🚀 go-pugleaf

<368ea7ed.26792224@news.u-net.com>, Jonathan Bromley
<jonathan@oxfordbromley.u-net.com> wrote:
>What an odd discussion for entirely rational folk to be engaged in!

I don't think it's anny oder than previous long wrangles......
>
>Even odder for me to side with Gareth Alun Evans, 

....especially the one with this redoubtable Cymro. It would appear that
DB shares much of his attitude: 'I am absolutely right, and all you
people who are only 99% right had better fall into line.'

[bigsnip]
>It is truly futile to have a religious war about whether 
>Ic=Hfe.Ib or Ic=Io.exp(Vbe. e/kT)  is the more appropriate
>description of BJT action.  Both are correct (or, more
>precisely, both are approximations that are good enough 
>to be useful in a wide range of cases).  Most designers
>make use of both.

Exactly: my gripe and that of others is that Mr. B won't accept that:
it's VCCS or nothing.
>
>However, it is VERY important to note that the first
>(Hfe, current-gain) description is intimately tied
>to details of the particular transistor's construction
>and so if you design a circuit that depends on a particular
>value of Hfe it will probably let you down when you use
>transistors near the edges of the gain spread. 
[snip]

I don't think anyone has denied that. I would put it as the second topic
in Transistors 001: first Ic is proportional to Ib and second Ic/Ib
varies typically 4:1 between transistors of the same type. In
transistors 001, many of the students do not know what an exponential
is, so one couldn't start with Ic/Vbe.

>For what it's worth, when I first look at a new circuit
>I generally try to decide whether it's linear or
>saturating.  If linear, then I find the exponential
>(VCCS, transconductance) model is often the best 
>starting point.  Your mileage may vary.

Again, I don't think anyone has denied that - for LTPs and Gilbert
cells. But for a simple voltage amplifier (i.e., before someone queries
that, I mean an amplifier whose power gain is mostly the result of
voltage gain), the *concept* of VCCS gives a pessimistic impression of
the likely linearity - until you calculate it (laboriously, of course,
unless...).

-- 
Regards, John Woodgate, Phone +44 (0)1268 747839 Fax +44 (0)1268 777124. 
OOO - Own Opinions Only. You can fool all of the people some of the time, but 
you can't please some of the people any of the time.