BJT's don't work like that

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Thread Starter

Ratch

Joined Mar 20, 2007
1,070
Dave,

Originally Posted by Ratch
You can talk all you want about how a BJT is designed and manufactured, but after it is made, Vbe controls its collector current.

Answered by Dave
Have you ever used a BJT in a real application? Suggesting such a proposition, I can only suggest that you have not.

Let me ask a simple question: voltage source connected to a light - is the light controlled (controlled being the act of being turned on) by the voltage of the source or current through the bulb?
Yes, I have many BJTs around. Why do you ask such a bad question?

Good question. Voltage. Even if you switched on a constant current source, the voltage would have to be there. Even if you modulated the light with a current, the voltage would still have to be there.

So if the base current is modified by a current source (i.e. a current source to base), then a current will be controlling Vbe? That'll be current-control then won't it.
No, not directly. The final control will be Vbe. That is what will determine the collector current.

Consider a BJT with the base driven by a switch thrown resistor, R, tied to Vdd. Emitter to ground and collector driving a load tied to Vdd (which for arguments sake is greater than twice the forward voltage of the b-e junction). For a given value of R Ib will be determined by the resistor. Charge flow to the base (as you would prefer it be called) will then force Vbe to ~0.6V to forward bias the b-e junction (in fact the potential divider created by throwing the switch causes charge to flow into the base which in turn creates the potential divider across the b-e junction). Currents in the circuit, including Ic, will change accordingly. If R is changed to a different value, the charge flow to the base will increase/decrease accordingly and will force Vbe to ~0.6V - by virtue of the dependence of Ib on Vbe and vice versa it will force Vbe to a slightly different value as changes on Ib are reflected on Vbe. The fundamental point is that the control mechanism is provided by the current to the base which sets the circuits behaviour including, Vbe and Ic. No-one denies the fact that the BJT is voltage-controlled, implicated by the characteristic of Vbe, but it is equally current controlled. Mathematics and intuition support support this idea, as does the theoretical and practical analysis of many experts in this field.
Many people are beguiled by the fact that Ic is proportional to Ib, and it is true that you are changing Vbe by changing Ib. But it is the Vbe that is controlling the collector current. In an automotive braking system, the driver controls the pressure on the brake piston, the piston controls the force on the brake shoes, and the brake shoes press against the rotor to produce friction. So who is controlling the braking? Some people say it is the driver, but I would say it is the brake shoes.

Originally Posted by Ratch
If somehow the base current did not exist, as it does not in low, low, low Vbe values, then the emitter still provides current to the collector. I keep trying to say that the base current is a side effect and not necessary to the control of the collector current. If the width of the base could be modulated physically, there would still be a waste base current because of the Vbe present. The presence of base current does not prove or indicate base current control.


Answered by Dave
I'm sorry but you are wrong. The base-current is a function of Vbe:



Ib is a function of Vbe: no Vbe - no Ib, no Ib where there is no Vbe (looking at this from a purely control perspective, i.e. ignoring thermal effects and so forth).

If you ignore the need to replenish majority-carriers in the base, then you can deduce that the base-current is superfluous. However, you cannot ignore this function of the base-current.
I don't deny that Ib is a function of Vbe. I am saying that Ib is unwanted and unnecessary. Notice how Ib would go to zero if you could make a transistor with infinite beta.

Majority carriers come from the emitter. That is why it is called the emitter. The base current is not involved in this process. The base current is a sideshow caused by Vbe. Vbe is needed to change the wide of the depletion region, which in turn controls how many carriers get to the collector.

You clearly don't want to accept the point that voltage-control through Vbe and current control through Ib are one and the same thing; how they differ is in their implementation. This is a notion supported by all the leading academics and practitioners on this subject. If you don't want to "believe" the BJT can be current-controlled (and I say "believe", because of in the face of overwhelming evidence, theory, and experimental citations to suggest to the contrary, and in the absence of any forthcoming experimental evidence on your part to disprove these, it necessitates a belief-system), then it is not my place to try and convince you differently.
Current control using Ib occurs because Vbe is present. Vbe is the dog that wags the tail. Ib is always present in a BJT, but it does not directly control the collector current even if it is proportional to it. I never said that a BJT cannot be controlled by current. I acknowedged that the Ib-Ic proportionality is useful for design. I only said that the real final response of the collector current is from Vbe. Perhaps I should have said the BJT is intrinsically voltage responsive.

