Voltage or current operated devices?

[BrownOut]

The charge cannot move until the barrier voltage is lowered. Although the individual voltage sources do not get lowered by another voltage source, the net voltage is lowered by Vbe.

That's incorrect. Charge moves as soon as an external source is connected. But you are correct that individual voltages don't get lowered by the external source, thus barrier voltage cannot be lowered by the voltage. It's lowered by charge that neutrializes ions in the depleation region, never by the voltage source.

False logic. Base current is always present when forward Vbe exists. Ib can be reduced by higher beta, but not eliminated. The existence of Ib does not prove it to be essential.

I'm guessing that song and dance means you are not able to prove BJT action can continue without ib. Yes, that does prove that ib is essential.

So why do you keep repeating yourself?

HA! That's what my sister used to ask when she was a baby.

False accusation. See BJT vs FET current Mirroring , post #4, second paragraph, first sentence. When folks worry about it, they may call it something else other than "waste". You acknowledge the loss everytime you realize that not all the emitter current winds up in the collector circuit.

That refers to the mismatch of currents in a current mirror, not that a generalized "waste current" exists ( the title is BJT vs. FET current mirror, and the quote illustrates a difference with the two technolodies). There is no such thing as waste current in BJT operation, only a difference between input(emitter) and output(collector) current. Still, nobody espouses that fantasy.

Most of the time they do, but they are human like everyone else here.

And? That has nothing to do with experience and background required to understand these concepts.

What cartoons? I believe in the voltage causality of a BJT. Control depends on the circuit where the BJT resides.

Believe all you want. That doesn't change the fact that BJT's are current controlled.

 

[crutschow]

"P.S. I totally agree with your sign-off phrase."

Why thank you. It is a warning and a statement of honesty. I was banned from another forum because I pointed out that the log of a negative number did exist. That was the last straw.

It wasn't intended to be a complement.

 

[Ratchit]

BrownOut,

That's incorrect. Charge moves as soon as an external source is connected. But you are correct that individual voltages don't get lowered by the external source, thus barrier voltage cannot be lowered by the voltage. It's lowered by charge that neutrializes ions in the depleation region, never by the voltage source.

The back voltage caused by the separation of the charges, caused by the diffusion prevents them from moving further. The Vbe counters that by causing the net back voltage to be lower. This increases the charge flow which again increases the number of charge separations, and causes the back voltage to be higher. Eventually a equilibrium is reached and a steady emitter current exists.

I'm guessing that song and dance means you are not able to prove BJT action can continue without ib. Yes, that does prove that ib is essential.

No song and dance. Just an explanation. You are confusing existence with essential. Ib is not essential.

HA! That's what my sister used to ask when she was a baby.

Good question. And your answer was?

That refers to the mismatch of currents in a current mirror, not that a generalized "waste current" exists ( the title is BJT vs. FET current mirror, and the quote illustrates a difference with the two technolodies). There is no such thing as waste current in BJT operation, only a difference between input(emitter) and output(collector) current. Still, nobody espouses that fantasy.

Everyone does when they acknowledge that the collector current is smaller than the emitter current. They just don't call it waste current and describe it differently.

And? That has nothing to do with experience and background required to understand these concepts.

That is a basic point of view concept. Great knowledge and experience is not necessary to understand it. Whether they chose to agree with it or not can be for various reasons. Such as indifference, point of view, go along with the crowd, or any number of human personal traits. I believe that we established I was not the only one who thinks this way. And those others are also knowledgeable and experienced.

Believe all you want. That doesn't change the fact that BJT's are current controlled.

If they were, the BJT's input resistance would be very low. It's not. One is able to establish a voltage across its base-emitter. A BJT without any external circuity acts like a transconductance amplifier, or semi-transconductor amplifier.

Ratch

 

[Ratchit]

crutschow,

It wasn't intended to be a complement.

Compliment is the correct word. But I took your remark in the best possible light.

Ratch

 

[BrownOut]

The back voltage caused by the separation of the charges, caused by the diffusion prevents them from moving further. The Vbe counters that by causing the net back voltage to be lower. This increases the charge flow which again increases the number of charge separations, and causes the back voltage to be higher. Eventually a equilibrium is reached and a steady emitter current exists.

