Op-amps and Transistors

In article <SFJ1d.13213$_66.12055@fe1.news.blueyonder.co.uk>,
"Kevin Aylward" <salesEXTRACT@anasoft.co.uk> writes:
Ken wrote:
On Tue, 14 Sep 2004 09:51:27 GMT, "Kevin Aylward"
salesEXTRACT@anasoft.co.uk> wrote:


*All* transisters are voltage controled. End of story.
http://www.anasoft.co.uk/EE/index.html


Not according to your page either (Ib).

Ho hummm again. What part of "controlled" do you have trouble with?
Look, dude, the first order equation for transistor operation, derived
in any elementary text book on semiconductor physics, is:

Ie = Io(T).(exp(Vbe.q/KT) - 1)

Ic ~= Ie

Now, prey tell me, where is the base current in this equation?

The fact that some base current flows dose not mean that the base
current is a *controlling* factor. You need to appreciate the difference
between causal relations and correlated relations.

My guess is that beginners tend to see the approximately constant Beta as
Click to expand...
implying that 'Ic = Beta * Ib' is the controlling relationship.

I like to show the uselessness of Beta by trying to simulate a transient
circuit (even with the intrinsic capacitances included.) The Beta
model is just wrong. (Well, not quite WRONG, but so insufficient as
to being wrong :)).

John
 
Ken wrote:
?
I know of no transisters that are not voltage controlled.


All normal transistors like 2N2222, BC547, BC650, BC141
and many, many more.
The big current flowing trough the transistor is controlled
by the current (not voltage). I know that because
I constructing many electronic circuits since the 60:s
and do so even today. Ther are curves in the data books
that tells the relationships, and that's I'm using.
Click to expand...
The transistors do what they do regardless of how
we model them. Current control is algebraically
easy and a good enough approximation for many
purposes. Voltage control is very accurate but
mathematically more difficult.


--
local optimization seldom leads to global optimization

my e-mail address is: <my first name> <my last name> AT mmm DOT com
 
Roy McCammon wrote:
Ken wrote:
?
I know of no transisters that are not voltage controlled.


All normal transistors like 2N2222, BC547, BC650, BC141
and many, many more.
The big current flowing trough the transistor is controlled
by the current (not voltage). I know that because
I constructing many electronic circuits since the 60:s
and do so even today. Ther are curves in the data books
that tells the relationships, and that's I'm using.

The transistors do what they do regardless of how
we model them.
Click to expand...
In the bigger and grand schemes of things, there may well be many models
for the same phenomena, but this is in a different context then is being
used here.

Current control is algebraically
easy and a good enough approximation for many
purposes. Voltage control is very accurate but
mathematically more difficult.
Click to expand...
You still miss the point. The transistor is a voltage controlled derive,
irrespective of the engineering model. This is getting exasperating. Its
applying a *voltage* to the base and emitter that injects carriers into
the base, that are then swept up by the collector. The base current is
simply irrelevant. That is, the flow of base current does not *cause*
transistor action. Therefore, the transistor is *not* "controlled" by
base current. Its that simple!!!

Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
 
You still miss the point. The transistor is a voltage controlled derive,
irrespective of the engineering model. This is getting exasperating. Its
applying a *voltage* to the base and emitter that injects carriers into
the base, that are then swept up by the collector. The base current is
simply irrelevant. That is, the flow of base current does not *cause*
transistor action. Therefore, the transistor is *not* "controlled" by
base current. Its that simple!!!
Click to expand...

NO, the base emitter voltage turns on the diode they form, the amount of
current that flows through the junction determines the collector current.
Because we are dealing with a diode junction we can use the relationship
between voltage and current in a diode to model with transconductance
equations. We also use transconductance model with voltage controlled
current devices like mosfets. BUT, mosfets have no beta/hfe because they
are voltage controlled devices...


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Kevin Aylward wrote:

irrespective of the engineering model. This is getting exasperating. Its
Click to expand...
It must be your destiny to feel that way.