My beliefs are based on facts.

I have published my insights on this. In this thread. Ratch
 

Thread Starter

Ratch

Joined Mar 20, 2007
1,070
comesoftware,

He probably has chosen to "drop out" because he realized that there was no point discussing with you (anyway, a very wise choice). Dave presented very strong points explaining why Beaty's theory about BJTs is not correct. What did you missed?
Everyone has to choose their own endeavors. I don't think he made any salient points that proved Beaty's propositon was false.

I did not miss anything. I refuted every false argument that was thrown at me.

I guess it is a matter of personal taste then. You keep yours, I keep mine, and everyone is happy. If you like to see BJTs working that way, fine. It doesn't mean that they actually work like that, though
As always. I am glad everyone is happy. It could just as well mean that they do work that way. Ratch
 

bloguetronica

Joined Apr 27, 2007
1,541
I did not miss anything. I refuted every false argument that was thrown at me.
Don't remember of someone throwing arguments. I have to talk to Dave requesting that all slingshots should remain at the login of the forum. I think he will solve this issue as soon as he can, since he is a diligent admin. If you have one to, you should be able to retrieve it when you logout. Of course I will request that to Dave as well. About firearms, don't worry, they can't get inside or else your argument would be killed by now.

About the false arguments, I don't think so. They seemed quite hard to me. I even stumbled upon one and broke a key. Now I have to replace the "v".

As always. I am glad everyone is happy. It could just as well mean that they do work that way. Ratch
Well, I see that it is a question of personal taste, then. I'm happy too.
 

Thread Starter

Ratch

Joined Mar 20, 2007
1,070
To the Ineffable All,

I finally found what I was looking for. An archived communication I had with a professor of electrical engineering at the University of Colorado back in Dec 2004. This is his website: http://ece-www.colorado.edu/fac_staff/personnel_pages/vanzeghbroeck.html . I once believed that BJTs were CC until I found out differently. I asked the professor about that, and this was his answer to me.

Ratch,
I hate to be the one telling you this but the BJT is indeed a voltage
controlled device. The voltage applied to the base emitter junction controls
the collector current and the base current is a result of the additional
hole injection (for an npn BJT) into the emitter as well as the
recombination in the base-emitter depletion region and the quasi-neutral
base region. It is tempting to claim that the BJT is controlled by the base
current, since that is how a BJT is typically biased; the exponential
variation of the current with the base-emitter voltage makes a voltage bias
impractical. Any circuit designer will also tell you that any voltage bias
can be replaced by its Thevenin equivalent current source. Hopefully this
provides you some ammunition to claim that either one can be claimed when
treating the device as a black box. Finally, you'll find that a MOSFET
biased in the subthreshold region has characteristics that are very similar
to that of a BJT.
Bart Van Zeghbroeck
Professor
University of Colorado
Department of Electrical and Computer Engineering
Campus Box 425
Boulder, CO 80309-0425
Office ECEE1B41
Tel: 303-492-2809
Fax: 303-492-2758
Email: b...@colorado.edu

I sent another e-mail to him a couple of days ago asking him to confirm it, but so far he has not answered me. Ratch
 

bloguetronica

Joined Apr 27, 2007
1,541
I don't see how your e-mail is not forged. But I can't see the contrary as well.

Is your formal first name Ratch? I think the usual way of addressing a person by e-mail is "Dear Mr. LastName", or "Dear Mr. FirstName LastName". And the end should be something like "Sincerely", "Regards", etc...

