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How does a transistor amplify current or voltage?

Discussion in 'General Electronics Chat' started by jac4b, Jul 23, 2010.

  1. Ratchit

    Ratchit Well-Known Member

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    BrownOut,

    And do you think that the professor publishes papers without doing that? As an academic, he would be more inclined than ever to do so. He gave me a quick off the cuff opinion about a question I asked, but I can't imagine him being surprised by that question. It would not be a stretch to assume that he has long ago thought long and hard about it. As I said before, his knowledge and experience has to be respected.

    You mean the forward current gain β? That is not what we were discussing. We are talking about the causal relationship of the voltage and current. If I come across that book, I will certainly look at it to see if it applies to what we are talking about.

    I think I stated before that design and calculation work well with the concept of current control. The causal relationship does not.

    I said in my previous post that I once believe as you do. So of course the opinion he gave me was counter to my own. I don't own or operate a semiconductor laboratory, so my "research" is reading and evaluating what other "experts" publish. The professor was an expert source of knowledge, so I was not wrong is asking his opinion.

    Ratch
     
  2. BrownOut

    BrownOut Banned

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    Knowledge and experience should indeed be respected. We have knowledgeable and experienced people here, like Eric, who as I've said has a half century of experience. That's the great thing about ETO; we don't need any stinking academic "experts". We have our own knowledgeable people.

    We are talking about current gain, which is given be hfe or β, and is a product of device and physical parameters. Simple as that. Causal relationships work well with current, better than with voltage, in fact, as has been detailed by other members.

    Sounds like you simply flipped your opinion upon heading his opinion, which was given without any proof. Reading and evaluating other's work means they have to share their actual work, not just some off the cuff remarks. Sorry, still not very convincing. Engineering demands something more, you know, engineering oriented.
     
    Last edited: Jul 26, 2010
  3. Ratchit

    Ratchit Well-Known Member

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    Brownout,

    There is experience and there is academic knowledge. Both are good. Can it not be said that academic knowledge is also in intertwined with experience? Every prof in the tech fields has access to a lab, don't they? So the academics don't just write papers. They also get their hands dirty.

    Why disparage academic scholars? The tech field owes a lot to them.

    [QUOTEWe are talking about current gain, which is given be hfe or β, and is a product of device and physical parameters. Simple as that. Causal relationships work well with current, better than with voltage, in fact, as has been detailed by other members.][/QUOTE]

    That is what I don't agree with.

    Now you are speculating about something you know nothing about. I thought about what he said, and over time, I considered him to be correct. You have no knowledge about how long it took me to arrive to that conclusion.

    As I said before, the causal relationship in not about engineering. Engineering uses your current model effectively. The voltage model is of academic interest. You seem to have a hard time keeping the two straight.

    Ratch
     
  4. dave

    Dave New Member

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  5. Claude Abraham

    Claude Abraham Member

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    Vbe & depletion width vary in unison due to energy & injected charge. Vbe does not "control" barrier width. They are related. You said that Sue's energy is external & that you wish to discuss internal "cause" of bjt operation. But in order to change Ic, we must change the E field value. Fields store energy. So in order to change the internal energy we must expend energy from an external source by injecting charge.

    To get charges to move, we must introduce other charges. That is in & of itself current, i.e. charge motion. But to do that requires work, i.e. voltage is by definition work per unit charge. Thus Sue externally provides energy which ultimately results in charge injection, which modifies the E field value, & depletion width. In the process, Ib & Vbe are both modified. But the key is Ie changing. A change in Ie results in a change in the number of e- emitted. Thus the number of e- collected changes. So a change in Ie directly results in a change in Ic.

    Another way to view this is that since E fields store energy, & a change in signal value is needed, a change in E field energy must take place. You keep mentioning "causal". So here is the question, "what causes the E field to change?". Anyone who says Ib only or Vbe only or Ie only does not undersand energy.

