On 1/23/2008, MACY wrote:
Does anyone know in RFI/EMI Line Filters how closely do Y Caps match? Hi Robert: Tolerances are usually specified, to some extent, in the data sheets. To determine the total variation, you have to consider two variables: 1) The specified tolerance on the nominal value, typically measured at 20 degrees C. 2) The variation with temperature, which is a function of the dielectric used. For ceramic Y-caps, the first parameter is typically +/- 20%, but I have seen some parts specified at 10%. The second parameter can be +/-10% for the B/Y5P/2B4 dielectrics or +20/-55% for the E/Y5U/2E4 dielectrics. Note that the variation with temperature of capacitors with the same dielectric will tend to track, which helps to maintain matching. However, the variation in nominal capacitance at 20 degrees C will typically be either 20% or 10% as specified by the manufacturer, so this is a limitation for matching if you use such parts. I have seen some applications where good matching was necessary in order to maintain balance, and capacitors that were matched closer than 10% (at 20 degrees C) were obtained by special order from the manufacturer. This was based on a simple screening test of existing production, at an additional cost. There may be some special form of precision Y-caps available somewhere, but I have not seen them. The standard application for Y-caps does not typically require precise matching, so the majority of the standard products are not very precise. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 (USA) [email protected] http://www.randolph-telecom.com <http://www.randolph-telecom.com/> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
