Author Topic: Current controlled device vs voltage controlled?  (Read 14109 times)

0 Members and 1 Guest are viewing this topic.

Online 2N3055

  • Super Contributor
  • ***
  • Posts: 2113
  • Country: hr
Re: Current controlled device vs voltage controlled?
« Reply #50 on: February 16, 2017, 10:08:49 pm »
This is simple misunderstanding.

"current controlled" and "voltage controlled" were never meant to be exact technical and physical explanation of exact physical phenomena inside transistor.

It is a simplification, from introductory texts, to draw attention to difference between bipolar and field effect devices. And it was mentioned only in regards of static operation.

My professor used to say that bipolar was called "current controlled" to help us remember that in a circuit we will have to account that at static operating point we will have a current going into the base (or out of ) as opposed to "voltage controlled" field effect devices that will not draw (or source) any mentionable current from the gate. And in making a circuit , we have to be mindful of that and account for it.

And that is all.  At AC all bets are off, so we have real models for that...

One "current controlled" device I know of is magnetic relay... 

And current and voltage is chicken and egg question.. They are inextricable from each other..

2N3055 - I am afraid you are in error.
Are you aware that you did nothing than to repeat a claim of your professor - without any attempt to justif your "belief" (it is nothing else).

And you kind of repeat yourself..

And I used my professor's quote because I can't say it better.. I don't like reinventing wheel...

I think you failed to understand what I wanted to say. 
My stance (not a belief) is that those two terms are wrong, imprecise and of "linguistic nature" and should not be taken as a scientific statement of any sort. 

If anything I agree with you.

Current doesn't activate bipolar transistor, Vbe does, but current WILL flow into base , and on a MOSFET it won't flow in a gate (static operating point, disregards charging of capacitances).
That is why some call it "current" or "voltage" to make that distinction... It's not explanation how it works but what it does.. And as I said, we used it only in that context, and only in an introductory course.. And my stance is that it was useful for that purpose at the time.

Your stance (or belief) is that there is no red color, but only 660 nm wavelength electromagnetic radiation.. I agree and understand your point.. But I will order red roses for my wife, because it is an OK approximation for that purpose... And I do order 660nm LED, or a laser.  So tool for the job.  Details and precision when appropriate...

It seems to me that you are confusing electronics engineers with theoretical solid state physicists and research scientists.. 
Many of us only use transistors, not many of us here work for semiconductor manufacturers and actually design and make transistors and ICs from silicon wafers. In engineering, simplification is welcome friend where appropriate.. Of course, only when appropriate...

I would like to thank you very much for invigorating discussion... It is nice to see people thinking hard and having passion about electronics...

Best regards,

Sinisa



 

Offline rfeecs

  • Frequent Contributor
  • **
  • Posts: 678
  • Country: us
Re: Current controlled device vs voltage controlled?
« Reply #51 on: February 17, 2017, 12:49:51 am »
This quote comes from Barrie Gilbert - one of the worlds most known designer and inventor of novel BJT applications .

A little bit OT, but Barrie Gilbert developed a number of "current mode" circuits.  (Good thing he didn't call them "current controlled").

Here is his paper "Current Mode, Voltage Mode, or Free Mode? A Few Sage Suggestions":
http://cas.ee.ic.ac.uk/people/dario/files/E416/gilbert-voltagemode-currentmode.pdf

Here is a great issue of IEEE SSCS dedicated to Barry Gilbert  with some interesting articles by him about his early life as an engineer, including the development of "current mode" circuits.  It also contains a full reprint of his paper describing his famous four quadrant multiplier, a prime example of a "current mode" circuit.  Interesting that almost every equation describing it contains relations between the transistor currents.:
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0ahUKEwj0-6z56JXSAhVJKyYKHU1ZDOMQFgglMAI&url=https%3A%2F%2Fwww.researchgate.net%2Ffile.PostFileLoader.html%3Fid%3D579ea28196b7e4872c4b79df%26assetKey%3DAS%253A390081484476416%25401470014081253&usg=AFQjCNFYXLul1orNXZlzXj6Jmr9AUCwtZQ&sig2=gtgn_2eD6SGRlfq6MjN0zQ&bvm=bv.147448319,d.eWE

This is despite the fact that the only true way to look at it is those currents are the result of applied voltages.  There are no current sources.  Everything is controlled by voltage.  This is a fundamental law of the universe.  :blah: :blah: :blah:
 

Offline LvW

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: de
Re: Current controlled device vs voltage controlled?
« Reply #52 on: February 17, 2017, 07:54:48 am »

It seems to me that you are confusing electronics engineers with theoretical solid state physicists and research scientists.. 
Many of us only use transistors, not many of us here work for semiconductor manufacturers and actually design and make transistors and ICs from silicon wafers. In engineering, simplification is welcome friend where appropriate.. Of course, only when appropriate...
.......
I would like to thank you very much for invigorating discussion... It is nice to see people thinking hard and having passion about electronics...
Sinisa

Hi Sinisa - thank you for the last sentence. You have used the word "discussion", which - to me - means: Questions and answers, OK?
Therefore, I like to ask the following two questions:
1.) In which post I have made "confusing" explanations with "theoretical solid state physicists and research scientists" ?

