Re: BJT Can be Considered a CCCS in some situations
From: John Larkin (jjlarkin_at_highlandSNIPtechTHISnologyPLEASE.com)
Date: 12/16/04
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Date: Thu, 16 Dec 2004 09:04:31 -0800
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 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.
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.
>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.
>>
>>> 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?
>
>********
>The reality is that collector charge motion is not the result of base
>charge *motion*, but simply the fact that applying a voltage at the base
>emitter causes charge to move from the emitter. It is *not* *motion* of
>base charge that instigates the motion of charge from the emitter. Any
>charge in the emitter will automatically move when subject to an
>electric field. Since *motion* of base charge is *not* required to cause
>*motion* of the *emitter charge*, the transistor cannot be (charge)
>motion
>controlled, i.e. base current controlled.
>************
>
>The point is about intrinsic device *physics* not about data sheet
>values and when and when not to include beta in the calculations.
This is not a physics newsgroup.
John
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