BJT's don't work like that

Discussion in 'Off-Topic' started by Ratch, Jun 15, 2008.

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  1. Ratch

    Thread Starter New Member

    Mar 20, 2007
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    Webby,

    Your confusion is apparent and understandable. There is lots of misinformation about how transistors work. They are voltage controlled devices, not current controlled like many would have you believe. The base current is "spillage" from the forward bias of the emitter-base junction that happens to be proportional to the collector current, but the emitter-base voltage really controls the current. Also the term current flow is wrong. Current does not flow, charge flows. Current is charge flow, and it does not flow within itself.

    Read the link below for a correct and easily understood explanation of how transistors really work.
    http://amasci.com/amateur/transis.html Ratch
     
  2. Ratch

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    Bill_Marsden,

    My suggestion is that he NOT read that section of the book. It contains lots of non factual material.

    1)
    The transistor was invented in 1923 by physicist Dr. J. Edgar Lilienfeld. He has patents to prove it. It was further developed, promoted, and put on a firm theoretical foundation by Bell Labs in 1947. See the reference I gave earlier in this thread.

    2)
    Wrong! The BJT is a voltage controlled creature, whose base current is a by-product or waste product of the forward bias of the emitter-base junction. The real control comes from the emitter-base voltage which controls the injection of charge carriers into the depletion region and onwards to the collector. It just happens that the base current is proportional to the collector current, but the base current is irrelevant to the control of the collector current.

    The introduction to the BJT of the AAC eBook makes no mention of the depletion regions, which are essential to understanding transistors work.

    The reference I gave earlier in this thread should perused to learn what really happens in BJTs. Ratch
     
    Last edited: Jun 16, 2008
  3. beenthere

    Retired Moderator

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    Ratch, a fervent assertion that a thing is so does not make it true, any more than a loud voice makes your ideas valid. Mr. Beaty may have alternative views of electricity/electronics, but that does not make him a modern Darwin.

    For the record, Mr. Beaty is on staff with the chemistry department at U. of Washington. He may or may not hold any degrees, but he certainly has no particular status by being employed by the institution. His position is that of a technician - probably a lot like mine at another state university. He has absolutely no academic significance (or peer-reviewed publications).

    While I knew a great deal more then the average EE in the area of troubleshooting and practical problem solving, I was never willing to assert that I knew more about electronics and electricity than they. My alternative explanation for hole flow was 'wire creep'. It was good for some laughs back in Basic Electricity/Electronics school in 1968. Mr. Beaty may think he has a better knowledge of the area, but it seems highly unlikely. Modern electronic theory is at a level beyond phlogiston flow or the luminiferous ether.
     
    Last edited: Jun 16, 2008
  4. Dave

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    Nov 17, 2003
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    The transistor proposed by J.E Lilienfield in 1925 (ref. USP 1745175) was a field-effect transistor analogous in descriptive function to the MOSFET. What Bardeen and Co. invented at the Bell Labs was the Bipolar transistor as accurately stated in the e-book. The original design by Bardeen and Co. was in-fact an failed attempt at replicating Lilienfields FET design. This paved the way in 1948 to the junction model BJT which is what is now considered the standard BJT. To suggest that what was invented by Lilienfield in 1925 is the same as what was invented at the Bell Labs in 1947/8 is frankly laughable, there are neither similar in function nor form (the MOSFET has a completely electrically-isolated terminal for starters!).

    I might sit down tomorrow and digest what is being said here. What I will say is that the text in the e-book has been reviewed and verified by many people. Furthermore the BJT detail in the e-book text is consistent with the published work of Sedra and Smith, Horowitz and Hill, and Hicks.

    I guess you think they are all wrong?

    The introduction to depletion regions is succinctly given in Chapter 3.2 and 3.3 before the treatise on BJTs. A convention followed in every published and reliable text on this subject.

    I may read it one day. If what you are proposing that the existing knowledge on BJTs is in some way incorrect, publish it, you will be a millionaire.

    Dave
     
  5. Ratch

    Thread Starter New Member

    Mar 20, 2007
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    beenthere,

    Correct, but he offers simple explanations for his beliefs. If you want to debunk him, then you have to show where his facts, logic, and reasoning are wrong. If he was not feverent in his beliefs, that would indicate doubt as to whether he really believes in what he says.

    Alternative or not, I am convinced it is the correct fact. Can you prove different? This miscarriage of fact concerning current control is almost as prevalent as the misconception of what Ohm's law really is, whether astronauts "walk in space", and most folks preceiving current as "flowing". All these thing are not subjective, and can be proven as true or false. Neither are they "views". They are hard science facts.