Well, forgetting about the e-mail, why didn't I heard about debates inside the scientific society on BJTs theory of operation?
 

studiot

Joined Nov 9, 2007
4,998
I say, take it easy Cume Old Chap!

There is after all a grain of truth in what Ratch says, although he does like to stir argument for the sake of it. I think he actually knows much better because he always ignore points he can't argue about.

It is true that the fundamental equation of a transistor's operation is

Ic = \(\alpha\)Ie + Ic0

In words this states that the collector current is the fraction of the emitter current reaching the collector plus the unbiased collector current.

Since Ie (not Ic) is a function of Vbe we can control Ic by varying Vbe.

BUT

We can also contol Ic by varying the current in the base circuit and thus the fraction of the emitter current which reaches the collector since

Ic = Ie - Ib.

So the good professor is correct when he says

...either one can be claimed .....
Note I deliberately avoided using beta as it is really only appropriate for the CE configuration.

Ratch I refer you to the following paper
"A Study of Charge Control Parameters of Transistors"

Sparkes J.J.

Proceedings IRE vol48 no10 pages 1696 - 1705, 1960.
 
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Thread Starter

Ratch

Joined Mar 20, 2007
1,070
comesoftware,

I don't see how your e-mail is not forged. But I can't see the contrary as well.
Well, it was not forged yesterday. I got the e-mail from a archived thread from 4 years ago. There is no way I could have changed the contents of archived Google Groups. I was going to spare you the whole thread, and the salty language that goes with it, but look at the end of this link and click on "show quoted text". http://groups.google.com/group/sci....a7de43bc86?hl=en&lnk=st&q=bart+van+zeghbroeck

Is your formal first name Ratch? I think the usual way of addressing a person by e-mail is "Dear Mr. LastName", or "Dear Mr. FirstName LastName". And the end should be something like "Sincerely", "Regards", etc...
Because I did not give the professor my full name. If you click on "show quoted text" at the end of the link, you can see my original communication with him.

Well, forgetting about the e-mail, why didn't I heard about debates inside the scientific society on BJTs theory of operation?
I don't know. At least you heard it from me. Ratch
 

Thread Starter

Ratch

Joined Mar 20, 2007
1,070
studiot,

There is after all a grain of truth in what Ratch says, although he does like to stir argument for the sake of it. I think he actually knows much better because he always ignore points he can't argue about.
That's not true. What is there about this discussion that I ignored, and cannot argue about. Haven't I been arguing about this?

It is true that the fundamental equation of a transistor's operation is

Ic = alpha*Ie + Ic0

In words this states that the collector current is the fraction of the emitter current reaching the collector plus the unbiased collector current.

Since Ie (not Ic) is a function of Vbe we can control Ic by varying Vbe.
Your last sentence does not make sense. Both Ie and Ic are controlled by Vbe.

We can also contol Ic by varying the current in the base circuit and thus the fraction of the emitter current which reaches the collector since

Ic = Ie - Ib.
Yes, we have been over this ground before. Sure you can change the base current, but it is really the corresponding Vbe change that makes the BJT respond.

So the good professor is correct when he says


Quote:
...either one can be claimed .....

Note I deliberately avoided using beta as it is really only appropriate for the CE configuration.
Please quote the professor completely. He said that either one can be claimed when presenting the BJT as a black box. But the transisitor is really responding physically to the Vbe.

No need to avoid beta, it is readily converted to alpha and vice versa.

Ratch I refer you to the following paper
"A Study of Charge Control Parameters of Transistors"

Sparkes J.J.

Proceedings IRE vol48 no10 pages 1696 - 1705, 1960
Is that available online, or do I have to go to a major library like MIT or the Library of Congress which keeps 50 year old references? Ratch
 

SgtWookie

Joined Jul 17, 2007
22,230
So if BJTs really are voltage-controlled devices, why is Ic vs Vbe extremely non-linear as compared to Ic vs Ib?

Graphs of those vectors should have settled this discussion six pages ago.

You cannot expect to get anything done with the absence of either voltage or current.

