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How Transistor works - verifying

by Nikarus
Tags: transistor, verifying
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cabraham
#37
Jun29-11, 06:10 PM
P: 1,045
http://www.physicsforums.com/showthr...ghlight=wbeaty

That should do it. It's never too late to ask a question. I'll clarify anything that needs to be understood better.

Claude
wbeaty
#38
Jun29-11, 10:51 PM
P: 116
Quote Quote by cabraham View Post
That should do it. It's never too late to ask a question. I'll clarify anything that needs to be understood better.
You said that you and I had a discussion, first linking to that other forum with "Rachit," then linking here where I'd posted one single message (and in that instance I never stayed around to read any responses.)

That's very odd. No, I've not been involved in any "discussion."

But now I'm wondering ...back during that enormous "current controlled" debate, did you suspect that the anonymous "Rachit" guy was actually myself? That you and I did have a discussion, but I was hiding my identity?
cabraham
#39
Jun30-11, 05:11 PM
P: 1,045
Quote Quote by wbeaty View Post
You said that you and I had a discussion, first linking to that other forum with "Rachit," then linking here where I'd posted one single message (and in that instance I never stayed around to read any responses.)

That's very odd. No, I've not been involved in any "discussion."

But now I'm wondering ...back during that enormous "current controlled" debate, did you suspect that the anonymous "Rachit" guy was actually myself? That you and I did have a discussion, but I was hiding my identity?
I only asked the question. I don't dislike Rachit, nor anybody who opposes me. I just want to re-examine everything until concensus can be reached. I have a pet peeve just like we all do. Mine happens to be debates that never end. At some point in time there needs to be a "Supreme Court" of some kind to resolve it. The SC is not always correct, & they have reversed themselves numerous times in US history.

The current controlled model of a bjt has always been presented as an external viewpoint, focused solely on driving the bjt w/ external circuitry, not examining the internal device physics. When this point was finally uinderstood after a lengthy debate concensus was reached. It has been universally accepted, even from critics of semicon OEMs, that the current control viewpoint does not address internal physics. Rather the CC approach is beneficial for driving the device, developing networks around the bjt. In short, a constant voltage source should never be used to drive the b-e jcn.

A constant current source biases said b-e jcn very well, but a CVS would likely destroy it. Nobody, including critics, disputes this assertion. So we had universal concensus, no dissent at all, that for an external view, CC is what works best.

We also concurred w/o dissent, that when operating a bjt at a speed high enough so that internal charge distribution & transit time, is no longer negligible, then the CC model is inadequate. I still repeat this - any time internal device physics is under examination, the CC model is inadequate.

So the debate then shifted to which internal model is best. The peer reviewed app notes from OEMs, & unis say QC, charge controlled. A handful of critics say VC, voltage controlled. Scan the debate & it was eventually settled w/ full agreement that QC is the best internal model.

Do not hesitate to ask for clarification. I want to be seen here as an approachable dude. I hope that everyone feels they can talk to me freely w/o contention. If I've erred somewhere I'll accept & welcome correction. If my explanations are not effective, I'll rephrase. Please feel that you can talk to me freely w/o any repercussions. So here it is.

External model neglecting internal device physics - current control.

Internal model considering internal device physics - charge control.

Atomic level considering the limits of physics knowledge - quantum mechanics.

I'll address any questions. Best regards.

Claude
wbeaty
#40
Jul1-11, 02:09 AM
P: 116
Quote Quote by cabraham View Post
I'll address any questions. Best regards.
Hmmm, a problem.

Again: did you suspect that "Rachit" and myself were actually the same person?
cabraham
#41
Jul1-11, 08:01 AM
P: 1,045
Quote Quote by wbeaty View Post
Hmmm, a problem.

Again: did you suspect that "Rachit" and myself were actually the same person?
I did not assume that. I just wasn't sure. Some of his phrasings sounded like yours but that could be because he relied on your site as a reference. Just curious, Rachit is not a bad person. I just wanted to know his reasoning & sources for his contrarian position.

Don't take any of this as personal. I ask everybody else, you included, to provide sources & proof when taking a contrarian stance against a well established position in science. I provide sources & proof to support my conformist positions.

