1.) Common base or emitter, e- from the emitter are collected by collector. Emitter follower works the same way. The origin of Ic is the same for all 3 configurations.
.................................
2.)....
Am I clear?
No, not at all.
to 1.) Excuse me, but I am not a beginner. I did already know that e- from the emitter are collected by the collector. Are you joking with me? Is this your answer to my request?
to 2.) My definition of gain: An input signal controls an output signal and the ratio of both signals is called "gain" (VCVS, VCCS, CCCS, CCVS). It seems you have another definition. Why not?
Thank you very much for answering my questions.
Please answer my questions as they are simple & should not be misconstrued. I will answer any question you put forth & elaborate further on earlier questions. BR.
Claude, one hour ago I was sure not to respond again. Because I've got the impression that you are not willing to discuss with me on a serious basis.
OK - I changed my mind.
And I will, of course, answer your questions because - as I have indicated - a fair, serious and objective discussion between engineers should consist of question and answers.
However, please understand that at first I would like to have answered at least some of MY questions - in particular question Nr. 1 and Nr. 2 of my last post.
OK - there is one question in your last post I can answer now:
I need to know if you wish to discuss the composite bjt amp stage, bias network & all, or just the raw bjt.
When we speak about the mechanism how the current Ic is controlled we have to assume that the BJT is equipped with a voltage between C and E and a kind of bias network which allows the BJT to act as a controlled current source. Is this a new information for you? This was the basis for all of the contributions in this thread up to today.
So - what do you mean with "composite bjt amp stage" in contrast to what you call "raw bjt"? Does the "raw bjt" behaves different when it is the heart of a complete gain stage?
Claude, your long explanation cannot satisfy me because it starts with the statement "... results in increase in Ib. At first, this is just a claim. And - as far as could understand - you are trying to justify this claim with a capacitor model: V lags I. Is this interpretation correct?
In this context - I see a kind of contradiction (as follows):
Quotation#106: Actually I did not say that Ie is the 1st control chronologically.
Quotation 96: The increase in Ie, which is caused by Sue & mic, accounts for Ie change, Ib change, Vbe change, & ultimately Ic change. Vbe is merely incidental
In the following I give you an excerpt from an internet contribution. I do not blindly trust all articles which are distributed by internet - however, it is interesting and - of course (!) - it supports my view.
The full article is available via the link given in the first line.
http://amasci.com/amateur/transis.html
Excerpt:
PPPPPPPPPPPS
This article apparently has triggered extensive debates if not flamewars on multiple hobbyist forums, newsgroups, and WP. It's as if many people see Ic=hfe*Ib as holy, while Ic=Is(e^Vbe/Vt) is dark blasphemy which must be kept from the delicate ears of children. The cause of controversy is fairly obvious: at early stages we're all taught that BJTs are current-controlled devices, and only in later engineering physics courses is this claim held up to questioning. Also, the current-control viewpoint works just fine as long as we give it lip service and then turn around and use Spice programs, or as long as we never look too closely at details of the inner workings of the physics. This situation leads most people to firmly decide that Ic really is affected by Ib and not by Vbe. (Or perhaps they believe that, in diodes, the Vf diode drop is caused by the current.) I note that these debates all seem to feature typical flaws:
Primary is a sort of backwards reasoning: first we take a stance for (or against) current control. Then we hotly defend that stance against all comers while cherry-picking the supporting evidence and ridiculing all contrary evidence. But that's not reason. That's religion or politics. It's how pseudoscientists operate. Science is the very opposite: in science, first we try like hell to avoid rigid preconceptions and emotional biases. We take no stand for or against. Then we honestly ask which side is actually right: ask whether transistors are controlled by voltage or by current. And then we take the answers seriously, without desperately twisting facts to avoid losing face in public, without breaking sweat while having steam shoot out our ears, and without descending into mild insanity triggered by psychological denial that we're genuinely on the 'losing' side.