    To change the E energy requires time. If work is w, & time is t, then dw/dt is non-zero. But isn't dw/dt,the time rate of energy change, nothing more than power, p? P = dw/dt. Hence a non-zero power is necessary to change the E field. But P is equal to the current voltage product. Hence at the b-e jcn, the power associated with transporting charge is Vbe*Ib, or Vbe*Ie. To say that Vbe is causal while treating Ib as a consequence flies in the face of conservation of energy.

    Thus at the internal level, Ib is just as significant in bjt operation as is Vbe. Both participate, both are important, neither one more or less.

    As far as OEMs stating CC because it is easier, I think not. I took semiconductor physics at the grad level, several courses, including advanced, using Kittel, Muller/Kamens, & Sze as texts, & nowhere was VC even mentioned. We went down to quantum mechanics, solving Schroedinger's differential equation.

    Also, you agree that we must externally drive a bjt w/ current, not voltage. But that is all the current control model implies. The internal physics of bjt & FET requires charge control & QM to accurately model. I conceded on page 1 of this post, that CC is only an external view. You keep insisting that the correct internal model is VC, but every semiconductor physics reference says charge control & QM.

    We have universal agreement that current control is the right external model. But the internal model is where you disagree. The science community says charge control & QM, you say VC. That is the crux. The CC model is not debatable because we agree it is only external.

    As far as the Vbe vs. Ic graphs on bjt data sheets, that is my point. They are not causal. Vbe does not cause Ic, nor does Ib. Ic is the result of many variables interacting. You first must inject charge, Ib/Ie. Work is needed, Vbe. Electrons are emitted, Ie. An E field is needed in the b-c region to collect e-, Vcb. To establish Vcb, a charging current is needed. All of these variables work in unison to produce Ic. It isn't just one or the other. Ib/Vbe/Ie are a mutual trio. It is impossible for just 1 or 2 of them to exist. All 3 are either zero, or all 3 are non-zero. You cannot separate them into "causal" & "consequence".

    That is just a prejudice with no supporting facts.
     
    Last edited: Jul 27, 2010
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  6. BrownOut

    BrownOut Banned

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    Having access to a tech lab doesn't mean someone is experienced. I respect the knowledge, insight and experience of the engineers here over any arbitrary academic. If I knew the prof as I know these people, I might have a different opinion. The knowledgeable, experienced engineers at ETO don't need anyone to tell them what to think. There is a difference between thinking about something and doing research. There is also a big difference between stating something and proving it. And as I've said, engineering demands proof. These are the simple facts.
     
  7. Ratchit

    Ratchit Well-Known Member

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    Claude,

    I agree with everything in the above paragraph except the part about Vbe not controlling the barrier width. I will say more about control further down.

    I agree with what you say about voltage, work and energy. I believe for our purposes, Ie and Ic are almost one and the same.

    I will have something to say about this further down.

    I basically agree with the physics part of the paragraph. See further down for my answer to the internal level.

    That does not sound like a marketing course you took. I can't imagine a OEM trying to sell a BJT with a Schroedinger activator.

    OK, here is my answer to the above. You could say the same thing in reverse for vacuum tubes (VT) and FET's. Everyone agrees that VT's and FET's are voltage controlled devices. Yet there is grid leak current, drain current, and all the other things you mentioned before that are involved. If I really wanted to be contrarian, I would insist that internally, VT's and FET's could also be considered current controlled devices.

    My prejudiced outlook is that charges don't change velocity or accelerate in a BJT without a voltage. I will give an analogy to illustrate what I mean, not to prove anything. An engine moves a train. The boxcars move with it simultaneously, but the engine is what really makes it happen. If the boxcars move, so does the engine. You cannot have one move without the other while they are connected. So what is really controlling the train?

    Ratch
     
  8. Ratchit

    Ratchit Well-Known Member

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    Brownout,

    True, but when someone is a professor, has written many papers, and has obtained many patents, then it is a good bet that s/he is experienced.

    It is a different type of knowledge and experience, with lots of overlap between the two.