Your arguement of "waste current is unnecessary" borders on witchcraft. It IS necessary, or the BJT could not function. If you think it is NOT necessary, then place a 1pf capacitor between your BJT's base driver circuit and the BJT's base. Good luck getting any output unless your input signal is 10GHz or higher. But then, you would have AC through the base.

There ARE voltage-controlled semiconductor devices.

They're called MOSFETs, not BJT's. However, they still require current to take care of the Miller charge, etc. But I'm sure you knew that already.

BJT's have been declared as current-controlled devices, because that is the most linear function attribute of the device in question.

So knock it off, Ratch. We're trying to help newbies to comprehend basic electronics. It does not help in the least when you interject with material like you have been.

I won't bring firearms to the forum - I can't upload them. But I will bring my Drill Instructors.

 
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Thread Starter

Ratch

Joined Mar 20, 2007
1,070
Howdy Sarge,

So if BJTs really are voltage-controlled devices, why is Ic vs Vbe extremely non-linear as compared to Ic vs Ib?
As was pointed out before, Ic vs Vbe is an expontiental relationship. That explains its nonlinearity. Ib vs Ic is proportional. That explains its linearity. Neither of those relationships is pertinent as to which one the Ic is responding.

Graphs of those vectors should have settled this discussion six pages ago.
Ic, Bbe, and Ib are not vectors.

You cannot expect to get anything done with the absence of either voltage or current.
It depends on what you expect to get done.

Your arguement of "waste current is unnecessary" borders on witchcraft. It IS necessary, or the BJT could not function. If you think it is NOT necessary, then place a 1pf capacitor between your BJT's base driver circuit and the BJT's base. Good luck getting any output unless you are up around 20GHz. But then, you would have current through the base.
Ib (waste current) is inevitable, but not necessary for the Vbe to control the Ic. If the transistor was perfect (beta = infinity), then there would not be any base current. A cap like you suggested would be such a high reactance that very little Vbe would be applied to the junction unless you applied a high driving voltage.

There ARE voltage-controlled semiconductor devices.
Yes, and the point being?

They're called MOSFETs, not BJT's. However, they still require current to take care of the Miller charge, etc. But I'm sure you knew that already.
And how does that tie into Vbe controllng Ic?

BJT's have been declared as current-controlled devices, because that is the most linear function attribute of the device in question.
Which has nothing to do the how the Ic responds to Vbe. Both the professor and I have pointed out that transistor circuits are designed as current controlled devices because of the proportionality of Ib vs Ic, but the transistor really responds to Vbe.

So knock it off, Ratch. We're trying to help newbies to comprehend basic electronics. It does not help in the least when you interject with material like you have been.
Just giving them the facts, sir. You cannot prove me wrong, so why try to hide and obfuscate the truth?

I won't bring firearms to the forum - I can't upload them. But I will bring my Drill Instructors.
I hope they have open minds so they can be educated to the truth. Ratch
 
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SgtWookie

Joined Jul 17, 2007
22,230
Howdy Sarge
I am not a "Sarge" - that is an Army term. Marines find that jocular nickname abhorrent.
You can call me "Sgt", "Sergeant" or "Wook" - your call.

QUOTE:
So if BJTs really are voltage-controlled devices, why is Ic vs Vbe extremely non-linear as compared to Ic vs Ib?

As was pointed out before, Ic vs Vbe is an expontiental relationship. That explains its nonlinearity. Ib vs Ic is proportional. That explains its linearity. Neither of those relationships is pertinent as to which one the Ic is responding.
What do you mean by "expontiental"? Did you invent a new word?
And are you attempting to tell me that despite Ib vs Ic compared to Ic vs Vbe is basically irrelevant?
They are tied to each other; this is an inescapable fact.

QUOTE:
Graphs of those vectors should have settled this discussion six pages ago.

Ic, Bbe, and Ib are not vectors.
Point granted. They are functions. Yet, they still should have settled this six pages ago.

QUOTE:
You cannot expect to get anything done with the absence of either voltage or current.

