BJT's don't work like that

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Thread Starter

Ratch

Joined Mar 20, 2007
1,070
cumesoftware,

My sincere apologies, but my doubt was reasonable, you have to admit.
Indeed. You are prudent to be skeptical.

However, I've noticed that you write "comesoftware". Please, address me as "cumesoftware" or "cume" next time, if you please.
Will do. I did not even notice that I was automatically writing come instead of cume.

That seems an "egg and chicken" issue here. Indeed, you can control the collector current by controlling the base voltage, because of the emitter diode characteristics. But you can't conclude that a BJT is a voltage controlled device. In order for a BJT to work, it needs to have current drawn form the base, and not a voltage present at the base (BJTs are not FETs). And the collector current is proportional to the base current. Thus, it is more accurate to say that a BJT is a current controlled device.
Well, that is where we disagree. Remember what the professor said?

"The voltage applied to the base emitter junction controls the collector current and the base current is a result of the additional hole injection (for an npn BJT) into the emitter as well as the recombination in the base-emitter depletion region and the quasi-neutral base region."

All this extra activity causing base current is inevitable, but not a part of what controls Ic. The base-emitter depletion region changes with the Vbe, and that is the real cause of Ic change. It just happens that Ib, like Ic, is also exponentially related to Vbe, so Ic is proportional to Ib, but not the cause of Ic.

Dave had shown hard evidence on that. However, it seems that this thread is going personal. Partly my fault, I must say. But I've only lit the fuse.
I did not think he did, and I replied as such. Yes, we were all primed to go.

Do they have a permit?
Automatically.

As my final note:
If BJTs had selenium cores and gold plated bolts, they could work as voltage controlled devices due to some spiritual turbulence. This idea was proposed by Ivo Shandor in the early 20's, I think.
Does he back up what he is saying? Ratch
 
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Thread Starter

Ratch

Joined Mar 20, 2007
1,070
studiot,

Let's all remember that nobody's perfect. We all dash off inaccuracies in the heat of the moment sometimes.

Ratch I assume you contradiction of my observation that you can control transistors with light, rather than Vbe, was just such a moment.
Would you be so kind as to give me the message number in this thread where I said transistors could not be controlled by light? After all, what is a phototransistor?

For the record
Phototransistors work by directing the light onto the Collector -Base junction, which is reverse biased. This stimulates flow of carriers across that junction.
It has nothing whatsoever to do with the Emitter - Base junction, where Vbe appears.
Why was it mentioned in the first place?

In fact we used to make erzatz phototransistors by scratching the black paint off early glass encapsulated transistors like the 0C71 and 0C45 as the effect occurs in all transistors.
I believe it. It is well known that photons have an effect of PN junctions.

If you are going to control the Base - Emitter junction, you must of necessity supply both suitable voltage and current. The junction has resistance defined by well known laws as Dave et al have expounded.
Thus far, I have not heard anything new or how it ties into the argument.

The whole proposition/argument was explored way back at the beginning of transistor electronics as my reference shows and was clearly stated in the first textbook on the subject I owned.
Just to be clear, do you mean the argument of whether the transistor is current responding/controlled or voltageresponding/controlled?

Semiconductor Junction Devices by J Frank Pierce, and also the Motorola & TI publications of that time.
Can you be a little more specific and refer to a page and maybe quote it, or explain how it bolsters your argument, assuming your argument is the above.

Ratch, as you have not done me the courtesy of stating where in the world you are, I have no idea how you would obtain referenced documents, nor am I inclined to help since you responded with a sarcastic comment to a genuine offer of additional useful information.
It is a matter of privacy, not courtesy. I will say I live in the US, but as to where is my choice to disclose or not. Maybe I will sometime. I live about 30 miles from a large university, but I doubt they would keep journals from 50 years back. But then, I know they are pack rats, so maybe they do. But again, you did not list anything within that I should look at. There is no help you can give me because no one but I knows what is available or can be ordered by interlibrary loan.