Second problem: is the BJT current-control viewpoint really held by all scientists and engineers everywhere, while voltage control is terribly wrong? WRONG.Look at the Ebers-Moll section of Sedra/Smith, Horowitz/Hill, or most any engineering text. Ask some engineering authors (many are online!) Ask semiconductor physicists. Ask professional engineers. Their answers will surprise you. And don't ask them about abstract models of black-box transistors, ask about the topic of this article: the internal physics: ask whether Vbe or Ib determines Ic, ask what is the origin of the Shockley equation, and what role does Ib and hfe actually play?)
Third problem: transient Ib current causes confusion. When Vbe changes value, charges must move during the changing profile of the depletion layer, and this requires a momentary charge flow in the base lead. I've seen several people proclaiming that this proves that Ib "causes" Vbe. No, that's a clear attempt to twist facts. The voltage across a capacitor sitting on a shelf isn't being "caused" by any continuing current. In truth it just means that a changing capacitor voltage always requires a momentary current. To explain the high frequency behavior, you need Gummel-Poon and not just Ebers-Moll. This issue doesn't apply to the low-freq or DC case of Ic=Is(e^Vbe/Vt) where Vbe is constant, yet the values of Vbe, Ic, and Ib are all connected together. The Ebers-Moll model shows that Ic is proportional to Vbe, but in order to see this, we must ignore the Emitter-Base capacitance and the transient currents which charge or discharge the EB capacitor during changing conditions.
Hello to Claude A. and Mr Rb,
yes - I think I can (partly) agree with Mr Rb. The "discussion" (I have explained why I sometimes have problems to call this disput "discussion") has come to a point where it seems impossible to come to common understanding. In this context, I remember (and you all know this) that there are textbooks supporting current control and other supporting voltage resp. charge control.
The problem of this thread is that each party simply claims something - without being able to deliver a convincing proof. And the reason for this dilemma - for my opinion - is the relationship in general between voltage and current.
More than that: What is current? Does it really flow? Or is it the charge that flows?. OK - let's stop at this point.
To Claude:
To be honest, nearly everything in your last reply is a repetition of commonly known facts. Nobody will deny that there is an alpha which must be included in the equations.
I don't know if alpha was forgotten in the cited equation or if the meaning of the symbol for the saturation current is Is=alpha*Ies.
But I do not consider this as important.
And also the second part of your reply starting with 4 basic and well-known equations does not help to bring the discussion one step further.
Why do you stress the importance of Vcc? Was there any disagreement about Vcc?
As far as I understand you claim that Bill Beaty is wrong. OK - but why? Where is his error?
This question touches the problem of transients and high-frequency signals.
And your comment is: Transients easily disprove the Vbe causal hypothesis
You will not be surprised that this argument cannot convince me.
It happens very often in electronics that we have
* to idealize some characteristics, or
* to neglect parasitics, or
* to suppress second-order effects
with the aim to isolate and identify the desired properties of a DUT.
As an example I mention the fact, that NO formula (gain, input/output resistance, ...) is correct by 100%. We restrict ourselves on the main parameters and accept errors.
Thus, I think during this discussion we really should have only rather low frequencies in mind. High-frequency effects can conceal the phenomena we are interested in.
As far as I remember, it was your key argument pro current control that Ib would lead Vbe (because of the diffusion capacitance).
After corresponding simulations I cannot confirm this observation (I have asked you already: Simulation or measurement?).
For frequencies up to the lower kHz range Vbe and Ib are in-phase. (BJT Spice model in active region, Ic=1.5 mA)
(By the way: this is a good point to demonstrate that high-frequency effects influence/disturb the effects we want to study).
Finally, at the moment I tend to follow Mr RB's suggestion to leave the thread.
W.
But am I viewing things from my narrow current control viewpoint> Do I have a tendency to define all things w/ current? People on my side who model the bjt as CC, also model FETs as VC, IGBT as VC, vacuum tube as VC, high-Z voltage feedback op amps as VC. I don't force everything to fit into a current control model. My opponents on the other hand, believe that nothing changes unless some voltage changes first. That is not true. Any examination of charge motion, fields, boundary conditions affirms my point.
I think I am going to bow out of this thread as others have done,
as this is taking on all the momentum of an argument about religion and people are too busy pedantically defending what happens inside a transistor to understand how to control the transistor.
As a parting shot, I think some people need to have a careful think about what "controlled" means.
