Maintaining a Vbe Multiplier's bias value
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From: Jon Kirwan on 11 Feb 2010 21:40 On Thu, 11 Feb 2010 17:46:42 -0800 (PST), "miso(a)sushi.com" <miso(a)sushi.com> wrote: >On Feb 11, 2:27�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 > >I'm not sure how you can sleuth out doping profiles in that manner. It's been 20 years now, but I used 1D and 2D models I found, which applied dopant concentrations to predict behavior. I could go find the book, I suppose, but I figured the information must be _generally_ understood. Certainly, when I was looking, it wasn't that hard to find. The issue was in plugging in the numbers. What I did was to take a series of measurements over a few weeks' time and then used a short program I wrote to "tinker" the parameters until the predictions came very close. I knew physical dimensions for the die. >When I've had the need to get such numbers, I would use an outside >lab. This was a one-off and the entire company was 20 people, including part time. I don't think they could have afforded the price. In my case, I got paid a few hours' work but the data collection just ran on its own. Most of what was needed to set it up was there and we bought a Burr-Brown board for the rest. >They can actually profile the device, so you don't just see the >net dopant, but how it changes. I can't say that I knew the dopant levels, for sure. It's a high quality photodiode, though. It's not complicated and the integrals weren't anything to write home about, as I recall. What I needed to model was dV/dI over temp. Not everything else. So maybe I got lucky. That was my focus, though. In the end, when I used those dopant figures and then re-used the equations from the book to predict behavior at points where I had _not_ measured it, but interpolated as well as extrapolated, and predicted very well. We had taken measurements down to -5C but the model nailed the observed dV/dI at -40C and at 55C, as well. Which is an impressive range to someone like me. Seemed to solve a problem, anyway. Equipment is still in the field and 'doing fine.' >I've managed to discover a few trade >secrets doing this. I can imagine. What had surprised me is that a neophyte like me could pick up some basic books on the subject, cold, and arrive at something that worked reasonably well and allowed me to deduce equations for automatic corrections that worked so well. Although it could be entirely accidental, when you get such results from the application of semiconductor theory it is hard to believe one could be _that_ lucky (so I think something was nailed down right and the physicists working on these things actually know their stuff pretty well.) >In the days before using epi for CMOS was common, >a company where I worked would ion implant the wafer from the back. >That was like a faux epi. A piece of cake for the outside lab to >spot. Hehe. I wish I knew more of this stuff. It's interesting. Jon
From: George Herold on 11 Feb 2010 22:04 On Feb 10, 10:34 pm, "Phil Allison" <phi...(a)tpg.com.au> wrote: > "George Herold" > "Phil Allison" > > > > > > > > > ** Push-pull class A is the MOST COMMON method use in tube and transistor > > audio power amplifiers. > > > With transistor amps, it is only necessary to set to standing bias current > > to a high value like an amp or two. > > > > You can, but it stops being class A for large signal swings or low load > > > impedances. > > > ** No need for either thing to happen. > > > One picks the load to suit the amplifier and the peak ( class A) current > > is > > double the bias setting current. > > > Eg: > > > With a bias of 2 amps, peak load current is 4amps which allows +/-32 volts > > into 8 ohms. > > > Class A power is then 64 watts rms. > > > The DC rails need to be about +/- 35 volts and the supply current a steady > > 2 > > amps. > > Do you just use a current source as bias as in the Amps from Pass labs? > > ** No - doing that is utterly STUPID. > > The only difference between a class A and class B push-pull amp IS the > bias setting. > > One just turns the bias trim pot to get the desired standing current or with > tubes adjust the grid bias to get the same result. > > > Tubes can't do push-pull because "it's hard to get positrons from the > > filament" to parapharse what I read. > > ** How pathetic. > > .... Phil- Hide quoted text - > > - Show quoted text - Excellent, Thanks Phil. Crank up the bias. I think almost everything I build runs class A. I set a DC bias and then modulate on top of it. I run an opamp into a pass element, apply feedback and then make the load 'look' as resistive as possible. (Then cross your fingers and see if that works.) So how do you do push pull with tubes, or say with only Jon's npn transistors? George H.
