Maintaining a Vbe Multiplier's bias value
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From: John Larkin on 10 Feb 2010 11:56 On Wed, 10 Feb 2010 08:35:04 -0800 (PST), George Herold <ggherold(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. �It�s 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?) If quiescent current exceeds peak load current, it's pretty much Class A. It could be symmetric, like a classic PNP-NPN class AB with tons of bias current, or asymmetric, like an emitter follower with a constant-current sink to ground. It's silly as much as any class A amp is silly: it wastes a lot of power. John
From: John Larkin on 10 Feb 2010 12:02 On Wed, 10 Feb 2010 10:43:22 -0600, "Tim Williams" <tmoranwms(a)charter.net> wrote: >"George Herold" <ggherold(a)gmail.com> wrote in message >news:b603649e-8d7c-4349-9edd-0f7ae3e6cffb(a)a5g2000yqi.googlegroups.com... >> Say can you make a push-pull stage run class A? (Or is that just a >> silly idea?) > >You can, but it stops being class A for large signal swings or low load >impedances. > >There's a monolithic structure which bends the output transistors' >characteristics so they never cut off. I forget who owns it. I suppose >that would count as class A at any signal/load condition. > >Tim The current mirror config, the one that uses the opamp rail currents to drive mirrors, can do that. If the top side mirror is pulling up the load, you can arrange for the bottom side to keep running at its quiescent current, as opposed to turning off and even off-er as the top side drives the load harder. Keeping both side on all the time has some nice dynamics when driving reactive loads. I don't know if that's still "class A". "A" is just a letter, after all. John
From: Jim Thompson on 10 Feb 2010 12:26 On Wed, 10 Feb 2010 09:02:50 -0800, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Wed, 10 Feb 2010 10:43:22 -0600, "Tim Williams" ><tmoranwms(a)charter.net> wrote: > >>"George Herold" <ggherold(a)gmail.com> wrote in message >>news:b603649e-8d7c-4349-9edd-0f7ae3e6cffb(a)a5g2000yqi.googlegroups.com... >>> Say can you make a push-pull stage run class A? (Or is that just a >>> silly idea?) >> >>You can, but it stops being class A for large signal swings or low load >>impedances. >> >>There's a monolithic structure which bends the output transistors' >>characteristics so they never cut off. I forget who owns it. I suppose >>that would count as class A at any signal/load condition. >> >>Tim > >The current mirror config, the one that uses the opamp rail currents >to drive mirrors, can do that. If the top side mirror is pulling up >the load, you can arrange for the bottom side to keep running at its >quiescent current, as opposed to turning off and even off-er as the >top side drives the load harder. Keeping both side on all the time has >some nice dynamics when driving reactive loads. > >I don't know if that's still "class A". "A" is just a letter, after >all. > >John And then there's SLIDING-class-A, which I've used successfully in hearing aids... better efficiency than class-B at really low voltages. ...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: Jon Kirwan on 10 Feb 2010 15:01 On Wed, 10 Feb 2010 07:46:16 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >On Tue, 09 Feb 2010 22:21:12 -0800, Jon Kirwan ><jonk(a)infinitefactors.org> wrote: > >>On Tue, 9 Feb 2010 20:55:07 -0800 (PST), "miso(a)sushi.com" >><miso(a)sushi.com> wrote: >> >>>I just lose interest if I have to look at ascii circuits. > >You really can't convey much more than a "basics" circuit with ASCII. >Post links or use LTspice listings... everyone seems to have that ;-) Agreed. Good advice, actually. In this case, the schematic _was_ pretty basic. But then the LTspice file would also have been similarly short, too. So it probably just makes sense, period. .... I had earlier been imagining what would be multiple views offered, so that others can choose their own poison more freely: (1) ASCII, where not crazy-minded, (2) GIF, JPG, or PNG schematic for browsing via http (3) as (2), but for associated signal/freq plots (4) .ASC file, for LTspice schematic/netlist (5) .NET file, where schematic layout isn't important (6) associated other inputs not in standard LTspice (7) PDF file documenting why and considerations (8) ZIP file boxing all this up in a package (9) .html page with clickable links and PDF info Looked like _work_ to me, though. ;) Jon
From: Jim Thompson on 10 Feb 2010 15:45
On Wed, 10 Feb 2010 12:01:02 -0800, Jon Kirwan <jonk(a)infinitefactors.org> wrote: >On Wed, 10 Feb 2010 07:46:16 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: > >>On Tue, 09 Feb 2010 22:21:12 -0800, Jon Kirwan >><jonk(a)infinitefactors.org> wrote: >> >>>On Tue, 9 Feb 2010 20:55:07 -0800 (PST), "miso(a)sushi.com" >>><miso(a)sushi.com> wrote: >>> >>>>I just lose interest if I have to look at ascii circuits. >> >>You really can't convey much more than a "basics" circuit with ASCII. >>Post links or use LTspice listings... everyone seems to have that ;-) > >Agreed. Good advice, actually. In this case, the schematic >_was_ pretty basic. But then the LTspice file would also >have been similarly short, too. So it probably just makes >sense, period. > >... > >I had earlier been imagining what would be multiple views >offered, so that others can choose their own poison more >freely: > > (1) ASCII, where not crazy-minded, > (2) GIF, JPG, or PNG schematic for browsing via http PNG and PDF are most readable and one or the other is marginally smaller depending on creating software tool. > (3) as (2), but for associated signal/freq plots > (4) .ASC file, for LTspice schematic/netlist > (5) .NET file, where schematic layout isn't important > (6) associated other inputs not in standard LTspice > (7) PDF file documenting why and considerations > (8) ZIP file boxing all this up in a package > (9) .html page with clickable links and PDF info > >Looked like _work_ to me, though. ;) > >Jon It always is ;-) ...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. |