John Larkin's LC oscillator
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From: Jon Kirwan on 9 Jun 2010 18:34 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... I believe Win is saying that the core in a transformer can be designed without necessarily caring so much for (or wanting) a known A_L and/or energy storage in interstitial vacuum. While an inductor usually has the L as a design parameter and in that case using _some_ transformer cores (iron) where the A_L isn't a goal in their design can mean that the L is not nearly as 'designable' with those materials. Energy is stored in vacuum, not atoms (most of it, anyway, though there is, I believe, a _miniscule_ storage of energy used in aligning.) Including an air gap (in iron) completely dominates by providing a huge, known gap for energy storage and what tiny bit of vacuum remains in the iron path is nearly completely swamped out by it. So that makes the A_L designable in that case. Another way of saying all the above is that in transformers the flux through the core links the windings together and energy storage is actually parasitic, not desired. The A_L is basically "not wanted" and therefore minimized, but not designed to some specific value. Inductors are designed for specific values and therefore the A_L needs to be known, not merely minimized, and otherwise the core is actually supposed to provide flux linkage to the known effective gap, not two windings. The 'flyback transformer' is kind of a misnomer to me, since in reality it is really an inductor that uses a known A_L or gap to store energy and also is designed to link the flux to the gap, except that it _also_ needs to provide subsequent linkage from the gap to a secondary winding, as well. Or, at least, that's how it seems to me. Jon
From: George Herold on 9 Jun 2010 21:43 On Jun 9, 2:18 pm, "Tim Williams" <tmoran...(a)charter.net> wrote: > "George Herold" <gher...(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. OK I wasn't talking about saturation, which is a whole other regieme. (sp) > > > 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. Cool, Though I'm not sure I'd call that peculiar. You're lining up all those spins in a piece of iron, that stores energy. > > 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.. > I never use Z5U for bypass. X7R is what I like... though some X5R creeps in via purchasing. George H. > Tim > > -- > Deep Friar: a very philosophical monk. > Website:http://webpages.charter.net/dawill/tmoranwms
From: George Herold on 9 Jun 2010 22:02 On Jun 9, 6:34 pm, Jon Kirwan <j...(a)infinitefactors.org> wrote: > On Wed, 09 Jun 2010 11:10:22 -0500, John Fields > > > > > > <jfie...(a)austininstruments.com> wrote: > >On 8 Jun 2010 10:11:18 -0700, Winfield Hill > ><Winfield_mem...(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... > > I believe Win is saying that the core in a transformer can be > designed without necessarily caring so much for (or wanting) > a known A_L and/or energy storage in interstitial vacuum. > While an inductor usually has the L as a design parameter and > in that case using _some_ transformer cores (iron) where the > A_L isn't a goal in their design can mean that the L is not > nearly as 'designable' with those materials. > > Energy is stored in vacuum, not atoms (most of it, anyway, > though there is, I believe, a _miniscule_ storage of energy > used in aligning.) Including an air gap (in iron) completely > dominates by providing a huge, known gap for energy storage > and what tiny bit of vacuum remains in the iron path is > nearly completely swamped out by it. Hi Jon, so good to see a post from you. Everything OK? I'm going to have to go an reread Fenyman on this... (I thought I got it the last time, but that's how it is with Feynman.) I think there's a magnetic field everywhere in the magnetic circuit. In an electro- magnet it starts with the current in the coils and is transfered to the gap by the magnetic material...iron. But the field is everywhere in the circuit. It may very well be that the gap determines the field strength. But the magnetic energy is stored over the entire volume of the field. George H. So that makes the A_L > designable in that case. > > Another way of saying all the above is that in transformers > the flux through the core links the windings together and > energy storage is actually parasitic, not desired. The A_L > is basically "not wanted" and therefore minimized, but not > designed to some specific value. Inductors are designed for > specific values and therefore the A_L needs to be known, not > merely minimized, and otherwise the core is actually supposed > to provide flux linkage to the known effective gap, not two > windings. The 'flyback transformer' is kind of a misnomer to > me, since in reality it is really an inductor that uses a > known A_L or gap to store energy and also is designed to link > the flux to the gap, except that it _also_ needs to provide > subsequent linkage from the gap to a secondary winding, as > well. > > Or, at least, that's how it seems to me. > > Jon- Hide quoted text - > > - Show quoted text -