2.) Regarding "simplification": All formulas and design strategies contain simplifications - this cannot be avoided.
Now my question: Can you agree that there is a big differeence between (a) simplifications (neglecting some minor influences) and (b) two different explanations for the working principle of a device ?

Comment: This difference wouldn`t matter too much if  it would not lead to some observable contradictions. However - as I have mentioned several times (but nobody reacts upon it) - there are many observable/measurable effects and circuit properties which can be explained with voltage control only: Transconductance, gain formula, RE-feedback, Early-effect, tan-h curve for diff. amplifier,....

I have some experience in teaching electronic fundamentals - and it has happened rather often that students came to me with questions like:
* Different books contain different explanations for the BJT`s working principle - which one is correct?
* How can the effect of RE-feedback be explained based on the assumption of current control?
* The voltage gain of a transistor stage does not depend on B resp. beta (same dc quiescent point) - how can the BJT be current-controlled?

That`s the reason I don`t think, the whole subject is a matter of "simplification" only - do you understand my point?


« Last Edit: February 17, 2017, 07:56:20 am by LvW »
 

Offline MrAl

  • Frequent Contributor
  • **
  • Posts: 481
Re: Current controlled device vs voltage controlled?
« Reply #53 on: February 17, 2017, 08:28:53 am »
This quote comes from Barrie Gilbert - one of the worlds most known designer and inventor of novel BJT applications .

A little bit OT, but Barrie Gilbert developed a number of "current mode" circuits.  (Good thing he didn't call them "current controlled").

Here is his paper "Current Mode, Voltage Mode, or Free Mode? A Few Sage Suggestions":
http://cas.ee.ic.ac.uk/people/dario/files/E416/gilbert-voltagemode-currentmode.pdf

Here is a great issue of IEEE SSCS dedicated to Barry Gilbert  with some interesting articles by him about his early life as an engineer, including the development of "current mode" circuits.  It also contains a full reprint of his paper describing his famous four quadrant multiplier, a prime example of a "current mode" circuit.  Interesting that almost every equation describing it contains relations between the transistor currents.:
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0ahUKEwj0-6z56JXSAhVJKyYKHU1ZDOMQFgglMAI&url=https%3A%2F%2Fwww.researchgate.net%2Ffile.PostFileLoader.html%3Fid%3D579ea28196b7e4872c4b79df%26assetKey%3DAS%253A390081484476416%25401470014081253&usg=AFQjCNFYXLul1orNXZlzXj6Jmr9AUCwtZQ&sig2=gtgn_2eD6SGRlfq6MjN0zQ&bvm=bv.147448319,d.eWE

This is despite the fact that the only true way to look at it is those currents are the result of applied voltages.  There are no current sources.  Everything is controlled by voltage.  This is a fundamental law of the universe.  :blah: :blah: :blah:

Hi,

An interesting read or two.  I like the use of the word "sage" which according to the context of the paper would mean: "wise, especially as a result of great experience".

He starts from the perspective of *energy* also (sound familiar?), and digresses into current and/or voltage due to the fact that although energy is the prime mover we often simplify by assuming one or the other as a matter of convenience.
He also notes that current and voltage are translated through what we call resistance.
« Last Edit: February 17, 2017, 08:30:31 am by MrAl »
 

Offline LvW

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: de
Re: Current controlled device vs voltage controlled?
« Reply #54 on: February 17, 2017, 08:29:22 am »
Hi MrAl,
I think your long reply deserves, of course, an answer. 

First about the emitter resistor...
I will say what i have said all along for the practical case, and that is that the type of analysis depends on what we want to know. In some cases it is easier to use a voltage based equation and sometimes it is easier to use a current based equation.

Here, the "case" is: How can we explain the stabilization effect of RE?.
Why didn`t you give a direct answer to this technical question?
Up to now - nobody from the "current-control party" has answered this simple question (let alone other questions regarding transconductance, etc).

I realize that it is sort of a convention of sorts though to call something voltage controlled.  But i would bet we can not find one practical circuit that does not vary the voltage at the gate or base and thus the current as well.
I think, nobody (including me) has denied the existence of a base current. But - does this automatically means that this current does physically controls (determines) the collector current? Remember how the simple relation Ic=B*IB came into being:
Because of IC=alpha*IE we have IB=(1-alpha)*IE and IB=[(1-a)/a]IC=(1/beta)IC.
Physically, this means: IB is a small part of IC.  Of course, we can rewrite the relation as IC=beta*IB - but this does not automatically allow us to interpret this as a ocntolling function (in the sense of "cause and effect").

So what do you say about the two coil or magnet example and the magnetic field?  Are the two magnets "field controlled" or not?

