Twin T circuit wanted
in [Design]
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From: BlindBaby on 10 Jun 2010 23:45 On Thu, 10 Jun 2010 19:59:50 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On 10 Jun 2010 17:55:23 -0700, Winfield Hill ><Winfield_member(a)newsguy.com> wrote: > >>John Larkin wrote... >>> >>> I have never called myself a "judge", and Win has never called >>> himself a "master." You and JT call us that, so you can then >>> abuse us for saying things we never said. How lame. >> >> That's correct. I work hard at what I do, but I'm always >> on the lookout for mistakes I may make, or more often, >> things I don't yet understand. Hopefully I'll not pipe >> up about something I don't yet understand, but oops, oops, >> sometimes one doesn't yet know that they don't understand >> something, or they may just make a silly thoughtless mistake. > >A lot depends on how fragile your ego is. If you are determined to >always be "right" in public, or you are determined that someone else >is always wrong, you'll be a fathead and not learn anything. > >Of course, there are some people who are AlwaysWrong. > >John John gazes into the mirror (guffaw) and details for us his... err... our dilemma. Yeah... sure... bub.
From: dagmargoodboat on 11 Jun 2010 00:45 John Larkin wrote: > dagmargoodb...(a)yahoo.com wrote: > >John Larkin wrote: > >> In my oscillator, a c-b schottky diode would keep the transistor c-b > >> junction from conducting, and keep the transistor out of saturation. > >> Tempco would still be low. That simplifies things considerably. Not > >> bad. > > >Good idea. > > >> >Oh, and John's oscillator really swings ~ 2* (Vcc + Vbe), not 2* (Vcc > >> >- Vbe). Reason being, the AGC operates as the average base voltage > >> >gets sucked down to near 0v, killing the gain. > > >> I seem to recall the DC base voltage being about +.6. So the collector > >> swings to just about zero, and the AC output is 2*Vcc p-p. Somebody > >> could Spice this, if they were interested, and see exactly what > >> happens. > > >I Spice'd all the circuits I posted. > > >> The transformer ratio gets involved some, too. > > >Yep, but to a 1rst order: average emitter voltage = 0, ignore the > >swing 'cause it's small, and that gets you pretty close. V(b) = 120mV > >in my 5KHz example. > > > How much p-p voltage on the emitter? 1 volt. That might be a bit hot, as I noted in the post. I did that on purpose, thinking a smaller conduction angle would give better frequency stability. You know, let the L-C ring unmolested as much as possible? Might not be helpful though--if the drive is sine-ish, the tendency to pull might not apply. Not sure. > That low a DC base voltage suggests more like class-C action. With > less turns on the emitter winding, the thing gets more class A-ish, > and I'd expect the DC base voltage to go up some. I think. Yes, class-C. > I wonder what happens to the DC base voltage as the base bias resistor > changes. I'm not even sure which direction things will go. > > Complicated, for 5 parts. I like the schottky. Takes trr(b-c) out of the equation. James
From: John Larkin on 11 Jun 2010 01:16 On Thu, 10 Jun 2010 21:45:08 -0700 (PDT), dagmargoodboat(a)yahoo.com wrote: >John Larkin wrote: >> dagmargoodb...(a)yahoo.com wrote: >> >John Larkin wrote: > >> >> In my oscillator, a c-b schottky diode would keep the transistor c-b >> >> junction from conducting, and keep the transistor out of saturation. >> >> Tempco would still be low. That simplifies things considerably. Not >> >> bad. >> >> >Good idea. >> >> >> >Oh, and John's oscillator really swings ~ 2* (Vcc + Vbe), not 2* (Vcc >> >> >- Vbe). Reason being, the AGC operates as the average base voltage >> >> >gets sucked down to near 0v, killing the gain. >> >> >> I seem to recall the DC base voltage being about +.6. So the collector >> >> swings to just about zero, and the AC output is 2*Vcc p-p. Somebody >> >> could Spice this, if they were interested, and see