"N channel" vs. "NPN" name confusion - Page 1
Forum section: electronics / projects

author: eee
author_rank: Contributor
timestamp: November 18, 2014, 08:33:36 am
content: Okay, so here's a basic question I can't find the answer to by googling... when they talk about N channel FET, what is the equivalent transistor of this in the other notation? Is it NPN or PNP? I.e. the "N" in "N" channel, what N is is this referring to in the other notation:NPNor PNP ?

author: Niklas
author_rank: Frequent Contributor
timestamp: November 18, 2014, 08:42:58 am
content: NPN - N channelPNP - P channel

author: eee
author_rank: Contributor
timestamp: November 18, 2014, 08:53:16 am
content: thank you so much!!

author: Jeroen3
author_rank: Super Contributor
timestamp: November 18, 2014, 09:13:07 am
content: If you compare how they work it is obvious.An N-Channel mosfet needs a positive Gate - Source voltage to conduct.An P-Channel mosfet needs a negative Gate - Source voltage to conduct.An NPN transistor needs a positive Base - Emitter current to conduct.An PNP transistor needs a negative Base - Emitter current to conduct.Notice how emitter/collector and source/drain are swapped in the symbols.

author: tggzzz
author_rank: Super Contributor
timestamp: November 18, 2014, 10:17:23 am
content: Quote from: eee on November 18, 2014, 08:33:36 amNPN and PNP devices are bipolar junction transistors. N and P channel devices are field effect transistors.Attempting to equate them will be as fruitful as trying to equate an egremont russett apple with a navel orange.

author: LvW
author_rank: Frequent Contributor
timestamp: November 18, 2014, 11:54:24 am
content: Both transistor types (BJT vs. FET) work completely different.That means: The only properties you can compare are perhaps the polarities of the both relevant voltages which are required to cause a current and/or a current change with the same direction.This attempt leads to the following:*N-MOS (enhancement): VDS>0 and VGS>0 to be compared with BJT (npn): VBE>0 and VCE>0.*P-MOS (enhancement): VDS<0 and VGS<0 to be compared with BJT (pnp): VBE<0 and VCE<0.Hence, the above approach only allows to compare the BJT with an NMOS-FET (enhancement).

author: eee
author_rank: Contributor
timestamp: November 18, 2014, 12:44:45 pm
content: Quote from: tggzzz on November 18, 2014, 10:17:23 amYes I know, it was more about the logic of the gate voltages that control how it switches on and off that I was comparing them by, as described by LvW below:Quote from: LvW on November 18, 2014, 11:54:24 amThanks for this!Quote from: 3roomlab on November 18, 2014, 10:33:24 amWow, he'sreallygood at explaining things!

author: LvW
author_rank: Frequent Contributor
timestamp: November 18, 2014, 01:39:19 pm
content: Quote from: 3roomlab on November 18, 2014, 10:33:24 amJust one (short) comment to the video:The speaker has made an error which - surprisingly - can be found in many "introductory" internet contributions (even in some textbooks):He did mention that the BJT would becurrent-controlled- in contrast to MOSFETs.This isnottrue - in spite of the fact that during design steps we use the simple formula Ic=beta*Ib.But this formula does not say anything about cause and effect.The BJT is a device that is controlled by the base-emitter voltage Vbe.Or is there anybody who can design an amplifier stage without using a suitable voltage Vbe ?

author: nitro2k01
author_rank: Frequent Contributor
timestamp: November 18, 2014, 02:54:04 pm
content: To say that a BJT is not a current controlled device is arguing semantics. It's not the current that directly controls the transistor per se, but you need to maintain a current between the base and the emitter in order to control Vbe. For a FET, it's sufficient to maintain a static VGS. To say that a BJT is not a current controlled device is like saying that a driver is not controlling their car through the steering wheel, because there's a servo motor helping (in a modern car). Technically correct, but not informative as a first approximation for someone who has never seen a car before.