One more point, & no offense is meant. Contrarian positions are, for some folks, a lot more fun to ponder than the official viewpoint. There is something about being in a vocal minority that gives them a sense of being more enlightened than the rest. They consider the official viewpoint as "misconception, myth, based on limited anecdotal evidence, etc." What the critics need to do is carefully examine their own positions, & they will find that they make assumptions at the start that are not valid, or anecdotal, holding under limited conditions. To these folks, there is little excitement in conformist positions because one cannot take credit for it. But once a fact is established based on solid proof, there is no need to knock it down to prove oneself capable. There are many new ideas & inventions waiting to be discovered. I suggest that their effort be redirected.

I always refute the critics with solid immutable laws like conservation of energy & charge, Kirchoff's 2 laws, Maxwell's equations, etc. These are Gibraltars of science. Any theory which cannot conform to these laws are nothing but heresy. To prove the contrarian view requires disproving these well proven laws.

Any theory which is contradicted by said laws cannot be taken seriously. The critics are the ones spreading myths & misconceptions. Everything we need to know is taught at the accredited unis in engineering (full) & physics curricula. Web sites preaching info which counters the uni teachings must be scrutinized, & I always find that assumptions are made early which are invalid, & hence produce invalid conclusions.

But admission of an error is rare. Once a critic has boldly declared the engr/phy community to be wrong, mountains of evidence refuting their erroneous view is futile. They are then in a position where they must defend their contrary view,& attack the official view just to save face. That is why I tend to be careful about debating an issue. If I am not experienced in a topic, I tend to trust those who are. Nothing is worse than taking a hard stand on an issue I am not an expert on, then after others present evidence to the contrary, I realize "Oh s***, I'm wrong!" I avoid that by debating only when I know the facts.

Oh well, I do run on. Best regards.

Claude
Studiot
#42
Jul1-11, 08:31 AM
P: 5,462
Everything we need to know is taught at the accredited unis in engineering (full) & physics curricula.
Probably the two most famous counterexamples to this declaration are

The gross miscalculation of the age of the Earth by Lord Kelvin.

The address to the Royal Society by Oliver Heaviside "Gentlemen, shall I refuse my dinner because I do not fully understand the process of digestion?"
cabraham
#43
Jul1-11, 11:06 AM
P: 1,045
Quote Quote by Studiot View Post
Probably the two most famous counterexamples to this declaration are

The gross miscalculation of the age of the Earth by Lord Kelvin.

The address to the Royal Society by Oliver Heaviside "Gentlemen, shall I refuse my dinner because I do not fully understand the process of digestion?"
I stand by what I posted. One person, such as Lord Kelvin, does not disprove my point. Lord Kelvin put his foot in his mouth on more than one occasion, esp in his later years. The unis teach what is known at this moment to the best of their ability. New discoveries will be made & the science/uni canon will be updated to reflect new info.

As far as OH & dinner goes, that is hardly a rebuttal to my point. I didn't say that all is known. Rather, if we wish to understand how to utilize a bjt to its full effectiveness, unis are a good source, as are semicon OEMs.

The internal physics involves QM, of which the science community has only a limited understanding. We have much to learn about QM, & the unis provide only a limited amount of enlightenment here, because man's knowledge of QM is limited.

I hope that clears up my statement. BR.

Claude
wbeaty
#44
Jul1-11, 09:08 PM
P: 116
Quote Quote by cabraham View Post
I did not assume that. I just wasn't sure.
Nope, I've never been on that forum. I think I registered long ago when I was adding forums to the big list on my Electronics Hobbyist page. I suspect that Rachit is this one professional chip designer who uses SED and other newsgroups, and appears to be a big fan of my articles. He probably emailed me a few times years ago.
wbeaty
#45
Jul1-11, 09:19 PM
P: 116
Quote Quote by cabraham View Post
Don't take any of this as personal. I ask everybody else, you included, to provide sources & proof when taking a contrarian stance against a well established position in science.
What contrarian position? What do you mean exactly?

My transistor article comes right out of standard textbooks. It's what I was taught in EE classes at the U. of Rochester. It's all based on the main bjt equation, the DC transconductance equation or "Shockley's Equation" which describes the effect of the potential barrier in the BE junction of the bjt: Ic=Is*(e^(Vbe/vt)-1). That equation appears in vast numbers of EE textbooks, if not all of them. I think Horowitz and Hill devote an entire chapter to it. In Art of Electronics, first they go over Ic=hfe*Ib and the "little man in the transistor." Then they drop the simple stuff and delve into professional-level design techniques. IIR, Sedra and Smith do the same. (Might you recall the undergrad semiconductor physics text you yourself used back in school?)

