RE: Ferrites for GND
Should I be using 10 Ohm here? -Original Message- From: Wan Juang Foo [mailto:f...@np.edu.sg] Sent: Friday, October 11, 2002 8:29 PM To: Dan Pierce; emc-p...@majordomo.ieee.org Subject: Re: Ferrites for GND Dan, It is a lossy material and most commercially available ferrite beads are 'tuned' to peak around the 100 MHz (VHF band II ?). I suppose there must be lots of exception but I have not use any outside this region. Most of them have different Q to describe their individual characteristics. Obviously, there are lots of RFI from many FM radio stations making it a necessity for many design. The material's 'lossy' property are subjected to saturation etc... Here is how I suppose it works :-) or fail to work often..., the presence of a ferrite bead in the ground path increases the inductance of the return path at some frequencies, it also introduces a form of RF losses that can be modelled as an ac resistance. Hence, it is a differential mode filter of sorts, it will not work against CM interference if the bead is only in the path of the return lead (signal ground). There is always other grounds that RF breakthrough can come around. However, so much being said, pay careful attention to the layout (installation and placement) because in general reference designs often do not provide reference 'photographs' for best layout practices. Some do provide PCB layout but very often in the interest to avoid verbosity, the all important 'notes' are absent. Inter-conductor capacitance can ruin the performance of the ferrite bead. Just my 2 ¢ cheerio... Tim Foo Dan Pierce dpie...@openglobe.net To: emc-p...@majordomo.ieee.org cc: (bcc: Wan Juang Foo/ece/staff/npnet) Sent by: Subject: Ferrites for GND owner-emc-pstc@majordo mo.ieee.org 10/12/02 03:01 AM Please respond to Dan Pierce I have always been reluctant to place ferrite beads in the ground path, but I see them frequently in reference designs for USB and Analog Audio. What kind material should this be and what characteristics would this type of ferrite have. I am assuming this ferrite would not have 600 Ohm impedance @ 100MHz Thanks in advance, Daniel J. Pierce Sr. Design Engineer OpenGlobe, Inc. (An Escient Technologies Affiliate) 6325 Digital Way Indianapolis, IN 46278 mailto:dpie...@openglobe.net P: (317) 616.6587 F: (317) 616.6587 (See attached file: Dan Pierce.vcf) --- 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
Re: Ferrites for GND
Dan, It is a lossy material and most commercially available ferrite beads are 'tuned' to peak around the 100 MHz (VHF band II ?). I suppose there must be lots of exception but I have not use any outside this region. Most of them have different Q to describe their individual characteristics. Obviously, there are lots of RFI from many FM radio stations making it a necessity for many design. The material's 'lossy' property are subjected to saturation etc... Here is how I suppose it works :-) or fail to work often..., the presence of a ferrite bead in the ground path increases the inductance of the return path at some frequencies, it also introduces a form of RF losses that can be modelled as an ac resistance. Hence, it is a differential mode filter of sorts, it will not work against CM interference if the bead is only in the path of the return lead (signal ground). There is always other grounds that RF breakthrough can come around. However, so much being said, pay careful attention to the layout (installation and placement) because in general reference designs often do not provide reference 'photographs' for best layout practices. Some do provide PCB layout but very often in the interest to avoid verbosity, the all important 'notes' are absent. Inter-conductor capacitance can ruin the performance of the ferrite bead. Just my 2 ¢ cheerio... Tim Foo Dan Pierce dpie...@openglobe.net To: emc-p...@majordomo.ieee.org cc: (bcc: Wan Juang Foo/ece/staff/npnet) Sent by: Subject: Ferrites for GND owner-emc-pstc@majordo mo.ieee.org 10/12/02 03:01 AM Please respond to Dan Pierce I have always been reluctant to place ferrite beads in the ground path, but I see them frequently in reference designs for USB and Analog Audio. What kind material should this be and what characteristics would this type of ferrite have. I am assuming this ferrite would not have 600 Ohm impedance @ 100MHz Thanks in advance, Daniel J. Pierce Sr. Design Engineer OpenGlobe, Inc. (An Escient Technologies Affiliate) 6325 Digital Way Indianapolis, IN 46278 mailto:dpie...@openglobe.net P: (317) 616.6587 F: (317) 616.6587 (See attached file: Dan Pierce.vcf) bindN572fe2aR.bin Description: Binary data
Re: Ferrites for GND
Hi Dan. Two ferrite manufacturers I use are Stewart and Fair-Rite. Both of them have catalogs containing great detail graphs of performance of their various materials. Some of the 43 and 44 ferrite materials have very good low frequency performance. I would suggest, because I have no further details, that you contact their respective engineers as to what materials, form factors, and other considerations would work best. Warren Birmingham Epsilon-Mu Consultants (510) 793-4806 email: war...@epsilon-mu.com website: http://www.epsilon-mu.com On Friday, Oct 11, 2002, at 12:01 US/Pacific, Dan Pierce wrote: I have always been reluctant to place ferrite beads in the ground path, but I see them frequently in reference designs for USB and Analog Audio. What kind material should this be and what characteristics would this type of ferrite have. I am assuming this ferrite would not have 600 Ohm impedance @ 100MHz Thanks in advance, Daniel J. Pierce Sr. Design Engineer OpenGlobe, Inc. (An Escient Technologies Affiliate) 6325 Digital Way Indianapolis, IN 46278 mailto:dpie...@openglobe.net P: (317) 616.6587 F: (317) 616.6587 Dan Pierce.vcf --- 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
Ferrites for GND
I have always been reluctant to place ferrite beads in the ground path, but I see them frequently in reference designs for USB and Analog Audio. What kind material should this be and what characteristics would this type of ferrite have. I am assuming this ferrite would not have 600 Ohm impedance @ 100MHz Thanks in advance, Daniel J. Pierce Sr. Design Engineer OpenGlobe, Inc. (An Escient Technologies Affiliate) 6325 Digital Way Indianapolis, IN 46278 mailto:dpie...@openglobe.net P: (317) 616.6587 F: (317) 616.6587 attachment: Dan_Pierce.vcf