author: tggzzz
author_rank: Super Contributor
timestamp: November 18, 2014, 03:56:52 pm
content: Quote from: eee on November 18, 2014, 12:44:45 pmIf you wanted an answer to that question it would have helped if you had asked that question in the first place!Your original question also implicitly involves junction FETs and depletion mode FETs, neither of which are covered by the answers you have received. For amusement, a little googling indicates there is a range of schematic symbols for different types of FET, each of which have different characteristics, e.g.:http://en.wikipedia.org/wiki/File:IGFET_P-Ch_Enh_Labelled.svg

author: LvW
author_rank: Frequent Contributor
timestamp: November 18, 2014, 04:15:09 pm
content: Quote from: nitro2k01 on November 18, 2014, 02:54:04 pmFor my opinion, it is not pure semantics. There are several circuits which cannot be explained (how and why they work) assuming current-control.According to my experience, students very often "stumble" over these different views how to explain the working principle of BJT`s.More than that, to me it sounds even contradictory to say that(1) a certain DC voltage Vbe is necessary to "open" the transistor and to allow a the desired quiescent current Ic (nobody will deny this fact), and(2) at the same time to think that anychangeof this current would be caused by the base current (that, of course cannot be avoided and must be considered during designing the circuit) and not by a change of the B-E voltage.Therefore - I think, it is more than only semantics.Who can tell me any good reason for relying on current-control only?(May I add the following? With all respect - I don`t think that your example "steering a car" really meets the point).

author: WarSim
author_rank: Frequent Contributor
timestamp: November 19, 2014, 08:57:54 pm
content: OMG! Seriously! I have never heard this voltage controlled BJT statement ever in 42 years.I haven't ever met a single designer of transistors nor thesis suggesting your statement.If you hadn't mentioned "students" I would not have replied. But if there is a chance you are a teacher/instructor/prof summarizing a BJT is sometimes a voltage controlled device to explain a schematic. I beg you to stop and research the physics more to come up with a better explanation.Sent from my iPad using Tapatalk

author: timb
author_rank: Super Contributor
timestamp: November 19, 2014, 09:25:09 pm
content: MOSFET types would always confuse me, as when I was a kid learning electronics someone told me NPN transistors Never Point iN, but N-Channel MOSFETS *do* point in and I couldn't get the phrase out of my head!Sent from my Smartphone

author: Warhawk
author_rank: Frequent Contributor
timestamp: November 19, 2014, 09:54:55 pm
content: Quote from: timb on November 19, 2014, 09:25:09 pmHave a look at this:http://electronics.stackexchange.com/questions/69311/mosfet-symbol-what-is-the-correct-symbolAnother thing is "saturation" region for BJT and MOS...

author: ehughes
author_rank: Frequent Contributor
timestamp: November 20, 2014, 12:05:49 am
content: QuoteThe problem is that you are applying "circuit" theory in a manner that separates current from potential. One simply cannot happen without the other. Circuit theory is approximation to Field Theory. You cannot separate potential from current just as you cannot separate Electric Field from Magentic Field. One of Einstein's (very significant) contributions to the theory was showing that they were the *same* field viewed from different (orthogonal) relativistic reference frames.Yes, vBe is a net effect of current mobility in the base loop. However, it is the current mobility here that allows current mobility in the collector loop. And yes there is a VCE in that loop. You cannot separate the concepts. Yes, there is a minimum vBe require in your source but that is not a separable concept the current control.This thinking is the same that teaches current "flows" from one side of a source through a circuit back to the other side. The forward and return currents travel simultaneous as a result of the fields!QuoteBJT's are different animals from MOSFETS While there are similar in how they are used. You are comparing apples to oranges.FETs are transconductance devices that relate *charge* to current. The fact that they turn on with a voltage is a effect of a charge threshold to enhance a channel (look at datasheet gate charge!) You must think of them as charge controlled devices. Anyone who saying they are purely voltage controlled have never switched on and off at a high rate. It is the charge doing the work, the voltage is just need to build the charge. (dQ/dt)!!! The most certainly need a dynamic current to turn them off and on!BJT's are current controlled (derivative of charge) Different Concept.You simply can't willy nilly swap them with understanding the differences in how they operate. There are similarities in circuit setup but you can't take those at face value.

