Maintaining a Vbe Multiplier's bias value
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From: George Herold on 11 Feb 2010 22:35 On Feb 11, 1:14 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Thu, 11 Feb 2010 10:08:38 -0600, "Tim Williams" > > <tmoran...(a)charter.net> wrote: > >"Jim Thompson" <To-Email-Use-The-Envelope-I...(a)My-Web-Site.com> wrote in > >messagenews:r358n59g5vkv4brn2vc795lhoineb2jvhd(a)4ax.com... > >> And a 2.5V "dead-band", but it _is_ precisely known, and temperature > >> stable. Interesting thought if you have high enough power supplies. > > >Bonus: the dead band allows you to use that TL431 "Vbe" mentinoed earlier. > > >Too bad they're so slow (hardly capable for audio). Does anyone make "fast" > >regulators (without being stupid LDOs)? > > >Tim > > If you drive both adjust pins with the signal input, the 317 output is > Vin+1.25 and the 337 output is Vin-1.25. Connect them to the output > through a couple of resistors, valued to set the idle current. Where's > the deadband? > > Or you can take the output from the 317 output pin, with the 337 now > acting like a constant-current sink to the 317. > > I like to use LM1117s as power emitter followers, inside the loop of > an opamp. That makes a cheap, well protected power driver, for load > cell excitation and such. I did a bunch of tests to see whether > flailing the adj pin can damage the regulator, and never managed to > break one. > > John Cool! I think I got it... though if I try it in the future and let the smoke out of something... then I might have questions. George H.
From: Jon Kirwan on 11 Feb 2010 22:37 On Thu, 11 Feb 2010 19:23:04 -0800 (PST), George Herold <ggherold(a)gmail.com> wrote: >On Feb 11, 3:24�am, Jon Kirwan <j...(a)infinitefactors.org> wrote: >> On Wed, 10 Feb 2010 19:55:44 -0800 (PST), George Herold >> >> <ggher...(a)gmail.com> wrote: >> >I'm perhaps more of a novice than you... >> >> Somehow, I doubt that. �I barely rate "hobbyist." >> >> >but I find opamp circuits complicated enough.... >> >> Don't sweat it. �While some opamps leave _some_ issues nearly >> ignorable, there is always some tough problem at that scale >> that makes it non-trivial and interesting to work on, I >> imagine. �Each macroscale view has it's own complexity. >> Telescoping levels, where the complexity at one stage doesn't >> take away from interesting complexity at another level. >> >> (I would say more but I'm keeping in mind your warning about >> long-windedness and will now muzzle myself.) >> >> >And tend to stick transistors >> >only on the edges of things. �(Mostly on the output side... on the >> >input you have to 'know more' than the guys who designed the opamp.. >> >hard to do for a novice.) >> >> I do the same things except that I enjoy math and BJTs give >> me an excuse, perhaps. �Maybe that's the only difference. >> >> >I guess if I was designing an audio amp I'd figure on an opamp driving >> >some sort of FET output stage. �The question of how to bias the output >> >stage is interesting. �And also of how all the NFB works. >> >> Might as well just get a power opamp like the OPA502 and be >> done with it. �Give it two rails, feed the input, and just >> drive the hell out of a speaker. �Or get two of them and do a >> bridge amplifier. �But where is the enjoyment in that? �Or >> the learning? �Someone else already did most of the fun stuff >> and there's nothing really left to do except some hook up and >> heat sinking. �It's not at all satisfying to me, anyway. >> >> An audio amplifier is basically a power opamp. �Using an >> opamp to make one feels to me like building a car by first >> buying a car without the tires, selecting and installing some >> tires, and then saying you designed and built yourself a car. >> >> Jon > >Big Grins! > >Yeah I applaud your effort, I wait for further posts. > >For me, I�m building electronics to either detect something or drive >something that�s detecting something. So the fun is in making good >detectors or drivers. > >George H. Well, I am wanting, eventually, to build something I need. Something I cannot buy in the market because the need is unique. This divides into two parts. Design and build. Since the item is unique, I can't just go out and buy it. And getting the features I need cannot just be "hacked" into existing designs without at least knowing _some_ stuff, first. I might as well turn the "design" part into a fair learning experience, as a separate project of its own. Get past that and when it comes time to build what I want I'll be able to build on what I learned and add what I need and then do a modest hobbyist level whack at actually making what I want to make. If someone else were to do this for me (hire a designer), they'd get all the fun of learning on the job and taking my money with it. They get the money, they get to further their own education, and I get a tool. One tool. Once. Next time, I get to pay someone else to learn for me. It almost feels like paying someone to go do your exercising for you. No satisfaction and no weight loss. They get all the _real_ benefits. Part of the fun isn't the destination itself but it is what you see and enjoy while getting there, too. You take a plane when all you need is to "get there" quick, but you drive when you want to enjoy stops along the way. I used to fly to Burbank every week for a year and a half. Slept in a hotel for 3 nights a week, worked day and night in between, flew home. Barely saw anything but hotel room walls, cubical walls, a few cement roads, pollution so thick you couldn't see the Burbank hills from the Lockheed center, and not much else. The destination was important, of course. Paid the bills and I enjoyed the work, too. But there is a lot more to see in the 1000 miles from here to there. Anyway, I'm driving this time, not flying. Besides, I'd rather _keep_ the money and _keep_ the education for myself. That way it pays off, again and again. Jon
