I want to add to that that any Hi-Q EMC filter is per definition a bad emc filter.
EMC filters should never be steep, have a narrow frequency band, or allow resonance. Easy design rule: use small L and BIG C's. Small L's do better at High frequency too ! Use low grade EMC ferrite as a core, no high grade RF ferrites. Never apply a low loss coil for EMC (such as smps coils). Regarding the MOV: for professional appliances a fused MOV is common; they Mostly have a "fused" indicator or even output. In ordinary (low cost) applications, apply the MOV behind the fuse and buy a approved type UL VDE or any other reputed tested version and not low cost far east models. Behind the fuse the end-of-life short does simply blow the fuse, and does not ignite the device. NEVER apply a MOV between line and ground (unless fixed installations) The ever increasing leakage current during the service life of the MOV may become lethal before any fuse operates. Gert Gremmen Van: [email protected] [mailto:[email protected]] Namens [email protected] Verzonden: zondag 16 december 2012 20:23 Aan: [email protected] Onderwerp: Re: [PSES] Why use an MOV? >From a safety perspective, it's much better to design to minimum clearance require w/o the MOVs and then to include them in the circuit. (e.g. what happens of the MOV fails open?) >From an EMC perspective, L-C filters with a hi-Q, like those used for RFI on mains input circuits, can increase the over-voltage problem. I've measured that scenario several years ago while doing debug for EMC surge immunity. ________________________________________________________________________ _______ Ralph McDiarmid | Schneider Electric | Solar Business | CANADA | Regulatory Compliance Engineering From: Doug Powell <[email protected]> To: [email protected], Date: 12/15/2012 03:20 PM Subject: Re: [PSES] Why use an MOV? ________________________________ In the case of IEC 61010-1 Ed 3, it is possible to reduce clearance requirements utilizing Annex K. In another case, say you have a brick power supply approve for use in OV Cat II but your application has an extended environmental condition of OV Cat III. In order to use this power supply, you must reduce the Category by one step. MOVs are just one possibility for achieving this. Of course, use of MOVs also has a certain added concerns that must be addressed. Doug Douglas E Powell http://www.linkedin.com/in/dougp01 http://www.linkedin.com/in/dougp01 ________________________________ From: Richard Nute <[email protected]> Date: Sat, 15 Dec 2012 11:08:53 -0800 To: <[email protected]> ReplyTo: Richard Nute <[email protected]> Subject: [PSES] Why use an MOV? Presumably, the MOVs in question are connected line to neutral. I would expect the designer would design his primary circuit to withstand the normally-expected 1500 V transient. Why use an MOV??? Best wishes for the holiday season, Rich ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. ______________________________________________________________________ - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ 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]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ 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]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ 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]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ 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]>