From: Winfield Hill on 9 Jun 2010 22:26 Jon Kirwan wrote... > > Another way of saying all the above is that in transformers > the flux through the core links the windings together and > energy storage is actually parasitic, not desired. The A_L > is basically "not wanted" and therefore minimized, but not ----------------------------------------- ^^^^^^^^^ ----------------------------------------- maximized > designed to some specific value. Inductors are designed for > specific values and therefore the A_L needs to be known, not > merely minimized, and otherwise the core is actually supposed > to provide flux linkage to the known effective gap, not two > windings. The 'flyback transformer' is kind of a misnomer to > me, since in reality it is really an inductor that uses a > known A_L or gap to store energy and also is designed to link > the flux to the gap, except that it _also_ needs to provide > subsequent linkage from the gap to a secondary winding, as > well. Yep, one winding has a well-establish inductance, not at all like a common transformer, but the second winding is well coupled to it, and with low leakage inductance, just like a good transformer. We really need a new name for these beasts, inductors with transformer windings. BTW, toroid cores need not apply. Very poor AL control. -- Thanks, - Win
From: Jon Kirwan on 9 Jun 2010 23:01
On Wed, 9 Jun 2010 19:02:56 -0700 (PDT), George Herold <gherold(a)teachspin.com> wrote: >Hi Jon, so good to see a post from you. Everything OK? Nah. Still horribly busy around here -- probably going to be killing myself through the summer... too much to do (or, at least, I hope I can force myself to keep at it without giving up at some point.) >I'm going to have to go an reread Fenyman on this... (I thought I got >it the last time, but that's how it is with Feynman.) I think there's >a magnetic field everywhere in the magnetic circuit. In an electro- >magnet it starts with the current in the coils and is transfered to >the gap by the magnetic material...iron. But the field is everywhere >in the circuit. It may very well be that the gap determines the field >strength. But the magnetic energy is stored over the entire volume >of the field. I _imagine_ aligned atoms as 'short circuits' that bridge vacuum. Vacuum is where the energy gets stored. (I think a tiny amount of energy is 'used' to align an iron atom, for example. But it is tiny and doesn't represent recoverable energy... I think it gets converted to heat in the end.) I'm very much open to being wrong, of course. With all this in mind, it's easy to imagine the concept of permeability arising. For air core, it's vacuum all the way down, so to speak. All of the loop length is, in effect, the magnetic path length where energy gets packed away. But when you insert iron atoms chained end to end they act as short circuits, each of them bridging across a small bit of vacuum to make the effective length of vacuum shorter (when aligned -- the molecules of O2 and N2 don't align and don't bridge so in effect they simply don't count and don't short the vacuum.) So if you imagine a core material inserted there, what counts is the interstitial vacuum that remains when computing the magnetic path length. But what remains?? Well, that depends. You can take a ruler and measure that core piece, of course. But that ruler won't help you figure out what the effective remaining vacuum length is and that is what you need to know. So in order to come up with a number that represents the percentage of the measurable length, you need a factor of some kind. This is the permeability figure. A permeability of 1000 would mean that if you had a toroid with a mean centerline path length measurable with a ruler of say 100mm, that the actual vacuum path length would be 100 microns and the other 99.9mm would be shorted out by the iron that is present there. A permeability of 100 would mean that 1mm would be vacuum and 99mm would be iron. Since all of us can only use observable measures, we need to have some idea about what it looks like from the magnetic field's point of view, vacuum wise. At least, this is how I like to imagine all of this... energy gets stored in vacuum and the rest is just fudge factors to get around how we practically measure lengths. Jon |