I am sorry, I cannot say anything to this example. I am not familiar with this subject - and, at the moment, I have not enough time to think about it (with the aim to give a substantial answer).
Regards
LvW
 

Offline MrAl

  • Frequent Contributor
  • **
  • Posts: 481
Re: Current controlled device vs voltage controlled?
« Reply #55 on: February 17, 2017, 08:41:33 am »
Hi MrAl,
I think your long reply deserves, of course, an answer. 

First about the emitter resistor...
I will say what i have said all along for the practical case, and that is that the type of analysis depends on what we want to know. In some cases it is easier to use a voltage based equation and sometimes it is easier to use a current based equation.

Here, the "case" is: How can we explain the stabilization effect of RE?.
Why didn`t you give a direct answer to this technical question?
Up to now - nobody from the "current-control party" has answered this simple question (let alone other questions regarding transconductance, etc).

I realize that it is sort of a convention of sorts though to call something voltage controlled.  But i would bet we can not find one practical circuit that does not vary the voltage at the gate or base and thus the current as well.
I think, nobody (including me) has denied the existence of a base current. But - does this automatically means that this current does physically controls (determines) the collector current? Remember how the simple relation Ic=B*IB came into being:
Because of IC=alpha*IE we have IB=(1-alpha)*IE and IB=[(1-a)/a]IC=(1/beta)IC.
Physically, this means: IB is a small part of IC.  Of course, we can rewrite the relation as IC=beta*IB - but this does not automatically allow us to interpret this as a ocntolling function (in the sense of "cause and effect").

So what do you say about the two coil or magnet example and the magnetic field?  Are the two magnets "field controlled" or not?

I am sorry, I cannot say anything to this example. I am not familiar with this subject - and, at the moment, I have not enough time to think about it (with the aim to give a substantial answer).
Regards
LvW

Hi again,

(Bipolar RE) What kind of answer are you looking for here, i would be happy to reply again :-)
But real quick, cant that be answered on the basis of the voltage difference across the base resistor (keeping the circuit simple) and that happens even if we keep the Vbe completely *constant* with no change in that itself.  That would immediately tell us that Vbe is not doing much if anything at all.  I will rectify this though if you want a different kind of answer.

Also, I posted one more time before your most recent reply, where i noted that in that Gilbert paper he starts from the perspective of *energy*.  Now why would anyone want to go and do something like that :-)

I am happy you are sticking with this as your interest is appreciated and your view is of course interesting as well.

 

Offline LvW

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: de
Re: Current controlled device vs voltage controlled?
« Reply #56 on: February 17, 2017, 08:47:55 am »
A little bit OT, but Barrie Gilbert developed a number of "current mode" circuits.  (Good thing he didn't call them "current controlled").

I know these papers - and some others dealing with the same subject.
However - I think, we clearly must distinguish between "circuits" and a single part like a "transistor".
Of course, there are complete circuits which we operate in a mode called "current mode" (Current conveyor, current-feedback amplifier,..) .
However, we are describing these circuits - more or less - from a practical point of view  (independent on transistor physics).
Summary: All of these papers do not provide any arguments for or against the working principle of a single transistor.

What is, in this context, the meaning of "practical"?
Simple example: Even all "defenders" of BJT`s current control consider an opamp (with a BJT input stage) as a voltage-controlled circuit. Why? Because - from the practical point of view - it makes sense (and is allowed in most cases) to neglect the input current (although they believe that this current is the controlling quantity). Do you understand what I mean? 
 
 

Offline LvW

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: de
Re: Current controlled device vs voltage controlled?
« Reply #57 on: February 17, 2017, 08:59:22 am »
(Bipolar RE) What kind of answer are you looking for here, i would be happy to reply again :-)

MrAl, I am sure, you will be not surprised to read my answer:
Any unwanted IC increase (temperature, tolerances) above the design value will increase the emitter voltage VE=IE*RE and, thus, reduce the base-emitter voltage VBE. This assumes a relatively constant ("stiff") base voltage VB. And exactly THIS requirement is the reason we design a voltage divider (for providing VB) with resistors which are as low as possible (rule of thumb: Divider current 10*IB) - with respect to other design constraints (power consumption, circuits input resistance). Where is the role of the (controlling?) base current?
I think, these are the commonly accepted and applied design rules - am I wrong?
In this context, I like to remind you again to my attachements in post#27. Both figures show and explain what`s really happening and how the bias points are determined.