It depends on what you expect to get done.
You must not like to get much done then. I can see we're not getting much done here.

QUOTE:
Your arguement of "waste current is unnecessary" borders on witchcraft. It IS necessary, or the BJT could not function. If you think it is NOT necessary, then place a 1pf capacitor between your BJT's base driver circuit and the BJT's base. Good luck getting any output unless you are up around 20GHz. But then, you would have current through the base.

Ib (waste current) is inevitable, but not necessary for the Vbe to control the Ic. If the transistor was perfect (beta = infinity), then there would not be any base current. A cap like you suggested would be such a high reactance that very little Vbe would be applied to the junction unless you applied a high driving voltage.
OK, if you think it's not necessary, then do without it. You'll make lots of money. MOSFETS, the topic coming up next, approach perfect beta - except it's a completely different animal when you get into high freqencies.
QUOTE:
There ARE voltage-controlled semiconductor devices.

Yes, and the point being?
Well, you're not very patient are you?

QUOTE:
They're called MOSFETs, not BJT's. However, they still require current to take care of the Miller charge, etc. But I'm sure you knew that already.

And how does that tie into Vbe controllng Ic?
I was attempting to support your theory that Ibe was not necessary. But if you choose to throw this card away, it's your call.
QUOTE:
BJT's have been declared as current-controlled devices, because that is the most linear function attribute of the device in question.

Which has nothing to do the how the Ic responds to Vbe. Both the professor and I have pointed out that transistor circuits are designed as current controlled devices because of the proportionality of Ib vs Ic, but the transistor really responds to Vbe.
So then why don't the transistor manufacturers publish data for Vbe vs Ic?

Because it's not a good model for real-world conditions.
QUOTE:
So knock it off, Ratch. We're trying to help newbies to comprehend basic electronics. It does not help in the least when you interject with material like you have been.

Just giving them the facts, sir. You cannot prove me wrong, so why try to hide and obfuscate the truth?
I am not a "Sir" - I was a Sergeant. Don't insult me like that again.
You have provided no real information that would cause me to change my way of thinking.
QUOTE:
I won't bring firearms to the forum - I can't upload them. But I will bring my Drill Instructors.

I hope they have open minds to they can be educated to the truth. Ratch
Stop it, Ratch. You're getting a similar reputation of snake-oil salesmen of the 30's and 40's.

There is absolutely no point in confusing new members with your assertions, as they fall outside of the accepted norms.

If someone about to take a test tried answering questions based upon your assertions, they would fail miserably.

Is that the kind of misery you wish to inflict upon the new members?

If you wish to continue to explore esoteric theories about electronics, I strongly suggest that this website is not the place for you; we serve "meat and potatoes" electronics.
 

recca02

Joined Apr 2, 2007
1,212
Ratch said:
Good question. Voltage. Even if you switched on a constant current source, the voltage would have to be there. Even if you modulated the light with a current, the voltage would still have to be there.
A very small off-topic point. (Can't comment on transistor being voltage controlled or current controlled.)
The heat producing effect is due to current not voltage. There won't be any glow in bulb if there is no current through it regardless of the voltage applied.
 

Thread Starter

Ratch

Joined Mar 20, 2007
1,070
Howdy Wook,

I am not a "Sarge" - that is an Army term. Marines find that jocular nickname abhorrent.
You can call me "Sgt", "Sergeant" or "Wook" - your call.
Sorry, I did not know.

What do you mean by "expontiental"? Did you invent a new word?
And are you attempting to tell me that despite Ib vs Ic compared to Ic vs Vbe is basically irrelevant?
They are tied to each other; this is an inescapable fact.
Sorry for the typo. As you must know, the correct word is exponential.

The are both relevant, but the transistor only responds to Vbe. Changing the Ib will change Vbe. The physics of the transistor determines that Vbe controls the emitter injection.

Point granted. They are functions. Yet, they still should have settled this six pages ago.
They are physical quantities that can be expressed as functions. Better to have it settled later than never. Did you see the prof's answer?