    I think you would find the professor a formidable source of knowledge. No one needs anyone to tell them what to think. But the opinion of such an expert should be carefully considered before rejecting it.
    And those are also well know principles that academics, more than any other group, try to follow. Engineers are result oriented, and researchers are explanation oriented. Neither one should look down upon the other. I have come across folks who say that technicians are what really support the electronics industry. They complain that the engineers sit on their ass all day in from of a computer screen playing with some design software, while the techs have to build a device, modify it, and debug it. They are all wrong, of course. Everyone has their own niche which is important.

    Ratch
     
  9. tvtech

    tvtech Well-Known Member Most Helpful Member

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    I will add something quickly here:

    This has been a great debate. IMHO however, my repair skills with TV's would be zero if I followed the "theoretical" instead of the hands on repair success.....

    You see, I repair products that have been built by Engineers. At least I have physical evidence that Engineers create something. Which I can then repair when it eventuallly goes faulty.

    Unlike theoretical stuff. I have yet to see a working example of a theory to repair on my bench. Engineers seem to have quite successfully provided us with working examples.

    Over and out.
     
    Last edited: Jul 27, 2010
  10. BrownOut

    BrownOut Banned

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    Yes, the opinions of experts should be carefully considered before rejecting it, and so the opinions of the expert engineers on ETO have more weight to me than some arbitrary researcher. He could be good at math, but not as strong at intuition when it comes to interpreting the results. I know the engineers here, and I know who has the capability to interpret and understand the results. That's why I put more importance in their opinions than some prof I'm not familiar with. Writing books doesn't put them on any pedestal in my opinion. I don't need anyone to tell me how to think about devices and their physics. I've studied and used them for decades, as have the other people who post factual information about them on here. You demonstrate poor understanding of engineering, what and how an engineer does and what he knows. Most successful engineers have a mastery level understanding of the devices they use, especially when we talk about the old school engineers on ETO. In their day, a mastery of the subject was absolutely required to be successful. You can learn from these guys if you are predisposed to do so.

    You've utterly failed to provide any analysis to support your claims, and most of what you've written has been pure boloney. You can't come here with your wiki-knowledge and expect to be taken seriously by those who've spent their life time learning the material. Those who successfully deploy these devices have the best understanding of their operation. No noob or academic can match their knowledge.
     
    Last edited: Jul 27, 2010
  11. Claude Abraham

    Claude Abraham Member

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    In a FET, ther current in the gate is not leakage. A FET operates by injecting charge into the channel & inverting the region from p to n type or vice-versa. In a FET, the current is as important as the voltage. So is a FET VC or CC?

    The answer lies in which type of power source should we employ at the gate to source. A dc constant current source, will indeed charge up the g-s capacitance & provide a voltage. But that voltage will ramp up indefinitely until the gate is punched through. A CCS is not a good way to drive a FET. But a CVS will charge up the gate to a particular voltage, prescribed to be less than the max g-s rating of the device. A good low internal impedance constant voltage source will provide enough current to charge up the gate in a short enough time to meet speed requirements.

    Again, with a FET, or a bjt, current & voltage are BOTH indispensible. Neither device can operate w/ just 1 & not the other. I & V cannot exist apart. But some devices are more suited for "voltage drive". i.e. FET. But a bjt is much better suiired for current drive". It's that basic.

    Regarding the engine "driving" the train, I've been saying that "Singing Sue" is the engine. Of course the boxcars do not drive the train. It happens that Ib, Vbe, & Ie are the boxcars. Sue is the engine. Ib/Vbe/Ie are the boxcars. Sue provides the energy just like the engine in the train. Neither Ib nor Vbe nor Ie are a "source" of energy. Sue is that source. She must replenish her energy supply by breathing, drinking, eating & sleeping, just as the train engine eventually needs more fuel.

    I don't know how to explain it better. I've been quite explicit. You have not addressed my energy conservation point. How can Vbe be the engine that provides the energy w/o Ib. The E field requires energy per time, or power. Power is the product of I & V. Sue's acoustic energy is transduced by the mic into electrical energy in the form of I & V. The energy viewpoint is unassailable. You cannot address it.

