Ferrites: L changes with current change.
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From: Leon on 21 Dec 2009 14:23 On 21 Dec, 17:30, Jim Thompson <To-Email-Use-The-Envelope-I...(a)My-Web- Site.com/Snicker> wrote: > On Mon, 21 Dec 2009 11:23:43 -0600, "amdx" <a...(a)knology.net> wrote: > > >"Jim Thompson" <To-Email-Use-The-Envelope-I...(a)My-Web-Site.com/Snicker> > >wrote in messagenews:c73vi59928raaaseeo0spcb17vut4ddmpj(a)4ax.com... > >> On Sun, 20 Dec 2009 23:34:41 -0600, "amdx" <a...(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 athttp://www.analog-innovations.com| 1962 | > > Help save the environment! > Please dispose of socialism properly! I've seen a VCO circuit using DC current through a winding on a ferrite core to control the frequency. Leon
From: Baron on 21 Dec 2009 16:24 Leon Inscribed thus: > On 21 Dec, 17:30, Jim Thompson <To-Email-Use-The-Envelope-I...(a)My-Web- > Site.com/Snicker> wrote: >> On Mon, 21 Dec 2009 11:23:43 -0600, "amdx" <a...(a)knology.net> wrote: >> >> >"Jim Thompson" >> ><To-Email-Use-The-Envelope-I...(a)My-Web-Site.com/Snicker> wrote in >> >messagenews:c73vi59928raaaseeo0spcb17vut4ddmpj(a)4ax.com... >> >> On Sun, 20 Dec 2009 23:34:41 -0600, "amdx" <a...(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 athttp://www.analog-innovations.com| 1962 | >> >> Help save the environment! >> Please dispose of socialism properly! > > I've seen a VCO circuit using DC current through a winding on a > ferrite core to control the frequency. > > Leon Rhode & Schwarz used that technique in some of their instruments. -- Best Regards: Baron.
From: Bill Sloman on 21 Dec 2009 21:02 On Dec 21, 6:30 pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)My- Web-Site.com/Snicker> wrote: > On Mon, 21 Dec 2009 11:23:43 -0600, "amdx" <a...(a)knology.net> wrote: > > >"Jim Thompson" <To-Email-Use-The-Envelope-I...(a)My-Web-Site.com/Snicker> > >wrote in messagenews:c73vi59928raaaseeo0spcb17vut4ddmpj(a)4ax.com... > >> On Sun, 20 Dec 2009 23:34:41 -0600, "amdx" <a...(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. Inductance is defined by V = L. dI/dt, which is to say that it is proportional to the rate of change of the magnetic flux threading the coil (B) divided by the rate of change of the current exciting the coil (H), which isn't the same thing. It can be dependent on the absolute value of the current through the coil if there is a ferro-magnetic core in the magnetic circuit whose permeability changes with B, but proportionality would be unexpected and very unusual. -- Bill Sloman, Nijmegen
From: whit3rd on 22 Dec 2009 13:32 On Dec 21, 11:23 am, Leon <leon...(a)btinternet.com> wrote: > I've seen a VCO circuit using DC current through a winding on a > ferrite core to control the frequency. Nowadays, that's the sign of a creative engineer. Someone went off the boundaries of the data sheet to do the design. Before VVC diodes (voltage-variable-capacitance) there were Increductors (I think that's the right spelling) intended for this kind of thing, with specifications and everything.
From: Paul Hovnanian P.E. on 22 Dec 2009 15:04
Leon wrote: > On 21 Dec, 17:30, Jim Thompson <To-Email-Use-The-Envelope-I...(a)My-Web- > Site.com/Snicker> wrote: >> On Mon, 21 Dec 2009 11:23:43 -0600, "amdx" <a...(a)knology.net> wrote: >> >> >"Jim Thompson" <To-Email-Use-The-Envelope-I...(a)My-Web-Site.com/Snicker> >> >wrote in messagenews:c73vi59928raaaseeo0spcb17vut4ddmpj(a)4ax.com... >> >> On Sun, 20 Dec 2009 23:34:41 -0600, "amdx" <a...(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 athttp://www.analog-innovations.com| 1962 | >> >> Help save the environment! >> Please dispose of socialism properly! > > I've seen a VCO circuit using DC current through a winding on a > ferrite core to control the frequency. http://en.wikipedia.org/wiki/Magnetic_amplifier I have a couple of old (discrete transistor) power supplies that use a form of mag amp to control the voltage output from the main transformer so as to reduce the series transistor dissipation. -- Paul Hovnanian paul(a)hovnanian.com ---------------------------------------------------------------------- Have gnu, will travel. |