Finally since you asked for subjects ignored, I commented that frequency response is controlled by current not voltage effects. The reasons for this (Early Effect etc) have also been expounded by others here.
I don't recall any discussion of frequency response caused by the Early effect. The Early effect is caused by voltage. I would think that the diffusion capacitance would have a much greater effect on frequency that the Early effect. How does this tie into the about whether the transistor is controlled/responding to voltage or current?

If this is how you treat your 'supporters'.................
Supporters? Ratch
 
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studiot

Joined Nov 9, 2007
4,998
Ratch,
I have formed the opinion that you are being argumentative just for sake of it on account of your responses to my posts.

You seem to ignore, deny or belittle anything said to you.

In my first post (#55) I made five points.

I placed my principal point first. Many of the others flow directly from this point.

You ignored it completely.

You then made flippant rejoinders to several subsequent points, suggesting that they were somehow irrelevant.

In the quotes that follow, my words are in italics, yours are normal.


1) Any physical quantity that can affect the operating conditions of a device can be used to 'control' it in some fashion, by varying that quantity.
In your attempt to belittle my second point you made a complete hash of your reply.

Quote:
2) As such you can control a transistor with a hairdryer or lightbulb. There are useful circuits based on either of these.

True, but thermal is slow. Photons are a substitute for Vbe
Vbe is strongly dependent upon temperature and many important circuits are based upon this voltage control. These include stabilisation and compensation circuits. Yes response is slow but that can also be a good thing.

Photons are not a substitute for Vbe. Suggesting they are is just plain old fashioned wrong.
In fact illumination of phototransistors affects the only part of the Ic equation I gave in post #66 that is not affected by Vbe.
This component is Ic0.
Vbe does not change one iota when a correctly setup phototransistor is illuminated. I can easily show this by direct measurement.
Further the ability to hold the transistor off by suitable Vbe or Ib until it is required and then switch it on at will by illumination is very very useful and not to be dismissed so lightly.

My third point you attempted to deny by diversion.

Quote:
3) If you wish you can affect circuit values by forcibly altering (suitably) either voltage or current. If you wish to use current control you are not limited to the base. Many circuits, especially within integrated cicuits use emitter injection.

This discussion is about BJTs.
Are you suggesting that integrated circuits do not contain BJTs? Or that your discussion is not relevant to BJTs in integrated circuits?
In any event I also included discrete circuitry (which obviously contains BJTs)
Or perhaps you are suggesting that emitter injection does not work and therefore the whole of logic and switching circuitry should be abandoned because Vbe control is not used?


In reply to my fourth point you attempt to belittle my comment by arguing over terminology in an attempt to divert attention from the substance.

Quote:
4) When you come to consider the frequency dependance it is aspects of curent flow within a transistor that control the behaviour, rather than inter-electrode voltages. This is also true of FETs. So from this point of view transistors are current controlled.

To be precise, you should say charge flow, not current flow. What aspects, and what controls the charge flow? Interelectrode? We are not talking about tubes, CCDs or FETs. Transistors are voltage controlled because the Vbe is what changes the collector current regardless what the Ib is.
Charge flow, current flow I really don’t care.
The real point is that charges have mechanical inertia. Voltage, (however it works) does not.
This means that you can change voltage quickly more easily than current in a circuit.
It is changing the movement of charges that degrades the high frequency performance of devices including transistors.
Voltages can be changed faster than anything else in this universe. In fact this is exactly what happens in the voltage component of a lightwave.

So if our BJT responded only to Vbe changes we would not see the frequency degradation of performance.

With regard to my fifth point I was simply trying to establish an historic reason for the desire to highlight current control of transistors. My earlier four points all amounting to an observation that transistors may be controlled by current, voltage or other means, none of which completely accounts for all effects by themselves.

In fact instead of smart-alec bickering we should all be celebrating the wondrous effect that transistor action brings to circuitry.