    Claude
     
    Last edited: Jul 27, 2010
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  12. tvtech

    tvtech Well-Known Member Most Helpful Member

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    And that is what it's all about. It's all about knowledge and experience. Not theory in the head. To impress.

    I for example, am pretty comfortable right now with my TV CRT chassis repair knowledge...only doing it for around 20 years.

    Cheers
     
  13. BrownOut

    BrownOut Banned

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    I started out in TV, but not gonna tell you how long ago :) Lets' just say the amplifiers were all tube-type back then :eek:
     
  14. tvtech

    tvtech Well-Known Member Most Helpful Member

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    Tube Amps are great. Sooo smooth.

    OK. I have successfully derailed this thread.

    Cheers
     
  15. Ratchit

    Ratchit Well-Known Member

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    Brownout,

    I think you are saying you would evaluate a message delivered by a messenger you know and are familiar with instead of by what it contains. Have I got that right?

    Actually, I have not demonstrated anything about engineering, good or bad. We have been arguing about a theoretical point. You and I can learn something from just about anyone.

    I have provided reasons. I don't think this is a problem that submits to analysis.

    Just because Wiki publishes it does not necessarily make it wrong. It appears that Wiki mostly copies what has been written elsewhere, whether right or wrong. And Wiki does provide a lot of references. Academics can match the years of knowledge of experienced engineers, because some of them have years of experience themselves. It is a different type of knowledge with a different outlook. I didn't just rely just Wiki. I referenced two other experts in the field, and I am sure there are more who agree with me.

    Ratch
     
    Last edited: Jul 27, 2010
  16. tvtech

    tvtech Well-Known Member Most Helpful Member

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    Eric and all the other brilliant ETO forum peoples out there...

    I wuvs you guys. We don't try and be clever here. We tell like it is. I, for example, will not post crap in a Forum that I have no knowledge about. Just to try and appear to be a smart ass. And impress a Newbie....

    With probably the wrong info too.

    I have seen most Electronics Forums around. And I have to say ETO is probably the most respected and well run and active out of the lot.

    There are some Forums that have been going for longer than than ETO. But they are dead. ETO is alive and well.
     
  17. Ratchit

    Ratchit Well-Known Member

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    tvtech,

    Yes, and how would they do it without the fundamental knowledge gathered by the theorists? Was the transister invented by engineers?

    Found your niche, did you?

    Do you have "golden ears"? Golden ear - Wikipedia, the free encyclopedia

    Ratch
     
  18. tvtech

    tvtech Well-Known Member Most Helpful Member

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    Sorry Ratch. It's called a transistor by me. You called it a transister. Fundamentally wrong.
    Spelling maybe??

    Therein lies a basic thing you cannot even spell correctly.....nevermind it's properties. We will speak another day. No offence.

    Cheers and lighten up. Life is not that serious.
     
  19. tvtech

    tvtech Well-Known Member Most Helpful Member

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  20. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Tube amps produce second and third harmonic distortion, no very high audio frequencies, boomy mid-bass frequencies and no deep bass frequencies. Is this "smooth" sound?? I don't like it.
     
  21. BrownOut

    BrownOut Banned

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    We don't think much of wikipedia. We've had too many over exuberant noobs try to force bad wiki information. And to try to use wiki to school engineers is a joke. Yes, if you're gonna make claims about devices and their underlying physics, you better damn well have you ducks in a row and be prepared to show some analysis to back up your claims. You can't seriously think anyone is going to buy your weak reasons, especially since most engineers here have learned device physics and already know what they are talking about. You've demonstrated enough about engineering to show your lack of experience and knowledge.

    Some noobs get it and some don't. Those who do come with an open mind, eager to learn. Those who don't come with a bunch of wiki-facts, act like they know what their talking about, contradict knowledgeable, experienced people and claim that analysis isn't necessary to prove their "beliefs."
     

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