Maintaining a Vbe Multiplier's bias value
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From: Tim Williams on 10 Feb 2010 01:15 <miso(a)sushi.com> wrote in message news:692726fc-bf7b-4fc7-bee3-e51e2706f81e(a)z39g2000vbb.googlegroups.com... > You realize you can just string diodes. Nobody says you have to VBE > multiply. It's just one of many biasing techinques. They don't make diodes with pots varying Eg. ;-) Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Jon Kirwan on 10 Feb 2010 01:21 On Tue, 9 Feb 2010 20:55:07 -0800 (PST), "miso(a)sushi.com" <miso(a)sushi.com> wrote: >On Feb 9, 2:44�am, Jon Kirwan <j...(a)infinitefactors.org> wrote: >> On Mon, 8 Feb 2010 18:23:16 -0800 (PST), "m...(a)sushi.com" >> >> <m...(a)sushi.com> wrote: >> ><snip> >> >Less words and real schematics would get you more readers. [The only >> >thing worse than ascii equations are ascii schematics.] >> >> ASCII is what I'll post. �It's the only way to get them >> archived or properly posted to a text newsgroup. �I no longer >> have access to the binary for schematics, sadly. �If I lose >> some people because they cannot manage fixed-spaced fonts, I >> guess I lose them. �I could place links up on my domain, I >> suppose. �But in this case, the schematics are really very >> basic and not overly burdensome in ASCII. �Besides, Win Hill >> posted some really nice examples here, before. �Folks seemed >> to live with that. �Not sure why you are picking on me, here. >> >> >In any event, just google improved vbe multiplier. I've seen all sorts >> >of circuits published to get lower impedance at the nodes. >> >> Okay. �I'll do that if folks here aren't interested at all in >> talking about it. >> >> Jon > >There are all sorts of free places to post images. Imageshack comes to >mind. I just lose interest if I have to look at ascii circuits. I have a domain I can use. It is just that it hardly seemed necessary, given the simplicity involved and the fact that this group is quite used to ASCII schematics, given the years I've been watching here. It has advantages in that it is archived for very long times, this way, as well. However, I will try and take your concerns into account and see about organizing a directory and smoothing through issues of dropping files there which have been massaged and arranged for easier viewing. >You realize you can just string diodes. Nobody says you have to VBE >multiply. It's just one of many biasing techinques. Yes, I think that's been well-posted in the thread and I was aware of it, before. It's one of the first things I saw when starting on this trek 2 weeks back. Hard to miss. The issue is more about learning, though. Not picking a specific solution and ignoring the others. I'd like to have some spectrum of options I've looked at well and discarded (as well as retained.) Jon
From: Jon Kirwan on 10 Feb 2010 01:22 On Wed, 10 Feb 2010 00:15:07 -0600, "Tim Williams" <tmoranwms(a)charter.net> wrote: ><miso(a)sushi.com> wrote in message >news:692726fc-bf7b-4fc7-bee3-e51e2706f81e(a)z39g2000vbb.googlegroups.com... >> You realize you can just string diodes. Nobody says you have to VBE >> multiply. It's just one of many biasing techinques. > >They don't make diodes with pots varying Eg. ;-) > >Tim :) Jon
From: Bitrex on 10 Feb 2010 03:41 Jim Thompson wrote: > On Tue, 09 Feb 2010 14:50:50 -0800, Jon Kirwan > <jonk(a)infinitefactors.org> wrote: > >> On Tue, 09 Feb 2010 15:42:48 -0700, Jim Thompson >> <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote: >> >>> What in the world ?:-) >> View in fixed-spaced font. And it's a rendition of the >> schematic that Bob Monson had posted, earlier, from EDN. He >> wrote, "On a related note, there was an article in a recent >> EDN about a self biasing preamp which was kinda cool. Instead >> of trying to track the difference using diodes or a >> multiplier, it used a couple of transistors and an opamp to >> set the correct values at the bases of the pass transistors. >> It was so novel (at least to me) that I typed it into >> LTSpice." >> >> I merely re-arranged it in LTspice to be a little more to my >> taste and then passed it through a program that generates >> ASCII from that. >> >> Jon > > Burr-Brown was famous for using bias compensation like that in the > front ends of some of their operational amplifiers, but I doubt its > efficacy in power output stages. > > The Burr-Brown scheme is similar to a discussion here a few (seven :-) > years ago... > > http://analog-innovations.com/SED/IB-Cancellation-WithTwoOpAmps.pdf > > ...Jim Thompson Could you give a quick explanation of how the circuit in the link works? I'm having a bit of trouble following what's going on...
From: Jon Kirwan on 10 Feb 2010 06:07
On Tue, 9 Feb 2010 17:58:30 -0800, "Bob Monsen" <rcmonsen(a)gmail.com> wrote: >"Jon Kirwan" <jonk(a)infinitefactors.org> wrote in message >news:1g34n513mhonq98prjqeggc6h15mtplfu2(a)4ax.com... >> On Tue, 09 Feb 2010 17:13:50 -0800, I wrote: >> >>>>BTW, do you have a link to that cool LTSpice -> ASCII program? I'd >>>>forgotten >>>>that you wrote it. I've been laboring over a hot 'andy's ascii' program >>>>for >>>>schematics that I already have in LTSpice... >>> >>>Hehe. Sure. >> >> Sorry... I didn't stick in the link. Because it isn't set >> up well, right now. Let me fix that and post it up and then >> I will add the link. >> >> Jon > >No hurry. Thanks, Bob Monsen It's at: http://www.infinitefactors.org/misc/asc.zip It contains just two files, the EXE and a library symbol file. Place both in some directory that is in the path. You need to use DOS, sadly. I didn't set these up for Windows -- wanted to focus on the task, not get mired in Windows sideshows. If you run the program without a filename, it will say: >: asc version 1.2.1, (library C:\TOOLS\BIN\ASC.SYM found) >: >: This program converts LTSpice schematics into ASCII schematic output (or >: files.) If you specify no files at all, it accepts the LTSpice schematic >: from its standard input device. If you specify exactly one file, it dis- >: plays the ASCII schematic output to the standard output device. If you >: specify more than one file, it then generates .TXT files otherwise having >: the same name as the specified schematics. >: >: These options are supported: >: +h requests this help message, -h disables it. >: +r enables rectangle drawing, -r disables it (default is -r) >: +c enables clipboard copying, -c disables it (default is -c) >: +c<char> enables clipboard copying and prepends <char> to each line >: >: Usage: asc <options> <filename> [<filename>]... There are some options, like the clipboard. But post Win2000, that mechanism was broken and I haven't set up the additional DLL I'd need to remedy it. (Something I may yet take care of.) So under WinXP, for example, I just run it into a file and use notepad to call it up. Something like: ASC amplify.asc >amplify.txt NOTEPAD amplify.txt It gets the job done. Under Win98SE, I just use the +c option and then paste the text, as desired, in Windows. The library is semi-okay. There's some symbols I've probably not yet added to it because I don't use the parts that much. I won't mind extending it (it's not hard to do) if there is anything you use and would like put in. I just use a text editor and hack in the new ASCII and then save it. The program automatically parses it every time it runs. Jon |