Quote:
5) It is also true that historically transistors followed electronic valves, which they are quite different from. With valves the mechanism to use voltage electrodes to control the flow of current is quite obvious. With transistors, however, the melding of two current loops is more obscure. So there was a desire to promote a simplifying distinction.

What does the above paragraph mean with regard to what controls a BJT
So let us see how you got on with my second post (#66)

Quote:
It is true that the fundamental equation of a transistor's operation is Ic = alpha*Ie + Ic0In words this states that the collector current is the fraction of the emitter current reaching the collector plus the unbiased collector current.Since Ie (not Ic) is a function of Vbe we can control Ic by varying Vbe.

Your last sentence does not make sense. Both Ie and Ic are controlled by Vbe.
Are you being deliberately argumentative or what?
The collector current Ic0 cannot, by definition, depend upon Vbe, which is , by definition zero for the collector current with the base open circuit!!!!!!!!!!

The equation actually states that the collector current depends on three components.

Alpha, which is a fixed characteristic of the particular transistor and not dependent upon Vbe.

Ie which is very definitely dependent upon Vbe - or is Vbe dependent on Ie – it really depends upon which way round you read the equation connecting them.

Ic0 Which I have already dealt with several times.

All I have done is a partial mesh analysis of the two loops mentioned in point 5 of post #55. A complete analysis must yield all the currents and voltages involved. This cannot be based upon relationships to Vbe alone as some of these parameters are independent of Vbe.

Quote:
Ratch I refer you to the following paper"A Study of Charge Control Parameters of Transistors"Sparkes J.J.Proceedings IRE vol48 no10 pages 1696 - 1705, 1960

Is that available online, or do I have to go to a major library like MIT or the Library of Congress which keeps 50 year old references? Ratch
Since you are actually in America I really would have thought that a reference from the IEEE would have been right up your street.
The IEEE is of course the governing American Institution for the Electronic Engineering profession and Standards in electronics.
So any self respecting librarian should have had no trouble finding the reference
Or you could ask the IEEE itself. (perhaps you are already a member?)

But apparently this was too tiresome.

Also apparently I am not allowed to refer to something 50 years old, but you can refer to something 75 years back.

Only my taxman can do that to me!
 

Thread Starter

Ratch

Joined Mar 20, 2007
1,070
studiot,

Ratch,
I have formed the opinion that you are being argumentative just for sake of it on account of your responses to my posts.

You seem to ignore, deny or belittle anything said to you.

In my first post (#55) I made five points.

I placed my principal point first. Many of the others flow directly from this point.

You ignored it completely.

You then made flippant rejoinders to several subsequent points, suggesting that they were somehow irrelevant.
Everyone is entitiled to their own opinion.

I ignore it if it is irrelevant, I deny it if it is false, I belittle it if it is foolish or silly.

You are right, I inadvertently missed answering your first point. It was an oversight which I shall correct below.

1) Any physical quantity that can affect the operating conditions of a device can be used to 'control' it in some fashion, by varying that quantity.
Let me address the above statement now. The argument of this thread is whether Ib or Vce control the Ic of a BJT operating in the active region. Although a lot of things can affect the operating conditions like the Q point, my contention is that in practice only Vbe is what is controlling the transistor. That makes it a voltage control/responding device. If Ib changes, so does Vbe. Remember my quote from the professor to cumesoftware?

"The voltage applied to the base emitter junction controls the collector current and the base current is a result of the additional hole injection (for an npn BJT) into the emitter as well as the recombination in the base-emitter depletion region and the quasi-neutral base region."

Quote by studiot
2) As such you can control a transistor with a hairdryer or lightbulb. There are useful circuits based on either of these.

Answer by Ratch
True, but thermal is slow. Photons are a substitute for Vbe

Quote by studiot
Vbe is strongly dependent upon temperature and many important circuits are based upon this voltage control. These include stabilisation and compensation circuits. Yes response is slow but that can also be a good thing.

