Ferrites: L changes with current change.
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From: amdx on 18 Dec 2009 14:47 I have ask before about changes of inductance vs. AC excitation in ferrites before and didn't get a satisfactory answer. We can use a particular potcore at 5ua or 10amps. but how much does the inductance change over this range? What current does the manufacturer use to make his curves. I'm thinking about a transformer at the input of a radio receiver with a signal measured in microvolts. Say we built a 50 ohm to 200 ohm transformer using the manufacturers specs, and made the primary inductance 4 times 50 ohms at our design freq.. It would work fine at 100 ma to many amps. But at 5ua is there enough inductance in the primary to make it function as a proper impedance transformer? Mike
From: Eeyore on 18 Dec 2009 16:02 amdx wrote: > I have ask before about changes of inductance vs. AC excitation in ferrites > before and didn't get a satisfactory answer. > We can use a particular potcore at 5ua or 10amps. but how much does the > inductance change over this range? Depends on the material. It'll change with temperature too. > What current does the manufacturer use to make his curves. They sweep the current. > I'm thinking about a transformer at the input of a radio receiver with a > signal measured in microvolts. > Say we built a 50 ohm to 200 ohm transformer using the manufacturers specs, > and made the primary > inductance 4 times 50 ohms at our design freq.. It would work fine at 100 ma > to many amps. > But at 5ua is there enough inductance in the primary to make it function as > a proper impedance transformer? Losses may be too high. Try winding one for the job. And get a copy of Epcos's Ferrite Magnetic Designer tool. http://www.epcos.com/web/generator/Web/Sections/DesignTools/Ferrites/Page,templateId=render,locale=en.html Most manufacturers make 'copies' of the popular ferrites. There are often direct cross-references beteen say Epcos, Ferroxcube/Philips/Yageo and TDK for example. http://www.pe-coils.com/MnZn_Feirrite/MATERIAL%20COMPARES.pdf http://www.dianyuan.com/blog/u/2008-12/6123_1230623550.pdf http://www.google.co.uk/search?hl=en&q=ferrite+cross-reference&meta=&aq=f&oq= The cheap Chinese manufacturers tend not to have the latest low-loss, high temp parts though but that's a PSU issue. Epcos's data also advises different ferrites for different applications. Graham -- due to the hugely increased level of spam please make the obvious adjustment to my email address
From: amdx on 18 Dec 2009 16:24 "Eeyore" <rabbitsfriendsandrelations(a)notcoldmail.com> wrote in message news:4B2BEDEE.6F9EE29A(a)notcoldmail.com... > > > amdx wrote: > >> I have ask before about changes of inductance vs. AC excitation in >> ferrites >> before and didn't get a satisfactory answer. >> We can use a particular potcore at 5ua or 10amps. but how much does the >> inductance change over this range? > > Depends on the material. It'll change with temperature too. > > >> What current does the manufacturer use to make his curves. > > They sweep the current. > > >> I'm thinking about a transformer at the input of a radio receiver with a >> signal measured in microvolts. >> Say we built a 50 ohm to 200 ohm transformer using the manufacturers >> specs, >> and made the primary >> inductance 4 times 50 ohms at our design freq.. It would work fine at 100 >> ma >> to many amps. >> But at 5ua is there enough inductance in the primary to make it function >> as >> a proper impedance transformer? > > Losses may be too high. Try winding one for the job. > > And get a copy of Epcos's Ferrite Magnetic Designer tool. > http://www.epcos.com/web/generator/Web/Sections/DesignTools/Ferrites/Page,templateId=render,locale=en.html > > Most manufacturers make 'copies' of the popular ferrites. There are often > direct > cross-references beteen say Epcos, Ferroxcube/Philips/Yageo and TDK for > example. > > http://www.pe-coils.com/MnZn_Feirrite/MATERIAL%20COMPARES.pdf > http://www.dianyuan.com/blog/u/2008-12/6123_1230623550.pdf > http://www.google.co.uk/search?hl=en&q=ferrite+cross-reference&meta=&aq=f&oq= > > The cheap Chinese manufacturers tend not to have the latest low-loss, high > temp > parts though but that's a PSU issue. > > Epcos's data also advises different ferrites for different applications. > > Graham I should add this a general question, I don't have a specific job in mind. Just wondering what happens to AsubL at 0.1 microamps. Mike