But my transistor article was written for the Electricity exhibit at the Boston Museum of Science (well, the initial version was.) Therefore my goal is to explain diode switching to little kids and grandmothers. I cannot introduce any math at all. I can't even use the central concept of "diode potential barrier." In order to translate the diode equation Id=Is*(e^(Vd/Vt)-1) into everyday language, I focus on visualizing the changing width of the depletion zone; the variable insulating region found in all PN junctions.

The general public can't deal with Id=Is*(e^(Vd/Vt)-1), but many of them can understand a thin flat insulator which dynamically grows and shrinks in thickness, and which presents a barrier between two conductors. My original transistor article was intended to have several animations where the Depletion Zone is depicted as glass, and the rest of the carrier-filled semiconductor material is depicted as metal. Also, I planned articles covering Diode first, then BJT later, so everyone can pick up a critical concept: the BJT is really just a fancy kind of diode switch.

You're totally familiar with Ic=Is*(e^(Vbe/Vt)-1), right? It's the "Ohm's Law" of the transistor.
Chunkysalsa
#46
Jul2-11, 05:43 PM
P: 311
Interesting article to read. I don't know anything about transistor yet to contribute to your discussion.

I thought it was interesting to see you responding here when the other day my intro circuit analysis professor gave us the link to that article as a source for writing a small mini-paper on how transistors work.
Studiot
#47
Jul2-11, 06:00 PM
P: 5,462
Out of interest, on what website was this 'discussion' with this 'rachit' fellow please?

I ask because I remember a member called ratch on who had a particularly frustrating discussion style on another forum. He kept referring to the amasci website.
wbeaty
#48
Jul2-11, 06:14 PM
P: 116
Quote Quote by Chunkysalsa View Post
I thought it was interesting to see you responding here when the other day my intro circuit analysis professor gave us the link to that article as a source for writing a small mini-paper on how transistors work.
Yeah, that article has attracted fairly huge web traffic, plus staggering amounts of ego-swelling congratulatory email, way too much for me to have any hope of answering. The physics educators love it. As S. Hawking discovered, any new explanations of physics, if they're purely verbal+pictures, tend to attract big crowds.

So I was a temporary minor online celeb. But you cannna makes a living on th intertubes, unlessuns you publishes a paper-based book.
wbeaty
#49
Jul2-11, 06:24 PM
P: 116
Quote Quote by Studiot View Post
Out of interest, on what website was this 'discussion' with this 'rachit' fellow please?
It's the same one Claude repeatedly posted here, the one with forty-three pages. I thought you participated? See the first page of this current thread, down near the bottom.

Quote Quote by Studiot View Post
I ask because I remember a member called ratch on who had a particularly frustrating discussion style on another forum. He kept referring to the amasci website.
Look back there again, it doesn't say 'ratch,' it says 'ratchit.'
cabraham
#50
Jul2-11, 08:10 PM
P: 1,045
Quote Quote by wbeaty View Post
What contrarian position? What do you mean exactly?

My transistor article comes right out of standard textbooks. It's what I was taught in EE classes at the U. of Rochester. It's all based on the main bjt equation, the DC transconductance equation or "Shockley's Equation" which describes the effect of the potential barrier in the BE junction of the bjt: Ic=Is*(e^(Vbe/vt)-1). That equation appears in vast numbers of EE textbooks, if not all of them. I think Horowitz and Hill devote an entire chapter to it. In Art of Electronics, first they go over Ic=hfe*Ib and the "little man in the transistor." Then they drop the simple stuff and delve into professional-level design techniques. IIR, Sedra and Smith do the same. (Might you recall the undergrad semiconductor physics text you yourself used back in school?)

But my transistor article was written for the Electricity exhibit at the Boston Museum of Science (well, the initial version was.) Therefore my goal is to explain diode switching to little kids and grandmothers. I cannot introduce any math at all. I can't even use the central concept of "diode potential barrier." In order to translate the diode equation Id=Is*(e^(Vd/Vt)-1) into everyday language, I focus on visualizing the changing width of the depletion zone; the variable insulating region found in all PN junctions.