That doesn't even make any sense. The barrier voltage is lowered by charge, which then allows more charge to flow. The net voltage isn't relevant. The barrier voltage must be reduced. The external voltage cannot reduce the barrier voltage, that can only happen when charge flows into the depleation region. No other mechanism reduces the barrier voltage.

No song and dance. Just an explanation. You are confusing existence with essential. Ib is not essential.

I'm still waiting to see a BJT that works with no ib. Ib is essential, without it there is no transistor action or operation.

Everyone does when they acknowledge that the collector current is smaller than the emitter current. They just don't call it waste current and describe it differently.

They don't call it that because there is no such thing.

Great knowledge and experience is not necessary to understand it.

Apparently it is necessary. I'll take knowledge and experience every time.

If they were, the BJT's input resistance would be very low. It's not. One is able to establish a voltage across its base-emitter.

First of all, that's illogical. The same can be said for voltage and high resistance. Secondly, that's incorrect. Input reisitance depends on the input current, and is lower with increasing base current. After the small barrier voltage is overcome, the voltage changes very little with increasing base current.

 

[MikeMl]

...
MikeMl,


Are you defining active elements as "ohmic" or not? ...

If the current is mostly proportional to applied voltage, then it is Ohmic, be it part of an active device, or not. I do not consider the base to emitter junction of a bipolar transistor to be "Ohmic".

For Beakie's benefit (before this thread degenerates further), here are the contents of the black boxes:

Note that you can easily infer the resistance of the hidden resistor from the plot. Note also, that a Green LED has a characteristic forward voltage when emitting light, and it has a rather low reverse breakdown voltage...

 

[BrownOut]

I guessed diode, but didn't pay enough attention to the forward voltage to guess what kind. Also too lazy to look up voltages of various color LED's ( not to mention I didn't want to give the answer away ).

 

[Ratchit]

BrownOut,

That doesn't even make any sense. The barrier voltage is lowered by charge, which then allows more charge to flow. The net voltage isn't relevant. The barrier voltage must be reduced. The external voltage cannot reduce the barrier voltage, that can only happen when charge flows into the depleation region. No other mechanism reduces the barrier voltage.

It doesn't make sense the way you describe it. The diffusion causes the uncovered charges to appear separated by the junction. This causes a barrier voltage which opposes the diffusive potential. The forward bias Vbe counteracts the barrier voltage allowing more charges to flow. This causes the barrier voltage to go higher by uncovering more charges. When the Vbe equalizes with the barrier voltage and the back voltage caused by the current and bulk resistance, then equilibrium is reached and the emitter and collector are steady at the value of Vbe. It is an exponential relationship that cannot be denied. I would not want to calculate currents and design circuits from those principles of causality, but that is the way a BJT works. I would instead use the functional model to design and calculate like everyone does. The basic principles I iterated are not complicated, and do not required years of insight and experience to comprehend.

I'm still waiting to see a BJT that works with no ib. Ib is essential, without it there is no transistor action or operation.

A BJT without a Ib or insignificant Ib would have to have a beta of infinity or a very high value, just by definition. As I said earlier, it is not possible to manufacture a BJT with that extreme parameter. I also said that existence does not necessary equate to essential. Ib will be with you always in a BJT, but it is not essential.

They don't call it that because there is no such thing.

I already explained the causal mechanism. Ib does not enter into it except as a by-product of its operation.

Apparently it is necessary. I'll take knowledge and experience every time.

And I take it into consideration, but I also like to think for myself.

First of all, that's illogical. The same can be said for voltage and high resistance. Secondly, that's incorrect. Input reisitance depends on the input current, and is lower with increasing base current. After the small barrier voltage is overcome, the voltage changes very little with increasing base current.

The fact that the resistance varies depending on the current is irrelevant. The BJT is "sold" as a current amplifier. If so, then it should not have any or insignificant input resistance to wonder about. Its characteristics are more related to a transconductance amplifier.

