John Larkin's LC oscillator
in [Basics]
|
Prev: Twin T circuit wanted
Next: And blocking oscillators
From: dagmargoodboat on 8 Jun 2010 18:09 On Jun 8, 10:04 am, George Herold <ggher...(a)gmail.com> wrote: > On Jun 8, 10:55 am, dagmargoodb...(a)yahoo.com wrote: > > > > > On Jun 8, 6:39 am, Winfield Hill <Winfield_mem...(a)newsguy.com> wrote: > > > > was Re: Twin T circuit wanted > > > > John Larkin wrote... > > > > ftp://jjlarkin.lmi.net/Ships_Bell.JPG > > > > > On Mon, 7 Jun 2010 George Herold wrote: > > > > >> I loved your bell circuit John! I didn't quite get how the > > > >> inductor was working. But still I got the idea. Thanks. > > > > >> George H. > > > > > This is kind of a cute circuit. I first designed it when I needed > > > > a very frequency and amplitude-stable sine wave to drive a Talyvel > > > > LVDT-like inclinometer, part of the Boresight Alignment Kit for > > > > the C5A. We had to measure level to arc-seconds of accuracy. > > > > > It's a transformer with a resonant tank in the collector and a > > > > positive feedback drive winding into the emitter. The emitter > > > > feedback is just a couple of tenths of a volt p-p. > > > > > The cool thing is that the collector swing is almost exactly 2xVcc > > > > peak-to-peak. As the amplitude builds up, at the negative swing peak > > > > the emitter goes a little bit negative, to get out of the way, and > > > > the collector swings to just about ground. That forward-biases the > > > > c-b junction and discharges the base cap, reducing transistor base > > > > current hence gain. So it has a built-in peak detecting AGC amplitude > > > > leveling loop with close to zero TC. All from 5 parts. Or sometimes > > > > six. > > > > > I tested the system on a 55 gallon drum full of sand, with a huge > > > > steel plate on top. We built a platform that pivoted on ball bearings > > > > and we moved a long lever arm with a micrometer, to tweak the sensor > > > > angle. I had to tell people not to walk nearby, because their weight > > > > would flex the concrete slab of the building. > > > > > I learned a bunch on this project: HeNe laser power supplies, > > > > synchronous detectors, optics. I've always sort of liked this > > > > oscillator. > > > > With your explanation, the oscillator is much more attractive. > > > Some folks can't stomach magnetics, perhaps that's part of the > > > criticism. Anyway, ignore JF and JT when they get bitchy, it > > > must be something they ate, or is age catching up with 'em? > > > > Our old friend, Tony Williams, R.I.P., would have been pleased. > > > > . John Larkin's LC oscillator, supply-V sets amplitude > > > . _________________ > > > . | | | > > > . | _|_C E || L > > > . Rb --- E || > > > . | | E || > > > . | | * | || > > > . | +-----' || > > > . | | || > > > . | C gnd || > > > . +- B | || > > > . _|_ E E || > > > . --- | * | || > > > . | +-----' || > > > . gnd | > > > . '--- out > > > > Tell us more about the inductor / transformer, turns ratio, etc. > > > Did I get the winding polarities right? I suppose you have to > > > keep the emitter's reverse-voltage under say 5V breakdown, so > > > 10Vpp max output? What are the prospects for making this into > > > a high-power oscillator? Drive a speaker directly? > > > > -- > > > Thanks, > > > - Win > > > Here's a quick implementation: > > > Vcc = +5v > > --+-------+------+-- > > | | | > > | | |_ || > > | | _)|| > > .-. --- L1a _)|| > > Rb | | C1 --- 1mH _)|| > > 100k | | 1uF | _)|| > > '-' | _)|| > > | | *| || > > | .-+------' || > > | |/ || > > +---| Q1 || > > | |>. 2n3904 || > > | | * || > > C2 --- +---------. || > > 1uF --- | L1b _)|| > > | | 25uH _)|| > > | | | > > === | === > > | > > '-------------> output > > > (5KHz values shown) > > > collector swing ~= 2*(Vcc+0.6v) > > emitter swing = Vc * sqrt(L1b/L1a) > > > 1 > > f(out) = ------------------- > > 2*pi*sqrt(L1a * C1) > > > That's a 1rst cut--I may have left L1b a little hot... > > > Simulates really nicely--sine waves. > > > -- > > Cheers, > > James Arthur > > > > > Cool thanks James, Say can you take it up to 10's of MHz? > On a lark...the UHF version. Vcc = +5v --+--------+--- | | | +--------. | | |_ | | _)|| .