The general public can't deal with Id=Is*(e^(Vd/Vt)-1), but many of them can understand a thin flat insulator which dynamically grows and shrinks in thickness, and which presents a barrier between two conductors. My original transistor article was intended to have several animations where the Depletion Zone is depicted as glass, and the rest of the carrier-filled semiconductor material is depicted as metal. Also, I planned articles covering Diode first, then BJT later, so everyone can pick up a critical concept: the BJT is really just a fancy kind of diode switch.

You're totally familiar with Ic=Is*(e^(Vbe/Vt)-1), right? It's the "Ohm's Law" of the transistor.
As I've stated repeatedly, there are 3 basic equations which can be labeled as "terminal relations":

1) Ic = beta*Ib

2) Ic = alpha*Ies*exp((Vbe/Vt) - 1)

3) Ic = alpha*Ie

Equation 3 is the law of transistor action. Equation 2 is often miswritten, as you just did. I've highlighted the factor "alpha" & the saturation current is "Ies". In a diode there is but one value of Is. In a bjt, there are 2 junctions each w/ their own value of "Is", due to differing doping densities in collector vs. emitter. Hence "Ics" & "Ies" are used in the Ebers-Moll equations.

All 3 equations are needed to fully describe a bjt. But only 1 of the 3 input quantities can be the directly controlled input, the other 2 being incidental, but inportant nonetheless. We can control the base current & then eq 1) gives us Ic. But this method results in beta dependency, which we usually avoid. Eq 3) is very reliable. If we set Ie to a known value, Ic is very predictable. Alpha is around 0.98 to 0.998.

We never control Ic w/ Vbe. The Ies term is very temp dependent. It also has a positive temp coefficient. A voltage source directly across the b-e jcn could kill the device. It's never done. We control a bjt by controlling its current.

In the process of doing so, a voltage develops across the b-e jcn. We use eqn 2) to compute transconductance of the device. This is the upper limit for the transconductance of the stage. The stage gm cannot exceed the devices gm.

Likewise, beta is the upper limit for the stage current gain. The stage current gain cannot exceed beta, that of the raw device.

Your presentation of bjt operation reads like a scathing indictment of OEM & uni app notes. It reads as if your version is the only valid one. My beef is that the explanation given in uni texts is spot on, & does not need any correction. You present E-M to the exclusion of the other 2. E-M is one law for bjt operation. The other 2 are just as important. A bjt is a 2 port device. It cannot be explained in 1 equation. Likewise for a FET.

As I said, to develop bjt networks, the CC model is good until storage/transit time becomes an issue at high speeds. Then QC takes over. I've used CC & QC forever, & haven't gone wrong. What have you used?

Claude
wbeaty
#51
Jul2-11, 10:38 PM
P: 116
Quote Quote by cabraham View Post
As I've stated repeatedly, there are 3 basic equations which can be labeled as "terminal relations":

1) Ic = beta*Ib

2) Ic = alpha*Ies*exp((Vbe/Vt) - 1)

3) Ic = alpha*Ie
Yep, dead normal textbook stuff.

But I begin to suspect that you didn't read my previous message (number 45.) Hint hint.

Quote Quote by cabraham View Post
Equation 3 is the law of transistor action. Equation 2 is often miswritten, as you just did.
Miswritten? No, it's simplified, just as uni texts commonly do, for devices where alpha ~= 1. Must we now go and make a list of the undergrad textbooks which do this? Does your school have an engineering library with all the current double-E texts behind the ref desk? Well, doing all that is irrelevant, for the reasons explained in my previous message.

And again as before: might you yet recall which text you yourself had in your undergrad semiconductor physics course, the one that first covered transistors?

Quote Quote by cabraham View Post
I've highlighted the factor "alpha" & the saturation current is "Ies". In a diode there is but one value of Is. In a bjt, there are 2 junctions each w/ their own value of "Is", due to differing doping densities in collector vs. emitter. Hence "Ics" & "Ies" are used in the Ebers-Moll equations.
Sure, but I think you're missing something important. Hint again: read my previous message 45, the one you quoted.

What is the goal of my transistor article?

That transistor article ...what was it's goal? What org was it written for, and who are their clients?
cabraham
#52
Jul3-11, 12:27 AM
P: 1,045
You say in article 45 that lay people cannot handle E-M eqn. So you went into physics & potential barrier. I just don't see how that explains bjt action. That explains diode action. The relation between I & V is a diode relation. E-M is derived from Shockley's diode eqn, then combined w/ eqn 3), the alpha eqn.