This is NOT a forum about theoretical semiconductor physics, it is an electronics forum. In electronics we "control" transistors.
Let's say I have another device (not a transistor), say a serial controlled light dimmer. I apply serial data to its input, and it adjusts phase angle and "controls" the current through the lamp filament. People could put forward all sorts of complex arguments about the inside of the component, that the lamp brightness is actually "controlled" by phase angle, or is actually "controlled" by a combination of phase angle and the PSU volts vs filament ohms.
But the FACT is that as a component, used by someone in electronics on an electronics forum, it is a serial controlled device. The mechanism of whatever control systems and voltage effects happen inside the device is fairly irrelevant, and only of importance to pedantic nitpickers.
Hi Claude,
Quote: I have stated repeatedly that CC is a good fit only externally. When considering internal storage, delays & such, the charge control model works best.
May be I couldn't find this view behind the lines written by you in former posts (due to my limited knowledge of your language), but for me this is a new "sound".
Perhaps we can meet each other using this formulation.
But - don't you also think it is surprising that experienced engineers discuss about the physical working principle of a device that was invented 60 years ago?
Quote: These same people do not accept the OEM op amp mode known as "current feedback". They insist it is really voltage feedback modified. In general, these critics cannot accept anything being controlled by a current. An error signal has to be a voltage. A control signal has to be a voltage.
I am 100% with you that - of course - current can serve as an error signal. The current mirror which is fed with the current through the inverting input is a clear indication of this principle.
Perhaps we meet again in another thread.
Regards
Winterstone
To the Ineffable All,
Now I would like to say something about BJT control. Whenever I study BJTs, I read that they are manufactured with two types of materials, each of which have a predominace of different charge carriers. That is why they call a BJT a bipolar device. Then I read that the two different charge carriers diffuse into the opposite slab of material, and either annihilate each other, or continue on to the next slab, or exit a contact. Continuing on, I observe that different amounts of doping are used to control the charge concentrations, which in turn controls the diffusion within the BJT. Then I learn that there are depletion regions in the boundary locations of the NP slabs where diffusion cannot take place due to the absence of charge carriers. I also come across terms like minority carrier diffusion currents. It does not take long to realize that unlike a FET or a vacuum tube, the mechanism for BJT operation is diffusion. So what controls diffusion? All the texts agree that charges from the emitter diffuse to the base and are, for the most part, accelerated on to the collecter by the collector voltage. There is no disagreement that this process cannot continue by itself due to the back voltage, also called barrier voltage. This barrier voltage can be neutralized by the application of Vbe, and the diffusion process can continue. That is why the equations for Ic show up in Sedra and Smith as being dependent only on Vbe and not Ib. This control by Vbe does not mean that the relationship between Ib and Ic should not be used for calculation and design. It only means that Ib is an indicator of Ic and not a control.
Some further opinions:
A model of a device is just that, a model. It may help determine what a device does, but it does not necessarily disclose or prove how the device works.
A storage charge may cause a current without any external voltage, because it has its own internal voltage.
Driving a device with a current source is the same as connecting a large external resistor to the device. That is not the same as connecting only a pure voltage source. It takes a voltage to initiate a current, unless there is already stored charge present. If you drive a device with a current, you are effectively applying a voltage to it.
The order in which events happen has no relevance in determining control. Control is determined by the physical cause of the changes.
The topology of the external components connected to a device does not change the way the device works, only the way it behaves.
Ratch
Again, we do not "apply Vbe", it is a consequence of an external source providing an E field & charges drift as a result.
The Ib/Ie currents do not depend on Vbe.
Then you state " It takes a voltage to initiate a current," which I respond with - how does the voltage appear?
Voltage does not cause current.
A power source be it battery, generator, photodiode, etc., generates both.
As long as you keep invoking the myth that "voltage initiates current" you will always view every electrical device as voltage driven.
What about an LED, universally described as current controlled? We adjust light output by varying current, albeit there has to be a forward voltage. Is an LED VC or CC? Please answer.
I think you have your own definition of "control". Reread my posts & I've explained in detail why Vbe is not the cause nor the control of the currents in the bjt.