-. C1 --- L1 _)|| Rb | | 10pF --- 10nH _)|| 100k | | | _)|| '-' | | | +--------' | | | .-. | | |Rc | | |47 | '-' | | | .-+--------. | |/ | +----| Q1 --- C3 | |>. MPSH10 --- 0.5pF | | | C2 --- +----------+-----> 460MHz out 100pF --- | | | .-. | | | | Re --- C4 === | | 1k --- 10pF '-' | | | === === C4 swamps some transistor parasitics, improving stability and repeatability. I threw in Rc for fun. It turns i(c) from a jackhammer into into a lovely, almost-sinewave--great for spectral purity--but it adds a phase shift that bugs me...not sure at a glance if that's kosher, so use at your peril. Back on topic, to simulate a (very tiny) bell, gang and sum several stages, and bias off a decaying R-C.... <ducking for cover> -- Cheers, James Arthur
From: dagmargoodboat on 8 Jun 2010 18:52 On Jun 8, 5:09 pm, dagmargoodb...(a)yahoo.com wrote: > On a lark...the UHF version. > > Vcc = +5v > --+--------+--- > | | > | +--------. > | | |_ > | | _)|| > .-. C1 --- L1 _)|| > Rb | | 10pF --- 10nH _)|| > 100k | | | _)|| > '-' | | > | +--------' > | | > | .-. > | | |Rc > | | |47 > | '-' > | | > | .-+--------. > | |/ | > +----| Q1 --- C3 > | |>. MPSH10 --- 0.5pF > | | | > C2 --- +----------+-----> 460MHz out > 100pF --- | | > | .-. | > | | | Re --- C4 > === | | 1k --- 10pF > '-' | > | | > === === > > C4 swamps some transistor parasitics, improving stability and > repeatability. > > I threw in Rc for fun. It turns i(c) from a jackhammer into into a > lovely, almost-sinewave--great for spectral purity--but it adds a > phase shift that bugs me...not sure at a glance if that's kosher, so > use at your peril. > > Back on topic, to simulate a (very tiny) bell, gang and sum several > stages, and bias off a decaying R-C.... Oh, dumb mistake--if it's spectral purity you want, it'll be better tapped off the tank circuit. Should've thought of that, but was too busy goofing around... If stability w.r.t. to load is more important, I think it's better as- drawn. YMMV. -- Cheers, James Arthur
From: George Herold on 8 Jun 2010 22:07 On Jun 8, 1:11 pm, 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. > > -- > Thanks, > - Win 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.) I was picturing coils wound in series on a rod... a nice big air gap. Would coils wound on a torroid give a different response? George H.
From: George Herold on 8 Jun 2010 22:23 On Jun 8, 6:09 pm, dagmargoodb...(a)yahoo.com wrote: > On Jun 8, 10:04 am, George Herold <ggher...(a)gmail.com> wrote: > > > > > > > On Jun 8, 10:55 am, dagmargoodb...(a)yahoo.com wrote: > > > > On Jun 8, 6:39 am, Winfield Hill <Winfield_mem...(a)newsguy.com> wrote: > > > > > was Re: Twin T circuit wanted > > > > > John Larkin wrote... > > > > > ftp://jjlarkin.lmi.net/Ships_Bell.JPG > > > > > > On Mon, 7 Jun 2010 George Herold wrote: > > > > > >> I loved your bell circuit John! I didn't quite get how the > > > > >> inductor was working. But still I got the idea. Thanks. > > > > > >> George H. > > > > > > This is kind of a cute circuit. I first designed it when I needed > > > > > a very frequency and amplitude-stable sine wave to drive a Talyvel > > > > > LVDT-like inclinometer, part of the Boresight Alignment Kit for > > > > > the C5A. We had to measure level to arc-seconds of accuracy. > > > > > > It's a transformer with a resonant tank in the collector and a > > > > > positive feedback drive winding into the emitter. The emitter > > > > > feedback is just a couple of tenths of a volt p-p. > > > > > > The cool thing is that the collector swing is almost exactly 2xVcc > > > > > peak-to-peak. As the amplitude builds up, at the negative swing peak > > > > > the emitter goes a little bit negative, to get out of the way, and > > > > > the collector swings to just about ground. That forward-biases the > > > > > c-b junction and discharges the base cap, reducing transistor base > > > > > current hence gain. So it has a built-in peak detecting