is common practice not to provide overvoltage protection. Of course, if that is true, then there appears to be a lot of power supplies in the world, perhaps including the one in my pc, that may or may not pass the fault testing of IEC950 depending on how the electrolytic capacitors fail. Obviously, my client does not want the extra cost of adding overvoltage protection when it appears that others dont do it. I would appreciate your comments concerning this failure mode, the use or non-use of protective circuits, and passing the IEC950 fault test if a protective circuit is not used. Regards, Bob _____________________________________________________________ Do You Yahoo!? Free instant messaging and more at http://messenger.yahoo.com --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
