bias of bjt current ot voltage controlled

[LvW]

My mean is , why we should involve ourselves with some definitions ?
For example , when we have two voltage divider resistors as base bias resistors . be can easily consider , VB is given by a simple divide between two resistors ! but the fact is we can't do it because of base current ! but because base current is negligible , we can do it !!

Just one comment:
The classical procedure for designing the voltage divider for base biasing is to select a current through the upper resistor that is (n+1)-times larger than the anticipated base current - with the result that a current n*Ib flows through the lower base resistor. And this approach gives us formulas for both resistors.
Thus, of course it is possible (and it is normally done) NOT to neglect the base current during this design step.
However, this does not mean the base current would assume any control functions.

 

[goldsmith]

Just one comment:
The classical procedure for designing the voltage divider for base biasing is to select a current through the upper resistor that is (n+1)-times larger than the anticipated base current - with the result that a current n*Ib flows through the lower base resistor. And this approach gives us formulas for both resistors.
Thus, of course it is possible (and it is normally done) NOT to neglect the base current during this design step.
However, this does not mean the base current would assume any control functions.

Hi again dear LvW
May you tell me your idea a bout this method please :
When input resistance of a CE amplifier isn't important for me , i will select IR1 = 6ib and IR2 = 5ib . and then i'll continue the design process . but when i have an amplifier with the known values of R1 and R2 and when i've to find quiescent point , i can neglect value of ib and then use this formula to find Vb and then VRE and then IC and then ...... For Vb ( base voltage we can neglect ib and then telling :
VCC*R2/R2+R1

my mean was something like this . so may i know your idea about it please ?
Thank you very much .
Yours Sincerely
Goldsmith

 

[Ratch]

goldsmith,

Recall :
Think about it , carefully , please :

I always think about these things carefully. No need to tell me to do so.

Why collector current has change when we are increasing VBE ? if we look into the semiconductor crystals of an NPN transistor , we'll see the BE voltage will has effect on conduction of a transistor .

Are you asking and answering your question?

but why collector current has changes ? because base current has changes !

For the third time, I will say that the base current does not affect the collector current. I carefully explained that in my last message to Jeffrey Samuel. Did you read it?

i hope you get what i mean and what i'm trying to refer .

I understand what you mean, and know that you are wrong. It won't do any good to repeat the same thing again. You need to look at my message to Jeffrey Samual, and discuss the points I made in my reasoning.

My mean is , why we should involve ourselves with some definitions ?
For example , when we have two voltage divider resistors as base bias resistors . be can easily consider , VB is given by a simple divide between two resistors ! but the fact is we can't do it because of base current ! but because base current is negligible , we can do it !!
What i mean is , up to know i didn't pay any attention to this issue , because it didn't have any benefit in design process . but i agree each peoples , should know the fact of this issue ! hence i'm not disgree with knowing this effect . but i'm completely disagree with thinking about this , in design process !

I consider the above paragraph incoherent. I attribute that to your lack of facility with the English language. It is not your fault that you cannot express yourself adequately in English.

What thread ? your threads ? why you don't search into your created threads ? of course all of us that are here , should tell each other ( ourselves ) about our problems or wrong ways ! thus we can increase our abilities .

I am referring to the threads where you "remembered" a concept of negative impedance in a transformer, and an input impedance calculation in a CE amplifier. Don't you remember asking about that?

Hence an advise :
Just using a paper and a pen and just theorem can't help ! and it won't have any benefit for you . try to design something ! then you'll learn while you're designing something ! it is a big lesson that many years ago , i've learned it . ( i believe when a project is involved with some complexity ! a thing has problem ! it is why i design all of my projects as simple as possible ! and i'm sure that practical issues and experiments are big professors )
I hope you get what i mean .

No, I don't get what you mean. I don't understand what "benefit" I will receive using a pen and paper plus a "theorem". I am happy that you learned a big lesson years ago doing that, although I am at a loss as to what that lesson was. A professor is a learned teacher, not a practical issue and experiment.

Ratch

 

[jeffrey samuel]

goldsmith,

No that is plain wrong. Collector current does not depend on base current. I carefully explained that in my last message to Jeffrey Samuel.


Ratch

Hey Bro how do you plan to get your output Characteristics of your CE amplifier

In definition sake I am sure about this equation

Ic= F(Ib,Vce)

That helps us to draw the output characteristic Graph.

