Maintaining a Vbe Multiplier's bias value
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From: Phil Hobbs on 12 Feb 2010 10:03 On 2/12/2010 9:36 AM, Jim Thompson wrote: > On Thu, 11 Feb 2010 19:37:27 -0800, Jon Kirwan > <jonk(a)infinitefactors.org> wrote: > >> 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 > > The fish/fish rule ?:-) > > ...Jim Thompson Build a man a fire, you keep him warm for a night. Set a man afire, you keep him warm for the rest of his life. ;) 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
From: Phil Hobbs on 12 Feb 2010 10:23 On 2/12/2010 9:52 AM, Jim Thompson wrote: > On Thu, 11 Feb 2010 23:13:24 -0500, Phil Hobbs > <pcdhSpamMeSenseless(a)electrooptical.net> wrote: > >> 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 > > Close, but no cigar, LM395 = LM317 with some metal rearrangements. > I was thinking 317 but then I decided that the 395 was older than that. I guess not. > I did this analysis for ICE back in 1980: > > http://analog-innovations.com/SED/ICE-LM195-LM117.pdf > > Additionally: Amusing myself with the thoughts of complementary- > follower-style power amplifiers made from LM317/LM337 pairs, it fails > because both, internally, are NPN's pass devices, so the LM337 has GBW > and stability issues plus it needs substantial idle load to stay > _vaguely_ stable. Non-LDO three-terminal regulators are so trouble-free that it's easy to confuse them with Newton's laws. ;) 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
From: George Herold on 12 Feb 2010 10:53 On Feb 11, 11:18 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Thu, 11 Feb 2010 19:04:07 -0800 (PST), George Herold > > > > > > <ggher...(a)gmail.com> wrote: > >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. > > Usually two "NPN" tubes whose plates drive a center-tapped output > transformer. > > John- Hide quoted text - > > - Show quoted text - Ahh OK a transformer 'sums' the signals. Thanks, George h.
From: George Herold on 12 Feb 2010 11:16 On Feb 12, 9:52 am, Jim Thompson <To-Email-Use-The-Envelope-I...(a)My- Web-Site.com> wrote: > On Thu, 11 Feb 2010 23:13:24 -0500, Phil Hobbs > > > > > > <pcdhSpamMeSensel...(a)electrooptical.net> wrote: > >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 > > Close, but no cigar, LM395 = LM317 with some metal rearrangements. > > I did this analysis for ICE back in 1980: > > http://analog-innovations.com/SED/ICE-LM195-LM117.pdf > > Additionally: Amusing myself with the thoughts of complementary- > follower-style power amplifiers made from LM317/LM337 pairs, it fails > because both, internally, are NPN's pass devices, so the LM337 has GBW > and stability issues plus it needs substantial idle load to stay > _vaguely_ stable. > > ...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 athttp://www.analog-innovations.com| 1962 | > > I love to cook with wine. Sometimes I even put it in the food.- Hide quoted text - > > - Show quoted text - Thanks Jim, I always wondered why there wasn't a compliment to the LM395. (And why the negative voltage regulators would 'wig out' if you didn't follow the cap reccomendations.) George H.
From: John Larkin on 12 Feb 2010 11:23
On Fri, 12 Feb 2010 10:23:24 -0500, Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >On 2/12/2010 9:52 AM, Jim Thompson wrote: >> On Thu, 11 Feb 2010 23:13:24 -0500, Phil Hobbs >> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >> >>> 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 >> >> Close, but no cigar, LM395 = LM317 with some metal rearrangements. >> >I was thinking 317 but then I decided that the 395 was older than that. > I guess not. > >> I did this analysis for ICE back in 1980: >> >> http://analog-innovations.com/SED/ICE-LM195-LM117.pdf >> >> Additionally: Amusing myself with the thoughts of complementary- >> follower-style power amplifiers made from LM317/LM337 pairs, it fails >> because both, internally, are NPN's pass devices, so the LM337 has GBW >> and stability issues plus it needs substantial idle load to stay >> _vaguely_ stable. > >Non-LDO three-terminal regulators are so trouble-free that it's easy to >confuse them with Newton's laws. ;) > >Cheers > >Phil Hobbs LM1117 is an "MDO" regulator. It has an NPN pass transistor but a bit lower dropout voltage than an LM317. Its ideal as a 3.3-to-1.25 volt FPGA core voltage source... no resistors! My purchasing notes say "Do not buy Fairchild per JL" but I can't recall why. As with all vregs, one has to be careful about the output capacitors. John |