You make declarations based on pure imagination.
This business that Vbe is what initiates Ib/Ie is flat out wrong. This is your view. Re Sedra & Smith, they acknowledge a relation between Vbe & Ic, but also between Ic & Ie, as well as Ic & Ib. You selectively focus all your attention on Vbe as the cause. I believe for you it is religion. Proof to the contrary is ignored by you.
Once again, the CC model is not meant to cover internal physics.
But the model which extends beyond CC is not VC, but rather QC.
When using a bjt as a saturated switch only charge control works. How can VC help with switching operation in saturation?
Lastly you say "If you drive a device with a current, you are effectively applying a voltage to it." That proves my point that you view voltage as more basic than current universally. You simply cannot accept that the 2 are inclusive, neither 1 more basic than the other. Here is my response - When you drive a device with voltage, you are effectively applying current to it. Unless the load resistance is 0 or infinite, you need both I & V. Driving a device w/ current only implies that should the resistance change, the source will output a different voltage in order to maintain the fixed current. Likewise, a voltage source does the reverse.
Another faux pas on your part - "Driving a device with a current source is the same as connecting a large external resistor to the device". Not true. A 1.0 milliamp CCS plus a 1.0 kohm shunt resistor may be electrically equivalent to a 1.0V CVS plus 1.0 kohm series resistor, but not thermally equivalent. If open, the CVS dissipates 0 power, CCS dissipates 1.0 mW. If shorted, CVS dissipates 1.0 mW, CCS disspates 0. The 2 are not completely equivalent. Also, a true CCS does exist.
Are you aware that the power company can just as well deliver constant current source to our homes? Spinning the turbines at constant torque will provide CCS operation. But they spin them at constant speed for CVS operation, & as a benefit we get constant frequency. You just cannot accept that current & voltage have no pecking order. Either one can be the independent variable, with the other determined by impedance.
Claude,
Are saying that "applying a voltage" to something is not correct? Of course a voltage difference causes a electrostatic field to form. How does that disprove that Vbe controls Ic?
Still don't believe Sedra? Then perhaps Neudeck in attachment #1. Notice how both Ic and Ib both vary with Vbe and temperature.
Countless ways. I believe we are talking about it being applied as a signal.
If there is a conduction path, it sure does.
Power sources may conduct current if there is a conduction path. Otherwise, only voltage is present.
Voltage has to be present for current to exist, but voltage can be present without any current also.
The current in a LED is physically controlled by the voltage across it according to Schockley's equation. The fact that the brightness corresponds to current does not make a LED current controlled physically. It still operates by bipolar diffusion, which is controlled by a external voltage.
Your explanations do not make sense.
I consider them well thought out.
If wrong, they why do Sedra and Neudeck publish those equatons? Of course since Ic is almost the same as Ie, there is going to be a relationship. My focus in on Vbe controlling Ib and Ic is because Sedra, Neudeck, and other textbooks say that Vbe controls the diffusion process. This is solid evidence that that proposition is true. I don't believe it on religious faith, I believe it on solid evidence.
Then why are you presenting it to disavow my claim?
Models tell you what a device does, but not how it works.
As I said before, we are firmly in the active region.
More basic? No, both have the same relevancy. Voltage is necessary for current to exist. If a voltage is present, current may or may not be present depending on a conduction path. If a current is present, an external or internal voltage is present also. Neither one is more basic that the other, and they have nothing to do with whether a BJT is controlled by Vbe or Ib. Driving the base with a current or voltage source is irrelevant, because it only responds physically to the Vbe presented.
I am looking for the first faux pas. You are right, they are not thermally equivalent. But that does not matter too much as to whether Vbe or Ib controls Ic, does it?
So does that mean that at constant current, all the outlets will have arcs across them to maintain the constant current until something is plugged into them? The physical relationship determines what is the control, and in a BJT or LED, which depend on diffusion, the voltage is in control because it regulates the diffusion.
Ratch
...As long as you keep invoking the myth that "voltage initiates current" you will always view every electrical device as voltage driven. What about an LED, universally described as current controlled? We adjust light output by varying current, albeit there has to be a forward voltage. Is an LED VC or CC? ...
...
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