(One final comment. You wrote: "I am happy you are sticking with this as your interest is appreciated and your view is of course interesting as well."
I like to mention that this is not only "my view" - this view is shared by high-quality books (e.g. Art of Electronics) and leading US-universities.)
« Last Edit: February 17, 2017, 10:09:28 am by LvW »
 

Offline MrAl

  • Frequent Contributor
  • **
  • Posts: 481
Re: Current controlled device vs voltage controlled?
« Reply #58 on: February 17, 2017, 01:45:15 pm »
(Bipolar RE) What kind of answer are you looking for here, i would be happy to reply again :-)

MrAl, I am sure, you will be not surprised to read my answer:
Any unwanted IC increase (temperature, tolerances) above the design value will increase the emitter voltage VE=IE*RE and, thus, reduce the base-emitter voltage VBE. This assumes a relatively constant ("stiff") base voltage VB. And exactly THIS requirement is the reason we design a voltage divider (for providing VB) with resistors which are as low as possible (rule of thumb: Divider current 10*IB) - with respect to other design constraints (power consumption, circuits input resistance). Where is the role of the (controlling?) base current?
I think, these are the commonly accepted and applied design rules - am I wrong?
In this context, I like to remind you again to my attachements in post#27. Both figures show and explain what`s really happening and how the bias points are determined.

(One final comment. You wrote: "I am happy you are sticking with this as your interest is appreciated and your view is of course interesting as well."
I like to mention that this is not only "my view" - this view is shared by high-quality books (e.g. Art of Electronics) and leading US-universities.)

Hi,

Am i wrong or does it seem like you wont accept any current based theory on the bipolar transistor?
It seems like you are just against any analysis that uses current as a basis for the calculations, such as feedback and bias.
I am probably wrong here, but it would be good to hear YOUR version of a current based theory on say how to bias the transistor.  Did you actually ever use one based on current?
I ask because i would like to hear your view on when we can use current based models/calculations.

As to the references you posted, i will check those out ASAP maybe i missed something.
But i can tell you that sometimes theory is not quite stated correctly or rather i should say 'completely'.  For example, in theory sometimes a short is not a zero Ohms resistance, sometimes it can be both a zero Ohms resistance and an open circuit at the same time.  This is interesting too because for current we consider this kind of short a zero Ohm resistance but for voltage we consider it an open circuit.  In the wording of the theory however it will not say anything except "short".
This brings up another question though, and that is what did you think about Gilbert's idea of "current mode" and "voltage mode", why do you think he called them that?


LATER:
In #27 it looks like you are saying that the change in Vbe is small?  Perhaps you can clarify.
I was going to suggest a mechanical model that can be easily understood which is like an analogy to the BJT.
If we have a large lever with a fulcrum with a sharp edge, one end of the lever goes down when we press down on it and the other end goes up.  If the end we press on has length 2 meters from the fulcrum and the other end has length 20 meters, when we press down 1cm on the 2 meter end the 20 meter end goes up by 10cm.  It's a simple gain in distance.
Now we change the fulcrum to one that has a logarithmic or exponentially shaped top surface rather than a sharp edge and it relatively short (say 1cm which is valid).  When we press on the 2 meter end now we get not only the gain of 10 as before, but the strange top causes an extra lift at the center thereby raising the end a little more.  But more to the point, the lever beam tracks the fulcrum strange surface as it tilts, and thus we can map out the behavior based on the position of where the lever beam TOUCHES the new fulcrum top surface, and there will be a one to one correspondence of that position to the height of the 20 meter end.
Now in the Vbe view of the transistor as compared to this lever, we would be looking at the minute change in position along the short topped fulcrum in order to calculate the height of the 20 meter end.  Does that make sense?  I dont think so.  It  is completely valid, in theory, to do so, but it just doesnt make sense.  It is better to track the 2 meter end and thereby compute the height of the 20 meter end.
« Last Edit: February 17, 2017, 02:05:18 pm by MrAl »
 

Offline LvW

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: de
Re: Current controlled device vs voltage controlled?
« Reply #59 on: February 17, 2017, 03:15:36 pm »
Am i wrong or does it seem like you wont accept any current based theory on the bipolar transistor?
It seems like you are just against any analysis that uses current as a basis for the calculations, such as feedback and bias.
I am probably wrong here, but it would be good to hear YOUR version of a current based theory on say how to bias the transistor.  Did you actually ever use one based on current?
I ask because i would like to hear your view on when we can use current based models/calculations.

The answer is very simple (and I gave it already in my post#27):
(For your convenience, here I repeat my steps for designinmg a simple emitter stage using the currents IC, IE and IB)

Design steps (common emitter stage with DC stabilization, Vcc given):
* Select IE (resp. IC) and collector/emitter resistors RC resp. RE,
* Calculate required base voltage VB - based on VE=IE*RE - and assuming a VOLTAGE VBE=(0.65...0.7) volts.
* Design voltage divider (rule of thumb: Divider current > 10*IB=10*IC/B).
* Voltage gain: G=-gm*RC/(1+gm*RE)
* Transconductance gm=d(IC)/d(VBE)=IC/VT (using the exponenetial equation IC=f(VBE)
* Voltage gain does NOT depend on B (same DC quiescent point)

Question: Current control? Does everybody realize WHY we normally have select a divider current of of app. 10*IB ? (Answer: Because we want that the value of IB resp. the uncertainties/tolerances of IB play a minor role only and will cause just a small shifting of the desired DC operational point.)