The barrier potential explains the I-V properties of diodes & all p-n junctions including bjt. But to explain bjt action, we need eqn 3). If the base region of a bjt was super wide, say 1.0 mm thick, & every electron emitted from emitter recombines in base w/ holes, then Ic is near zero. Yet the I-V relation per Shockley is still valid.

A bjt w/ a thick base is merely 2 back to back diodes w/ no transistor action. Ebers-Moll equations include alpha to account for bjt action. With alpha near or at zero, Ic is near zero. Vbe can be 0.85 volts, but Ic is about 0. Without high alpha, Vbe matters not.

Again, the potential barrier description accounts for I-V log/exp properties. Of course Vbe must be non-zero in order to sustain emitter current which gives rise to collector current. But Ic = alpha*Ie is the eqn that separates a true bjt from back to back diodes.

FWIW, it's very hard to explain bjt action to lay people. But I've had the greatest success w/ the base region being so thin, carriers are yanked into the collector before they get a chance to recombine. Potential barrier details involve thermally generated electron hole pairs, phonon interaction due to lattice vibrationm thermal energy, band gaps, Fermi levels, recombination, etc.

The thin base region resulting in carriers yanked into collector before recombination can occur is simple, less involved, & requires no advanced math. Your web site article chastises the whole science community for not explaining bjt action well enough. As I said, I've had hundreds of colleagues enjoy great success as an EE in hardware development, whos understanding of bjt is based on OEM app notes & uni teachings.

Also, I've aleady stated that the 3 terminal eqns are simple external models not accounting for device physics. But you then say that to go deeper we use E-M. I've already told you that charge control is the model used when transit time & charge distribution are relevant. Increase a bjt speed to hundreds of MHz. None of the 3 terminal eqns give a good answer. Or to take a bjt out of saturation requires knowledge of the stored exces minority carrier charge value. Neith eqns 1, 2, or 3, provide this. The QC model is needed.

Then to go even deeper, we need QM. Transconductance is not more basic than current gain. THey are both terminal quantities. You seem to think eqn 2) in more basic than 1) or 3). That is not so. I can elaborate if needed.

Anyway, let's not make this an endless campaign. You & others can have the last word. I'll answer a question if asked. BR.

Claude
wbeaty
#53
Jul3-11, 03:20 AM
P: 116
Quote Quote by cabraham View Post
I'll answer a question if asked
Just two questions.

First, might you yet recall which text you yourself had in your undergrad semiconductor physics course, the one that first covered transistors?

Second question:

Quote Quote by cabraham View Post
You say in article 45 that lay people cannot handle E-M eqn. So you went into physics & potential barrier. I just don't see how that explains bjt action.
I haven't clearly stated my reasoning yet, so do you want to hear it? That's my second question.
Studiot
#54
Jul3-11, 11:56 AM
P: 5,462
Originally Posted by Studiot
Out of interest, on what website was this 'discussion' with this 'rachit' fellow please?

It's the same one Claude repeatedly posted here, the one with forty-three pages. I thought you participated? See the first page of this current thread, down near the bottom.


Originally Posted by Studiot
I ask because I remember a member called ratch on who had a particularly frustrating discussion style on another forum. He kept referring to the amasci website.

Look back there again, it doesn't say 'ratch,' it says 'ratchit.'
Many thanks for this answer. I have now had time to review this website with the following results.

Comparing this website with the one I linked to in post#21 of this thread I think that 'Ratch' and 'Ratchit' are one and the same person. I note he signs himself Ratch in cabraham's E-Tech thread, although his handle is 'ratchit'.

In June 2008 he started the thread I linked to (post#21) by referring to your site (amasci) as proof that 'transistors are voltage controlled not current controlled'.
There was significant discussion, including the nature of the term 'control', though not of the gargantuan proportions of the one in 2010 in cabraham's link.

I apologise to claude if we had primed the pump for that argument in 2008.
I felt that his summary in post#39 here was particularly good.

However I would take issue with equations posted in post#50.

My version of equation (3) has another term which is significant in certain types of transistor and reminds us that there are other agents that affect, and therefore can 'control', the collector current.


3) Ic = alpha*Ie + Ico


go well


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