Re: BJT Can be Considered a CCCS in some situations

From: Kevin Aylward (salesEXTRACT_at_anasoft.co.uk)
Date: 12/16/04 

Date: Thu, 16 Dec 2004 18:16:07 GMT

John Larkin wrote:
> On Thu, 16 Dec 2004 16:47:13 GMT, "Kevin Aylward"
> <salesEXTRACT@anasoft.co.uk> wrote:
>
>> John Larkin wrote:
>>> On Thu, 16 Dec 2004 09:24:13 +0000 (UTC), toor@iquest.net (John S.
>>> Dyson) wrote:
>>>
>>>> People who persist in claiming that a transistor is physically a
>>>> CCCS are of similar ilk as those who post (publish) various kinds
>>>> of nonsense theoretical nonsense on the physics groups.
>>>
>>> No, there's a big difference.
>>
>> Nonsense. John, you usually quite together, but you seem to be
>> missing the point. I shall phrase it to make it really clearly what
>> the issue is.
>>
>> What part of "...a transistor is not physically a CCCS..." did you
>> fail to understand?
>>
>
> What you may not understand is the I don't give a damn about device
> physics

I don't have a problem with that. The issue is that *my* statement has
*always* been about *device physics*. For the purposes of my statement I
don't care a dam, about any higher behavioural level model, so why
people keep bringing this up is beyond me. I was never discussing
circuit models.

>except as it occasionally helps me visualize device behavior
> in unusual situations, like maybe c-b junction reverse recovery or
> something. I don't design transistors, I design electronics, so I
> simply need working models appropriate to the situation. And as Jim
> notes, all device models are just varying degrees of imperfection.
>
>
>>> The beta model works, quantitatively, in
>>> 90% of design situations,
>>
>> No one is claiming that hfe is immaterial. One is discussing the
>> *intrinsic* device physics. What is the physical mechanism as to how
>> the transistor works. It is *physically* a VCCS. Period. End of
>> story.
>>
>
> I don't recall anybody discussing intrinsic device physics here.

Oh dear... Right from the bloody well start of the debate I did. It was
when I stated "the bipolar transistor is a voltage controlled device".

When anyone tried to steer it away, I restated exactly what I was
claiming. Many simply ignored this and continued debating something not
in debate.

> Nobody mentioned valence structures, Fermi levels, doping profiles,
> device geometry, anything remorely like that. A few people did present
> simplified cookbook equations for Ic versus Vbe, to which I presented
> some practical counter-cases where that model was grossly inadequate.
>
> Oh, the "end of story" thing is un-original and tedious.

And correct.

>
>
>> This makes no sense at all. The full equations work very well indeed.
>> That is, ones that treat base current as an effect of applied
>> voltage.
>
> Only at low currents, and at DC.

By this I assume you mean the the main spice models don't always have a
good fit for hfe at all current ranges.

>
>>>
>>>> Perhaps people who are
>>>> totally clueless will be influenced by the incorrect rhetoric, but
>>>> at least, it makes NO difference to the world that the idiots are
>>>> misled.
>>>
>>> I suppose "idiots" includes everyone who publishes bipolar
>>> transistor datasheets; I've never seen one that didn't specify beta.
>>>
>>
>> This is completely irrelevant to the question as to how the bipolar
>> transistor works.
>>
>> Time and time again, people just don't seem to understand the point
>> being made.
>>
>> for the last time, I will repeat the argument:
>
> Promise?

Yeah...

Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
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