()blivion
Active Member
I understand that, and I know it to be 0.98<α<0.998. I also have never needed to know it's precise part specific value though. I know it as essentially unity, and that has served me fine.Ratchit said:Alpha in known in electronics as the common base current gain. Beta is the common emitter current gain.
I'm sorry, that was very clumsily spoken wasn't it. Not unusual for me honestly. That statement should really have been...Ratchit said:Its concept is useful.Myself said:But other than that, alpha is rather useless for analyzing a transistor from what I know.
Myself said:But other than that, [the exact] alpha is rather useless for analyzing a transistor from what I know.
Though, it seems like you may have understood what I was implying without me giving a perfect description. So, +1 for not playing petty word games with me here.
Speaking of petty word games...
Ratchit said:Back to the textbooks for you.
I did specifically say that "I could easily be slightly off", though I may have been more than "slightly". Also, I am actually reading up on the subject vigorously, if nothing more than to sort the matter out for myself as I'm clearly not 100% certain what goes on in a BJT at the subatomic level.
But that is all pretty irrelevant.
I strongly doubt that a vastly deeper insight into the exact quantum mechanics of the BJT is going to significantly change the overview of the rudimentary physics and operation of the device. BJT's themselves work very much in accordance with I[SUB]c[/SUB]=β*I[SUB]B[/SUB], even if internally the charge carriers are actually making conga lines from conductor to conductor.
Again, I was poorly spoken here. And I was expecting someone to play that card because of this.Ratchit said:An insulator can have a voltage without any current existing through it. A fully energized capacitor can have a voltage across it with[out?] any current existing in the the cap's branch.Myself said:Conversely, a load can not have a voltage across it without having a current going through it.
The word "load" is commonly understood to mean "reasonably low impedance". Although all things have some conductivity, so with potential some current will always exist, an insulator does not constitute a load in the above context, as it does not continually draw reasonable currents. Neither does a capacitor. And in both cases, a current had to have existed in the first place to charge it up, so both reduce to "chicken or the egg" arguments.
A forward biased semiconductor junction on the other hand has a relatively low impedance, which will constantly draw a current. Any such impedance obviously can not develop a voltage across it unless there is a continuous current through it that is also in alignment with Ohm's/Diode law. Thus continuing to support my position that you can't have one without the other.
Another typographical blunder...Ratchit said:Sure we can. Many scientific facts and mathematical relations can be proven beyond a shadow of a doubt.Myself said:We can never really know what physically true is as we can only rely on the 5 limited human senses and our imagination.
Myself said:[If it is not "from first principle" math or physics,] We can never really know what physically true is, as we can [then] only rely on [empirical models].
The equation I[SUB]c[/SUB]=I[SUB]S[/SUB]*(e^(V[SUB]BE[/SUB]/VT)-1), (which from what I can tell is just a simplified form of Ebers–Moll model) is not from first principle because some of the constants and relationships in it are derived from empirical models. This therefore invalidates it as a "physical fact". I[SUB]C[/SUB]=β*I[SUB]B[/SUB] is no different really. Which all makes perfect sense considering both are known to just be close approximations and not exact solutions for the transistor.
As far as I know, the closest you can get to "physical fact" with a BJT is the Gummel–Poon (charge-control) model. And wouldn't you know it, the Gummel–Poon model is neither voltage nor current, but a combination of both... sound somewhat familiar?
Ratchit said:No it isn't. The physics of the system determine what controls what.Myself said:Therefore neither can be in control of the other, and to argue otherwise is just a different kind of "chicken or the egg" argument.
Man this is terrible. Just know that I am aware I imply much of what I mean when I really should clearly say it. I am introspectively "working on it".
Myself said:Therefore neither can be [determined as being] in control of the other, and to argue [over the two] is just a different kind of "chicken or the egg" argument.
If that suffices, I'll be moving on...
No... you really don't. But I suspect I know what you're getting at...Ratchit said:One of these days, I will have to show you what Ohm's law really is.
Ohm's law is the LINEAR relationship between current, voltage, and resistance, with the formulas I=V/R, V=I*R, R=V/I. Diode law is similar in nature, but is an exponential relationship. These are not the same thing. I was never unaware of this.
My focus with the text you quote was that SOME KIND of interdependent, coexisting, mutually inclusive, relationship exists between voltage and current when dealing with finite loads. Whether the relationship be linear, exponential or X=Δfeng shui^(groundhog shadows/sqrt(moon phases)) doesn't particularly matter to the heart of my argument.
Yes of course it is, it is a circuit design strategy. And just as it is not any of those other things, it also does not prove that a transistor internally works from voltage control. Nor does it disprove that a BJT is not internally current controlled.Ratchit said:Winfield Hill's method is a design strategy. It is not an analysis tool, proof of what controls a device, or proof that beta does not influence a BJT circuit. Also, it does not mean that the signal applied to the BJT is going to be directly applied to Vbe.
But you are clearly focusing on practical concerns, so let's be practical.
The mathematical model that design philosophy is centered around uses many approximations, [an] irrational number
I[SUB]C[/SUB]=β*I[SUB]B[/SUB] on the other hand, uses less approximations, no irrational constants, no exponential math, is less complicated, and uses values that are published in every single BJT technical paper that has ever been made. And if you can't find β, you can measure it. (Which is also just as possible for the above methods required parameters.)
Now, given the two, I don't see the sense in going out of your way to use a more complex and obscure formula, that also requires more obscure data, to try and design a real and practical circuit, in situations where the other one is just as acceptable.
[SUB]Honestly, for practical concerns I don't see why one wouldn't just use known circuit building blocks and simulators with already correct models, but... let's just put a pin in that. /)[/SUB]
(Self proclaimed) electronics guru Winfield Hill of harvard might say this, and he may be right. But my texts say that I[SUB]CO[/SUB] increases 6% every °C. Though admittedly my text is just the 1957 Ditto machined lecture notes from some random professor of a "Technical Institute" in Massachusetts. It's Massachusetts, I bet they probably let just anyone teach and learn in their institutes, right?Ratchit said:Ico doubles for every 6°C for silicon transistors.
Hummm, for a second I was thinking this institute had an acronym, but it escapes me for now.
Speaking of Winfield Hill though...
I wait to analyze, or see analysis of the circuits and methodologies Winfield Hill himself (or possibly an imposter) posted in the following thread...
https://cr4.globalspec.com/thread/68055/voltage-vs-current I'm sure a conventional explanation and analysis can be found for those circuits just as well.
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