Next up is this the input impedance of a CE amplifier is in the order of kohms I agree to it. Whereas the Input impedance of a FET amplifier is well above Mohms This makes the Ig current have no part or role in the function of the FET

But in the case of the BJT the Ib current plays a very significant role making it to be called "The Current Controlled Device"

Period...

 

[Ratch]

jeffrey samuel,

how do you plan to get your output Characteristics of your CE amplifier

In definition sake I am sure about this equation

Ic= F(Ib,Vce)

That helps us to draw the output characteristic Graph.

I already explained that previously. Ib is an indicator of what the Ic is, but Ib does not control Ic. As an analogy, you can put an ammeter in the base circuit, and determine the amount of Ib current. But, the ammeter does not control what the Ic current is. So, you are looking at the Ib, and saying to yourself and others, "Look, the Ic goes up proportionally with Ib. Therefore, Ib is controlling Ic." Do you see the fallacy in that reasoning?

Next up is this the input impedance of a CE amplifier is in the order of kohms I agree to it. Whereas the Input impedance of a FET amplifier is well above Mohms This makes the Ig current have no part or role in the function of the FET

Who cares what the input impedance is? The voltage Vbe determines what the Ic will be regardless of whether the Vbe sees a high or low impedance.

But in the case of the BJT the Ib current plays a very significant role making it to be called "The Current Controlled Device"

Period...

The Ib plays no role in designating a BJT as a current controlled device. Ib only indicates the Ic, it does not control it.

Ratch

 

[LvW]

Hey Bro how do you plan to get your output Characteristics of your CE amplifier
In definition sake I am sure about this equation
Ic= F(Ib,Vce)
That helps us to draw the output characteristic Graph.
............
But in the case of the BJT the Ib current plays a very significant role making it to be called "The Current Controlled Device"

Hi Jeffrey,

I like to remind you that there is also another output characteristic graph with Vbe=parameter (constant).
Thus, the fact that a characteristic with Ib=const exists doesn`t say anything about physical truth.

As another argument I like to remind you (and all other defender of Ib-control) that the proper function of some BJT circuits can be explained/justified
based on voltage-controlled Ic only (current mirror, translinear circuits....and also Ic stabilization using an emitter resistor.)

- - - Updated - - -

When input resistance of a CE amplifier isn't important for me , i will select IR1 = 6ib and IR2 = 5ib . and then i'll continue the design process . but when i have an amplifier with the known values of R1 and R2 and when i've to find quiescent point , i can neglect value of ib and then use this formula to find Vb and then VRE and then IC and then ...... For Vb ( base voltage we can neglect ib and then telling :
VCC*R2/R2+R1

Hi Goldsmith,

at first, I see a contradiction in your sentence "When input resistance of a CE amplifier isn't important for me , i will select IR1 = 6ib and IR2 = 5ib".
Why do you consider the current Ib into this input resistance if it isn`t important for you?

Moreover, I am afraid there is a big misunderstanding on your side. The question is NOT if Ib can be neglected or not during the design of a transistor stage. That is a complete different problem
Of course, Ib is present and should not be neglected for calculating resistor values. But we speak about the question if Ib controls Ic (from the physical point of view).
And this has nothing to do with the existence of Ib. OK?

 

[goldsmith]

Are you asking and answering your question?

Hi Ratch
Not i'm trying to open your mine with question and answer !!

I understand what you mean, and know that you are wrong. It won't do any good to repeat the same thing again. You need to look at my message to Jeffrey Samual, and discuss the points I made in my reasoning.

Listen carefully ! I don't need to waste my time with some definitions ! because i know the correct term of this issue and i'm using my methods to design a circuit , if i want to teach someone the principles of operation of a transistor i'll tell that someone , about the fact of issue and then i'll tell that someone to don't pay attention to that fact in design process ! it is what i'm doing !
Did you ask yourself ever , that why we're studying electronics ? to just playing with paper and pen and just theorem ? or doing something in the real world ? i don't know how should i transfer my meaning to your mind , but i know i'm living in the real world ! and in this real world most of the times i'm designing many things without playing with definitions .
For my opinion you'd better to refer to the FvM's post in former page too !

I am referring to the threads where you "remembered" a concept of negative impedance in a transformer, and an input impedance calculation in a CE amplifier. Don't you remember asking about that?