Comment 1: IB was used only for providing the required voltage VB.
Comment 2: Unexpected IC increase VE=IE*RE and reduces VBE (current controlled voltage feedback)

But i can tell you that sometimes theory is not quite stated correctly or rather i should say 'completely'. 
This brings up another question though, and that is what did you think about Gilbert's idea of "current mode" and "voltage mode", why do you think he called them that?
If you read my contributions again, you will notice that I did NOT need theoretical considerations for explaining my arguments - in contrary, observable and measurable effects only. (Again: Up to now, nobody gave any comments to these examples!)

I think, it was not B. Gilberts "idea" to create the terms "current mode". It was already invented and used earlier (in conjunction with the speed of analog signal processing). I do not intend to discuss these terms here, because there is no direct connection to the subject here under discussion. I have explained this before (these terms are primary related to signal processing properties within a complex circuit).   

LATER:
In #27 it looks like you are saying that the change in Vbe is small?  Perhaps you can clarify.
No - this was not my saying. In contrary, everybody can see what happens for good stabilization: When the slope of the stabilization line is small (and at the vertical axis one can see how to make it small), the IC uncertainty d(IC) is also small - in spite of a relatively large (allowed) VBE uncertainty d(VBE). Of course, this is not a new finding but can be found in many books.
But it is an important property of such circuits because very often I`ve heard the question (not only from beginners):
How can VBE determine the current IC when it is (a) not known exactly and (b) assumed to be a constant value ??
« Last Edit: February 17, 2017, 03:22:49 pm by LvW »
 

Offline MrAl

  • Frequent Contributor
  • **
  • Posts: 481
Re: Current controlled device vs voltage controlled?
« Reply #60 on: February 17, 2017, 06:34:34 pm »
Hi,

Actually i meant did you ever do something like:
Ic=Ib*Beta

and be happy with it without invoking Vbe or any voltage for that matter?
 

Offline rfeecs

  • Frequent Contributor
  • **
  • Posts: 678
  • Country: us
Re: Current controlled device vs voltage controlled?
« Reply #61 on: February 17, 2017, 07:19:20 pm »
With regard to language and definitions, just for fun I went back and looked at the textbook that UC Berkeley used when I went there way back when.  It was "Basic Circuit Theory" by Desour and Kuh, 1969 edition.

Attached is an excerpt where they talk about non-linear resistors and define the terms "current controlled" and "voltage controlled".  They define a "voltage controlled" resistor as one where the current is a single valued function of the voltage.  A "current controlled" resistor is one where the voltage is a single valued function of the current.  So a linear resistor is both "voltage controlled" and "current controlled".  The same applies to an ideal diode.  A tunnel diode would be "voltage controlled" but not "current controlled".

Clearly their definition is not the same as LvW's or Mr. Carlson's.

Another consideration is circuit theory classes dealt strictly with mathematical models of circuit elements.  They did not go into the physics of the devices.  The physical operation of circuit elements was covered in physics classes.

So apart from clearly defining your terms, it is also important to distinguish whether you are talking about the physics of device operation vs just the purely mathematical model of the device.
 

Offline LvW

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: de
Re: Current controlled device vs voltage controlled?
« Reply #62 on: February 17, 2017, 09:24:52 pm »
Hi,
Actually i meant did you ever do something like:
Ic=Ib*Beta
and be happy with it without invoking Vbe or any voltage for that matter?

Ohh - such a short reply (in fact, not an answer) to my last contribution.
Let me think about your question.......no, as far as I remember: Only in the form Ib=Ic/beta because I always select at first a suitable collector current and treat the base current Ib as a result. No doubt about it - the base current does exist. However, for some designs it can even be neglected (I have already mentioned the opamp).
May ask you back - in which situation did YOU use the mentioned relation in the form given in your question (without invoking the voltage Vbe) ??
 

Offline rfeecs

  • Frequent Contributor
  • **
  • Posts: 678
  • Country: us
Re: Current controlled device vs voltage controlled?
« Reply #63 on: February 17, 2017, 10:18:16 pm »
Another fun thing. :)

Here is a video of Barrie Gilbert discussing translinear circuits where he says, around time 7:45, to forget what you have learned about a transistor as a current controlled current source... the best way to view the transistor at least for the purposes of this discussion is as a voltage controlled current source.

https://youtu.be/LQNJVtcFrCc
 

Offline MrAl

  • Frequent Contributor
  • **
  • Posts: 481
Re: Current controlled device vs voltage controlled?
« Reply #64 on: February 18, 2017, 07:16:10 am »
Hi,
Actually i meant did you ever do something like:
Ic=Ib*Beta
and be happy with it without invoking Vbe or any voltage for that matter?

