How Transistor works - verifying

[cabraham]

Same here: 31yrs in EE, but half the time in embedded sw.

Area of specialization/dissertation?

At times I've been tempted by PhD when I can eventually afford it, but in physics of high-Q plasmon effects in non-contact friction and micromachines. There's all of three papers on that topic.

PS sorry for the delay, I've been out of town and checking laptop rarely.

My dissertation is tentatively solar enrgy panels & associated power conversion electronics. I'm awaiting the funding to be finalized. As far as affording it goes, I applied in fall 2006 when I was employed by a company that agreed to finance my tuition & book expenses. Then, two thirds of the way through, the company encountered weak sales, & had to make cutbacks. The educational assistance program was hit. I was placed on "temporary furlough" along w/ dozens of others, mostly middle aged engineers, told I would be recalled, but no set date was given. They still plan to recall me. I've worked temp jobs since.

So my employer paid the 1st two thirds of my Ph.D. program, & I paid the final one third. It
s a private school, so the cost is really high. But, it should be worth it. I'd advise you to not put it off. The sooner you get it, the more years in life you will have to use it. BR.

Claude

 

[wbeaty]

Guys, please, can you not just give me another explanations, but read my own and tell me what is wrong there on my picture. So I could use my own understanding as a reference point to move from.

Diagram 1 looks OK, showing the polarity of mobile carriers in the three regions.

Those circled charges... I assume that they're immobile lattice ions of the depletion zones? There must be some better way to show that these ions cannot move and can't participate in currents in the DC case.

Diagram 2 isn't correct. Since the transistor is still turned off at that point, the Base region will still be full of holes as before, and since the EB depletion width doesn't change, the entire device should look almost like #1. Differences: the CB depletion zone is strongly reverse biased and becomes significantly wider, which shrinks the Base region a bit (look up "Early effect.") Also, net surface charge from the power suppl;y should be placed on the left and right ends of the device adjacent to the connecting wires for E and C. These surface charges always are associated with the power supply voltage, and they're the cause of the currents in circuit conductors. Remember that the applied voltage coming from power supplies has little effect upon the charge density inside a wire (little effect upon its resistance.)

For some excellent (and extensive!) info about these surface charges associated with power supply voltage, see this preprint below. It's very worthwhile going through it and understanding every detail.

A unified treatment of electrostatics and circuits, Chabay and Sherwood (1999)
http://www.matterandinteractions.org/Content/Articles/circuit.pdf
​

Diagram 3 isn't correct. The base is p-type and should still contain holes, even though a flood of negative carriers is pouring in from the Emitter. The CB depletion region should be wide because of reverse bias. The EB depletion zone should be narrow, showing the lowered potential barrier because of forward bias.

Do you have "Art of Electronics" by Horowitz and Hill? They go into the voltage controlled BJT, Shockley equation etc., where their transistor section is titled "Ebers-Moll Model Applied to Basic Transistor Circuits, Improved transistor model: transconductance amp." For the normal operation in active region, Ebers-Moll reduces to a transconductance equation: voltage in, current out. That's basically where the name "trans-istor" came from.


PS
It's probably better to start by analyzing interior diagrams of single diodes under forward bias and under reverse bias. Once you work out those concepts completely and draw accurate diagrams, then you can build your transistor diagram.

It's harder to teach yourself about diodes and transistors at the same time. Also, if transistor diagrams aren't GIF animations, they're almost impossible to understand! That's one reason we traditionally hold off on transistor explanations until the students acquire the skills to understand the math models. But one situation is different: science museum exhibits on semiconductor physics. Explaining it ...to my grandmother.

 

[wbeaty]

So my employer paid the 1st two thirds of my Ph.D. program, & I paid the final one third. Its a private school, so the cost is really high. But, it should be worth it. I'd advise you to not put it off. The sooner you get it, the more years in life you will have to use it. BR.

Claude

Whew, that sounds a bit familiar. Our entire eng staff in industrial laser scanners was laid off in 2004 during the first internet bubble. I'm a staff engineer in academia since then, at half the pay of the outside world. Interesting instrument design work, but the majority of time is spent in debugging failed systems and keeping ancient equipment alive.

PhDs aren't required for the work that's on the horizon: three private R&D orgs looking to develop some really radical solar stuff. Start-ups are searching for scientists; for idea-generators who've developed their "serendipity of mind" as in the quote below. The trouble with advanced degrees is that the usual employee pipelines are already choked with PhDs. So don't show them the piece of paper, instead provide copies of your unpublished research, and give them an off the cuff Feynman-esque physics rant. Deliver insights which send them reeling with delusions of ...patentable embodiments! :) Well, actually it's all just fantasy at this point since their funding is still "approaching."

