Discussion forum problems are challenging problems to say the least. One thing you might want to try is to add a ground plane into the bottom of the case with a piece of copper plate or foil. Connect the plate (or foil) to the return side of the power leads. Then, if you've got some fische paper (heck even masking tape and several sheets of printer paper will work in a moment of crisis), use that to insulate the plate from the bottom of the board. And get the plate as close as possible to the bottom of the board.
But to really understand what's going on, you'd probably have to set up something with current probes or differential probes to follow the effect of the pulse. Most likely what's happening is the power supply is acting as the source of the pulse out to your product (obvious but bear with me) and the power leads and your product are simply acting as an arm of a distorted dipole, i.e., low impedance source (the power supply), high impedance end of the arm (your product). Think for a moment of the power supply is the source of a dipole and the two cables from it, the ac input cord and the power output cord are the arms of a dipole. You're whole effort here is to disrupt that construction. Thus, it is possible that by adding ferrites to the product end of the power leads, you could actually enhance this dipole effect. This is possibly why adding ferrites to the power cord to your product may not be working. In other words, the ferrite increases the impedance of the end of the dipole arm (your product) even higher. This has been demonstrated time and again by Doug Smith in his many demonstrations. The effect of the plate *hopefully* disrupts this pseudo-dipole construction. It may, it may not. The position of ferrites can be important. If you're in a real bind, then you might want to simply load up the entire construction with ferrites all over the place to see if that works. Start removing ferrites until you get a minimal setup that works and go from there. The positions of the remaining ferrites in a working setup can sometimes telll you what's going on in a setup that's modelled after a dipole. Good luck ... Regards, Doug McKean ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