    A further link is given below to bolster my position.

    http://www.kevinaylward.co.uk/ee/voltagecontrolledbipolar/voltagecontrolledbipolar.html

    Why should he need any if he presents factual cogent arguments?

    But you probably did in some limited areas of EE.

    I would hope he think he does, at least on the point we are discussing. But you cannot evaluate his argument on his credentials, you have to show where he is wrong, if he is.

    Irrelevant as to whether he is correct or not. Ratch
     
    Last edited: Jun 16, 2008
  6. beenthere

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    Mr. Aylward has a "B. Sc." I believe Dr. Science has something similar....
     
  7. Ratch

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    Dave,

    OK, I will acknowledge that correction. What is not always stated when Bell Labs is credited with the invention of the transistor was that it was a point contact junction transistor.

    A concensus of agreement does not always lead to correct knowledge. I submit that in this case it does not. I own a copy of Microelectronic Circuits by Adel Sedra and Kenneth Smith, both of the University of Toronto, third edition. On page 196, the equation for the collector current is Ic=Is*exp(Vbe/Vt) where Is is the saturation currect and Vt is the thermal voltage. A similar equation exists for the emitter current which is usually close to the same value. On page 197 under Recapitulation they say, "We have presented a first-order model for the operation of the npn transistor in the active mode. Basically, the forward-bias voltage Vbe causes an exponentially related current Ic to flow in the collector terminal." That is what Beaty and myself agree upon.

    The review panel is, but not Sedra and Smith. I don't know about the other two references you gave, because I don't have them handy.

    Yes, but it is not tied into the introduction of the BJTs and its importance is not mentioned therein.

    Many people have, but it has not made them rich or famous. But correct knowledge is its own reward. Ratch
     
  8. Ratch

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    Mar 20, 2007
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    beenthere,

    And the point being, with respect to the correctness of his proposition and explanation? Ratch
     
  9. cumesoftware

    Senior Member

    Apr 27, 2007
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    Well, I don't believe that BJTs are voltage controlled devices. To illustrate that, why when the base voltage is below 0.6V there is no current, and when the voltage is a bit above 0.6V (or 0.7V) you over-saturate the transistor?

    I already read Mr Beaty theory and some parts make no sense to me. It is like Hovind's theory about creationism: It has many holes. It is like saying that by protecting a LED with a transistor you are controlling voltage and not current, and it is voltage that kills the LEDs. Of course the drop voltages on LEDs vary with the current biasing them, but it is also true that every device has different I/V curves. The same with BJTs.

    Now FETs are true voltage controlled devices. You can vary the voltage of the gate from GND to Vcc without any resistor.
     
  10. Ratch

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    Mar 20, 2007
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    cumesoftware,

    Why is that? How do you explain the dependence of Ic on Vbe in the equation I posted from Sedra & Smith in my reply to Dave 3 or 4 messages ago?

    You are mistaken. The only way to pass no current through a diode is to bias it to zero. Below the 0.6-0.7 volts for a silicon diode, the current drops precipitously, but it does not go to zero until Vbe becomes zero. Above 0.6-0.7 volts it increases very fast. This is because the V-I curve of a forward diode is exponential, as illustrated in equation from Sedra & Smith shown earlier. That shows that a transistor is a voltage controlled device even when current is present and proportional in the base circuit.

    What parts of Mr. Beaty's explanation (not theory) don't you understand?

    Let's stay on topic. Creationism has no relevance to theory of operation of BJTs.

    Would you show one?

    Would you explain that more clearly? As long as you keep the diode current below the max level, you are OK. The way to do that is to insert resistance in series with the diode.

    Very little due to the exponential I-V curve.

    Feedback can be used to make Q point stable despite variations of parameters.

    As are BJTs. Ratch
     
  11. beenthere

    Retired Moderator

    Apr 20, 2004
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    My strongly sceptical position comes from the lack of credentials on the part of these people with alternative views. I see no experimental methodologies to illustrate their positions, or anything to indicate they can produce convincing results that somehow invalidate the accepted theories.

    To assert that this site's Ebook and, indeed, all accepted texts are grossly incorrect based on the unverified writings of an unrecognized authority with absolutely no academic credentials is somewhat outrageous. Produce the large body of experimental data to support the alternative explanation and we can have a worthwhile discussion.

    Telling us we have it all wrong because a third party says so is not good enough. Even I, with no engineering degree, can spot statements in the opening material of Beaty's stuff that are absurd. They are meant only to impress the credulous.

    This alternative stuff can get kicked around in the Off-Topic section to anyone's heart's content. It does not belong in an informative thread.
     
  12. Ratch

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    Mar 20, 2007
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    beenthere,

    It would be better than just skepicism if you could point out a significant falsehood that undermines what he is saying.

