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Article #15426Re: Query - How valves and transistors work
From: Roy McCammon
Date: Sun, 03 Jan 1999 00:00
Date: Sun, 03 Jan 1999 00:00
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3142 bytes
Duncan Barclay wrote: > > In article <76ja03$gud$1@news-2.news.gte.net>, > Doug <do@not.spam> writes: > > Duncan Barclay wrote: > >> > >> This thread started with someone (Nightjar) asking how they worked. > >> Out of four replies I followed up on one thread was not asking how > > > > Getting back to NightJar ... > > > > BJTs can be thought of a CURRENT CONTROLLING DEVICES > > and valves can be thought of VOLTAGE CONTROLLING DEVICES. > > > > BJTs offer variations in the emitter-base CURRENT controlling > > variations in emitter-collector CURRENT. > This is NOT correct. > > How does this explain the way a long-tailed pair works? > > A BJT allows you to control a current by varying the base emitter > voltage. > > Certain circuit configurations make it appear that you can control the > collector current by changing the base current. But as this ratio > varies with temperature, device, process, batch, which direction the > circuit board is facing, it's not very useful. I think Doug said "current controlling", not "current controlled" which I take to mean that the output of a bjt is modeled as a current output rather than a voltage output. That would apply whether you viewed the bjt as a current (beta) amplifier or a transconductance (gm) amp. I agree that when I am analyzing a circuit for gain, margin, or stability, I think of the bjt's as transconductance amps, but when I am just trying to figure out how the circuit works, I just consider bjt's as current amps (beta).
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X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 114713,6f59d673fceaf3aa X-Google-Attributes: gid114713,public X-Google-Thread: 10b271,6f59d673fceaf3aa X-Google-Attributes: gid10b271,public X-Google-Thread: 107d45,6f59d673fceaf3aa X-Google-Attributes: gid107d45,public X-Google-Thread: 112d1e,6f59d673fceaf3aa X-Google-Attributes: gid112d1e,public X-Google-Thread: 1110fe,6f59d673fceaf3aa X-Google-Attributes: gid1110fe,public X-Google-Thread: 1118be,6f59d673fceaf3aa X-Google-Attributes: gid1118be,public X-Google-Thread: 111d0a,6f59d673fceaf3aa X-Google-Attributes: gid111d0a,public X-Google-Thread: fcc1a,6f59d673fceaf3aa X-Google-Attributes: gidfcc1a,public From: Roy McCammon <rbmccammon@ieee.org> Subject: Re: Query - How valves and transistors work Date: 1999/01/03 Message-ID: <369027B3.6090E241@ieee.org> X-Deja-AN: 428494954 Content-Transfer-Encoding: 7bit References: <368691bc.0@stargazer.actinet.net> <76b08g$jo4$1@news-1.news.gte.net> <76b8i0$rqm$1@computer.my.domain> <fuNEGVAumei2EwR5@jmwa.demon.co.uk> <76dss3$fhq$1@computer.my.domain> <d1dLzCAjKri2EwAr@jmwa.demon.co.uk> <76ibj9$rhc$1@computer.my.domain> <76ja03$gud$1@news-2.news.gte.net> <76jqau$ltt$1@computer.my.domain> Organization: MindSpring Enterprises X-Server-Date: 4 Jan 1999 02:29:51 GMT Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 Reply-To: rbmccammon@ieee.org Newsgroups: sci.physics,fj.sci.physics,sci.physics.electromag,tnn.physics,news.electronics.basics,sci.electronics.basics,sci.electronics.components,sci.electronics.design,sci.electronics.misc