--
local optimization seldom leads to global optimization

my e-mail address is: <my first name> <my last name> AT mmm DOT com
 
"Kevin Aylward" <salesEXTRACT@anasoft.co.uk> wrote in message
news:Rl_1d.1690$U04.558@fe1.news.blueyonder.co.uk...
Roy McCammon wrote:
Ken wrote:
?
I know of no transisters that are not voltage controlled.


All normal transistors like 2N2222, BC547, BC650, BC141
and many, many more.
The big current flowing trough the transistor is controlled
by the current (not voltage). I know that because
I constructing many electronic circuits since the 60:s
and do so even today. Ther are curves in the data books
that tells the relationships, and that's I'm using.

The transistors do what they do regardless of how
we model them.

In the bigger and grand schemes of things, there may well be many models
for the same phenomena, but this is in a different context then is being
used here.

Current control is algebraically
easy and a good enough approximation for many
purposes. Voltage control is very accurate but
mathematically more difficult.

You still miss the point. The transistor is a voltage controlled derive,
irrespective of the engineering model. This is getting exasperating. Its
applying a *voltage* to the base and emitter that injects carriers into
the base, that are then swept up by the collector. The base current is
simply irrelevant. That is, the flow of base current does not *cause*
transistor action. Therefore, the transistor is *not* "controlled" by
base current. Its that simple!!!
Click to expand...
When you come right down to it, all currents are controlled, and generated,
by voltage. I think a certain Herr Ohm said something about this.

cap
 
Captain wrote:
"Kevin Aylward" <salesEXTRACT@anasoft.co.uk> wrote in message
news:Rl_1d.1690$U04.558@fe1.news.blueyonder.co.uk...
Roy McCammon wrote:
Ken wrote:
?
I know of no transisters that are not voltage controlled.


All normal transistors like 2N2222, BC547, BC650, BC141
and many, many more.
The big current flowing trough the transistor is controlled
by the current (not voltage). I know that because
I constructing many electronic circuits since the 60:s
and do so even today. Ther are curves in the data books
that tells the relationships, and that's I'm using.

The transistors do what they do regardless of how
we model them.

In the bigger and grand schemes of things, there may well be many
models for the same phenomena, but this is in a different context
then is being used here.

Current control is algebraically
easy and a good enough approximation for many
purposes. Voltage control is very accurate but
mathematically more difficult.

You still miss the point. The transistor is a voltage controlled
derive, irrespective of the engineering model. This is getting
exasperating. Its applying a *voltage* to the base and emitter that
injects carriers into the base, that are then swept up by the
collector. The base current is simply irrelevant. That is, the flow
of base current does not *cause* transistor action. Therefore, the
transistor is *not* "controlled" by base current. Its that simple!!!

When you come right down to it, all currents are controlled, and
generated, by voltage.
Click to expand...
Exactly. Fundermenatlly, there is a charge that produces a voltage
differance. This voltaege is usually referred to as an accelerating
voltage as it is this that accelerates other charges. The flow of charge
is an effect. However..., there is a somewhat subtle complication in
that all effects are due to an exchange of motion at a deeper level:)


Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
 
On Sunday 19 September 2004 10:58 pm, Le Chaud Lapin did deign to grace us
with the following:

"Kevin Aylward" <salesEXTRACT@anasoft.co.uk> wrote in message
news:<uaz1d.2387$846.928@fe2.news.blueyonder.co.uk>...
Well, I wouldn't go that far;-) I am really just trying to correct this
incredible widespread misconception that surrounds basic transistor
operation. Its potential differances that make charge move.

Base current is obviously something that needs to be accounted for.
Right off the bat, if your doing a power amp, you have to work out the
drive current from Iload/Hfemin.

Kevin is right. There is a subtlety here, and if you're not
-- ---
quasi-anal about how you let knowledge to get into your head, you
---------- implied "then" -^
might miss it.
----
Click to expand...

This means I have to be quasi-anal to get it.

;-)
Rich
 
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