    Well, how many lab students have breadboarded a transistor, then biased it into the active region, and noticed how the collector current rises and falls greatly when the Vbe changes slightly? Anyway, I don't recall seeing any experiments referenced in the introductory e-book on BJTs either. Is there any part of something you can point out which can be challenged and not proven to be correct?

    I am doing no such thing. I am asserting that he is correct based upon what his facts and explanation are, not his credentials. You will notice that Sedra & Smith agrees with him.

    Wouldn't it be easier if you could provide just one fact that blows his explanation out of the water?

    Right you are. Unless the third party has an extraordinary explanation for a extraordinary statement. Can you find anything wrong with what he avers to build his case?

    Well then, please point them out so we can have a meaningful discussion.

    This topic is a very important concept and is very much on topic about how BJTs operate. It should be discussed and put to bed one way or the other, and not just dismissed out of hand. Beaty and other of his ilk should not be treated like Galileo. Ratch
     
  13. thingmaker3

    Retired Moderator

    May 16, 2005
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    That is not how it works Ratch. It is YOU and Beaty who are making the extraordinary claims, not the rest of us. It is therefore YOU and Beaty who must provide extraordinary evidence.

    An explanation is not evidence. There is no evidence.
     
  14. beenthere

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    Beaty's stuff appears to be pure sophistry. Like the "no such thing as current" assertion. The definition of an ampere of current is one coulomb of charge moving past a point in one second. Some mechanism carries the charge. Possibly it really is electrons, as they do carry charge, and are mobile.

    So what doesn't flow? Or is a movement of charge somehow fundamentally not an electric current (which is defined as a movement of charge)?
     
  15. thingmaker3

    Retired Moderator

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    "Current flow" is indeed a redundant term. I'm not fond of the phrase "ATM machine" as it is also redundant. But you don't see me insisting the banks all change their ways.

    None of the "meat" (what little of it there is) in Beaty's material on charge is anything new. He embellishes this with smoke and mirrors - simply holding up common semantic practice as a straw-man argument while launching ad-hominem attacks at an undefined "them" and "they."

    Beaty is in love with the embellishment of the argument. The argument itself is contained in most textbooks. I've no clue why Beaty (and others) are unable to go from "current is a flow of charge carriers" and "current density is proportional to conductivity and electric field" to "base current times Hfe equals collector current." Maybe they didn't read the text books as well as they thought they did.:rolleyes:
     
  16. Ratch

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    Mar 20, 2007
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    thingmaker3,

    And so Beaty does. His explanation is clear and concise.

    Actually, it is those who say that a transistor is a current controlled amplifier who are making extraordinary claims, even when they see that the current is dependent on Vbe. The physics of the junction transistor prove that it is voltage controlled.

    Sure it is, when it points to evidence. How can you say no evidence when the collector current equations show a Vbe dependence. Ratch
     
  17. thingmaker3

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    May 16, 2005
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    Wrong. That is the common and accepted (by everyone except you and Beaty) model. It is the model used by Intel, Texas Instruments, and a host of other manufacturers who's products work exactly as the model predicts.



    That has to do with the relationship between EMF, resistance, and current - but you don't believe in EMF either, do you? How convenient for you.
     
  18. Ratch

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    Mar 20, 2007
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    beenthere,

    Sophistry means to be plausible, but false. So what has he said that is false?

    He never said that. You did not read it carefully. He said that current does not travel, flow or move. As I said before, current means charge flow, so current flow means charge flow flow which is redundant and ridiculous.

    Yes, we can all agree on that.

    Yes, electrons and holes are mobile charge carriers.

    Current for one. Current IS charge flow already, it does not flow twice.

    Of course not. Beaty makes it a point to show that charge movement is current. Ratch
     
  19. beenthere

    Retired Moderator

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    Perhaps we could confine this to the current question. This is a very early assertion of Beaty's, and I think we can let the remainder stand or fall on just this point. Legalisticaly, that will be falsibus in uno, falsibus in omnes (unless I've misremembered another Latin tag). That might be rendered as: false in one thing, false in all things.

    So - does Beaty disprove the notion of current?
     
  20. thingmaker3

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    May 16, 2005
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    I would concur, as Beaty basis his transistor semantics rantings on his current semantic rantings. But we must not decree "correct in one thing, correct in all things."

    Beaty's claim is "an electric current is not a stuff." I call "straw man."

    Beaty then goes on with extensive "water analogy" use. Water analogy has been dismissed even by Ratch himself.

    Next comes some nonsense about "uncharged charges." Beaty shows again that his problem is limited solely and exclusively to semantics. He decires the (admittedly) poor semantics of others while himself spewing non-sequiturs and force entendres. Please not I am not making a tu quoqu claim - I am simply decrying Beaty's inability to divorce his argument from his passion.
     
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