Ratch

 

[Ratchit]

MikeML,

If the current is mostly proportional to applied voltage, then it is Ohmic, be it part of an active device, or not. I do not consider the base to emitter junction of a bipolar transistor to be "Ohmic".

Yes, I agree. Linearity between voltage vs. current is a definition of ohmic.

Ratch

 

[MrAl]

Hello again,

This is starting to look like the old thread again. Ratch, did you read my most recent post before this one?

 

[BrownOut]

The forward bias Vbe counteracts the barrier voltage allowing more charges to flow. This causes the barrier voltage to go higher by uncovering more charges.

None of that makes any sense at all. Basic physics dictates that a voltage cannot change another voltage, and thus no external voltage can change the barrier voltage. Any voltage arises as a space-charge distribution, and the one and only way to change a voltage is to change the charge distribution. No external voltage can change the charge distribution, and so what you're proposing is impossible. Since you don't know enough about basic physics, then you're not prepared to discuss this.

A BJT without a Ib or insignificant Ib would have to have a beta of infinity or a very high value, just by definition. As I said earlier, it is not possible to manufacture a BJT with that extreme parameter. I also said that existence does not necessary equate to essential. Ib will be with you always in a BJT, but it is not essential.

If it's impossible to make a transistor that works with insignificant ib, then ib is proven to be essential. Basic logical reasoning.

And I take it into consideration, but I also like to think for myself.

Thinking requires consideration of basic knowledge. Making up stuff isn't really thinking.

The fact that the resistance varies depending on the current is irrelevant. The BJT is "sold" as a current amplifier. If so, then it should not have any or insignificant input resistance to wonder about. Its characteristics are more related to a transconductance amplifier.

Inconvenient facts all seem irrelevant to you. The resistance becomes insignificant as low values of input current. That's why transistors require series bias resistors. If resistance didn't become insignificant, then bias resistors would not be required. Transconductance is but one method of simplifying the transistor model, but the transistor itself operates as a current amplifier.

 

[gary350]

Tubes are voltage operated devices. Transistors are current operated devices.

 

[Ratchit]

MrAl,

This is starting to look like the old thread again. Ratch, did you read my most recent post before this one?

Do you mean post #19 of this thread? Yes, I did. You did not specify whether you are trying to determine its functional or causal classification. Did you read my comments about a true current source not having little or no voltage across its input terminals? It doesn't matter much, however. By adding external circuitry, we can make a voltage source into a current source or vise versa. All I am saying is that at the quantum level, it is voltage that determines the charge flow.

Ratch

 

[Ratchit]

BrownOut,

None of that makes any sense at all. Basic physics dictates that a voltage cannot change another voltage, and thus no external voltage can change the barrier voltage. Any voltage arises as a space-charge distribution, and the one and only way to change a voltage is to change the charge distribution. No external voltage can change the charge distribution, and so what you're proposing is impossible. Since you don't know enough about basic physics, then you're not prepared to discuss this.

The uncovered charges form a barrier voltage. Then there is the diffusion voltage, the Vbe, and the bulk resistance voltage from the current. The all combine together in equilibrium. No one says that the barrier voltage is changed by the Vbe, only the net voltage is. Sort of like putting several independent voltage sources in series. The collector current is voltage dependent, and is given by Ic=Is*exp(Vbe/.026), where Is is the saturation current. Notice that Ib does not enter into this equation.

If it's impossible to make a transistor that works with insignificant ib, then ib is proven to be essential. Basic logical reasoning.

If it is impossible to make the defoliant agent orange without producing the toxic by-product dioxin, does that make dioxin an essential ingredient? Basic faulty logical reasoning.

Thinking requires consideration of basic knowledge. Making up stuff isn't really thinking.

I know what thinking requires. Who is making up stuff? For you to say that about me, you would have to know my state of mind. That you cannot have done, so it is you who is "making stuff up".

Inconvenient facts all seem irrelevant to you. The resistance becomes insignificant as low values of input current. That's why transistors require series bias resistors. If resistance didn't become insignificant, then bias resistors would not be required. Transconductance is but one method of simplifying the transistor model, but the transistor itself operates as a current amplifier.