Photons are not a substitute for Vbe. Suggesting they are is just plain old fashioned wrong.
In fact illumination of phototransistors affects the only part of the Ic equation I gave in post #66 that is not affected by Vbe.
This component is Ic0.
Vbe does not change one iota when a correctly setup phototransistor is illuminated. I can easily show this by direct measurement.
Further the ability to hold the transistor off by suitable Vbe or Ib until it is required and then switch it on at will by illumination is very very useful and not to be dismissed so lightly.
True, Vbe is dependent on temperature, but so what? Since I aver that Vbe controls Ic, it does not change the argument any more than saying Ib affects Vbe. In fact a lot of extra effort is made to insure that temperature change of Vbe does not affect the Q point. That does not appear to be temperature control to me.

When I said that light was a substitute for Vbe, I meant that since Vbe controls Ic, and photons can control Ic, Vbe and photons were sort of equivalent. Photons can affect a PN junction, but that is not what we were talking about. If photons do not change Vbe in a phototransistor, then they do not change Ib either. So I should have terminated any discussion about phototransistors as irrelevant to the discussion about whether Ib or Vbe controls Ic.

3)
Quoted by studiot
If you wish you can affect circuit values by forcibly altering (suitably) either voltage or current. If you wish to use current control you are not limited to the base. Many circuits, especially within integrated cicuits use emitter injection.

Answered by Ratch
This discussion is about BJTs.

Answered by studiot
Are you suggesting that integrated circuits do not contain BJTs? Or that your discussion is not relevant to BJTs in integrated circuits?
In any event I also included discrete circuitry (which obviously contains BJTs)
Or perhaps you are suggesting that emitter injection does not work and therefore the whole of logic and switching circuitry should be abandoned because Vbe control is not used?
I looked in the book by Sedra and Smith, called Microelectronic Circuits. They mention the BJT as a digital circuit element. They also have a section on "Early Forms of BJT Digital Circuits" In switching circuits, the object is to try to get from the saturated region to the nonsaturated as quickly as possible. I cannot prove it for sure, but I don't think you will find many BJTs operated in the active mode in integrated circuits. Anyway, it is irrelevant because we are not arguing about BJT applications and it does not bolster your argument about what controls a BJT.

Quote by studiot
4) When you come to consider the frequency dependance it is aspects of curent flow within a transistor that control the behaviour, rather than inter-electrode voltages. This is also true of FETs. So from this point of view transistors are current controlled.

Answer by Ratch
To be precise, you should say charge flow, not current flow. What aspects, and what controls the charge flow? Interelectrode? We are not talking about tubes, CCDs or FETs. Transistors are voltage controlled because the Vbe is what changes the collector current regardless what the Ib is.

Answer by studiot
Charge flow, current flow I really don’t care.
The real point is that charges have mechanical inertia. Voltage, (however it works) does not.
This means that you can change voltage quickly more easily than current in a circuit.
It is changing the movement of charges that degrades the high frequency performance of devices including transistors.
Voltages can be changed faster than anything else in this universe. In fact this is exactly what happens in the voltage component of a lightwave.

So if our BJT responded only to Vbe changes we would not see the frequency degradation of performance.
I really did not understand your original statement. Charges don't have mechanical inertia. Perhaps the charge carriers do, but I don't think that matters in the discussion. Lightwaves don't have a voltage component, they have a magnetic field and a electric field component. That is why physicists call light an electromagnetic wave. I think you need to come up with a better explanation of what you are talking about. Be sure to tie it into our Ib vs Vbe controversy at a frequency below that of visible light.

Quote be studiot
With regard to my fifth point I was simply trying to establish an historic reason for the desire to highlight current control of transistors. My earlier four points all amounting to an observation that transistors may be controlled by current, voltage or other means, none of which completely accounts for all effects by themselves.