Ohh - such a short reply (in fact, not an answer) to my last contribution.
Let me think about your question.......no, as far as I remember: Only in the form Ib=Ic/beta because I always select at first a suitable collector current and treat the base current Ib as a result. No doubt about it - the base current does exist. However, for some designs it can even be neglected (I have already mentioned the opamp).
May ask you back - in which situation did YOU use the mentioned relation in the form given in your question (without invoking the voltage Vbe) ??

Hello again,

Yeah, when i ask someone a simple generic question like if they ever used:
"c=a*b"

and they feel compelled to answer:
"No, i only used it as a=c/b"

I know the conversation is not going anywhere.

There are some diehard advocates of one theory over another, and that's entirely up to them.  It is always up to the individual what they want to use and i wont try and take that away from them.

I used the form:
Beta=iC/iB

many times to test a bipolar for basic operation, if that makes you happy :-)
The Beta can change drastically in some transistors if they have been abused.  If the Beta is too low you know something is wrong right away.  And no, i did not have to measure Vbe and see if the reading was 0.5125 instead of 0.5124 i only had to see that when i APPLY 1ma to the base i get at least 20ma or higher in the collector.

But as i said before, go ahead and feel free to measure the Vbe voltage, it's always your choice.  Maybe you can get all the transistor companies to stop publishing the Beta values on the data sheets too.

« Last Edit: February 18, 2017, 07:18:43 am by MrAl »
 

Offline LvW

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: de
Re: Current controlled device vs voltage controlled?
« Reply #65 on: February 18, 2017, 08:44:40 am »
MrAl, with all respect - what is the purpose of such polemic words like
Maybe you can get all the transistor companies to stop publishing the Beta values on the data sheets too.“

Why do you completely ignore my use of  B resp. beta values in all of my posts ? Didn`t you notice the appearance of  B in the design steps listed in my post#59 and in my drawings (post#27) ?
Do you recognize the B value on the vertical axis of the 2nd figure? This B value determines the slope of the stabilization line! The same applies to the 1st figure because the shown factor alpha is the basis for defining beta. Didn`t you recognize this? 

Quote: „But as i said before, go ahead and feel free to measure the Vbe voltage, it's always your choice.“

May I ask you: Why do you insinuate that I would suggest to measure Vbe?  Didn`t you understand the meaning and the background of my drawings in post#27 ? Both figures are nothing else than a visual representation of well-known formulas for designing amplifier stages.
OK - I will again explain it to you: Both figures demonstrate why it is sufficient to assume a Vbe guess value of app. 0.7V - WITHOUT knowing the exact values !

Sorry to say - but I very much regret that it seems not to be possible to discuss on a fair and factual basis using exclusively pure technical questions and answers (answers and comments - for instance  - to the technical examples I have given in my various posts).
LvW

PS: I have discussed this subject (current vs, voltage controlled) not for the first time.
And each time I am really surprised that this subject causes a very emotionally charged controversy.
A real exchange of technical arguments appears not to be possible.
(Perhaps, because the "current-control believer" have nothing else than one single equation Ic=B*IB that - in my opinion - is misinterpreted as a false sequence of cause and effect ? Whereas voltage control is supported by many observations and measurable circuit properties.)

« Last Edit: February 18, 2017, 09:01:49 am by LvW »
 

Offline MrAl

  • Frequent Contributor
  • **
  • Posts: 481
Re: Current controlled device vs voltage controlled?
« Reply #66 on: February 18, 2017, 09:08:33 am »
MrAl, with all respect - what is the purpose of such polemic words like
Maybe you can get all the transistor companies to stop publishing the Beta values on the data sheets too.“

Why do you completely ignore my use of  B resp. beta values in all of my posts ? Didn`t you notice the appearance of  B in the design steps listed in my post#59 and in my drawings (post#27) ?
Do you recognize the B value on the vertical axis of the 2nd figure? This B value determines the slope of the stabilization line! The same applies to the 1st figure because the shown factor alpha is the basis for defining beta. Didn`t you recognize this? 

Quote: „But as i said before, go ahead and feel free to measure the Vbe voltage, it's always your choice.“

May I ask you: Why do you insinuate that I would suggest to measure Vbe?  Didn`t you understand the meaning and the background of my drawings in post#27 ? Both figures are nothing else than a visual representation of well-known formulas for designing amplifier stages.
OK - I will again explain it to you: Both figures demonstrate why it is sufficient to assume a Vbe guess value of app. 0.7V - WITHOUT knowing the exact values !

Sorry to say - but I very much regret that it seems not to be possible to discuss on a fair and factual basis using exclusively pure technical questions and answers (answers and comments - for instance  - to the technical examples I have given in my various posts).
LvW

PS: I have discussed this subject (current vs, voltage controlled) not for the first time.
And each time I am really surprised that this subject causes a very emotionally charged controversy.
A real exchange of technical arguments appears not to be possible (perhaps, because the "current-control believer" have nothing else than one single equation Ic=B*IB that - in my opinion - is misinterpreted as a false sequence of cause and effect ? Whereas voltage control is supported by many observations and measurable circuit properties.)