You must not like to get much done then. I can see we're not getting much done here.
Progress is slow all right. Hang on, we will get there.

OK, if you think it's not necessary, then do without it. You'll make lots of money. MOSFETS, the topic coming up next, approach perfect beta - except it's a completely different animal when you get into high freqencies.
As I said in a previous post, Ib is immutable, so a BJT cannot do without it. But even though present it does not affect the Vbe response of the BJT. All semi's have different characteristics when operating at high freqenency.

I was attempting to support your theory that Ibe was not necessary. But if you choose to throw this card away, it's your call.
FETs are one semi type, BJTs are another.

So then why don't the transistor manufacturers publish data for Vbe vs Ic?

Because it's not a good model for real-world conditions.
Yes, that is what the prof said. But the collector current really responds to Vbe even though the BJT is designed as a current control device.

I am not a "Sir" - I was a Sergeant. Don't insult me like that again.
You have provided no real information that would cause me to change my way of thinking.
Golly gee whiz, many of the Hollywood movies show recruits answering their sergeant as YES SIR! What about the email from the professor? Surely he is a formidable and respected resource.

Stop it, Ratch. You're getting a similar reputation of snake-oil salesmen of the 30's and 40's.
Are you calling the professor and Kevin Aylward a purveyor of snake oil too?

There is absolutely no point in confusing new members with your assertions, as they fall outside of the accepted norms.
No confusion, just facts. I keep saying BJTs are designed as current control devices due to their highly nonlinear Vbe vs Ic relationship. But they really respond to Vbe. No conflict or confusion there.

If someone about to take a test tried answering questions based upon your assertions, they would fail miserably.
Then the test would be faulty.

Is that the kind of misery you wish to inflict upon the new members?
What? Failing a faulty test?

If you wish to continue to explore esoteric theories about electronics, I strongly suggest that this website is not the place for you; we serve "meat and potatoes" electronics.
It is not an esoteric theory, and I like meat and potatoes. Ratch
 
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Thread Starter

Ratch

Joined Mar 20, 2007
1,070
recca02,

Originally Posted by Ratch
Good question. Voltage. Even if you switched on a constant current source, the voltage would have to be there. Even if you modulated the light with a current, the voltage would still have to be there.A very small off-topic point. (Can't comment on transistor being voltage controlled or current controlled.)

Answered by recca02
The heat producing effect is due to current not voltage. There won't be any glow in bulb if there is no current through it regardless of the voltage applied.
True, but that would be because the filament is broken, not because of how the bulb is controlled. Ratch
 

recca02

Joined Apr 2, 2007
1,212
recca02,
True, but that would be because the filament is broken, not because of how the bulb is controlled. Ratch
An example posted by you.
In an automotive braking system, the driver controls the pressure on the brake piston, the piston controls the force on the brake shoes, and the brake shoes press against the rotor to produce friction. So who is controlling the braking? Some people say it is the driver, but I would say it is the brake shoes.
Here there will be no braking if any link is broken or constrained from moving.
So like if voltage is the control then in this case the force applied to the brake shoe (not the driver nor the brake shoe in itself) is analogous to voltage.
If you say brake-shoe is controlling the braking and not the force acting on it(which would be my reply to such a question) then I see no reason as to why you should disagree with current being the actual control for bulbs.

Its our limitation if we can not directly control the current in a bulb but rather change a voltage across it to effect a current change through it.

Lets consider a thought experiment where a current can be changed without effecting a change in voltage. Regardless of how impractical the experiment may sound it is a fact that it will always be the change in current which will cause any change in the power output of bulb. No current irrespective of voltage , irrespective of healthiness of circuit will always result in no bulb glow.
 