By itself, the transistor has a input voltage that can be measured. If it were a true current amplifier, you would not be able to measure its input voltage. You cannot get away from that fact. A transistor is conveniently made into a current amplifier by the addition of external circuitry.

Ratch

 

[Ratchit]

gary350,

Tubes are voltage operated devices. /QUOTE]

True, it is a transconductance amplifier.

Transistors are current operated devices

False, they mimic current operated devices in their functionality, but by themselves and devoid of any external circuitry, they are semi-transconductance amplifiers.

Ratch

 

[BrownOut]

Then there is the diffusion voltage, the Vbe, and the bulk resistance voltage from the current. The all combine together in equilibrium. No one says that the barrier voltage is changed by the Vbe, only the net voltage is.

None of that is possible, by the laws of physics. Voltage can only arise from charge distribution. There is no "net" voltage. Vbe arises from the reduction in the barrier voltage, and there are no other sources. Any other explanation would violate basic laws of charge physics.

I know what thinking requires. Who is making up stuff? For you to say that about me, you would have to know my state of mind. That you cannot have done, so it is you who is "making stuff up".

I have to know nothing of your state of mind. I only need to know what is true and what is fantasy. What you've presented is pure fantasy.

If it is impossible to make the defoliant agent orange without producing the toxic by-product dioxin, does that make dioxin an essential ingredient? Basic faulty logical reasoning.

We're not talking about agent orange. If you cannot make a transistor that operates without base current that means base current is essential to the operation of the device. Your songs and dances are meaningless.

By itself, the transistor has a input voltage that can be measured. If it were a true current amplifier, you would not be able to measure its input voltage. You cannot get away from that fact. A transistor is conveniently made into a current amplifier by the addition of external circuitry.

The presence of an input voltage does not mean the transistor isn't a true current amplifier. The mechanisms of amplification are dependent on input current, as described to you over and over. That's what makes it a current amplifier. By your definition, there would be no true voltage or current amplifier, because every device depends upon both to varying degrees.

 

[Ratchit]

BrownOut,

None of that is possible, by the laws of physics. Voltage can only arise from charge distribution. There is no "net" voltage. Vbe arises from the reduction in the barrier voltage, and there are no other sources. Any other explanation would violate basic laws of charge physics.

Vbe arises from the application of external voltage on the junction. There is no Vbe on a transistor not connected to anything. Otherwise current would exist when the base-emitter diode are shorted. It doesn't. There is always a barrier voltage on a PN junction, even when nothing is connected to the junction terminals. An equilibrium is established between the diffusive potential of the contentration gradient and the barrier potential of the uncovered charges. Nothing just described violates the laws of charge physics.

I have to know nothing of your state of mind. I only need to know what is true and what is fantasy. What you've presented is pure fantasy.

Wrong. That is assuming you are right and I am wrong. That has yet to be decided. Even if I am wrong, then I could be mistaken. A mistake is not a deliberate concoction known to be false, which is what a fantasy is. Get your definitions correct, please.

We're not talking about agent orange. If you cannot make a transistor that operates without base current that means base current is essential to the operation of the device. Your songs and dances are meaningless.

I was talking about the principle you espouse by using agent orange as a illustrative example. You think that just because a quantity is present in a process, it is essential. That is false reasoning.

The presence of an input voltage does not mean the transistor isn't a true current amplifier. The mechanisms of amplification are dependent on input current, as described to you over and over. That's what makes it a current amplifier. By your definition, there would be no true voltage or current amplifier, because every device depends upon both to varying degrees.

Yes, nothing is perfect, but some devices have more definite characteristics than others. A BJT by itself has way too much resistance to be called a current amplifier. It is more like a semi-transconductance amplifier. It can easily be made to appear as a current amplifier by loading the base circuit with a lot of resistance to swamp out the BJT's input resistance. Then the BJT acts almost as if it were a true current amplifier, i.e., it has insignificant input resistance when compared with the base circuit resistance.