Yes i can remember it exactly and i can remember the answer of the other expert members of this forum to you ! and i can remember many of famous textbooks that are references in famous universities of this world ! and i can remember that i didn't use that funny theorem until know and i didn't have any problem with my transformers without that negative impedance theorem until now .

I have a suggestion for you . i think you need to think more ! just think why you need to go to the university ? to learn ! why you need to learn ? to be able to use each thing that you've learned in the real world ! why you need to use them in real world ? to handle an aim .
It is enough that you think , what is the benefit of a thing that has not any benefit in the real world and in the practical issues ?
For example , consider that you have received a new project , what you'll do ? will you try to solve it on a piece of paper and play with theorem ? we are living in the real world not in pice of paper !
I've learned that we are learning to do everything in practice !
You can't tell me that my method is wrong ! because i know gang of peoples in this world with this method ! and after these days that i'm in electronics , i know exactly , i'm in electronics because i want use theorem to achieve a design method ! what is the benefit of things that you can't use them in practice ?
Clarification : we all know how a transistor does work but many of the things that are applied in a transistor are not useful in the real world ! hence we know them but we won't use them .
( when you use that concept in a design process ??!! never !! )
For my opinion : try to live in the real world , my friend ! ;-)

Regards !





__________________________________________________________________

Hi Goldsmith,

at first, I see a contradiction in your sentence "When input resistance of a CE amplifier isn't important for me , i will select IR1 = 6ib and IR2 = 5ib".
Why do you consider the current Ib into this input resistance if it isn`t important for you?

Moreover, I am afraid there is a big misunderstanding on your side. The question is NOT if Ib can be neglected or not during the design of a transistor stage. That is a complete different problem
Of course, Ib is present and should not be neglected for calculating resistor values. But we speak about the question if Ib controls Ic (from the physical point of view).
And this has nothing to do with the existence of Ib. OK?

Hi dear LvW
Pardon me if i couldn't transfer my meaning as well .
My mean with neglecting ib was not for this issue ( the description of this thread ) my mean was we can neglect some of the facts in this world ! i wanted to tell that when a thing is available in fact , we can neglect it to simplify a process . but in fact that is available ! but we can neglect it because it's effect isn't important , really . i wanted to tell , that we should neglect some of the facts in this world to simplify everything . i've learned that we should simplify each thing as we can . am i right ?

at first, I see a contradiction in your sentence "When input resistance of a CE amplifier isn't important for me , i will select IR1 = 6ib and IR2 = 5ib".
Why do you consider the current Ib into this input resistance if it isn`t important for you?

Let me tell my meaning , accurately .
For example , consider please that we want design a CE amplifier which it's input impedance isn't important for us ( it can have each value ! but it's value isn't important for us) . but when we want have input impedance of 2 k ohms , we can't use the rule of thumb of 6ib and 5ib because we're looking for an special input resistance . hence values of R1 and R2 are pretty important for us .
if you precept me to show it with a circuit , i'll do it . ( for example you can tell me we need an amplifier with these specifications ...... and then i'll show how i'm design such a stage in real world i think it would be ok ,isn't it ? ) or if you want i can show my meaning with an example ( a random one ) from my side ?
I think thus all of the misunderstandings will be removed . may i know your idea please ?
Yours Sincerely
Goldsmith

 

[LvW]

.........
but when we want have input impedance of 2 k ohms , we can't use the rule of thumb of 6ib and 5ib because we're looking for an special input resistance

Sorry, but this claim is simply false. It is no "rule of thumb". Instead, it is correct by 100%.
When a current I1=k*Ib flows through R1, which then is split into two currents one of which is Ib, then the current through R2 is I2=(k-1)*Ib. That´s for sure.

I like to add that - with respect to the original question in post#1 - I don`t appreciate the discussion "real world vs. theory" because we deviate from the original problem.
If somebody neglects Ib during the design process - this is a complete different story.
More than that, sometimes it can be neglected (for example if we set: Ic=Ie) and sometimes it shouldn`t (for my opinion for calculation of the resistive divider) - and sometimes it cannot at all (biasing with one resistor only).

Because I like the sentence from FvM in post#17 I repeat it here again. I think it can serve as an appropriate summary and outcome of the previous discussion:

In other words, don't mix up basic models of transistor operation and calculation methods used in practical design.