In fact instead of smart-alec bickering we should all be celebrating the wondrous effect that transistor action brings to circuitry.


5) It is also true ..... Sorry I had to truncate this because of the 10000 limit.
Answer by Ratch
What does the above paragraph mean with regard to what controls a BJT

Answer by studiot
So let us see how you got on with my second post (#66)

It is true that the fundamental equation of a transistor's operation is Ic = alpha*Ie + Ic0In words this states that the collector current is the fraction of the emitter current reaching the collector plus the unbiased collector current.Since Ie (not Ic) is a function of Vbe we can control Ic by varying Vbe.

Answered by Ratch
Your last sentence does not make sense. Both Ie and Ic are controlled by Vbe.

Answered by studiot
Are you being deliberately argumentative or what?
The collector current Ic0 cannot, by definition, depend upon Vbe, which is , by definition zero for the collector current with the base open circuit!!!!!!!!!!

The equation actually states that the collector current depends on three components.

Alpha, which is a fixed characteristic of the particular transistor and not dependent upon Vbe.

Ie which is very definitely dependent upon Vbe - or is Vbe dependent on Ie – it really depends upon which way round you read the equation connecting them.

Ic0 Which I have already dealt with several times.

All I have done is a partial mesh analysis of the two loops mentioned in point 5 of post #55. A complete analysis must yield all the currents and voltages involved. This cannot be based upon relationships to Vbe alone as some of these parameters are independent of Vbe.
Establishing a historic reason of why something was presented wrong is not a proof of a argument.

Simplifying something is not a reason to present it wrong.

You said, "Since Ie (not Ic) is a function of Vbe we can control Ic by varying Vbe." First you say that Ic is not a function of Vbe, then you say it is controlled by Vbe. I don't understand what you are saying.

Who said that Ico depended on Vbe? We all know it is a themally generated current.

I don't understand how you can come to the conclusion that just because some of the parameters including Ico do not depend of Vbe, that Vbe is not controlling Ic. Changing Vbe will control the Ic as the professor said it would.


Yes, I have heard of the IEEE. They charge $$$ for a membership and also for any reprints of former articles. It would take a heavy duty library to keep all those journals from 50 years back. I know my company library got rid of journals over 5 years old. They just did not have the space to store them. What reference did I give that was 75 years old? I did not get the joke about the taxman. Ratch
 

Dave

Joined Nov 17, 2003
6,969
Let me address the above statement now. The argument of this thread is whether Ib or Vce control the Ic of a BJT operating in the active region.
Actually Ratch, this thread is about the assertion in your very first post of this thread that BJTs:

...are voltage controlled devices, not current controlled like many would have you believe.
Ib, Ic, Ie, Vbe, Vce, active-region, saturated region etc, as specifics are irrelevant, this is generic discussion about the BJT as voltage-controlled and/or current-controlled devices as espoused in your opening post. Or have the goal-posts shifted now?

Dave
 

thingmaker3

Joined May 16, 2005
5,083
I concur. It is as though Ratch has a passion for debate as an entertainment form. But these debates serve no useful purpose for anyone but Ratch.
 

Thread Starter

Ratch

Joined Mar 20, 2007
1,070
Dave,

Quote from Dave
Actually Ratch, this thread is about the assertion in your very first post of this thread that BJTs:


Quote from Ratch
...are voltage controlled devices, not current controlled like many would have you believe.


Answer from Dave
Ib, Ic, Ie, Vbe, Vce, active-region, saturated region etc, as specifics are irrelevant, this is generic discussion about the BJT as voltage-controlled and/or current-controlled devices as espoused in your opening post. Or have the goal-posts shifted now?
I completely agree that his thread is about whether the BJT is a voltage or current controlled device.