From: George Herold on 11 Feb 2010 22:07 On Feb 10, 11:47 pm, "m...(a)sushi.com" <m...(a)sushi.com> wrote: > On Feb 10, 8:35 am, George Herold <ggher...(a)gmail.com> wrote: > > > > > > > On Feb 9, 4:05 pm, Jon Kirwan <j...(a)infinitefactors.org> wrote: > > > > On Tue, 9 Feb 2010 11:35:36 -0800 (PST), George Herold > > > > <ggher...(a)gmail.com> wrote: > > > >On Feb 9, 5:39 am, Jon Kirwan <j...(a)infinitefactors.org> wrote: > > > >> On Mon, 8 Feb 2010 19:16:24 -0800 (PST), George Herold > > > > >> <ggher...(a)gmail.com> wrote: > > > >> >><snip> > > > >> >"I'm wondering about additional topology changes to improve > > > >> >the performance still more." > > > > >> >Hi Jon, I've been 'sorta' following your thread on s.e.basics. I > > > >> >wonder if you abandoned class A operation too early? Why not keep > > > >> >things linear evreywhere and avoid the dead band? So what if you > > > >> >need a bigger heat sink. Its certainly a lot simpler. > > > > >> >George H. > > > > >> Well, George... No, I've not abandoned it. Actually, it's my > > > >> hope to wind up building the amplifier and then operating it > > > >> (by hopefully choosing a design where that is possible) in > > > >> different modes for the learning experience of it. I hope > > > >> that is in the cards. I really do. > > > > >> But to make a sharp point on it, although it's probably just > > > >> an extreme case, I remember reading about a 10W amplifier, > > > >> single channel, dissipating 120W! Creeps me out. So I > > > >> definitely _want_ to consider other classes of operation. And > > > >> cripes, I want to learn, anyway. So why not keep my options > > > >> open? > > > > >> Jon > > > > >" I remember reading about a 10W amplifier, > > > >> single channel, dissipating 120W! " > > > > >It might have been here, > > > >http://www.passdiy.com/default.html > > > >I got to reading about amplifiers on the above site... Do in part to > > > >your interest. > > > > >George H. > > > > Egads. Loads of PDF files. Now I have to create a > > > directory, download them one by one, and then call them up > > > with my slow machine to look. Any particular page or file > > > where you saw it? (No, that isn't where I saw the comment.) > > > > But thanks for the link. I'll add it to those I read, also. > > > > Jon- Hide quoted text - > > > > - Show quoted text - > > > Ohh sorry about that... Don't bother reading them... He (Nelson Pass) > > has designs for Class A amps using a FET. (named Zen) One of his > > variations (son of Zen?) was made with no NFB and I think wasted your > > stated 120 Watts of power for 10W into the speaker. But this seemed > > pretty pointless to me... some audio guys wanted an amp with out > > NFB.... Don't aks me why! > > > Say can you make a push-pull stage run class A? (Or is that just a > > silly idea?) > > > George H. > > Pass designs are interesting reading. Nobody says you have to build > them. ;-) Nelson is the opposite of Randy Slone, who is Mr. Practical. > Doug Self is somewhere in the middle.- Hide quoted text - > > - Show quoted text - I only found them last week, I'd never seen a FET biased with a current source. It looked kinda cool...(Though Phil said it was stupid... anyone ever tried it?) George H.
From: George Herold on 11 Feb 2010 22:11 On Feb 10, 11:55 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Wed, 10 Feb 2010 20:47:33 -0800 (PST), "m...(a)sushi.com" > > > > > > <m...(a)sushi.com> wrote: > >On Feb 10, 8:35 am, George Herold <ggher...(a)gmail.com> wrote: > >> On Feb 9, 4:05 pm, Jon Kirwan <j...(a)infinitefactors.org> wrote: > > >> > On Tue, 9 Feb 2010 11:35:36 -0800 (PST), George Herold > > >> > <ggher...(a)gmail.com> wrote: > >> > >On Feb 9, 5:39 am, Jon Kirwan <j...(a)infinitefactors.org> wrote: > >> > >> On Mon, 8 Feb 2010 19:16:24 -0800 (PST), George Herold > > >> > >> <ggher...(a)gmail.com> wrote: > >> > >> >><snip> > >> > >> >"I'm wondering about additional topology changes to improve > >> > >> >the performance still more." > > >> > >> >Hi Jon, I've been 'sorta' following your thread on s.e.basics.. I > >> > >> >wonder if you abandoned class A operation too early? Why not keep > >> > >> >things linear evreywhere and avoid the dead band? So what if you > >> > >> >need a bigger heat sink. Its certainly a lot simpler. > > >> > >> >George H. > > >> > >> Well, George... No, I've not abandoned it. Actually, it's my > >> > >> hope to wind up building the amplifier and then operating it > >> > >> (by hopefully choosing a design where that is possible) in > >> > >> different modes for the learning experience of it. I hope > >> > >> that is in the cards. I really do. > > >> > >> But to make a sharp point on it, although it's probably just > >> > >> an extreme case, I remember reading about a 10W amplifier, > >> > >> single channel, dissipating 120W! Creeps me out. So I > >> > >> definitely _want_ to consider other classes of operation. And > >> > >> cripes, I want to learn, anyway. So why not keep my options > >> > >> open? > > >> > >> Jon > > >> > >" I remember reading about a 10W amplifier, > >> > >> single channel, dissipating 120W! " > > >> > >It might have been here, > >> > >http://www.passdiy.com/default.html > >> > >I got to reading about amplifiers on the above site... Do in part to > >> > >your interest. > > >> > >George H. > > >> > Egads. Loads of PDF files. Now I have to create a > >> > directory, download them one by one, and then call them up > >> > with my slow machine to look. Any particular page or file > >> > where you saw it? (No, that isn't where I saw the comment.) > > >> > But thanks for the link. I'll add it to those I read, also. > > >> > Jon- Hide quoted text - > > >> > - Show quoted text - > > >> Ohh sorry about that... Don't bother reading them... He (Nelson Pass) > >> has designs for Class A amps using a FET. (named Zen) One of his > >> variations (son of Zen?) was made with no NFB and I think wasted your > >> stated 120 Watts of power for 10W into the speaker. But this seemed > >> pretty pointless to me... some audio guys wanted an amp with out > >> NFB.... Don't aks me why! > > >> Say can you make a push-pull stage run class A? (Or is that just a > >> silly idea?) > > >> George H. > > >Pass designs are interesting reading. Nobody says you have to build > >them. ;-) Nelson is the opposite of Randy Slone, who is Mr. Practical. > >Doug Self is somewhere in the middle. > > How about an amp using complementary voltage regulators as the output > stage, like LM317 and LM337? Nice current and thermal protections. > > John- Hide quoted text - > > - Show quoted text - Ohh, I like using the ....LM395?? LM375?? I can't remember the part number. You treat it like a power NPN but it has the built in thermal protection of the voltage regualtors. George H.
From: George Herold on 11 Feb 2010 22:23
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, Im building electronics to either detect something or drive something thats detecting something. So the fun is in making good detectors or drivers. George H. |