From: Bill Sloman on 18 Dec 2009 18:15 On Dec 18, 10:24 pm, "amdx" <a...(a)knology.net> wrote: > "Eeyore" <rabbitsfriendsandrelati...(a)notcoldmail.com> wrote in message > > news:4B2BEDEE.6F9EE29A(a)notcoldmail.com... > > > amdx wrote: > > >> I have ask before about changes of inductance vs. AC excitation in > >> ferrites > >> before and didn't get a satisfactory answer. > >> We can use a particular potcore at 5ua or 10amps. but how much does the > >> inductance change over this range? > > > Depends on the material. It'll change with temperature too. > > >> What current does the manufacturer use to make his curves. > > > They sweep the current. > > >> I'm thinking about a transformer at the input of a radio receiver with a > >> signal measured in microvolts. > >> Say we built a 50 ohm to 200 ohm transformer using the manufacturers > >> specs, > >> and made the primary > >> inductance 4 times 50 ohms at our design freq.. It would work fine at 100 > >> ma > >> to many amps. > >> But at 5ua is there enough inductance in the primary to make it function > >> as > >> a proper impedance transformer? > > > Losses may be too high. Try winding one for the job. > > > And get a copy of Epcos's Ferrite Magnetic Designer tool. > >http://www.epcos.com/web/generator/Web/Sections/DesignTools/Ferrites/... > > > Most manufacturers make 'copies' of the popular ferrites. There are often > > direct > > cross-references beteen say Epcos, Ferroxcube/Philips/Yageo and TDK for > > example. > > >http://www.pe-coils.com/MnZn_Feirrite/MATERIAL%20COMPARES.pdf > >http://www.dianyuan.com/blog/u/2008-12/6123_1230623550.pdf > >http://www.google.co.uk/search?hl=en&q=ferrite+cross-reference&meta=&... > > > The cheap Chinese manufacturers tend not to have the latest low-loss, high > > temp parts though but that's a PSU issue. > > > Epcos's data also advises different ferrites for different applications.. > > > Graham > > I should add this a general question, I don't have a specific job in mind. > Just wondering what happens to AsubL at 0.1 microamps. Get hold of a data book on ferrite cores. Most of them include flux density versus field strength curves for the various ferrites used in their cores. EPCOS at least makes the data availlable on the web - here's the link for their N27 material http://www.epcos.com/web/generator/Web/Sections/ProductCatalog/Ferrites/Materials/PDF/PDF__N27,property=Data__en.pdf;/PDF_N27.pdf -- Bill Sloman, Nijmegen
From: amdx on 18 Dec 2009 19:46
"Bill Sloman" <bill.sloman(a)ieee.org> wrote in message news:a9f61b7d-4521-4bc1-8657-7ace03993f14(a)j19g2000yqk.googlegroups.com... On Dec 18, 10:24 pm, "amdx" <a...(a)knology.net> wrote: > "Eeyore" <rabbitsfriendsandrelati...(a)notcoldmail.com> wrote in message > > news:4B2BEDEE.6F9EE29A(a)notcoldmail.com... > > > amdx wrote: > > >> I have ask before about changes of inductance vs. AC excitation in > >> ferrites > >> before and didn't get a satisfactory answer. > >> We can use a particular potcore at 5ua or 10amps. but how much does the > >> inductance change over this range? > > > Depends on the material. It'll change with temperature too. > > >> What current does the manufacturer use to make his curves. > > > They sweep the current. > > >> I'm thinking about a transformer at the input of a radio receiver with > >> a > >> signal measured in microvolts. > >> Say we built a 50 ohm to 200 ohm transformer using the manufacturers > >> specs, > >> and made the primary > >> inductance 4 times 50 ohms at our design freq.. It would work fine at > >> 100 > >> ma > >> to many amps. > >> But at 5ua is there enough inductance in the primary to make it > >> function > >> as > >> a proper impedance transformer? > > > Losses may be too high. Try winding one for the job. > > > And get a copy of Epcos's Ferrite Magnetic Designer tool. > >http://www.epcos.com/web/generator/Web/Sections/DesignTools/Ferrites/... > > > Most manufacturers make 'copies' of the popular ferrites. There are > > often > > direct > > cross-references beteen say Epcos, Ferroxcube/Philips/Yageo and TDK for > > example. > > >http://www.pe-coils.com/MnZn_Feirrite/MATERIAL%20COMPARES.pdf > >http://www.dianyuan.com/blog/u/2008-12/6123_1230623550.pdf > >http://www.google.co.uk/search?hl=en&q=ferrite+cross-reference&meta=&... > > > The cheap Chinese manufacturers tend not to have the latest low-loss, > > high > > temp parts though but that's a PSU issue. > > > Epcos's data also advises different ferrites for different applications. > > > Graham > > I should add this a general question, I don't have a specific job in mind. > Just wondering what happens to AsubL at 0.1 microamps. Get hold of a data book on ferrite cores. Most of them include flux density versus field strength curves for the various ferrites used in their cores. EPCOS at least makes the data availlable on the web - here's the link for their N27 material http://www.epcos.com/web/generator/Web/Sections/ProductCatalog/Ferrites/Materials/PDF/PDF__N27,property=Data__en.pdf;/PDF_N27.pdf -- Bill Sloman, Nijmegen Ok Bill, I'm over my head on this because I don't understand all the terms. If we look at page 3 of the link you gave, first graph, you will see the B vs u(o) curve. At 25mT it is already down 34% from the peak and I would bet a dollar that the curve drops faster the lower you go with the B field. My guess (only a guess) is that if I wound my theoretical transformer (described above) and had my 0.1 microamp driving it, it would be no where near 25mT. Somehow this B vs u(o) curve will relate to permeability which is then related to (A sub L). I would then use (A sub L) to calculate the turns on the theoretical 50 ohm primary (200 ohms inductance). It just seems that at very low currents the permeability will drop so low I will not have my 200 ohms inductance and the transformer will not work as designed. Since I have never seen this discussed and people build working radios everyday, I'm probably all wrong, but I'm not sure where. Thanks, Mike |