Hi,

I have to admire your patience.  I may have lost mine just a little bit here while you have kept yours intact so i must admire that.

I am afraid that i just dont understand your BASIC line of reasoning.  You're saying on the one hand that you believe in BJT voltage controlled, yet you are keeping Vbe constant.  There are some other things too but i am trying to keep each reply as simple as possible.  I would even, if i could, keep it down to a 'yes' or 'no' answer so that we could get to the bottom of this :-)

For example, and i am keeping this short and simple, do you believe that the form Ic=Beta*Ib is useful?
I think your answer is 'yes' from what you said, and you also said that Vbe doesnt matter.  If Vbe does not matter than why try to push voltage control?

Please try to keep the reply down as short as possible as this makes it easier to understand and reply.  Thanks in advance.

I also like to keep the conversation friendly and non combative :-)

One small point:
The BJT can be modeled as EITHER a voltage controlled current source OR a current controlled current source.  Anyone that says to 'forget' about calling it a current controlled current source is hell bent on world domination or else is just trying to make a point and get others to want to see their point of view (ie the WOW factor which gains more attention).  Sometimes (more often today than in the past) writers use their artistic license to use sarcasm to illustrate a point...i do it once in a while myself.

« Last Edit: February 18, 2017, 09:16:52 am by MrAl »
 

Offline LvW

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: de
Re: Current controlled device vs voltage controlled?
« Reply #67 on: February 18, 2017, 02:21:39 pm »
I have to admire your patience.  I may have lost mine just a little bit here while you have kept yours intact so i must admire that.

Thank you. Yes - I am trying to remain patient - but there are limits.

Please try to keep the reply down as short as possible as this makes it easier to understand and reply. 

Yes - I will do that.

You're saying on the one hand that you believe in BJT voltage controlled, yet you are keeping Vbe constant.

Simply wrong.
Show me one sentence where I propose/suggest to „keep Vbe constant“?
(I hope you do not mean the classical method where for calculation purposes all of us start with a „best guess“ for Vbe).

For example......do you believe that the form Ic=Beta*Ib is useful?

It is not only „useful“ - it is a valid relation (resp. definition) and all of us - including me - use it (as I did in my list of design steps). However, we must not misinterpret this relation.

I think your answer is 'yes' from what you said, and you also said that Vbe doesnt matter.  If Vbe does not matter than why try to push voltage control?

Again simply wrong. For the second time you are using a misquotation (entirely fictitious).
Why? I never have written something like „Vbe doesn`t matter“..

The BJT can be modeled as EITHER a voltage controlled current source OR a current controlled current source. 

At least 4 small-signal two-port BJT models are in common use: h-parameters, g-parameters, y-parameters, z-parameters. All four models have a signal voltage as input quantity. However, I am aware that this fact alone cannot be regarded as a final proof  for real voltage control because they are only „models“. Hence, I did not use these models as justification. 

I also like to keep the conversation friendly and non combative :-)

Fine - but why do you quote incorrectly ?

 

Offline MrAl

  • Frequent Contributor
  • **
  • Posts: 481
Re: Current controlled device vs voltage controlled?
« Reply #68 on: February 18, 2017, 03:08:40 pm »
Hi,

From your #59:
"How can VBE determine the current IC when it is (a) not known exactly and (b) assumed to be a constant value ??"

If VBE in your statement is "assumed to be a constant value" then you are stating that it does not change.
How is that a misquote?

Not only that, but i cant see how you can say that the device is "voltage controlled" and ask the question above that implies that you can NOT determine the collector current from VBE.

I hope you are not hinting that just because the base voltage changes that means it is voltage controlled.
 

Offline LvW

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: de
Re: Current controlled device vs voltage controlled?
« Reply #69 on: February 18, 2017, 04:53:42 pm »
Hi,
From your #59:
"How can VBE determine the current IC when it is (a) not known exactly and (b) assumed to be a constant value ??"

Here I repeat what I really have written in my post#59

".....very often I`ve heard the question (not only from beginners):
How can VBE determine the current IC when it is (a) not known exactly and (b) assumed to be a constant value ??"

As everybody can read - I have quoted a question I often have heard from other persons.
And what are you doing? You give the impression as if that were my statement. 

OK - no chance for a fair exchange of arguments. I stop the discussion now because you are falsifying my words.
Bye
LvW





 

Offline MrAl

  • Frequent Contributor
  • **
  • Posts: 481
Re: Current controlled device vs voltage controlled?
« Reply #70 on: February 19, 2017, 09:12:57 am »
Hi,
From your #59:
"How can VBE determine the current IC when it is (a) not known exactly and (b) assumed to be a constant value ??"

Here I repeat what I really have written in my post#59

".....very often I`ve heard the question (not only from beginners):
How can VBE determine the current IC when it is (a) not known exactly and (b) assumed to be a constant value ??"

As everybody can read - I have quoted a question I often have heard from other persons.
And what are you doing? You give the impression as if that were my statement. 

