John Larkin's LC oscillator
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From: George Herold on 9 Jun 2010 09:15 On Jun 9, 3:16 am, "Tim Williams" <tmoran...(a)charter.net> wrote: > "George Herold" <gher...(a)teachspin.com> wrote in message > > news:6395c407-b936-4a6e-b4c7-dbbe72ca3e1d(a)k17g2000pro.googlegroups.com... > > > Thanks Win, I'm not much of a magnetic materials guy. I like magnetic > > fields best when they are in free space. Helmholtz coils and such. > > > I've read about gaps in magnetic materials and transformers, but never > > quite 'gotten' the importance. (I never had to make one.) > > This might be of some help?http://webpages.charter.net/dawill/tmoranwms/Elec_Magnetics.html > What gap does is increase the path length, reducing inductivity > proportionally (the average permeability of the path gets closer to 1), > while flux remains constant. Since L = Phi/I, L drops. Since mu_eff drops, > the amps required for a given flux goes up, so you get proportionally more > current at saturation, and since energy goes as I^2, you get more energy > storage too. The core looks like pole pieces, concentrating magnetization > into the airgaps, where the energy is stored. Thanks Tim, I've been through the math. The air gap helps to smooth out the terrible non-linearity of the magnetic material. I've just never done it in practice. (Which for me, makes all the difference.) > > > Would coils wound on a torroid give a different response? > > If the toroid (not "rr") has high permeability, it will saturate pretty > quickly and that's that. If it's powdered iron (low permeability), you can > drive lots of amp-turns into it (though the stuff tends to be lossy). Sorry I'm a terrible speller. (If it's a long post I'll run it through a spell checker.) But I see the problem. Even with iron the non-linearity means that the inductance changes with the current, so the resonance frequency changes as the supply voltage decreases. George H. > > Tim > > -- > Deep Friar: a very philosophical monk. > Website:http://webpages.charter.net/dawill/tmoranwms
From: John Fields on 9 Jun 2010 12:10 On 8 Jun 2010 10:11:18 -0700, Winfield Hill <Winfield_member(a)newsguy.com> wrote: >George Herold wrote... >> >> default wrote: > >>> I'd be curious to see values. It isn't "necessary" but I would like >>> to know what core, type, size and material you used. Did you tweak >>> the tuning? Running with banks of them to simulate a real bell, did >>> you calculate and tune for specific harmonics? >> >> OK not my circuit, but try whatever they build audio transformers >> out of. The LC on the collector sets the freqeuncy so that pretty >> much determines your L. > > Right, it's an L, not a transformer. Inductors can be wound > from the same ferrite cores as transformers, etc., but with > one *big* difference: They need an intentional air gap, to > set a predictable A_L value, and insure a stable inductance. --- Strange, but I thought that two (or more) magnetically coupled inductors comprised a transformer...
From: Jim Thompson on 9 Jun 2010 12:23 On Wed, 09 Jun 2010 11:10:22 -0500, John Fields <jfields(a)austininstruments.com> wrote: >On 8 Jun 2010 10:11:18 -0700, Winfield Hill ><Winfield_member(a)newsguy.com> wrote: > >>George Herold wrote... >>> >>> default wrote: >> >>>> I'd be curious to see values. It isn't "necessary" but I would like >>>> to know what core, type, size and material you used. Did you tweak >>>> the tuning? Running with banks of them to simulate a real bell, did >>>> you calculate and tune for specific harmonics? >>> >>> OK not my circuit, but try whatever they build audio transformers >>> out of. The LC on the collector sets the freqeuncy so that pretty >>> much determines your L. >> >> Right, it's an L, not a transformer. Inductors can be wound >> from the same ferrite cores as transformers, etc., but with >> one *big* difference: They need an intentional air gap, to >> set a predictable A_L value, and insure a stable inductance. > >--- >Strange, but I thought that two (or more) magnetically coupled >inductors comprised a transformer... Depends on your definition of "transformer" :-) ...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 | The only thing bipartisan in this country is hypocrisy
From: Tim Williams on 9 Jun 2010 14:18 "George Herold" <gherold(a)teachspin.com> wrote in message news:f6583252-3a4f-4fe9-8c1f-ad3b1f4c6037(a)g19g2000yqc.googlegroups.com... > Thanks Tim, I've been through the math. The air gap helps to smooth > out the terrible non-linearity of the magnetic material. I've just > never done it in practice. (Which for me, makes all the > difference.) This is partly true, but flux is still flux, so for example, saturation occurs at the exact same time if you're applying the same square wave, regardless of gap (in practice, fringing flux spreads it out slightly). If you're testing an inductor by applying a squarewave and measuring current, and you see the current jump up when it saturates, the time that occurs does not change as you move the core in and out. > But I see the problem. Even with iron the non-linearity means that > the inductance changes with the current, so the resonance frequency > changes as the supply voltage decreases. Powdered iron inductors are kind of peculiar. They store lots of energy at high magnetization, and they saturate gradually (even a widely gapped ferrite saturates fairly suddenly, though you may not notice the difference because the gap is so wide to begin with). A 10uH inductor might drop to 3uH at peak current handling. It's just like using a Z5U ceramic to bypass a power line, but its capacitance drops 70% because you're using it at rated voltage.. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Fred Bartoli on 9 Jun 2010 14:28
John Fields a �crit : > On 8 Jun 2010 10:11:18 -0700, Winfield Hill > <Winfield_member(a)newsguy.com> wrote: > >> George Herold wrote... >>> default wrote: >>>> I'd be curious to see values. It isn't "necessary" but I would like >>>> to know what core, type, size and material you used. Did you tweak >>>> the tuning? Running with banks of them to simulate a real bell, did >>>> you calculate and tune for specific harmonics? >>> OK not my circuit, but try whatever they build audio transformers >>> out of. The LC on the collector sets the freqeuncy so that pretty >>> much determines your L. >> Right, it's an L, not a transformer. Inductors can be wound >> from the same ferrite cores as transformers, etc., but with >> one *big* difference: They need an intentional air gap, to >> set a predictable A_L value, and insure a stable inductance. > > --- > Strange, but I thought that two (or more) magnetically coupled > inductors comprised a transformer... > It's more related to how the xfrmer/inductor is used. An xfrmer is used to directly transfer energy from its primary to its secondary. An inductor is used to store it then release it. In an xfrmer the magnetizing inductance does not matter much provided it's high enough and it can often be non linear without any worries. Here it'll have to have a well defined value and be linear. -- Thanks, Fred. |