Thread Starter

Ratch

Joined Mar 20, 2007
1,070
recca02

Originally Posted by Ratch
recca02,
True, but that would be because the filament is broken, not because of how the bulb is controlled. Ratch

Answered by recca02
Here there will be no braking if any link is broken or constrained from moving. So like if voltage is the control then in this case the force applied to the brake shoe (not the driver nor the brake shoe in itself) is analogous to voltage.
If you say brake-shoe is controlling the braking and not the force acting on it(which would be my reply to such a question) then I see no reason as to why you should disagree with current being the actual control for bulbs.
The friction of the brake shoe is the final thing thing to which the car braking responds. Defects in the linkage or the absence of a driver is irrelevant and a red herring. Think about voltage being the control for a bulb because you have to apply voltage before charge can flow. Even a current supply is a controlled voltage source.

Its our limitation if we can not directly control the current in a bulb but rather change a voltage across it to effect a current change through it.
All of us are limited by the laws of physics. In this case it is the resistance formula, V=IR.

Lets consider a thought experiment where a current can be changed without effecting a change in voltage. Regardless of how impractical the experiment may sound it is a fact that it will always be the change in current which will cause any change in the power output of bulb. No current irrespective of voltage , irrespective of healthiness of circuit will always result in no bulb glow.
That can never be, it would violate the always correct resistance formula. So you would have to change the resistance of the bulb also. No bulb glow would mean either a below operational voltage or an incorrectly manufactured filament with a too high resistance. Ratch
 

recca02

Joined Apr 2, 2007
1,212
Lets compare the two example.

Friction of breaks is the effect causing the braking = Heat generation due to collision of electrons causing the generation of radiation falling in visible range.

Brake shoe contact causes friction = current causes collision.

Force (again not the driver but one can consider driver if he wishes) on break shoe causes shoe contact, the nature of force(magnitude ,etc) being the control element = voltage causing current flow, control in nature of voltage controls current.

Which one should we now choose?
Defects in the linkage or the absence of a driver is irrelevant and a red herring
So is defect in healthiness of circuit.
Think about voltage being the control for a bulb because you have to apply voltage before charge can flow.
Think about the force exerted by driver on brake shoes as in this mechanism the driver has to apply force so that brake shoe can brake.(any other external factor causing braking is not included in mechanism and is hence similar to causing a change in bulb glow with external factors.)

It is the current flow to which bulb responds. Voltage control is hence an indirect way of control in this case.

Even a current supply is a controlled voltage source.
That is our limitation not a law of physics.
All of us are limited by the laws of physics. In this case it is the resistance formula, V=IR.
Which doesn't change the fact that voltage is an effect caused by the flow of current if an ideal current source or some phenomenon causing rate of change of electron flow without application of voltage is used (maybe some way of physically providing electrons with the energy to traverse through the bulb).

That can never be, it would violate the always correct resistance formula. So you would have to change the resistance of the bulb also. No bulb glow would mean either a below operational voltage or an incorrectly manufactured filament with a too high resistance.
Since thought experiments are always hard to digest.
Consider a threshold lower limit on voltage to cause any current. What do you say about voltage control below this limit? Current control will still apply form zero to infinite value, voltage control is now not 'exact' or in other words there is now an exception to voltage control.
 

Thread Starter

Ratch

Joined Mar 20, 2007
1,070
recca02,

Lets compare the two example.

Friction of breaks is the effect causing the braking = Heat generation due to collision of electrons causing the generation of radiation falling in visible range.

Brake shoe contact causes friction = current causes collision.

Force (again not the driver but one can consider driver if he wishes) on break shoe causes shoe contact, the nature of force(magnitude ,etc) being the control element = voltage causing current flow, control in nature of voltage controls current.

Which one should we now choose?
Question asked and answered previously. The auto responds to the action of the friction of the drum shoes. What more can anyone say about this?

Originally Posted by Ratch
Defects in the linkage or the absence of a driver is irrelevant and a red herring

Answered by Recca02,
So is defect in healthiness of circuit.
And the point being?

Think about the force exerted by driver on brake shoes as in this mechanism the driver has to apply force so that brake shoe can brake.(any other external factor causing braking is not included in mechanism and is hence similar to causing a change in bulb glow with external factors.)

