Hi all, Paralleling low-esr capacitors is a little scairy. With 8 caps in parallel and each allotted its maximum ripple current, one capacitor, theoretically, could conduct 8 times its allowable rating! This, of course, is the theoretical limit---all other caps would have to be "open."
That's a ridiculous example, but perhaps you get my drift. With two in parallel, the worst case is twice the current. Esr is not well controlled; it's unusual to see it bounded both with a "max." and a "min." With lot-to-lot variations, and with 8 in parallel, I wouldn't be a bit surprised to see one getting two or three times its rated current. The more in parallel, the worse it gets. Your choices: 1. Use the largest available caps to parallel, thus reducing the total number. 2. Design with 2x to 4x margin of esr. 3. Place small "equalizing" resistors in series with each to "swamp out" the variation in esr. Cheers, Chuck ------------------------------------------- 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: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] 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"
