Ferrites: L changes with current change.
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From: amdx on 21 Dec 2009 00:18 "Eeyore" <rabbitsfriendsandrelations(a)notcoldmail.com> wrote in message news:4B2EE4CF.1E2F3F1A(a)notcoldmail.com... > > > amdx wrote: > >> Ok Bill, I'm over my head on this because I don't understand all the >> terms. > > So study the subject ! I had to. > >> 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. > > Guesses are a waste of time. Either you KNOW or DON'T KNOW ! Thanks Eeyore, finally someone that KNOWS this stuff. I have a 50 ohm to 200 ohm transformer, 4 turns to 8 turns on a FT37 toroid of material 75. I have 2 microvolts driving the 50 ohm primary at 1Mhz. The effective volume of the core .163 cm^3 What is the B field? You will KNOW what other data you need if any (I'd have to guess) so let me KNOW and I'll look it up for you. It sure will be interesting to see how far off my guess was. >> 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 > > At what frequency ? And that's the vector sum of Xj ohms + Rdc ohms by > the way. 1Mhz, Xj=200 Rdc=0.025 >> 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. > > Take the advice and get the Epcos program. It tells you all about > saturation and change in inductance with >amps. I'll look at it, when you calculate the B field quantity, we'll see if the Epcos program goes to that low level. Thanks again for your help, Mike > > Graham > > -- > due to the hugely increased level of spam please make the obvious > adjustment to my email address > >
From: amdx on 21 Dec 2009 00:34 "Eeyore" <rabbitsfriendsandrelations(a)notcoldmail.com> wrote in message news:4B2EE3CB.D6A422D5(a)notcoldmail.com... > > > amdx wrote: > >> "Eeyore" <rabbitsfriendsandrelations(a)notcoldmail.com> wrote >> > 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 between 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. > > You must have too much spare time on your hands ! > > Graham Hey Graham, I reposted a graph from Fred Bartoli on alt.binaries.schematics.electronic, it shows inductance dropping with decreasing drive voltage. It doesn't go low enough though. Mike
From: Jim Thompson on 21 Dec 2009 09:59 On Sun, 20 Dec 2009 23:34:41 -0600, "amdx" <amdx(a)knology.net> wrote: [snip] > > Hey Graham, > I reposted a graph from Fred Bartoli on >alt.binaries.schematics.electronic, it shows >inductance dropping with decreasing drive voltage. It doesn't go low enough >though. > Mike > Sonnova gun! I wonder what might be causing that? Get out your textbooks ;-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Help save the environment! Please dispose of socialism properly!
From: amdx on 21 Dec 2009 12:23 "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com/Snicker> wrote in message news:c73vi59928raaaseeo0spcb17vut4ddmpj(a)4ax.com... > On Sun, 20 Dec 2009 23:34:41 -0600, "amdx" <amdx(a)knology.net> wrote: > > [snip] >> >> Hey Graham, >> I reposted a graph from Fred Bartoli on >>alt.binaries.schematics.electronic, it shows >>inductance dropping with decreasing drive voltage. It doesn't go low >>enough >>though. >> Mike >> > > Sonnova gun! I wonder what might be causing that? > > Get out your textbooks ;-) > > ...Jim Thompson Causing what ? This is my third attempt at finding out if my postulation has any merit at all. I've been told forget it, just build the transformer. It is just a curiosity for me, I have used the same core at 300 watts power levels and at microwatt levels. Would it have been a better transformer at lower frequencies if I had added more turns. I don't know and I have know way to measure microvolts Note his graph only goes down to 2Vrms, I'd like to see a graph down to 2 microvolts. Hey Jim, I'm a little surprised at your response, is Phil rubbing off on you? Have a drink of fine wine on me :-) Mike
From: Jim Thompson on 21 Dec 2009 12:30
On Mon, 21 Dec 2009 11:23:43 -0600, "amdx" <amdx(a)knology.net> wrote: > >"Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com/Snicker> >wrote in message news:c73vi59928raaaseeo0spcb17vut4ddmpj(a)4ax.com... >> On Sun, 20 Dec 2009 23:34:41 -0600, "amdx" <amdx(a)knology.net> wrote: >> >> [snip] >>> >>> Hey Graham, >>> I reposted a graph from Fred Bartoli on >>>alt.binaries.schematics.electronic, it shows >>>inductance dropping with decreasing drive voltage. It doesn't go low >>>enough >>>though. >>> Mike >>> >> >> Sonnova gun! I wonder what might be causing that? >> >> Get out your textbooks ;-) >> >> ...Jim Thompson > Causing what ? This is my third attempt at finding out if my postulation >has any merit at all. >I've been told forget it, just build the transformer. > It is just a curiosity for me, I have used the same core at 300 watts power >levels and at microwatt levels. >Would it have been a better transformer at lower frequencies if I had added >more turns. I don't know and >I have know way to measure microvolts >Note his graph only goes down to 2Vrms, I'd like to see a graph down to 2 >microvolts. > Hey Jim, I'm a little surprised at your response, is Phil rubbing off on >you? > Have a drink of fine wine on me :-) > Mike > I was just pointing out that the effect is not unexpected. Inductance is proportional to B/H. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Help save the environment! Please dispose of socialism properly! |