OK - no chance for a fair exchange of arguments. I stop the discussion now because you are falsifying my words.
Bye
LvW

Hi,

Well, i have to chuckle a little there :-)

But i do apologize if i misquoted you.  It is harder to talk about something so specific in a message board forum because we can not correct each other right away, it takes sometimes 1/2 day or even a full day before one or more of us can get back to reply.  I've also had a host of other things going on in my court the last week or so that demand a lot of attention so being preoccupied does not help at all.

But be sure i am not trying to 'falsify' your comments, if anything i am trying to verify and understand what you were saying.  However, we all have our way of looking at things and i dont think your view will change much and i dont think my view will change much, and i think the only reason we got into this discussion in the first place was because we dont understand each others points of view entirely.  For example, it's not the first time i have heard the "voltage controlled" idea come up in BJT analysis, and i reject it outright for a number of reasons, and some of those reasons have to do with the history of electronics and how hard it is to change the trend that follows in those footsteps. [Note: of course i meant not voltage controlled only not that we can never use the voltage control idea.]

Because i have studied this problem in detail before, i should have just stated from the start that probably the only way i would accept a 'final' definition of what causes one or the other (voltage or current, or as we say charge) is a proof that there is a *delay* in one when the other somehow appears by itself without the other.  In the context of this discussion, that would mean i would have to see a proof that voltage can appear all by itself, and then sometime later, even if it is such an extremely tiny time period later, that then and only then does the charge start to move (or current starts to flow).  The delay i am talking about here could be on the order of 1e-30 seconds, and even though that is probably not measurable i would still accept that if a good proof was shown.
But to add to that, i would then have to take that argument and *apply* it to a circuit and try to determine if it has any practical significance.  If we can *never* measure that then there is no practical significance, at least probably not in our lifetimes.  At some point technology may be able to measure such an extremely short time, at which case it *could* become significant, but for our time it may not be so.

So to convince me there is only one way that i know of, and that is to show that there is at least sometimes a delay between the time that a voltage appears to the time that charge begins to flow.  Once we have a numerical figure to work with we can then go on to determine the practical significance, if any.  Without that extra step though i could still probably accept that there is at least some time no matter how small, but i would have to at least see that there is some time delay.
Since we are talking about an electrical behavior, we also limit the discussion to electrical behavior alone without the possibility of mechanical or other types of intervention.  A photo transistor will obviously change the properties because of the photo electric effect, but we block all light from reaching the transistor junctions so we can concentrate on the purely electrical (voltage and current) properties alone.

So show me that and i will probably be at least partially convinced.  Of course if that were to happen, we would then have an awful lot of data sheets to change :-)
Since this probably isnt going to happen, i will respect your decision to not discuss this any further.  I realize that it would be very hard to prove this without a good lab unless we could find someone else who did work in this area already, which could be a possibility, and then we would just have to find that work.

BTW an analogy may come in the form of a purely mechanical system.  We have a hard, small ball that is on a frictionless surface and we apply a force to one side of the ball.  What comes first, the force on the ball or the movement of the ball?
Amazingly, with no friction (inertia only) from the moment the force is applied the ball BEGINS to move, and there is no delay in this process.  In fact, i think dynamic friction would not change that either however static friction would because it would hold the ball in position until some significant non zero level of force was achieved.  So again we see no delay between one thing and the other, between the applied force and the movement of the object.





« Last Edit: February 19, 2017, 09:32:31 am by MrAl »
 

Offline LvW

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: de
Re: Current controlled device vs voltage controlled?
« Reply #71 on: February 19, 2017, 02:57:30 pm »
MrAl, I do not want to be impolite - however, as stated in my last post: In my opinion, it makes no sense to futher continue THIS discussion.
All I can contribute for explaining/justifying my position is contained in my previous posts - in particular posts#7, 27 and 59.
LvW
« Last Edit: February 19, 2017, 02:59:30 pm by LvW »
 

Offline MrAl

  • Frequent Contributor
  • **
  • Posts: 481
Re: Current controlled device vs voltage controlled?
« Reply #72 on: February 19, 2017, 04:02:04 pm »
MrAl, I do not want to be impolite - however, as stated in my last post: In my opinion, it makes no sense to futher continue THIS discussion.
All I can contribute for explaining/justifying my position is contained in my previous posts - in particular posts#7, 27 and 59.
LvW

Hi again,

Ok sure, no problem.  If i find anything (except my own work) i'll post it here if i think it will help.  Websites with information help sometimes and sometimes not, but if i find anything good i'll post it here at a later time.

Take care for now, and good luck with your future projects/studies.
 

Offline LvW

  • Frequent Contributor
  • **
  • Posts: 282
  • Country: de
Re: Current controlled device vs voltage controlled?
« Reply #73 on: February 19, 2017, 04:28:08 pm »
Take care for now, and good luck with your future projects/studies.
Thank you - same to you.
Regards
LvW
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf