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Collector current of an NPN common emitter circuit

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Winterstone:
Yes you are, now get to work or else you get graded with an "F" for this semester and i have to call your parents on the phone :)
Seriously though, you didnt want to do the original circuit and asked for a new circuit, and i provided one and you did not like that one either, so i provided another one with all the things you wanted and now you say you dont want to do it. Why even bother responding in this thread if you dont want to do the circuit posted in the thread? Start your own thread and do the circuit you want done then. It's that simple.

All:
See, as predicted there is still no analysis of the circuit i wanted to see (except by those who already had done so and didnt constantly complain about the circuit) :)

Sorry to say - you didn`t understand anything. Instead - you can answer in a polemic way only.
Several times I have stated that it does not matter if I "like" or "dislike" a circuit - and I have shown you what authors with excellent reputation think about the configuration as proposed by you ("disaster").
I have seen no reason to follow your desire and apply basic rules (Ohm`s law, KVL,..) to an unrealistic circuit.
By the way: what is the reason you want me to analyze "your circuits"? I am not in an examination!

There is no need to start my own thread because I have no problems (that means no open questions).
All I have tried up to now is to convince you that there are two commonly used bias schemes that work much more better than "your circuit".
And - in contrast to your statements - I have done a calculation (post#16).
However, you ignore every substantial answer - a very unfortunate discussion (better: exchange of opinions).
I will stop it now from my side.

Respectfully yours
Winterstone

A final remark: Why didn`t you comment the very informative contribution from Claude Abraham (post#73)?
Excerpts:
"The circuit in post #1 can never be employed, regardless of application, "
"Using Ib to control Ic is not good, because of beta variation. "
 
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Sorry to say - you didn`t understand anything. Instead - you can answer in a polemic way only.
Several times I have stated that it does not matter if I "like" or "dislike" a circuit - and I have shown you what authors with excellent reputation think about the configuration as proposed by you ("disaster").
I have seen no reason to follow your desire and apply basic rules (Ohm`s law, KVL,..) to an unrealistic circuit.
By the way: what is the reason you want me to analyze "your circuits"? I am not in an examination!

There is no need to start my own thread because I have no problems (that means no open questions).
All I have tried up to now is to convince you that there are two commonly used bias schemes that work much more better than "your circuit".
And - in contrast to your statements - I have done a calculation (post#16).
However, you ignore every substantial answer - a very unfortunate discussion (better: exchange of opinions).
I will stop it now from my side.

Respectfully yours
Winterstone

A final remark: Why didn`t you comment the very informative contribution from Claude Abraham (post#73)?
Excerpts:
"The circuit in post #1 can never be employed, regardless of application, "
"Using Ib to control Ic is not good, because of beta variation. "


Hello again,


Thank you. As you see from my more recent posts, we moved on to a new circuit with all the resistors you and audioguru had asked for. We have all that you asked for, yet you still wish to argue about the 'first' circuit. This i dont understand. You and audioguru did not like the circuits before, so i changed it according to your requirements, yet you still come back with an argument rather than a simple analysis.

My only guess at this point is that there is something lost in the translation from one language to another, or you are assuming something that isnt so.

Anyone else care to comment about what is going on here?

Perhaps i will do the analysis and show the results here to save time.
 
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Hello Al,

As you certainly know the circuit in your first post is just a model or a symbol saying how a transistor can be biased.
So in your first pic, becuase you did not use a resistor for the base of the transistor, can we assume that the transistor is in saturation or so called hard saturation? If we try to do such an assumption then we can simply solve it and calculte Ic.
 
Hello there Wizard,


Yes, there are some assumptions in the first circuit. But as i said later, i have changed the circuit (adding 3 resistors) to accommodate the replies yet i still get a lot of criticism about the circuit :)
 
But I think that your traget is the first circuit right? The other changes as I noticed are done so that make other guys satisfied!:)
Anyway if we try to suppose that the circuit is in saturation then everything we be solved! I even prefer to suppose that the transistor itself does not burn due to Vbe...

Yes, there are some assumptions in the first circuit. But as i said later, i have changed the circuit (adding 3 resistors) to accommodate the replies yet i still get a lot of criticism about the circuit :)

So Maybe it is better you try to give them Ib and hfe of the transistor as well and I am sure that all guys here would be ok with your circuit. lol.
 
Hi again Wizard,

No it is not in saturation, and Vbe is quite low for that transistor. So assume it does not burn :)
Also note that later we *measure* Vbe after it has been biased with large resistors.
 
Hello Al,

As you certainly know the circuit in your first post is just a model or a symbol saying how a transistor can be biased.
So in your first pic, becuase you did not use a resistor for the base of the transistor, can we assume that the transistor is in saturation or so called hard saturation? If we try to do such an assumption then we can simply solve it and calculte Ic.

hi wiz,

Just for reference is MrAl's original circuit running in LTSpice.

Its not a serious circuit design, its only to demonstrate a problem.

Image03 shows the effect of temperature from 0C thru 100C

E.
 

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Hi again Wizard,

No it is not in saturation, and Vbe is quite low for that transistor. So assume it does not burn :)
Also note that later we *measure* Vbe after it has been biased with large resistors.

Actaully As I told before I just considered the First pic in your first post.
So what voltage for Vbe is needed to cause the transistor to go to the saturation you think?? I guess because we do not have any resistor for the base then the current is high enough so that cause the transistor to go to the saturation.
You may know that as rule of thumb if Rb happens to be 10 times of Rc or less then the transistor is in the saturation. you do not haave any restor as Rb.. Of course the wold is so wide and we can make a lot of ASSUMPTIONs if you know what I mean? So we can either solve the problem of Rb by another assumption:).
 
Hello Wizard and Eric,


Eric:
Thanks for posting that simulation. I'll take a look at it next.

Wizard:
Look at the circuit in post #77 now.

audioguru:
I have changed the transistor of the circuit in post #77 to 2N3904 as requested. I have also changed the base resistor RB1 to 78500 ohm. Again assume this causes a Vbe of 0.65 volts.
 
hi wiz,

Just for reference is MrAl's original circuit running in LTSpice.

Its not a serious circuit design, its only to demonstrate a problem.

Image03 shows the effect of temperature from 0C thru 100C

E.

Hi Eric,
Well, to be honest I did not take any care to other posts other than the FIRST one started by MrAl. And he wanted to calculte "Rc". So I think that I was not in the bypass way!
 
Wizard:
Look at the circuit in post #77 now.

Ok, so do you want "Ic" again in that post?
You seem to not have hfe and do not like to give it to us:).
I can simulate both circuits in post #1 and 77 if you'd like.
 
Hello again Wizard,


Well i did not give Beta because we dont really know what Beta is exactly unless we look at the data sheet, and there we see it has a range of values depending on what Ic is. So we have to do a little trial and error perhaps and maybe some extrapolation.

But according to the other formula it includes Vbe as the controlling parameter, with "Is" the unknown, so i thought we could look at that too.
 
You cannot order a transistor to have a certain hFE (beta). You get whatever they have which is a range of numbers and it varies with the collector current and temperature.

So a transistor circuit should be designed to work with any transistor having that part number and at any temperature you will use.
 
Hello again,


That is what we would like to do, using the two different methods
1. Voltage control
2. Beta (current control)
 
Hello again,


That is what we would like to do, using the two different methods
1. Voltage control
2. Beta (current control)

We need to add 3) Alpha (current control). Ic = alpha*Ie, is the best control method ever devised. Alpha is very predictable and consistent, unlike beta. Vbe is uncontrollable, Ies varies much greater than beta does, and Vbe control incurs thermal runaway.

I can post some bias networks this weekend if time permits, detailing the operation. BR.
 
Hello there Claude,


First, sorry i didnt reply to your other post which was very good. I wanted to wait until the smoke cleared from the other discussions if you know what i mean :)

I was actually hoping that people would come up with ways to calculate this kind of circuit, with or without extra resistors. My main goal is to compare methods and see what happens. I started this thread because someone suggested that the voltage control method is better than the current control method using Beta, so i had hoped to see how this works or else disprove it. But i am open to suggestions that show that one method is better than the other for some reason, and if your added method is better than i hope you can take the time to show how it works and why it is better as you said. But what you would have to do probably is show the same circuit being analyzed using two methods and one of those methods should show some improvement over the predictability of the result, or something like that.

One of the things i would like to see in such a proof is how the Beta of the transistor can be left out of the picture so as to more or less ignore it. But when i say ignore it i mean ignore it somehow more than we would ignore it if we used the Beta method outright. We know that once we have the circuit working properly and have done it right then the Beta becomes less significant for any analysis but that even includes the analysis using the Beta itself. I hope i am making this clear.

And yes if you would care to show a couple bias networks that would be just fine too. We can look at them in different ways and see what we come up with. The only thing that i ask is that you use a common transistor like the 2N2222A as i suggested or the 2N3904 like audioguru suggested. If people want to try this with a real circuit they have to be able to get the transistor without too much difficulty.
 
Hello there Claude,


First, sorry i didnt reply to your other post which was very good. I wanted to wait until the smoke cleared from the other discussions if you know what i mean :)

I was actually hoping that people would come up with ways to calculate this kind of circuit, with or without extra resistors. My main goal is to compare methods and see what happens. I started this thread because someone suggested that the voltage control method is better than the current control method using Beta, so i had hoped to see how this works or else disprove it. But i am open to suggestions that show that one method is better than the other for some reason, ----- And yes if you would care to show a couple bias networks that would be just fine too. We can look at them in different ways and see what we come up with. The only thing that i ask is that you use a common transistor like the 2N2222A as i suggested or the 2N3904 like audioguru suggested. If people want to try this with a real circuit they have to be able to get the transistor without too much difficulty.

Thanks Mr. Al, I figured that is what you were doing with this thread. A few years ago I went throught this exercise working on an RF amp stage which was a single stage npn am/fm amplifier in the 100 to 400 kHz range. I have computation sheets in Excel and long hand detailing the methods I used to make said amp stage temperature-proof, power supply rail-proof, Ies-proof, beta-proof, gm-proof, re-proof, etc.

I will dig them up and post this weekend. In the mean time i just feel compelled to emphasize that in order to make a design beta-proof, we need to design around a worst case minimum value of beta. Devices having beta values above this minimum incur the effect of emitter degeneration and the stage gain is held fairly constant despite variations in device parameters like beta, gm, Ies, temperature, etc.

Beta has an influence but with good skillful bias network design, we can make a stage that performs consistently well over a broad range of device parameter values. Make no mistake however, it is not possible to produce a stage that has a gain value completely "beta-proof". If beta varies over specimen and temp from 50 to 500, a 900% increase, I can make the stage gain vary only 5%, or 1%, or 0.2%, but not 0.000%. Every bjt network (linear amplification, switching, whatever), is always at least slightly beta dependent.

Likewise when 2 devices are used in a differential front end, the mismatch in Vbe, and Ies results in output errors. These are errors due to input offset and voltage offset. Vbe and Ies unbalance can be mitigated through proper fabrication and circuit topology, but never completely eliminated. But we don't really need perfection. Best regards, and thanks to Mr. Al for a great thread and making valuable contributions, as well as many others who have participated. Also thanks to Winterstone for his input.
 
This is a funny little thread. I hesitated to join sooner as I am not strong in the maths. But I conferred with MrAl and he convinced me.


The mistake
The disparity in the two sides on this issue seems to be due to the difference in the analyzing of a circuit and analyzing of tools, for analyzing circuits.

Multiple people said:
That circuit sucks bad, don't ever use it.
LOL... Guys... I'm sure MrAl was fully aware of this from the start. This is like grade school knowledge of the electronics world. From what I was reading, he was not defending the circuit and it's practical use. That is not really the issue under debate. To paraphrase Eric, "you are moving the goalposts" (changing the argument) if you keep going on and on about the failures of that one circuit. The circuit is not the issue. The circuit obviously sucks.


The point
What I believe MrAL is really saying, and I would have to agree, is that favoring one of the two proposed methods as a tool to analyze any such circuit, crappy or not, makes no difference whatsoever. To me, thats a given. It's like arguing over which is a more valid way to measure automobile velocity. In miles per hour? Car lengths per minute? Or a tire circumference vs RPM? Although they seem somewhat different, they all equate to the same thing in the end. Distance/Time.

Or to be specific.

The forward voltage drop of Vbe will be about 0.65 volts. But it's EXACT (to more significant digits) momentaneous voltage drop is directly dependant on the current through it. The parameters are fundamentally related to each other, connected at the hip, inseparable, best friends, mates, pals, et cetera. This is obvious, it's basic Ohm's law. The current through a resistance (Ibe) determines the voltage across it (Vbe). This is why a transistor can internally be a voltage controlled system, but also can be current controlled at the same time. And also why a method focusing on one of the parameters can just as easily be adapted to use the other. So there is no point in saying one is better than the other, QED... it's just like Distance/Time above.

It seems to me everyone opposing MrAl's view just wants to focus on why the circuit sucks, and not ways we can analyze why the circuit sucks.


Transistor Maths
As for a formula that can be used to calculate a transistor general parameters without knowing Hfe/β, I don't think such a thing exists. As amplifying devices, β is the most important factor, this is the gain of the transistor, it's the reason for having a transistor. To suggest that the β of a transistor can be canceled out or ignored in such an equation is quite preposterous. It's like trying not to use the capacity of a capacitor, or the resistance of a resistor in a circuit calculation.

Now... there are circuits that exist that intentionally make these factors less meaningful when need be, but really that is apples and oranges.

Transistor Alpha
The transistor alpha certainly is a real parameter of a transistor, to be sure. And it is very "progressive" or "out of the box" thinking to try and use it for something meaningful. But as far as I know, transistor alpha only plays an important role with common-base configurations, and can almost always be considered unity. It's not really a gain factor, as much as it is attenuation.

So again, kinda apples and oranges.

One interesting thing is that α and β are related to each other via this formula.
ef869b748fb8acde7ebaab5d4b3dd811.png

But other than that, alpha is rather useless for analyzing a transistor from what I know.
 
Last edited:
This is a funny little thread. I hesitated to join sooner as I am not strong in the maths. But I conferred with MrAl and he convinced me.


The mistake
The disparity in the two sides on this issue seems to be due to the difference in the analyzing of a circuit and analyzing of tools, for analyzing circuits.


LOL... Guys... I'm sure MrAl was fully aware of this from the start. This is like grade school knowledge of the electronics world. From what I was reading, he was not defending the circuit and it's practical use. That is not really the issue under debate. To paraphrase Eric, "you are moving the goalposts" (changing the argument) if you keep going on and on about the failures of that one circuit. The circuit is not the issue. The circuit obviously sucks.


The point
What I believe MrAL is really saying, and I would have to agree, is that favoring one of the two proposed methods as a tool to analyze any such circuit, crappy or not, makes no difference whatsoever. To me, thats a given. It's like arguing over which is a more valid way to measure automobile velocity. In miles per hour? Car lengths per minute? Or a tire circumference vs RPM? Although they seem somewhat different, they all equate to the same thing in the end. Distance/Time.

Or to be specific.

The forward voltage drop of Vbe will be about 0.65 volts. But it's EXACT (to more significant digits) momentaneous voltage drop is directly dependant on the current through it. The parameters are fundamentally related to each other, connected at the hip, inseparable, best friends, mates, pals, et cetera. This is obvious, it's basic Ohm's law. The current through a resistance (Ibe) determines the voltage across it (Vbe). This is why a transistor can internally be a voltage controlled system, but also can be current controlled at the same time. And also why a method focusing on one of the parameters can just as easily be adapted to use the other. So there is no point in saying one is better than the other, QED... it's just like Distance/Time above.

It seems to me everyone opposing MrAl's view just wants to focus on why the circuit sucks, and not ways we can analyze why the circuit sucks.


Transistor Maths
As for a formula that can be used to calculate a transistor general parameters without knowing Hfe/β, I don't think such a thing exists. As amplifying devices, β is the most important factor, this is the gain of the transistor, it's the reason for having a transistor. To suggest that the β of a transistor can be canceled out or ignored in an equation is quite preposterous. It's like trying not to use the capacity of a capacitor, or the resistance of a resistor in a circuit calculation.

Now... there are circuits that exist that intentionally make these factors less meaningful when need be, but really that is apples and oranges.

Transistor Alpha
The transistor alpha certainly is a real parameter of a transistor, to be sure. And it is very "progressive" or "out of the box" thinking to try and use it for something meaningful. But as far as I know, transistor alpha only plays an important role with common-base configurations, and can almost always be considered unity. It's not really a gain factor, as much as it is attenuation.

So again, kinda apples and oranges.

One interesting thing is that α and β are related to each other via this formula.
View attachment 74053

But other than that, alpha is rather useless for analyzing a transistor from what I know.

You make some valid points but I assure you that alpha is important for all amp stages, common emitter, common base, and emitter follower. Alpha is a good concept to grasp because it conveys how *transistor action* takes place. The equation Ic = alpha*Ie, is not very exciting since alpha is so close to unity that the Ic/Ie relation is pretty constant with any device, any current, at any temp. But that is the point. A bias network designed to force Ie to a specific value will have an Ic value very predictable and consistent. If Ie = 1.00 mA, then we know that Ic is 0.98 to 0.998 mA for any functioning bjt device at any temp in its range, for any sustainable conditions.

Alpha is very useful at high frequencies, RF, since the bandwidth limitation is encountered. As frequency increases, alpha eventually drops well below 1, and beta drops well below its low frequency value. Analyzing alpha or beta at high freq gives us insight into the speed limitations of the device.

Also alpha is very useful when using the device as a switch such as in logic gates. Alpha in both the normal and inverse modes of operation comes into play. Two good references are "pulse, Digital, & Switching Networks" and "Digital Integrated Electronics", by Taub & Schilling, and Millman & Taub. Analyzing TTL logic relies heavily on alpha and beta in normal and inverse modes. Since the 60's, TTL logic gate inputs function in inverse mode when driven LOW.

Believe me, alpha is something any serious electronics practitioner must appreciate. I wouldn't bring it up if it weren't. Otherwise I agree with you that Mr. Al was presenting an example for discussion. He does not recommend the circuit in post #1 at all. I will post some computations maybe Sunday if I can find them, or if not I can derive them. Best regards.
 
This is a funny little thread. I hesitated to join sooner as I am not strong in the maths. But I conferred with MrAl and he convinced me.


The mistake
The disparity in the two sides on this issue seems to be due to the difference in the analyzing of a circuit and analyzing of tools, for analyzing circuits.


LOL... Guys... I'm sure MrAl was fully aware of this from the start. This is like grade school knowledge of the electronics world. From what I was reading, he was not defending the circuit and it's practical use. That is not really the issue under debate. To paraphrase Eric, "you are moving the goalposts" (changing the argument) if you keep going on and on about the failures of that one circuit. The circuit is not the issue. The circuit obviously sucks.


The point
What I believe MrAL is really saying, and I would have to agree, is that favoring one of the two proposed methods as a tool to analyze any such circuit, crappy or not, makes no difference whatsoever. To me, thats a given. It's like arguing over which is a more valid way to measure automobile velocity. In miles per hour? Car lengths per minute? Or a tire circumference vs RPM? Although they seem somewhat different, they all equate to the same thing in the end. Distance/Time.

Or to be specific.

The forward voltage drop of Vbe will be about 0.65 volts. But it's EXACT (to more significant digits) momentaneous voltage drop is directly dependant on the current through it. The parameters are fundamentally related to each other, connected at the hip, inseparable, best friends, mates, pals, et cetera. This is obvious, it's basic Ohm's law. The current through a resistance (Ibe) determines the voltage across it (Vbe). This is why a transistor can internally be a voltage controlled system, but also can be current controlled at the same time. And also why a method focusing on one of the parameters can just as easily be adapted to use the other. So there is no point in saying one is better than the other, QED... it's just like Distance/Time above.

It seems to me everyone opposing MrAl's view just wants to focus on why the circuit sucks, and not ways we can analyze why the circuit sucks.


Transistor Maths
As for a formula that can be used to calculate a transistor general parameters without knowing Hfe/β, I don't think such a thing exists. As amplifying devices, β is the most important factor, this is the gain of the transistor, it's the reason for having a transistor. To suggest that the β of a transistor can be canceled out or ignored in an equation is quite preposterous. It's like trying not to use the capacity of a capacitor, or the resistance of a resistor in a circuit calculation.

Now... there are circuits that exist that intentionally make these factors less meaningful when need be, but really that is apples and oranges.

Transistor Alpha
The transistor alpha certainly is a real parameter of a transistor, to be sure. And it is very "progressive" or "out of the box" thinking to try and use it for something meaningful. But as far as I know, transistor alpha only plays an important role with common-base configurations, and can almost always be considered unity. It's not really a gain factor, as much as it is attenuation.

So again, kinda apples and oranges.

One interesting thing is that α and β are related to each other via this formula.
View attachment 74053

But other than that, alpha is rather useless for analyzing a transistor from what I know.

You make some valid points but I assure you that alpha is important for all amp stages, common emitter, common base, and emitter follower. Alpha is a good concept to grasp because it conveys how *transistor action* takes place. The equation Ic = alpha*Ie, is not very exciting since alpha is so close to unity that the Ic/Ie relation is pretty constant with any device, any current, at any temp. But that is the point. A bias network designed to force Ie to a specific value will have an Ic value very predictable and consistent. If Ie = 1.00 mA, then we know that Ic is 0.98 to 0.998 mA for any functioning bjt device at any temp in its range, for any sustainable conditions.

Alpha is very useful at high frequencies, RF, since the bandwidth limitation is encountered. As frequency increases, alpha eventually drops well below 1, and beta drops well below its low frequency value. Analyzing alpha or beta at high freq gives us insight into the speed limitations of the device.

Also alpha is very useful when using the device as a switch such as in logic gates. Alpha in both the normal and inverse modes of operation comes into play. Two good references are "pulse, Digital, & Switching Networks" and "Digital Integrated Electronics", by Taub & Schilling, and Millman & Taub. Analyzing TTL logic relies heavily on alpha and beta in normal and inverse modes. Since the 60's, TTL logic gate inputs function in inverse mode when driven LOW.

Believe me, alpha is something any serious electronics practitioner must appreciate. I wouldn't bring it up if it weren't. Otherwise I agree with you that Mr. Al was presenting an example for discussion. He does not recommend the circuit in post #1 at all. I will post some computations maybe Sunday if I can find them, or if not I can derive them. Best regards.
 
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