"Many very serious-minded, solid and knowledgeable people work hard in science
all their lives and produce nothing of the smallest importance, while others, few by
comparison and not highly erudite, exhibit a serendipity of mind that enables them to
have valuable ideas in any subject they may choose to take up." - R.A. Lyttleton​

 

[wbeaty]

I actually enjoyed reading Mr. Beaty's site, but there should be a rebuttal to it, or a summary of the epic thread published on the web. I think a lot of confused people would appreciate it. Thanks for sharing.

If speaking for all the confused people ...which parts of http://amasci.com/ele-edu.html are giving the problems?

URL, and snip of specific paragraphs would be best.

 

[cabraham]

If speaking for all the confused people ...which parts of http://amasci.com/ele-edu.html are giving the problems?

URL, and snip of specific paragraphs would be best.

Honestly Bill, the rebuttals to your site have been thoroughly presented. A more fitting question is "which points in the rebuttals need clarification?" Everything I've presented is backed up with known proven science. You need to address what, if any, points I may have overlooked.

Once again, here is the thread where the matter was well discussed:

https://www.physicsforums.com/showthr...ghlight=wbeaty

BR, Claude

 

[wbeaty]

Honestly Bill, the rebuttals to your site have been thoroughly presented.

Yes, I had my chance and now it's too late!

It's a very regretful situation, but that's just how things must be.

And besides, who do I think I am?! Someone coming in at this late date, wanting to give input long after the timer has expired.

I should be ashamed.


(Also, prev msg link is bad.)

 

[cabraham]

https://www.physicsforums.com/showthread.php?t=390291&highlight=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]

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]

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 consensus 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 consensus 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]

I'll address any questions. Best regards.

Hmmm, a problem.

Again: did you suspect that "Rachit" and myself were actually the same person?

 

[cabraham]

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]

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]

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]

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]

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]

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]

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]

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]

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.

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]

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]

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.

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?

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]

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 website 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]

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:

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]

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

 

[cabraham]

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:

I haven't clearly stated my reasoning yet, so do you want to hear it? That's my second question.

Kittel - solid state physics as undergrad.
Muller & Kamens - Device Fabrication For Integrated Electronics at grad school, MSEE.
Sze - Physics of Semiconductor Devices, grad school Ph.D.-EE.

If you have reasoning you'd like to explain, sure, by all means do so.

Claude

 

[cabraham]

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

Thanks for your feedback. I am well aware of the additional "Ico" term in eqn 3), & what you've presented is correct. But when we describe quantities that "control" a device, we are not usually referring to leakage & other parasitic flaws.

In a bjt, the objective is to control collector current w/ some sort of input signal, as found in uctlrs, transducers, photodiodes, etc. The inherent leakage current Ico, which exists due to the non-ideal nature of the reverse biased c-b jcn, is present & varies greatly w/ temp.

Of course Ico plays a role in determining Ic, but it is not something we use to control Ic. It is an inherent property of the bjt, one which fortunately has a very small influence on bjt Ic behavior, for silicon material.

In the 1950's when germanium was the dominant bjt material, Ico was a real problem at medium to high temps. Designers had to account for the large Ico c-b leakage when employing Ge devices at temps above 50 or 75 C. The limit was around 100 C.

Then silicon replaced Ge around 1959, & Ico for Si is generally small enough to neglect. Again, it's there, but Si devices can operate to the mil temp range of 125 C & beyond w/o Ico being too large an eror. It is an error term for sure, & your eqn is more precise than the simplified version I presented.

But Ico, & I believe I'll get universal backing/concensus on this, is NOT a "control" quantity. It influences Ic for sure, but we don't control Ic by setting a value for Ico. I think this whole question revolves around the meaning of "control".

Ib, Vbe, Ie, Vbc, Ies, Vt, Ico, etc., all have influence over Ic depending how the device is driven. If the b-e jcn is driven by a true current source or voltage source w/ a large series resistor, then Vt, & Ies determine the Vbe value at a given temp. Also, Ico adds to whatever Ic value is obtained from eqn 1) or 3).

Which quantity are we adjusting to get a specific value of Ic? That is what we mean by control. Again, your version of eqn 3) is more precise than my simplified version. Ico exists indeed & influences Ic. But if Ico is 2.7 uA, & we bias the bjt at Ic value of 1.0 mA, the error is just 0.27%. For larger Ic value, the error is less.

Again, w/ Ge devices, the presence of large Ico values forced the designer to take it into consideration. Circuit topology was built around the need to mitigate large Ico values. EEs from the 1950's can give you insight into this practice. BR.

Claude

 

[Studiot]

I think this whole question revolves around the meaning of "control".

I have no doubt you have great knowledge of semiconductors and have already commented how worthwhile your technical analyses are.

But I also feel there is a lack of acceptance that others may also have something valid to say and a corresponding willingness to listen to them as well as to expound to them.

Here is a simple experiment to prove that it is possible to 'control' Ic with the base not even connected.

You can show this by allowing photons to enter the transistor, biased suitably between collector and emitter only. It is possible to switch on the transistor by this means.

As a matter of interest how do multiple emitter transistors fit into your control scheme? and how do you describe control by emitter injection?

 

[cabraham]

I have no doubt you have great knowledge of semiconductors and have already commented how worthwhile your technical analyses are.

But I also feel there is a lack of acceptance that others may also have something valid to say and a corresponding willingness to listen to them as well as to expound to them.

Here is a simple experiment to prove that it is possible to 'control' Ic with the base not even connected.

You can show this by allowing photons to enter the transistor, biased suitably between collector and emitter only. It is possible to switch on the transistor by this means.

As a matter of interest how do multiple emitter transistors fit into your control scheme? and how do you describe control by emitter injection?

Thanks again Studiot for your feedback. With photon stimulation, instead of forward biasing the base-emitter junction, photons provide the energy to transition valence electrons into conduction. Though the base lead is not brought out to the outside world, the base-emitter junction carries a conduction current due to photon stimulation.

There is no base lead terminal, but there is a base region internally. Emitter region emits electrons which are yanked into the collector via the E field of the reverse biased c-b jcn. Have I answered your question.

Your last question is a good one. "Control by emitter injection" is how I describe the bjt in general. Emitter electrons injected towards the base quickly become collector current. Base holes injected into the emitter recombine there w/ electrons in the emitter. But base injection does not directly produce collector current.

The reason the base is doped w/ acceptor ions (for a p type base, i.e. npn bjt device), is to improve c-b reverse breakdown voltage & leakage current. A heavy doping of acceptor atoms into the p base results in more base current for a given collector curret, an undesirable thing. But doing so reduces Ico, a bad thing, & improves c-b junction blocking voltage ability.

What function does the injection component of base current serve is as follows. THe lower the doping density in the base, the lower the base injection current & the higher the beta value. Superbeta bjt's at op amp inputs use these devices. But the c-b blocking voltage ability is a few volts, & the leakage current from c-b is horrendous.

For bjt devices that are to operate w/ a Vce of 50, 100, or more volts, w/ low leakage current c-b, i.e. Ico, the base must be doped heavier than is optimum for high beta. Thus current gain is sacrificed for low Ico & high c-b blocking voltage.

It's all about tradeoffs. Ic is produced by Ie. Ib is needed, but we wish to minimize it. If we minimize Ib too much, Ico goes through the roof, & Vce,blocking plummets. So base doping is optimized according to how high Vce must block, & how low Ico needs to be. Higher voltage devices have lower beta. Can't get around that. Did I help?

Claude

 

[Studiot]

Thanks again Studiot for your feedback.

When I look over this thread I see many of the same points and formulae that were raised in the 2008 thread I linked to.

In particular, since others may have missed them

1)What happens if you try to force current control via the base.

2)What happens if you force voltage control via the base.

3)What happens at different frequencies - a very important point since the bjt is not only a DC device.

4)Whether you are interested in the internal workings of the bjt or worings of a circuit using a bjt.

5)The role of the emitter.

The 2008 thread I linked to contains some further information, including references to orifinal articles and other practical demonstrations on how to vary Ic including by varying the input frequency only (= control of Ic by frequency) and a great deal more on the photon aspect.

I would agree the demonstrations were contrived to show that anyone method only achieves partial control, since it can be subverted by another.
I also agree that the weight of practical experience of countless engineers and scientists ove the years have found current control configurations to be the most useful.

Thank you for some excellent insights.

 

[wbeaty]

Kittel - solid state physics as undergrad.
Muller & Kamens - Device Fabrication For Integrated Electronics at grad school, MSEE.
Sze - Physics of Semiconductor Devices, grad school Ph.D.-EE.

Thanks! I wanted to make sure we were "on the same page," approximately. My own text titles I don't quite recall, but I think they're in a cellar box from 1979. I'm almost certain that the main one was Sze above.

If you have reasoning you'd like to explain, sure, by all means do so.

OK. But first...

Do you now understand that my article is not aimed at engineers? Right? Did you take note of who the original intended audience was?