Talking about how Vbe controls Ic is not irrelevant. It is the heart of the argument because it defines the BJT as voltage controlled. I talk about those other things because others talk about them in their arguments against my assertion. Ratch
 
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Thread Starter

Ratch

Joined Mar 20, 2007
1,070
hgmjr,

I have decided that ratch is the "energizer-bunny" of idiots. He just keeps going and going.
Are we switching to ad hominem now?

The only good I can see that may possibly come of this thread is that ratch will be very careful to pick his battles within the forum in the future since he has to be tired of continuously defending his assertion. He has failed to convince anyone to come forward and whole-heartedly endorsed the accuracy of his point of view.
Nonsense. I always speak out when I think something is not right. I can be persuaded by salient facts and reason, but so far I have not seen very much in this thread.

I think he would argue that Ohm's Law does not govern the behaviour of BJTs if someone pressed him on the matter.
Now we need some definition from you. When you say Ohm's law, are you referring to the resistance or impedance formula V=IR, or are you referring to the true definition of Ohm's law as espoused in this thread. http://forum.allaboutcircuits.com/showthread.php?t=11674&highlight=Ohm's+law . They both apply in all electrical activity including transistors, of course. Ratch
 

Thread Starter

Ratch

Joined Mar 20, 2007
1,070
thingmaker3,

I concur. It is as though Ratch has a passion for debate as an entertainment form. But these debates serve no useful purpose for anyone but Ratch.
Sure they do, they cause everyone who reads them to think, just like it did for me. I used to believe just what you do now with respect to BJT current control until I communicated with Professor Van Zeghbroeck. Ratch
 

Dave

Joined Nov 17, 2003
6,969
Talking about how Vce controls Ic is not irrelevant. It is the heart of the argument because it defines the BJT as voltage controlled. I talk about those other things because others talk about them in their arguments against my assertion. Ratch
Sometimes you are saying it is Vbe controlling Ic - now (as you have twice mentioned) it is Vce. Vbe and Vce serve very different purposes.

Dave
 

studiot

Joined Nov 9, 2007
4,998
Now laying odds on who will have the last word in this thread.

white horse 7 to 1 on
red horse 15 to 1 against
the field 33 to 1 bar
 

Thread Starter

Ratch

Joined Mar 20, 2007
1,070
Dave,

Sometimes you are saying it is Vbe controlling Ic - now (as you have twice mentioned) it is Vce. Vbe and Vce serve very different purposes.
Sorry, it is a typo on my part. Thanks for bringing it to my attention, and I hope it did not cause any undue confusion. It should be Vbe, not Vce. Ratch
 

Ron H

Joined Apr 14, 2005
7,063
I have wasted about an hour, reading this entire thread from beginning to end.
Control implies a forcing function. I can force the base-emitter voltage, and get a very nice and predictable exponential relationship between base voltage and collector current, while giving very little thought to the base current. On the other hand, I can force a base current, and get excellent control of collector current (at least in a digital circuit, where the object is saturation or cutoff), while giving little or no thought to the Ebers-Moll equation. Others (especially Dave) have made this point in different words.
Ratch, you will say, "Ah, but when forcing the base current, the base-emitter voltage is actually controlling the collector current". Who gives a rat's ass? I prefer to think of Vbe in this situation as an artifact of the current.
I'll probably regret getting involved in this.:rolleyes:
 

Thread Starter

Ratch

Joined Mar 20, 2007
1,070
Ron H,

Welcome to this thread.

I have wasted about an hour, reading this entire thread from beginning to end.
Control implies a forcing function. I can force the base-emitter voltage, and get a very nice and predictable exponential relationship between base voltage and collector current, while giving very little thought to the base current. On the other hand, I can force a base current, and get excellent control of collector current (at least in a digital circuit, where the object is saturation or cutoff), while giving little or no thought to the Ebers-Moll equation. Others (especially Dave) have made this point in different words.
Ratch, you will say, "Ah, but when forcing the base current, the base-emitter voltage is actually controlling the collector current". Who gives a rat's ass? I prefer to think of Vbe in this situation as an artifact of the current.
Actually it is the base current which is the artifact. Remember the quote from Professor Van Zeghbroeck back in post #64 of this thread?