author: WarSim
author_rank: Frequent Contributor
timestamp: November 20, 2014, 05:19:27 am
content: Because I responded negatively before. I want to take this chance to respond positively.Good explanation, much more accurate than I expected.In case you are wondering why saying a charge controlled device doesn't contradict calling it a voltage controlled device. Capacitors are called voltage dependant devices, and the term transferred to MOSFETs. BJT base is basically a diode. MOSFET gate is basically a capacitor.Sent from my iPad using Tapatalk

author: LvW
author_rank: Frequent Contributor
timestamp: November 20, 2014, 09:10:12 am
content: Quote from: WarSim on November 19, 2014, 08:57:54 pm1.) I am aware that many people rely on the current-control approach for BJT`s. Hence, I am not surprised - on the other hand, it is surprising that such a false explanation of the BJT`s physical working principle could survive in some heads over the years. To make it clear - of course, I do not deny the fact that there is a base current and that it must be included in the design steps. That`s not the question. But - from the physical point of view it is NOT the current Ib that "controls" Ic. (By the way: Even from the energy point of view it is impossible that a smaller quantity can havedirectcontrol over a larger quantity of thesamekind.)You can believe me - I do not write such a comment without knowing what I am speaking about.2.) To mention only three "witnesses" who are supporting voltage-control : (a) William Shockley (doctoral thesis), (b) Barry Gilbert (I suppose you know his name) and (c) Winfield Hill (co-author "Art of electronics"). Do you need references?3.)Questions:* Can you explain, for example, the function of the simple current mirror without using the voltage-control principle?* Can you explain Barry Gilberts famous principle of "translinear circuits" with the current-control approach?* How do you explain the effect of negative feedback caused by an emitter resistance ?* And finally: Do you agree that Re feedback doesincreasethe resulting input resistance of an emitter stage? And - from feedback theory we all know that such an increase is connected with current-controlledvoltagefeedback only (current feedback reduces the input resistance).Do you still think that I must "stop and research the physics more" deeply - unless you can answer my questions above?RegardsLvW

author: LvW
author_rank: Frequent Contributor
timestamp: November 20, 2014, 09:17:45 am
content: Quote from: ehughes on November 20, 2014, 12:05:49 amAs my reply - just two sentences: I cannot see where I have "separated" current from potential (voltage). The basic question is: Is it the voltage that causes a current or is it the current that causes a voltage?

author: peufeu
author_rank: Contributor
timestamp: November 20, 2014, 10:53:01 am
content: Quote from: LvW on November 20, 2014, 09:17:45 amI guess that would depend on yow you use that transistor.If the base is driven by a low impedance (ie, a voltage source), that will provide whatever base current is necessary, then it is voltage driven, and you can consider that the Vbe causes a base current (and obviously a collector current as the transistor does its job as a follower). In this case, Vbe matters, so the design may have to consider its dispertion and temperature drift.If the base is driven by a high impedance (current source, collector of another transistor, etc), then Vbe will set itself depending on the current that is injected in the base, and you could say that the current causes a Vbe voltage. In this case, Vbe doesn't really matter.Of course, on top of that, the various capacitances inside the transistor all require current (ie, dQ/dt) if we want to process AC signals ; when the collector moves, the current through Cbc will add or substract to the base current and introduce a HF pole.So, if your transistor is in a common emitter, non cascoded amplifier, with a collector load and the base driven by, say, 330 ohms, you could say that at DC it is mostly voltage driven, but at AC it is current driven (current through base resistor will be used mostly to drive Cbc through Miller effect, and what remains is the actual base current).Anyway, who cares O0

author: rs20
author_rank: Super Contributor
timestamp: November 20, 2014, 11:31:53 am
content: Quote from: 3roomlab on November 18, 2014, 10:33:24 amYes, modern MOSFETs are fundamentally no different, and will pinch-off if you have a small gate voltage / large current. Look at any datasheet, you'll see that characteristic flattening off of the characteristic curves.However, a random N-channel MOSFET you find lying around will have a pinch-off current of 20A or something massive like that at 5V Vgs, so for your average little motor driver, you are so far from this limit that you're fine.Put it another, look at the graph he drew. You want your MOSFET to be super efficient, which means that it should drop no voltage, which means Vds should be very very small (since power wasted is Vds * Id). So what's on the graph there, right at the very left? The Ohmic region, not the Saturation region. You should be driving your switches in the Ohmic region, where saturation isn't a thing. Just like you should drive your BJTs switches in saturation rather than active mode (well, some people run their BJT switches in active for fast switching, but I digress and there's no corresponding hack in FETland.)

