To calc PF you would need to know the true power and apparent power at a particular test configuration.
PF for an unit with active (more expensive) PFC should vary very little over the rated input range. PF for units with passive (less expensive) PFC will probably vary several percent over the rated input and output ranges. PF for unit with no PFC (cheap) vary significantly with changes in line quality, and significantly over the rated input and output ranges. No free lunch... It is important to measure PF with an instrument intended for the measurement. There are many ways to measure PF using just scopes and/or meters, but unless you have instruments with very high crest factors, that can make phase-relative measurements, and can accurately integrate over many cycles, your resultant number could be suspect. Final caveat, I have tested component power supplies from various sources. And I have noted a few atypical cases where a unit reliably maintained a consistent and high PF, but was operating at the limits or failing (depending on the Class) according to CISPRs and the 61000-3-2 conducted immunity test. luck, Brian -----Original Message----- From: robert Macy [ mailto:[email protected]] Sent: Monday, October 11, 2004 4:16 PM To: Gary McInturff; [email protected] Subject: Re: Power Factor correction Gary, Is it possible to calculate the pfc from the spec? - Robert - On Mon, 11 Oct 2004 10:54:01 -0700 Gary McInturff <[email protected]> wrote: > Ladies and Gentlemen > I think I may be stuck between a rock and a hard > place. > We have a new project that is, for all practical > purposes a custom > design for a client. > We purchase a supply that indicates compliance with > EN61000-3-2 > harmonics. Our customer wants a more quantitative number. > Is it 90% PFC, 95% > etc. > I can't tell that from the spec sheet and quite > frankly at this point I > can't lay my hands on a power supply yet and obviously we > haven't gone to > test yet with this in our equipment so I don't believe I > have any way of > determining this (not sure that I could tell from the > conformance test > anyway - can I?) > When I call the power supply manufacturer, I can't > directly address the > design engineer and all they can tell me is that it meets > the requirements > for Class A waveform. > Am I overlooking something here in the datasheet? Is > there anyway to > infer what what the PFC % is? > Gary ---------------------------------------------------------------- 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/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: [email protected] Scott Douglas [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://www.ieeecommunities.org/emc-pstc