It is the current flow to which bulb responds. Voltage control is hence an indirect way of control in this case.
You really mean charge flow, not current flow. Current already is charge flow. Current flow means charge flow flow. Anyway to answer your reply, The voltage controls the current. In other words, switching on the voltage will switch on the current. That's control.

Originally posted by Ratch
Even a current supply is a controlled voltage source.

That is our limitation not a law of physics.
That is a circumstance caused by a law of physics.

Which doesn't change the fact that voltage is an effect caused by the flow of current if an ideal current source or some phenomenon causing rate of change of electron flow without application of voltage is used (maybe some way of physically providing electrons with the energy to traverse through the bulb).
You are talking about "pie in the sky". Here on Earth, voltage controls current through a resistor.

Since thought experiments are always hard to digest.
Consider a threshold lower limit on voltage to cause any current. What do you say about voltage control below this limit? Current control will still apply form zero to infinite value, voltage control is now not 'exact' or in other words there is now an exception to voltage control.
And what can you imagine has this nonlinear relationship? Ratch
 

bloguetronica

Joined Apr 27, 2007
1,541
comesoftware,

Well, it was not forged yesterday. I got the e-mail from a archived thread from 4 years ago. There is no way I could have changed the contents of archived Google Groups. I was going to spare you the whole thread, and the salty language that goes with it, but look at the end of this link and click on "show quoted text".
...
My sincere apologies, but my doubt was reasonable, you have to admit.

However, I've noticed that you write "comesoftware". Please, address me as "cumesoftware" or "cume" next time, if you please.

I say, take it easy Cume Old Chap!

There is after all a grain of truth in what Ratch says, although he does like to stir argument for the sake of it. I think he actually knows much better because he always ignore points he can't argue about.
...
That seems an "egg and chicken" issue here. Indeed, you can control the collector current by controlling the base voltage, because of the emitter diode characteristics. But you can't conclude that a BJT is a voltage controlled device. In order for a BJT to work, it needs to have current drawn form the base, and not a voltage present at the base (BJTs are not FETs). And the collector current is proportional to the base current. Thus, it is more accurate to say that a BJT is a current controlled device.

Dave had shown hard evidence on that. However, it seems that this thread is going personal. Partly my fault, I must say. But I've only lit the fuse.

I won't bring firearms to the forum - I can't upload them. But I will bring my Drill Instructors.

Do they have a permit? :D

As my final note:
If BJTs had selenium cores and gold plated bolts, they could work as voltage controlled devices due to some spiritual turbulence. This idea was proposed by Ivo Shandor in the early 20's, I think.
 
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studiot

Joined Nov 9, 2007
4,998
Let's all remember that nobody's perfect. We all dash off inaccuracies in the heat of the moment sometimes.

Ratch I assume you contradiction of my observation that you can control transistors with light, rather than Vbe, was just such a moment.

For the record
Phototransistors work by directing the light onto the Collector -Base junction, which is reverse biased. This stimulates flow of carriers across that junction.
It has nothing whatsoever to do with the Emitter - Base junction, where Vbe appears.

In fact we used to make erzatz phototransistors by scratching the black paint off early glass encapsulated transistors like the 0C71 and 0C45 as the effect occurs in all transistors.

If you are going to control the Base - Emitter junction, you must of necessity supply both suitable voltage and current. The junction has resistance defined by well known laws as Dave et al have expounded.

The whole proposition/argument was explored way back at the beginning of transistor electronics as my reference shows and was clearly stated in the first textbook on the subject I owned.

Semiconductor Junction Devices by J Frank Pierce, and also the Motorola & TI publications of that time.

Ratch, as you have not done me the courtesy of stating where in the world you are, I have no idea how you would obtain referenced documents, nor am I inclined to help since you responded with a sarcastic comment to a genuine offer of additional useful information.

Finally since you asked for subjects ignored, I commented that frequency response is controlled by current not voltage effects. The reasons for this (Early Effect etc) have also been expounded by others here.

If this is how you treat your 'supporters'.................
 
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