To me, this means the following:
A good engineer has to know what`s really going on and what the operating principles of the various active parts are.
Only then he is able to decide if and when he is allowed to simplify things and to use formulas, which are handsome and exact enough for his particular application - even if they do not reflect the physical truth resp. the physical causality.

Besides the BJT I have two other examples:
* Don`t we sometimes treat the NIC (active current source) as a passive part with the value "-R" ?
* Don`t we treat the MILLER effect as an "artificial" reduction of a resistance - although the input current increase it is caused by a second source within the active circuit ?
(Thus, of course anybody uses the equation Ic=beta*Ib but this does not necessarily mean that he does not know about the physical truth).

LvW

 

[goldsmith]

.........
but when we want have input impedance of 2 k ohms , we can't use the rule of thumb of 6ib and 5ib because we're looking for an special input resistance

Sorry, but this claim is simply false. It is no "rule of thumb". Instead, it is correct by 100%.
When a current I1=k*Ib flows through R1, which then is split into two currents one of which is Ib, then the current through R2 is I2=(k-1)*Ib. That´s for sure.

I like to add that - with respect to the original question in post#1 - I don`t appreciate the discussion "real world vs. theory" because we deviate from the original problem.
If somebody neglects Ib during the design process - this is a complete different story.
More than that, sometimes it can be neglected (for example if we set: Ic=Ie) and sometimes it shouldn`t (for my opinion for calculation of the resistive divider) - and sometimes it cannot at all (biasing with one resistor only).

Because I like the sentence from FvM in post#17 I repeat it here again. I think it can serve as an appropriate summary and outcome of the previous discussion:

In other words, don't mix up basic models of transistor operation and calculation methods used in practical design.

To me, this means the following:
A good engineer has to know what`s really going on and what the operating principles of the various active parts are.
Only then he is able to decide if and when he is allowed to simplify things and to use formulas, which are handsome and exact enough for his particular application - even if they do not reflect the physical truth resp. the physical causality.

Besides the BJT I have two other examples:
* Don`t we sometimes treat the NIC (active current source) as a passive part with the value "-R" ?
* Don`t we treat the MILLER effect as an "artificial" reduction of a resistance - although the input current increase it is caused by a second source within the active circuit ?
(Thus, of course anybody uses the equation Ic=beta*Ib but this does not necessarily mean that he does not know about the physical truth).

LvW

Hi dear LvW
I'm really sorry . yes you're absolutely right and now i'm completely contented with your statement . and i can't tell any thing about it because you are quite right . and i should accept the right issues .
Thank you very much because of your patience and your clarification
Sincerely Yours
Goldsmith

 

[Ratch]

goldsmith,

You seem to have a hard time staying on topic. The topic is whether BJT is voltage or current controlled. Your answers are usually rambling random musings that have hardly any relationship to the reasons and arguments others give to your often mistaken and absurd statements. The participants of this thread are looking for good factual reasoning that either support your assertions, or disprove their arguments. Instead, they receive philosophical dissertations of often inconsequential, nonapplicable, nonessential, irrelevant, and off topic subjects that are unrelated to the subject being discussed.

So, you should try to stay focused on the thread subject, answer others arguments when they present them, and don't stray into areas that don't pertain to the subject being discussed. If you want to discuss another subject, then you should start another thread.

Ratch

 

[goldsmith]

You seem to have a hard time staying on topic. The topic is whether BJT is voltage or current controlled. Your answers are usually rambling random musings that have hardly any relationship to the reasons and arguments others give to your often mistaken and absurd statements. The participants of this thread are looking for good factual reasoning that either support your assertions, or disprove their arguments. Instead, they receive philosophical dissertations of often inconsequential, nonapplicable, nonessential, irrelevant, and off topic subjects that are unrelated to the subject being discussed.

So, you should try to stay focused on the thread subject, answer others arguments when they present them, and don't stray into areas that don't pertain to the subject being discussed. If you want to discuss another subject, then you should start another thread.

Ratch

Hi Ratch
A misunderstanding has been happened but when i saw LvW's statement , i could get the point ! on the other hands , he understood that what is my misunderstanding as well and his statement improved my misunderstanding . so now the problem is solved . isn't it my friend ? ;-)
Regards
Goldsmith