I asked two power supply design engineers. bypass capacitor - intended to provide a low impedance path for the higher freqs.
decoupling capacitor - considered an incorrect term. Note that the wikipedia entry (http://en.wikipedia.org/wiki/Decoupling_capacitor), for what its worth, indicates that the two terms are interchangeable. In my opinion, the terms should not be interchangeable, and should indicate different actions/properties. A bypass will shunt the bad signal, so is a lo Z. A decouple is to isolate, so should be a higher Z to the bad stuff. whatever... luck, Brian From: [email protected] [mailto:[email protected]]On Behalf Of Denomme, Paul S. Sent: Wednesday, April 16, 2008 8:41 AM To: [email protected] Subject: Bypass and decoupling capacitor definitions. Hi All, Not sure if this is the right post to ask this question but feedback would be appreciated. Can anyone provide me with the difference between a bypass and decoupling capacitor? My understanding is that bypass caps are used for stabilizing a power supply, and would be used to provide low end AC filtering on a power supply up to a couple hundred MHz and they could be located from the power supply output to being scattered through a board to stabilize the power distribution system and normally have higher than .1uF cap values. Also, decoupling caps would be used local to the ICs on the PCB and provide high frequency noise coupling as well as provide some local power stabilization for the switching noise that will occur due to the high frequency switching of the transistors in the IC. When I looked online for these definitions, it seems like some people are using these terms interchangeably. It may just be semantics, but I am looking for some confirmations from people with a bit more experience on this subject. Thanks in advance for your help. Paul Denomme - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] 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] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