From: George Herold on 11 Feb 2010 22:39 On Feb 11, 5:27 pm, Jon Kirwan <j...(a)infinitefactors.org> wrote: > On Thu, 11 Feb 2010 11:50:23 -0700, Jim Thompson > > > > > > <To-Email-Use-The-Envelope-I...(a)My-Web-Site.com> wrote: > >On Thu, 11 Feb 2010 10:03:16 -0800, Jon Kirwan > ><j...(a)infinitefactors.org> wrote: > > >>On Thu, 11 Feb 2010 09:53:37 -0800, Jon Kirwan > >><j...(a)infinitefactors.org> wrote: > > >>><snip> > >>>In other words, although OnSemi has a realistic model for > >>>their own parts, which is fine for simulating their parts > >>>more accurately -- is there a reason to shop around and > >>>actually _select_ someone else's parts for some application > >>>reason. And in what cases would you not bother wasting time > >>>shopping around and for what other cases would you decide to > >>>spend the time, because you know enough about how they are > >>>made and what differences that can make to be worth that > >>>effort to test and verify when making a selection? > > >>To further clarify this question, I already know that some > >>manufacturers provide 2N2222A's with 40V and with 60V max Vce > >>specifications. I assume this is a function of differences > >>in the FAB processes they choose to apply in making their > >>parts. That's what I'm talking about... not only for > >>differences in model parameters but _useful_ differences, > >>too. > > >>And how do I learn the salient details of various FAB > >>processes? > > >>Thanks, > >>Jon > > >Once upon a time there was JEDEC, and all 2N2222A's had to be the > >same in regards to essential specifications. > > Okay. That's gone, then. > > >But I'd use the OnSemi model, irrespective... the LTspice version lets > >too many variables drop back to their default values... might not > >matter, but who knows. > > > ...Jim Thompson > > I'd still like to _learn_ about FAB processes, geometries, > mask steps, subtrates (and if any BJTs include a bond to such > things), and differences between them. For example, I've > heard you talk about processes that include gold as a step > (or more?) I'd like to know what does what. I can (and have > attempted) a few 2D spatial integrals aka Hauser's analysis > of crowding on r_b many years ago, and I'm vaguely aware of > the fact that he neglected to account for lateral base > diffusion which happens when the crowding and some local base > widening takes place. I actually _did_ take measurements of > real Hamamatsu diodes, years ago, and reversed out from the > measurements what the dopant concentrations had to have been > so that I could better model the behavior over a wide range > of temperature operations (Hamamatsu flatly refused to give > me any such information.) The resulting model I created > _did_ model that photodiode at -40C to 55C better than I'd > expected it to do and much better than the gross models I had > at the time were able. So at some point, I'd like to study > these things to get a better feel... but I'd like to know who > has what FABs and what the processes are capable of and > produce. > > I hope it's not as difficult as pulling dopant numbers out of > Hamamatsu was! I'm not wanting to know specific recipes or > anything -- just process capabilities. Hopefully, FAB and > process capabilities and locations are something that is > known about and published. I can hope. > > Jon- Hide quoted text - > > - Show quoted text - Hmmm must be lotsa good books out there. I've got Streetman and Szu. (sp?) George H.
From: Phil Allison on 11 Feb 2010 23:08 "George Herold So how do you do push pull with tubes, or say with only Jon's npn transistors? ** There are literally *millions* of push-pull tube amps in use - the vast majority of tube hifi and guitar amps are push pull designs. NPN output transistor amps are called "quasi-complementary push pull " - many millions of them made and sold too. Use Google to find the schems. Idiot. ..... Phil
From: Phil Hobbs on 11 Feb 2010 23:13
On 2/11/2010 10:35 PM, George Herold wrote: > On Feb 11, 1:14 pm, John Larkin > <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> On Thu, 11 Feb 2010 10:08:38 -0600, "Tim Williams" >> >> <tmoran...(a)charter.net> wrote: >>> "Jim Thompson"<To-Email-Use-The-Envelope-I...(a)My-Web-Site.com> wrote in >>> messagenews:r358n59g5vkv4brn2vc795lhoineb2jvhd(a)4ax.com... >>>> And a 2.5V "dead-band", but it _is_ precisely known, and temperature >>>> stable. Interesting thought if you have high enough power supplies. >> >>> Bonus: the dead band allows you to use that TL431 "Vbe" mentinoed earlier. >> >>> Too bad they're so slow (hardly capable for audio). Does anyone make "fast" >>> regulators (without being stupid LDOs)? >> >>> Tim >> >> If you drive both adjust pins with the signal input, the 317 output is >> Vin+1.25 and the 337 output is Vin-1.25. Connect them to the output >> through a couple of resistors, valued to set the idle current. Where's >> the deadband? >> >> Or you can take the output from the 317 output pin, with the 337 now >> acting like a constant-current sink to the 317. >> >> I like to use LM1117s as power emitter followers, inside the loop of >> an opamp. That makes a cheap, well protected power driver, for load >> cell excitation and such. I did a bunch of tests to see whether >> flailing the adj pin can damage the regulator, and never managed to >> break one. >> >> John > > Cool! I think I got it... though if I try it in the future and let > the smoke out of something... then I might have questions. > > George H. IIRC the LM395 is basically an LM309 with the voltage reference removed. Emitter-follower regulators are nearly bulletproof unless you discharge a cap into the output. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 email: hobbs at electrooptical dot net http://electrooptical.net |