Maintaining a Vbe Multiplier's bias value
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From: Jim Thompson on 11 Feb 2010 13:56 On Thu, 11 Feb 2010 10:14:43 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Thu, 11 Feb 2010 10:08:38 -0600, "Tim Williams" ><tmoranwms(a)charter.net> wrote: > >>"Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote in >>message news: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? Yep, I got the REF polarity reversed in my mind, but you still have an issue if you expect this to source any significant power. Thru resistors ?:-) > >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 > Show us that configuration in class-B, say 10 Watt output into 8 Ohms :-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
From: Ban on 11 Feb 2010 13:56 "Jon Kirwan" <jonk(a)infinitefactors.org> schrieb im Newsbeitrag news:k6g8n5t1ma6ag352mncb3a2lm6c8oijs5c(a)4ax.com... > On Thu, 11 Feb 2010 07:34:40 -0700, Jim Thompson > <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> 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? > > Jon Hi Jon, I like your approach coming from equations to analysing practical circuits. But then follows the verification with real parts. I wouldn't worry with small details, as long as the general idea is understood and followed. When you have performed some measurements on real parts, it is good to understand the important parameters, so you can tweak them yourself. ciao Ban
From: Jon Kirwan on 11 Feb 2010 17:27 On Thu, 11 Feb 2010 11:50:23 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >On Thu, 11 Feb 2010 10:03:16 -0800, Jon Kirwan ><jonk(a)infinitefactors.org> wrote: > >>On Thu, 11 Feb 2010 09:53:37 -0800, Jon Kirwan >><jonk(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
From: Jon Kirwan on 11 Feb 2010 17:42 On Thu, 11 Feb 2010 19:56:59 +0100, "Ban" <bansuri(a)web.de> wrote: >"Jon Kirwan" <jonk(a)infinitefactors.org> schrieb im Newsbeitrag >news:k6g8n5t1ma6ag352mncb3a2lm6c8oijs5c(a)4ax.com... >> On Thu, 11 Feb 2010 07:34:40 -0700, Jim Thompson >> <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> 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? >> >> Jon > >I like your approach coming from equations to analysing practical circuits. It's the thinking processes that I'd like to encourage in myself. Being able to deduce to specific cases from theory seems a vital part of not just copying others but being able to think on my own, at times. Of course, theory doesn't necessarily tell me what the constants are -- to get those, I can always scout for models... but as this part of this thread clearly shows, that only gets you within some very vague area. But theory remains VERY important all the same, even if in practice the detailed constants applied may be just about anything. Even with the same part numbers, as the recent discussion shows. >But then follows the verification with real parts. Yes! Of course. Theory can be used to deduce math models and models to express the math order of error terms ignored in them or the frequencies involved (for example, theory can tell you whether or not even order harmonics are possible from the deduction in hand), sans calibrated constants. To compute quantities, though, it helps either to have accurate model constants or else go to the bench and test out the facets you care about at the time. >I wouldn't worry with >small details, as long as the general idea is understood and followed. When >you have performed some measurements on real parts, it is good to understand >the important parameters, so you can tweak them yourself. I have some idea how to measure most useful parameters of BJTs. Problem is, it can be pretty hard to get for some. (Read: "work+equipment.") One of the things I'd like to do, when I get further along, is to design and build a BJT tester with a micro that can extract parameters and generate models at the EM1, EM2, EM3, and GP levels, at least. Maybe even VBIC, if I can grasp for it. That will teach me so much and I can take it in steps, so long as I can think out what I need in the first place. For example, I will need to be able to set voltages, monitor pin currents; or set currents, and monitor pin voltages; or just observe voltage after setting high impedance; etc. It would be nice to do a lot more than just curve tracing. And I'd learn a great deal from all this, spread out over a time by which I can assimilate each part in mind. Thanks, Jon
From: miso on 11 Feb 2010 20:46
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. When I've had the need to get such numbers, I would use an outside lab. They can actually profile the device, so you don't just see the net dopant, but how it changes. I've managed to discover a few trade secrets doing this. 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. |