author: LvW
author_rank: Frequent Contributor
timestamp: November 20, 2014, 01:22:05 pm
content: Quote from: peufeu on November 20, 2014, 10:53:01 amRight - "Vbe will set itself depending on the current", and therefore, it is finally the VOLTAGE that controls Ic. How can you say "Vbe doesn't really matter" ?In summary, I don`t think that the physical working principle of a device can depend on its applicaton.More than that, of course, I agree that at higher frequencies the amplifying properties of the BJT are modified - but do you really think, that the PHYSICAL principles are changed fundamentally? Suddenly? At which frequency?

author: LvW
author_rank: Frequent Contributor
timestamp: November 20, 2014, 01:30:08 pm
content: Ohh - I forgot to present one of the most impressive examples (see my reply'17): The classicaldifferential amplifier(long-tailed pair) - and one of its most important features:The input-output relationship which follows atanh function.Questionto all people who believe in current-control of the BJT:How can you explain/derive the tanh characteristics of the diff. amplifier without using voltage control and the corresponding exponential input-output function ?

author: WarSim
author_rank: Frequent Contributor
timestamp: November 20, 2014, 03:12:47 pm
content: BTW yes I understand the physics. And yes I do get your point. You are completely missing mine.Yes because every single device made by man has inductive, capacitive and resistive properties every device can be said to be voltage controlled and current controlled. That is not the point being discussed.The convention of calling a transistor a current controlled device and a MOSFET a voltage controlled device is a convention. Just like we have conventional current flow and the competing papers on other current definitions. This convention is used to form a base to build from not the complete picture. In truth it is not necessary for most technician, technologist or engineers to work in that high or order. From my experience most don't. Besides almost all manufactures hide all specifications above 3rd order. If anything greater is required the specs will be derived or empirical characterization.My expressed issue is with your clouding the the established convention. A person with limited knowledge on the subject asked a question and the convention was offered. Yes it is simplified, no it is not completely accurate. The point is that with these convention ever cct can be defined in first order with them. Also an effective short description can be given to someone without involving higher physics. We are here to enable others not deter them by burring them in physics.IMHO I see it as arrogance and like someone arguing number theory to prove someone cheated at craps.Lastly I believe the issue with explaining the offered ccts with the offered convention is you are mixing the different order conventions. The convention of BJT are current controlled devices is a first order convention that happens to be useful in second order just like in first order a resistor is considered to be purely resistive and at higher orders their inductance and capacitance is taken into account.Sent from my iPad using Tapatalk

author: nitro2k01
author_rank: Frequent Contributor
timestamp: November 20, 2014, 03:49:10 pm
content: For the record, WarSim explained what I was trying to argue before, in a much better way than I could.

author: LvW
author_rank: Frequent Contributor
timestamp: November 20, 2014, 04:02:46 pm
content: Quote from: WarSim on November 20, 2014, 03:12:47 pmHi warsim - with all respect, reading again your reply'12 I cannot see that I did miss your point.From the beginning, I spoke about the PHYSICAL working principle only. And your answer was that "I should stop and research the physics more and come up with a better explanation".I think, it is simply not true that the "current-control description" is a convention only. I have mentioned, for example, the "designers bible" (AoE) which clearly supports voltage-control.For all electronic parts it is possible to give one single explanation how it physically works. Why should we rely on a "convention" in case of BJT`s? Shouldn`t it be possible to explain it`s function unambigouosly? Of course, it is possible and can be found in many textbooks.A convention must allow to explain all observed effects (without exception) - otherwise, it is a bad convention that cannot be used as such (a "good" and working convention is the direction of the current).Finally - what are your answers to the five examples as given in my posts #17 and #22 ? Can a convention of "current-control" be used to explain the circuits as mentioned in these examples?

author: WarSim
author_rank: Frequent Contributor
timestamp: November 20, 2014, 04:47:43 pm
content: Well isn't it peachy that a first order convention has been over extended past its intended application. With that information of course it is wrong where it is applied beyond first order. Same goes for voltage control.Thanks for supporting my position with you repeating that you answered a first order question with a third order principal. The "physical" model is introduced in second order and not significantly implemented until forth order.We have conventions for the same reason we have things like right hand rule, left hand rule , etc. nobody needs to delve into the magnetic domain calculations and theories to make use of a motor and the like.There is a possibility that I assumed that you mentioned students being confused about BJTs as new students. I assumed that by the time they are delving into the higher orders it should be clear why the convention is altered or how the non-convention has developed.You are pressing the physical model point and I am not going to discuss physics here. If I want to make my point further than first or second order, I will write a paper on it. I have said before I know allot of stuff but at this point in my life I want what I say to be just my opinion. I stated my opinion, you disagree, I'm ok with that.In summary with your opinion that the current controlled device description of a BJT is more than a convention and the original question was something more than a first order question you are correct.Sent from my iPad using Tapatalk

author: langwadt
author_rank: Super Contributor
timestamp: November 20, 2014, 08:56:40 pm
content: Quote from: tggzzz on November 18, 2014, 10:17:23 amI don't see why, there are differences but also similaritiesIt makes sense to know that the polarities of NPN/NFET and PNP/PFET are the sameand the configurations that a common with bipolars are common with fets

author: dannyf
author_rank: Super Contributor
timestamp: November 20, 2014, 09:02:36 pm
content: QuoteWhy not? You can use bjt or fet to construct current mirrors so the answer is yes.I don't know why it is so puzzling.

author: macboy
author_rank: Super Contributor
timestamp: November 20, 2014, 09:41:01 pm
content: Quote from: WarSim on November 19, 2014, 08:57:54 pmI agree, it is a ridiculous statement, one from someone who doesn't understand the physics of how the devices work. Obviously, one can observe a varying base-emitter voltage with varying collector current. That does NOT imply that the collector current is controlled by base-emitter voltage. Correlation does not imply causation.

author: WarSim
author_rank: Frequent Contributor
timestamp: November 20, 2014, 09:56:11 pm
content: Quote from: macboy on November 20, 2014, 09:41:01 pmYes it is funny how a simplified statement created to remember the primary datasheet characteristic curve general shape has turned into a subject of such debate.Besides last time I checked there hasn't even been a consensus across the physics word on what the definition of current is.. Personally my definition is : it's the A in ohms law.Sent from my iPad using Tapatalk

author: lapm
author_rank: Frequent Contributor
timestamp: November 20, 2014, 10:49:55 pm
content: Quote from: WarSim on November 20, 2014, 09:56:11 pmActually there is, what current is well defined.http://www.si-units-explained.info/ElectricCurrent/

author: WarSim
author_rank: Frequent Contributor
timestamp: November 20, 2014, 11:14:03 pm
content: Quote from: lapm on November 20, 2014, 10:49:55 pmI must be speaking an unknown language people are missing my points and jokes.Hint the smiley face means humor.There are perfectly good usable definitions for current. The point is that the physics community can't agree on one.It seems if you can't say I disagree and propose a competing point of view within 5 seconds you booted out of the physicist club.Assuming we can agree on a frame of reference, how long a second is and what 5 is of course.Sent from my iPad using Tapatalk

author: LvW
author_rank: Frequent Contributor
timestamp: November 21, 2014, 09:52:21 am
content: Quote from: macboy on November 20, 2014, 09:41:01 pmHi macboy - You must be very sure to give such a harsh answer.Have you ever made up your mind to find out why RE increases the input resistances and/or how the tanh function for the diff. pair is derived?Perhaps you have time to read some additional sources for completing your knowledge? Here are some of them - most probably more credible than me:1.) Berkeley University (page 292, 8th line from the bottom and page 297, begin of chapt. 8.3)www.eecs.berkeley.edu/~hu/Chenming-Hu_ch8.pdf(„IB is an undesirable but inevitable side effect of producing ICby forward biasing the BE junction“)2.) Book Sedra-Smith, pages 8, 9, 11, 13, 15, 17, 30http://www.csie.ntpu.edu.tw/~dalton/course/microelectronics/ch5.pdf3.) Two answers from Winfield Hill (co-author "Art of Electronics")http://cr4.globalspec.com/thread/68055/voltage-vs-current4.) Stanford-University (see pdf attachement, top of second page)Perhaps you are fair enough to revise your reply?RegardsLvW

author: LvW
author_rank: Frequent Contributor
timestamp: November 21, 2014, 10:16:00 am
content: Quote from: WarSim on November 20, 2014, 03:12:47 pmHi warsim - I am afraid, it makes not too much sense to continue this discussion.Perhaps we have a communication problem due to different languages.(Quote: „I am not going to discuss physics here“). My question: Why not ? From the beginning, I spoke about physical effects - and you are stressing „conventions" of first and higher order only. I do not know any document, article or textbook which classifies the control mechanism of a BJT as a pure "convention" only.I must admit that I am a bit disappointed not to see any answers to my pure technical and circuit-oriented questions in my posts#17 and #22. I think, we all are engineers and should be able and willing to answer technical questions?OK - let`s stop the „discussion“ (unfortunately in most parts non-technical) and let mesummarize:1.) Up to now, I have seennot a singlepublication/textbook which contains some arguments against the voltage-control property of BJT`s (simply stating it would be current-controlled is no counter argument).2.) However, there are many circuit-based effects and examples (and I have listed some of them in post #17 and #22) which can be explained using voltage-control only (and NOT on the basis of current-control). Unfortunately, no comments from your side.3.) More than that, the technical fact of BJT`s voltage-control is emphasized by many serious and credible engineers/scientists (see some examples in my former post#33).Now - every reader of this thread may create his own view.

author: dannyf
author_rank: Super Contributor
timestamp: November 21, 2014, 11:41:27 am
content: QuoteIt is precisely the physical effects that dictate such devices to be current controlled rather than voltage controlled. a NPN works through electron combination at the b-c junction. So if you control the electrons flowing into the base, you have controlled the collector current. So this whole thing is current (=charge / time) driven or controlled.QuoteAppeal to authority probably isn't the best argument in any discussion. There are just as many morons among "serious and credible" experts as they are among lay persons, regardless of how many books such experts may have published.

author: LvW
author_rank: Frequent Contributor
timestamp: November 21, 2014, 12:13:00 pm
content: Quote from: dannyf on November 21, 2014, 11:41:27 amDid you realize that this was only one of three arguments?It would be interesting to learn how YOU would explain why a resistor RE increases the input resistance of a common emitter stage and/or how the tanh function of a diff. amplifier is derived?

author: c4757p
author_rank: Super Contributor
timestamp: November 21, 2014, 12:14:25 pm
content: Oh, not this again.Quote from: dannyf on November 21, 2014, 11:41:27 amIt's the carriers flowing across the BC junction which cause the transistor to conduct, but you don't get to push them across that junction yourself. I'd like to see how you plan to do that. (Possibly something involving voltage?) Applying a voltage between base and emitter draws carriers up from the emitter, and most pass to the collector because of device geometry. This is a result of thevoltageacross the BE junction. Applying current to the base does not force a proportional current to flow to the collector, it's the voltage that develops as a result of the current that pulls the carriers from the emitter.Quote from: dannyf on November 21, 2014, 11:41:27 amThe EEVblog Fallacy: If an authority speaks, he must be wrong because something something appeal to authority.

author: dannyf
author_rank: Super Contributor
timestamp: November 21, 2014, 12:26:23 pm
content: QuoteIt shouldn't be any part of a rigorous discussion. By itself, the fact that someone, however authoritative s/he is, approved of something doesn't make that something correct. It is correct only because it is correct, not because someone approved of it.QuoteI wouldn't mind giving it a shot, if you could tell me 1) how those questions and associated answers support your assertion or disproves the other side's arguments; and 2) what is "resistor RE" and "tanh function".Explain it in as plain language as you can, or you don't understand it.

author: LvW
author_rank: Frequent Contributor
timestamp: November 21, 2014, 01:11:42 pm
content: Quote from: dannyf on November 21, 2014, 12:26:23 pm(Nice wording).I am very sorry for my assumption that you would know 1) the meaning of a resistor RE in a common emitter stage and 2) by what mathematical function the input-output characteristic of a BJT based diff. amplifier stage is described. My fault - sorry.

author: LvW
author_rank: Frequent Contributor
timestamp: November 21, 2014, 01:26:04 pm
content: Quote from: c4757p on November 21, 2014, 12:14:25 pmYes - intentionally, I have tried to explain my viewnotbased on carrier physics (holes/electrons) but on application circuits and their behaviour.

author: WarSim
author_rank: Frequent Contributor
timestamp: November 21, 2014, 03:07:58 pm
content: Quote from: LvW on November 21, 2014, 10:16:00 amHere is my answer to all your questions to me. You are an argumentative arse.You are creating a disagreement where there isn't one. I have said ,in your context, following the papers you have given, you are correct. You have repeatedly demanded that I play the papers war because the papers I subscribe to vary from the ones you cited. I do not want to discuss why the differences between the various physicist or EE papers. In my prior comment I mistakenly assumed you would want to investigate the opposing papers. Your next response proved it was a waisted response. Lastly if the paper or research brief is more that 7 years old I read it. If it is newer I haven't, I stopped caring.My one request was stop confusing people new to electronics with such papers. Two statements where made to help remember the shape of their primary characteristic curve back when transistors where new. They are BJTs are current control MOSFETs are voltage control. Because the primary datasheet characteristic curves are Ibe/Ice and Vg/Ids. It was/is a memory helper only, ergo a convention. This is the basic answer for a basic question asked by the OP.I don't give a ---- if a learned Doctor hijacked the phrase. Nor do I care if a few papers exist that makes it unsupportable in higher orders. The fact is almost every beginner only needs the basics, and wholly relies on spice for anything more detailed. For crying out loud I have seen EEs go down this route. It doesn't flipping matter!I am convinced that you are not a doctor. Therefore have no right to dictate how I express my understanding. No, I am not a doctor but the people who have accepted me as a peer are. Frankly any doctor would be an idiot not to at lease consider the thoughts of anyone in the top 2 percentile IQ. Seven years ago I got tired of the constant debates and now I don't care if anyone disagrees with me. If I personally encounter something I don't understand I will figure it out. Until then I am out of the papers game.If such arguments are your hobby you will have one for life. There are many more devices coming that will offer many more opportunities for you to debate/orate with/to the unwilling. If you do have a high IQ I strongly urge you to find a group that loves to debate. Ie genius join Mensa, gifted join councils, etc. Just stop trying urge me into debating the merits of papers.Sent from my iPad using Tapatalk

author: LvW
author_rank: Frequent Contributor
timestamp: November 21, 2014, 05:28:08 pm
content: Quote from: WarSim on November 21, 2014, 03:07:58 pmMaybe it is good that English is not my native language- so I do not understand all the intricacies of your reply.I am really surprised and disappointed about the style and the tone of this debate.Are we really engineers/lecturers who - controversely - are discussing technical matters?As I have mentioned, I will not resume the discussion - however, for my opinion you have, indeed, expressed your severe disagreement:Quote: "OMG! Seriously! I have never heard this voltage controlled BJT statement ever in 42 years.I haven't ever met a single designer of transistors nor thesis suggesting your statement..........................I beg you to stop and research the physics more to come up with a better explanation.Well - I did follow your recommendation and I have tried to explain/justify my position in the subsequent posts.If there was no disagreement between us - where did you express your agreement as far as the main question is concerned (voltage vs. current control)?Perhaps, I missed something, and - as I have indicated already - it is possible that "language problems" are responsible. If this should be the case - sorry, my fault.On the other hand - a short comment from your side to some of my technical examples/questions could have perhaps made the the situation somewhat clearer.RegardsLvW

author: WarSim
author_rank: Frequent Contributor
timestamp: November 21, 2014, 05:49:09 pm
content: One more time.When I assumed you where using the term current controlled device as intended when the phrase was initially coined as a primary characteristic curve descriptor as a learning/memory tool for first order questions your response was wrong.When I realized that your response was just inappropriate I said so. I tried to explain that I did not like it when you answered a first order question with a statement referencing the physics of the physical model. If you want to help answer the OPs question answer their question appropriately. If you want to debate the physical model then start a thread for that purpose. Hijacking this thread for this debate is considered rude by accepted forum behaviour.Because of the papers you have cited in support of your position it would require referencing other papers and detail why the answer of the others are also deemed valid. This is where I refused, but you keep prodding. This prodding is why I am annoyed. This is why you are getting negative responses from me.Sent from my iPad using Tapatalk

author: Zero999
author_rank: Super Contributor
timestamp: November 21, 2014, 06:08:26 pm
content: There's always an argument when this crops up.Anyway, here's how I prefer to explain why the input impedance of an emitter follower is high.

author: dannyf
author_rank: Super Contributor
timestamp: November 21, 2014, 06:32:42 pm
content: QuoteBecause of the current feedback - in the sense that the collector current goes through the emitter resistor.All you need is to take a look at the small signal model for a bjt: on the output side, it is a current sink, controlled by the base current (aka current-controlled current sink).The typical small signal model describes the input as a (variable) resistor, and the output current varies with the input current (=base current).The original question has zero bearing on if a device is current- or voltage-controlled and is totally irrelevant to this discussion.

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: November 21, 2014, 07:46:50 pm
content: is that some kind of obsession to make things way more complicated ... it's simple Ic = beta Ib , a discussion longer than some ppl life story with an absolute confidence that current control is FALSEInnocent question cause i have to take the opportunity to ask irrelevant question in a totally irrelevant discussion to the OP questionis a diode or a LED a current control device or a voltage control device, where datasheet clearly show led as CC device, it will not pass current until the voltage rich certain level , so it must be voltage control too .. blow my mind

author: dannyf
author_rank: Super Contributor
timestamp: November 21, 2014, 08:33:00 pm
content: QuoteNot so simple. All that says is how beta is defined, not how Ic changes with Ib.The same with Ohm's law - it is used to define resistance, not to define voltage / current from current / voltage across a resistor.

author: LvW
author_rank: Frequent Contributor
timestamp: November 21, 2014, 09:18:57 pm
content: Quote from: WarSim on November 21, 2014, 05:49:09 pmPerhaps you have overlooked that I have answered the OP`s question in my post#6.But I agree with you - it would have been better to open a new thread for dicussing the BJT control mechanism.Why didn`t you come up with this earlier?

author: WarSim
author_rank: Frequent Contributor
timestamp: November 21, 2014, 09:38:21 pm
content: Quote from: LvW on November 21, 2014, 09:18:57 pmYes you did, reply 6 post 7 was a great answer. And the OP thanked you for it.I did imply not here a little earlier, but I agree my position on this point was not stated clearly stated. Communication is a tow way street so I will share blame in this.Sent from my iPad using Tapatalk

author: LvW
author_rank: Frequent Contributor
timestamp: November 22, 2014, 08:41:39 am
content: Quote from: WarSim on November 21, 2014, 05:49:09 pmWarsim - after having some time (over night) to think about your personal accusations I cannot resist to reply as follows:The OP`s question was if there are some commonalities between BJT`s and FET`s. And, I think, in this context it is NOT a "rude hijack" to bring up the question:"Is the BJT current-controlled or voltage-controlled (like the FET)?". Did I really violate forum rules in a rude manner? I don`t think so.(By the way: There was a discussion - post 30...32 - in which you took part about the definition of current; ...Hijack?).

author: WarSim
author_rank: Frequent Contributor
timestamp: November 22, 2014, 02:46:29 pm
content: Quote from: LvW on November 22, 2014, 08:41:39 amThis has to stop, please!Yes I made a joke, complete with smily faces, to try and kill the topic derail.Yes you could create a position that I should have use elite speak instead.Elite speak is not my generation the original emoticons set are.The fact is I used emoticons to tell people it was a re-ductus obserdium.The fact is not every person will get every joke.Do you want me to apologize for not clearly getting across that it was a joke to everyone?We disagree, are you going to hound me until every small perceived slight is throughly discussed? I hope not.Sent from my iPad using Tapatalk

author: LvW
author_rank: Frequent Contributor
timestamp: November 22, 2014, 03:18:30 pm
content: Quote from: WarSim on November 22, 2014, 02:46:29 pmNo - certainly not.It was my only intention to state that your personal attacks - in my opinion - were unjustified.

author: peufeu
author_rank: Contributor
timestamp: November 30, 2014, 04:30:12 pm
content: Quote from: LvW on November 20, 2014, 01:22:05 pmIt simply means that it does not matter to the designer. Of course it matters to the transistor.You can also current-drive a MOSFET gate BTW. Neat way to get high DC gain.

author: LvW
author_rank: Frequent Contributor
timestamp: November 30, 2014, 05:43:08 pm
content: Quote from: peufeu on November 30, 2014, 04:30:12 pmYes - agreed.