Susan, I was just recently looking up ferrites for a different application and have stumbled over a few manufactures not included in other responses.
AEM: www.aem-usa.com Murata: Top Magnetics: www.topmagnetics.com WorldProducts: www.worldproducts.com Ferrishield Ferrite itself has both inductive loss (usually peaks in the low Mhz range, has a phase shift) and resistive loss (usually peaks in the 100Mhz range, has no phase shift). To see what effect the ferrite would have, look at its loss and inductance curve and then model this loss and inductance in-line with your lightning transient. You will see that the ferrite has a differing effect depending on the impedance of the system into which it is inserted. Ferrites work better with a low impedance on the "protected" side (the side away from the transient). If you have a high impedance on the protected side; you're better off with a capacitor, tranzorb, sidactor... But, if your heart is stuck on a ferrite....In order to maximize blockage of a lightning transient: 1. Select a ferrite optimized for low Mhz frequencies. (Say, around 1 or 10Mhz). 2. Maximize inductive loss by taking advantage of turns. The inductive loss of the ferrite will go up by a factor equal to the square of the number of terms. In the low Mhz range, the inductance is usually substantial and turns help immensely. 3. Lightning is such a powerful phenomena that you may have to account for other unexpected effects, such as arcing across turns and just plain blowing the ferrite to smithereens. 4. If you have substantial inductance (i.e. many turns); be careful of resonant effects which can be caused by nearby capacitors coupling with your inductors to form "tank" circuits. These resonant effects can actually allow a ferrite to magnify a transient...not good. Typically, we block lightning with common mode capacitor, small ferrite bead (mostly for radiated emissions, not lightning), sidactor, series resistor and a fuse. It's a real balancing act and this circuit was perfected with the help of other list members. I hope this helps Chris ------------------------------------------- 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: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com 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: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