exactly what >> >> happens. >> >> >I Spice'd all the circuits I posted. >> >> >> The transformer ratio gets involved some, too. >> >> >Yep, but to a 1rst order: average emitter voltage = 0, ignore the >> >swing 'cause it's small, and that gets you pretty close. V(b) = 120mV >> >in my 5KHz example. >> >> >> How much p-p voltage on the emitter? > >1 volt. That might be a bit hot, as I noted in the post. I did that >on purpose, thinking a smaller conduction angle would give better >frequency stability. You know, let the L-C ring unmolested as much as >possible? Might not be helpful though--if the drive is sine-ish, the >tendency to pull might not apply. Not sure. I prefer smaller drive, a tenth or so p-p on the emitter. Maybe even less, basically class A. The whole thing behaves differently if the secondary drive is large and the transistor conduction angle is small: the emitter voltage will swing down, way below ground, and pull the base down with it before the collector voltage gets down to ground... blasting a spike of collector current into the tank. Then it will swing way up and turn the base off. Brutality! Chaos! I prefer a more delicate touch: the collector dips down elegantly, like a swan landing on a pond. It just barely touches the water, err, emitter, and together they remove a bit of charge from the base cap. And then it flies away. Did I mention the sunset in the background? John
From: dagmargoodboat on 11 Jun 2010 01:34 On Jun 10, 11:45 pm, dagmargoodb...(a)yahoo.com wrote: > John Larkin wrote: > > dagmargoodb...(a)yahoo.com wrote: > > >John Larkin wrote: > > >> The transformer ratio gets involved some, too. > > > >Yep, but to a 1rst order: average emitter voltage = 0, ignore the > > >swing 'cause it's small, and that gets you pretty close. V(b) = 120mV > > >in my 5KHz example. > > > How much p-p voltage on the emitter? > > 1 volt. That might be a bit hot, as I noted in the post. I did that --^^^^^^ Ooops. That was for another sim, which uses 1mH and 10uH. The posted 5 KHz ckt used 1mH / 25uH, so the emitter swing was about 1.8v p-p. James Arthur
From: Grant on 11 Jun 2010 04:23
On Thu, 10 Jun 2010 18:11:44 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Thu, 10 Jun 2010 17:21:02 -0700 (PDT), MooseFET ><kensmith(a)rahul.net> wrote: > >>On Jun 11, 12:01 am, John Larkin >>[....] >>> I don't think so. People designed radar, magnetrons and klystrons and >>> waveguides and servos and all that, without computers. They did the >>> math. Early computers were obviously designed without help from >>> computers. >> >><PITA> >>Make that "electronic computers". At one time, a computer was >>a person who computed. Companies had rooms full of people >>grinding through the numbers to make sure that the sums were >>right. >></PITA> > > ><OLDFARTSTORY> > >My first real job was a research assistant in microwave spectroscopy, >a summer tech job. Two grad students on the same project spent the >entire summer hunched over a Friden calculator in a small room, >calculating rotational resonances for some organic thing. My PC could >do all that now in, probably, a millisecond. > ></OLDFARTSTORY> > > > >> >>There were also some analog computers and mechanical >>computers. Each generation has used the tools made by >>the previous. Just try to imagine designing with Roman >>numerals and not even a slide rule. >> >> >>> I don't use Spice a lot, and could certainly get along without it. It >>> is helpful when evaluating nonlinear systems, where math solutions >get messy. >> >>I use spice as a sanity check. Sometimes it even finds some. >> >>LTSpice is also nice for making a schematic to email to someone. > >It is just about the only portable schematic format the industry has >ever seen. Not a bad editor, but the circuits seem to wander all over >the screen as you zoom. I have to keep selecting my whole circuit and >dragging it back into sight. Minor problem, return for full refund? :) Grant. > >John > -- http://bugs.id.au/ |