Ratch

 

[BrownOut]

Vbe arises from the application of external voltage on the junction

Not possible. External voltage cannot be applied to the junction. The only way the junction voltage can change is for the charge within the junction to change. Until you can show a change in the charge within the junction, then there cannot possible be a change in junction voltage. Basic, basic physics.

Wrong. That is assuming you are right and I am wrong.

I know I'm right and you're wrong. I assume nothing.

A mistake is not a deliberate concoction known to be false, which is what a fantasy is. Get your definitions correct, please.

Making up fantasy things like "waste current" to support wrong assumptions is the very definition of what I'm talking about. None of your assertions are supported by the known laws of physics, and so I conclude you're making them up to support all your wrong conclusions.

I was talking about the principle you espouse by using agent orange as a illustrative example. You think that just because a quantity is present in a process, it is essential. That is false reasoning.

It's a poor example. We are engineers not chemists. Unless you can prove a transistor can operate without base current, then the current is essential. Everything else is just a distraction.

A BJT by itself has way too much resistance to be called a current amplifier

.

A BJT has very little resistance in the base input when used as an amplifier. Try connecting a voltage with no series reisistor, and you'll quickly find out I am right.

 

[Ratchit]

BrownOut,

Not possible. External voltage cannot be applied to the junction. The only way the junction voltage can change is for the charge within the junction to change. Until you can show a change in the charge within the junction, then there cannot possible be a change in junction voltage. Basic, basic physics.

The junction is affected by Vbe, even if the voltage has to travel through the P and N slabs of semiconductor. Basic, basic physics.

I know I'm right and you're wrong. I assume nothing.

Makes no difference. If you do, then you should assume I made a mistake instead of accusing me of making up a fantasy.

Making up fantasy things like "waste current" to support wrong assumptions is the very definition of what I'm talking about. None of your assertions are supported by the known laws of physics, and so I conclude you're making them up to support all your wrong conclusions.

To draw that conclusion, you would have to know my state of mind. Since you cannot possibly know that, your conclusion that I am just making thing up without regard to the facts are in your mind a fantasy. You are accusing me of what you are doing.

It's a poor example. We are engineers not chemists. Unless you can prove a transistor can operate without base current, then the current is essential. Everything else is just a distraction.

Good example. You don't have to be a chemist to appreciate and understand a chemical manufacturing process. Manufacturing processes are standard across all branches of engineering. You should have no trouble discerning my point that the existence of something does not prove it to be essential.

A BJT has very little resistance in the base input when used as an amplifier. Try connecting a voltage with no series reisistor, and you'll quickly find out I am right.

I am aware of the exponential relationship of voltage versus current in a diode. The input resistance is smaller than what a good transconductance amplifier like a tube would be, but it is finite nevertheless. That is why I call a BJT a semi-transconductance amplifier.

Ratch

 

[BrownOut]

The junction is affected by Vbe, even if the voltage has to travel through the P and N slabs of semiconductor. Basic, basic physics.

Voltage doesn't travel. Learn your basic physics.

To draw that conclusion, you would have to know my state of mind.

I need to know nothing of your state of mind, only what's real and what's imagined.

Good example. You don't have to be a chemist to appreciate and understand a chemical manufacturing process. Manufacturing processes are standard across all branches of engineering. You should have no trouble discerning my point that the existence of something does not prove it to be essential.

Poor example. I'm interested in devices, not chemistry. If you want to show an example, use a device. You're point isn't relevant, since I never made that claim. I claim that if a device cannot function without a current, then the current is necessary. I never calimed anything about existance. More song and dance.

I am aware of the exponential relationship of voltage versus current in a diode. The input resistance is smaller than what a good transconductance amplifier like a tube would be, but it is finite nevertheless..

It is both small and finite. Small was your first criteria, now you change to finite. No device will ever have infinite or zero input reistance, so by your flawed logic, there can be no voltage or current devices. So we're back to that again. Nothing more than same old rationalization.

That is why I call a BJT a semi-transconductance amplifier

Oh really? In post #18 you said:

But I take umbrage when they say it is a BJT by itself is current amlifier when in fact, it is a transconductance amplifier.

You don't seem to know what you call it.