"The voltage applied to the base emitter junction controls the collector current and the base current is a result of the additional hole injection (for an npn BJT) into the emitter as well as the recombination in the base-emitter depletion region and the quasi-neutral base region. It is tempting to claim that the BJT is controlled by the base current, since that is how a BJT is typically biased; the exponential variation of the current with the base-emitter voltage makes a voltage bias
impractical."

I cannot say it more concise than that. The collector current is proportional to the base current, but it is really the Vbe that is controlling Ic by affecting the carrier injection from the emitter. Vbe is the cause of Ic and Ib is the consequence, as the professor says. I said in the thread that I am only discussing the active region, not the cut-off and saturation regions used for digital applications. The Ebers-Moll model tells you what happens, not the physics of how it happens. Who cares you say? Only those who want to understand, really understand how BJT's work, not just how to apply them to applications. Ratch
 

Ron H

Joined Apr 14, 2005
7,063
Ron H,

Welcome to this thread.



Actually it is the base current which is the artifact. Remember the quote from Professor Van Zeghbroeck back in post #64 of this thread?
I predicted you would say that. How can base current be an artifact when I specifically stated that the base current is forced?
I am taking issue with your statement that base-emitter voltage controls collector current. I think we (myself and most others on this thread) have a problem with your implied definition of the word "control" in this situation.
In some circuits, such as a switching transistor where the collector current is in transition, Ebers-Moll may apply, but is generally irrelevant. That was my reason for saying "Who gives a rat's ass?". If I am forcing base current, I probably don't.
"The voltage applied to the base emitter junction controls the collector current and the base current is a result of the additional hole injection (for an npn BJT) into the emitter as well as the recombination in the base-emitter depletion region and the quasi-neutral base region. It is tempting to claim that the BJT is controlled by the base current, since that is how a BJT is typically biased; the exponential variation of the current with the base-emitter voltage makes a voltage bias
impractical."

I cannot say it more concise than that. The collector current is proportional to the base current, but it is really the Vbe that is controlling Ic by affecting the carrier injection from the emitter. Vbe is the cause of Ic and Ib is the consequence, as the professor says. I said in the thread that I am only discussing the active region, not the cut-off and saturation regions used for digital applications. The Ebers-Moll model tells you what happens, not the physics of how it happens. Who cares you say? Only those who want to understand, really understand how BJT's work, not just how to apply them to applications. Ratch
 

Thread Starter

Ratch

Joined Mar 20, 2007
1,070
circuitashes,

Shouldn't it rather be: "Vbe is the cause of Ib and Ic is the consequence"?
No, Vbe controls the charge carriers from the emitter. Ideally they should all pass through the base and continue on to the collector. Unfortunately some are inevitably caught by the base to become Ib. Ib current is not needed to control Ic, but it is proportional to Ic. Although this relationship is exploited to bias the transistor, saying it controls Ic it is like saying that the ammeter in a series circuit controls the current instead of the voltage source. Ratch
 

Thread Starter

Ratch

Joined Mar 20, 2007
1,070
Ron H,

I predicted you would say that. How can base current be an artifact when I specifically stated that the base current is forced?
I am taking issue with your statement that base-emitter voltage controls collector current. I think we (myself and most others on this thread) have a problem with your implied definition of the word "control" in this situation.
In some circuits, such as a switching transistor where the collector current is in transition, Ebers-Moll may apply, but is generally irrelevant. That was my reason for saying "Who gives a rat's ass?". If I am forcing base current, I probably don't.
Because as far as control in concerned, you are forcing Vbe when you set up Ib. Putting it another way, Ib is the the indicator, not the cause of Ic. As the prof said about Ib, it begiles you into thinking that it is controlling Ic due to its proportionality with Ic. Ratch
 
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