Two things: a well tuned snubber across switching part. The RCD on the hi side is not it. And a couple or 4 Dcaps 0.1uF between 12v and 5v. Bill on cell Phone
Ken Javor <[email protected]> wrote: >Am working a small plastic box that is failing FCC Class B radiated >emissions 30 400 MHz. Box input power is 12 Vdc; it converts that to 5 >Vdc (not isolated 5 Vrtn is 12 Vrtn) using a small PCB dc/dc converter. >The 5 Vdc is in turn routed using wire pairs to three load boards with >digital circuitry. Each of these boards is off-the-shelf; i.e., >non-modifiable. > >Applied decoupling caps at each board power entry point and at the 12 Vdc >entry point to the dc/dc converter and that helped some, but the box is >generating significant common mode noise current from 30 to 400+ MHz on the >12 Vdc input, which is causing RE problems. Inserting a common mode choke >or rf bead doesn't help here because the impedance at source and load is >very high (80 cm above ground and the 12 Vdc is floated from ground as >well). > >Am wondering if an image plane here is the solution to providing a local >reference for the cm current to locally circulate. If so, is there any >connection between a board 5 Vrtn and the image plane, or is it totally >floated from the culprit PCB? Keep in mind this will not be an extra plane >in the stack up, but a separate foil or similar laid as close as possible to >the culprit PCB. How close is close enough? > >There is one other interface: Ethernet. That also has some cm current. Does >a filtered female Ethernet jack require reference to an image plane, or is >the 5 Vrtn ground plane sufficient (or even necessary)? > >Thank you, > >Ken Javor >Phone: (256) 650-5261 > >- >---------------------------------------------------------------- >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]>