AGC amplitude > > > > > leveling loop with close to zero TC. All from 5 parts. Or sometimes > > > > > six. > > > > > > I tested the system on a 55 gallon drum full of sand, with a huge > > > > > steel plate on top. We built a platform that pivoted on ball bearings > > > > > and we moved a long lever arm with a micrometer, to tweak the sensor > > > > > angle. I had to tell people not to walk nearby, because their weight > > > > > would flex the concrete slab of the building. > > > > > > I learned a bunch on this project: HeNe laser power supplies, > > > > > synchronous detectors, optics. I've always sort of liked this > > > > > oscillator. > > > > > With your explanation, the oscillator is much more attractive. > > > > Some folks can't stomach magnetics, perhaps that's part of the > > > > criticism. Anyway, ignore JF and JT when they get bitchy, it > > > > must be something they ate, or is age catching up with 'em? > > > > > Our old friend, Tony Williams, R.I.P., would have been pleased. > > > > > . John Larkin's LC oscillator, supply-V sets amplitude > > > > . _________________ > > > > . | | | > > > > . | _|_C E || L > > > > . Rb --- E || > > > > . | | E || > > > > . | | * | || > > > > . | +-----' || > > > > . | | || > > > > . | C gnd || > > > > . +- B | || > > > > . _|_ E E || > > > > . --- | * | || > > > > . | +-----' || > > > > . gnd | > > > > . '--- out > > > > > Tell us more about the inductor / transformer, turns ratio, etc. > > > > Did I get the winding polarities right? I suppose you have to > > > > keep the emitter's reverse-voltage under say 5V breakdown, so > > > > 10Vpp max output? What are the prospects for making this into > > > > a high-power oscillator? Drive a speaker directly? > > > > > -- > > > > Thanks, > > > > - Win > > > > Here's a quick implementation: > > > > Vcc = +5v > > > --+-------+------+-- > > > | | | > > > | | |_ || > > > | | _)|| > > > .-. --- L1a _)|| > > > Rb | | C1 --- 1mH _)|| > > > 100k | | 1uF | _)|| > > > '-' | _)|| > > > | | *| || > > > | .-+------' || > > > | |/ || > > > +---| Q1 || > > > | |>. 2n3904 || > > > | | * || > > > C2 --- +---------. || > > > 1uF --- | L1b _)|| > > > | | 25uH _)|| > > > | | | > > > === | === > > > | > > > '-------------> output > > > > (5KHz values shown) > > > > collector swing ~= 2*(Vcc+0.6v) > > > emitter swing = Vc * sqrt(L1b/L1a) > > > > 1 > > > f(out) = ------------------- > > > 2*pi*sqrt(L1a * C1) > > > > That's a 1rst cut--I may have left L1b a little hot... > > > > Simulates really nicely--sine waves. > > > > -- > > > Cheers, > > > James Arthur > > > Cool thanks James, Say can you take it up to 10's of MHz? > > On a lark...the UHF version. > > Vcc = +5v > --+--------+--- > | | > | +--------. > | | |_ > | | _)|| > .-. C1 --- L1 _)|| > Rb | | 10pF --- 10nH _)|| > 100k | | | _)|| > '-' | | > | +--------' > | | > | .-. > | | |Rc > | | |47 > | '-' > | | > | .-+--------. > | |/ | > +----| Q1 --- C3 > | |>. MPSH10 --- 0.5pF > | | | > C2 --- +----------+-----> 460MHz out > 100pF --- | | > | .-. | > | | | Re --- C4 > === | | 1k --- 10pF > '-' | > | | > === === > > C4 swamps some transistor parasitics, improving stability and > repeatability. > > I threw in Rc for fun. It turns i(c) from a jackhammer into into a > lovely, almost-sinewave--great for spectral purity--but it adds a > phase shift that bugs me...not sure at a glance if that's kosher, so > use at your peril. > > Back on topic, to simulate a (very tiny) bell, gang and sum several > stages, and bias off a decaying R-C.... > > <ducking for cover> > > -- > Cheers, > James Arthur- Hide quoted text - > > - Show quoted text - Thanks James, I use a 70MHz ~1 watt oscillator to run the Rb discharge lamp for an optical pumping apparatus. I'd like to have some 'back-up' ideas if the npn-RF transistor ever disappears. George H.
From: Tim Williams on 9 Jun 2010 03:16
"George Herold" <gherold(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. > 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). Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms |