Timeline for Why is a BJT considered "current-controlled"?
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| Aug 22, 2016 at 4:59 | history | edited | jbord39 | CC BY-SA 3.0 |
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| Aug 21, 2016 at 16:57 | comment | added | jbord39 | @LvW: I have never once tried to make a case for the base current having a controlling function in linear applications. Suddenly bring up Flash memory?? Not only is Flash memory in my answer, it is in 3 or more of my comments directed at YOU. You do not read, listen, or pay attention. You clearly have been on this tirade for a long time, and are just spouting off the same thing in every comment. I have given proof, and so has Centauri, enough that a reasonable person could find a middle ground. You are arguing with yourself and look like a fool. | |
| Aug 21, 2016 at 16:52 | comment | added | LvW | @jbord39, how often shall I repeat that the base current does exist ? Why are you continuosly ignoring this fact? By the way - I am still waiting for a proof/justification of its controlling function in linear applications. Why do you suddenly bring the Flash Memory into the discussion? | |
| Aug 21, 2016 at 16:32 | comment | added | jbord39 | @LvW: still never responding either to the obvious differences highlighted by FLASH MEMORY. Try building flash memory with a BJT and I will be impressed (because the constant base current draw you will have a very hard time)! Maybe you have not heard of Flash memory (it is kind of new, maybe the last 20 years), I will explain. It is memory which stores data as charge on the MOSFET gate. The presence/absence of this charge is measured through the conduction of the gate. The whole thing requires no power to hold state! Only possible with MOSFETs since BJT's are current controlled! | |
| Aug 21, 2016 at 16:31 | comment | added | jbord39 | @LvW:What? The fact that base current is required for a BJT is something that you gloss over, only admitting to this when cornered with obviousness of it. You cannot reconcile the fact that DC bias current must flow into the base of a BJT for it conduct. A FET does not need this. Descending deeper into theory and 2nd order effects is pointless and gives no insight. You act like those who are not throwing about unrelated technobabble don't KNOW the technobabble, this is what is rude. I DO know it, I just disagree with your conclusions. The ego you get from teaching this is very obvious to all. | |
| Aug 21, 2016 at 16:25 | comment | added | LvW | @jbord39, I gave you an answer as a comment to another detailed answer. More than that, you have chosen a wording ("incredibly rude") which primarily speaks against the person who has used it. | |
| Aug 21, 2016 at 15:46 | comment | added | jbord39 | @LvW: Your responses are incredibly rude because you are pressupposing that I am ignorant. I am not. Yes, I know how the early effect works (base width modulation), as I mentioned last time. Again, this is not the question. Again, this is not the question. The question is "why is a bjt CONSIDERED current controlled". You are arguing for nothing. No one asked "how does a BJT work". No one asked "Should a BJT be considered current controlled". The OP asked "WHY is a BJT considered current controlled". Just stick with your statement please: "My last answer" because you are like a parakeet. | |
| Aug 21, 2016 at 15:43 | comment | added | jbord39 | @LvW: again, his question is not "how a BJT works", but "why is a BJT considered current controlled". I don't know how to get this through to you, since you keep ignoring me when I mention this. You are explaining something he is not asking. He wants to know why it's considered current controlled. The distinction only makes sense when you compare it to the OTHER GIANT IN THE ROOM ( aka MOSFET), which is truly NOT current controlled. You have never been able to respond to this fact, and just droll on about theory and 2nd order effects which everyone knows! | |
| Aug 21, 2016 at 9:17 | comment | added | LvW | jbord39, are you aware that you are just repeating assertions again and again? We do not need a comparison to MOSFETs for explaining how a BJT really works. I am still awaiting some proofs and justifications from your side. By the way - I did not ask you if you have heard about the Early effect. I have asked you if you can EXPLAIN this effect. And if you can EXPLAIN the meaning of the VBE tempco of -2mV/K (this value was not only measured, it was theoretically found based on the charged carrier physics). Do you need references? | |
| Aug 20, 2016 at 17:45 | history | edited | jbord39 | CC BY-SA 3.0 |
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| Aug 20, 2016 at 17:24 | comment | added | jbord39 | @LvW: but, you keep bringing these things up like they change the initial statement. It is in contrast to the MOSFET which the phrase arises. And yes, I do know of the early effect (base width modulation) and I know how BJT's work. I understand the angle you are coming from. But, there is an undeniable aspect when comparing the MOSFET vs. the BJT, that the MOSFET is clearly voltage controlled, and the BJT is current/voltage controlled. You keep ignoring this distinction. Also, the OP is not asking "SHOULD" it be considered, but "WHY IS IT". For the 5th + time. | |
| Aug 20, 2016 at 17:19 | comment | added | LvW | My last answer (because you have mentioned "ignorance"): In this thread, at least 5 times I have mentioned that the base current does exist. Who will deny this? Why are you continuously claiming that that I would propose to operate the BJT w/o base current? Have you no other arguments? Did you ever think about the Early effect and the principle behind it? Did you ever think about the meaning of the tempco -2mV/K? Most questions can be answered by simple reflection. | |
| Aug 20, 2016 at 17:10 | comment | added | jbord39 | @LvW: Thanks, your words were kind as well. Still no answer for how BJT cannot conduct w/o base current, and a mosfet can conduct w/o gate current. Still no answer on how the OP's original question is "should" and not "is". | |
| Aug 20, 2016 at 17:08 | comment | added | LvW | Thank you for your nice words. Certainly, you are right (and better in English than me). | |
| Aug 20, 2016 at 15:39 | comment | added | jbord39 | Since you cannot even use the word "prove" properly (i've seen proof and proove so far from you; words someone so educated should understand by now), as well as quoting of my name as "jboard39" quite a few times now (you know when you are spelling it right, it will auto-complete for you?), I have a hard time thinking you could "proove" your way out of the instructor position you've held for 25+ years apparently into a professorship. I have met many people like you during my times at university. Confronted with obvious facts you take a digression. Base current is required, reread the question | |
| Aug 20, 2016 at 15:35 | comment | added | LvW | Of course, I can - because I am able to proove and justify my statements. And that is in contrast to the "current-control promotors" who - up to now - could not present any justification. | |
| Aug 18, 2016 at 18:53 | history | edited | jbord39 | CC BY-SA 3.0 |
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| Aug 17, 2016 at 20:15 | history | edited | jbord39 | CC BY-SA 3.0 |
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| Aug 17, 2016 at 20:13 | comment | added | horta | @LvW electronics.stackexchange.com/questions/201533/… Since voltage and current in devices don't exist without eachother, you cannot say that the BJT is truly a voltage-controlled device. Even the Ebers-Moll model is nothing more than a model (an approximation that humans use to abstract away messy details of the real world). | |
| Aug 17, 2016 at 20:07 | history | edited | jbord39 | CC BY-SA 3.0 |
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| Aug 17, 2016 at 20:03 | comment | added | jbord39 | @LvW: On top of that his question is not "Is a BJT current controlled" but "Why is a BJT considered current controlled". | |
| Aug 17, 2016 at 19:54 | comment | added | LvW | horta, it is simply not true that the BJT`s output is "very much dependent on the input current". Each reliable (!!!) book and home pages from leading US univesities can tell you the opposite. Nobody denies that a base current does exist but it can be seen simply as a "nuisance or a defect" (as mentioned by the well-known BJT specialist Barrie Gilbert). | |
| Aug 17, 2016 at 19:41 | comment | added | horta | @LvW I think the point jbord39 is making is that you can't have voltage without current and vice versa. Therefore, by the strictest definition, nothing can truly be a current or voltage controlled device (alone). Therefore he/she's trying to answer the question of why textbooks even bother to make the distinction. A BJT's output is very much dependent on the input current unlike a MOSFET, which is I'm assuming why textbooks state that certain devices are current or voltage controlled (when in reality that's never truly the case). | |
| Aug 17, 2016 at 19:37 | comment | added | LvW | Sorry - this is not a correct description of the working principle of the BJT. Have you ever heard about Shockley`s exponential equation Ic=f(Vbe)? Do you know that the transconductance gm=d(Ic)/d(Vbe) is the key parameter for the amplification process? Do you know that two different transistors with different beta values (100 and 200) will provide the same voltage gain (identical quiescent current Ic)? | |
| Aug 17, 2016 at 19:09 | history | answered | jbord39 | CC BY-SA 3.0 |