BJT Transistor operation on simple transistor-zener voltage regulator circuit

[crutschow]

Oh yes there is. The current source is a voltage source with a relatively large resistor. Therefore, anytime you hook up a current source to the base of a BJT you are making a transistor circuit by adding the external resistor of the current source.

No there isn't.

Why do you make the assumption that the only way to make a current source is with a voltage source and a resistor? A current source, by itself, is just as valid a component as a voltage source, by itself, although voltage sources are more common.

One current source with no added resistance that comes to mind is a photocell.

Another is a Van de Graaff or Wimshurst generator (I'll admit that's a bit of a reach but they are current generators although that's not their normal use).

Also a superconductor inductor with a circulating current.

Yes it is a circuit due to the added resistance in the base from the current source.

No added resistance needed.

So, where did I go wrong in my reasoning?

Assuming that the only way to make a current source is with a voltage source and a resistor. Rather narrow minded of you.

Ping

 

[MikeMl]

...the transistor controls its CE current according to the voltage applied to its base....

Yada, yada, yada. Here we go again....

 

[Ratchit]

No there isn't.

Why do you make the assumption that the only way to make a current source is with a voltage source and a resistor? A current source, by itself, is just as valid a component as a voltage source, by itself, although voltage sources are more common.

I never said or assumed a voltage and large resistor was the one and only way to produce a current source. Whomever said I did? But, no matter how a current source is made, it is still equivalent to a voltage in series with a resistor. A circuit driven by a differently constructed current source will still behaves the same way as a voltage in series with a large resistor. No matter how the input resistance changes, the same current will be present in the input terminals.

One current source with no added resistance that comes to mind is a photocell.

Another is a Van de Graaff or Wimshurst generator (I'll admit that's a bit of a reach but they are current generators although that's not their normal use).

If you can make a current source of out those two items, then they will act in the circuit like they have a large resistor.

Also a superconductor inductor with a circulating current.
No added resistance needed.
Assuming that the only way to make a current source is with a voltage source and a resistor. Rather narrow minded of you.

Name 50 more examples and the equivalency is the same. A current source, no matter how it is constructed, will possess a large internal resistance.

Ping

Pong

Ratch

 

[Ratchit]

Yada, yada, yada. Here we go again....

What's the problem? Are not different ideas and concepts being exchanged? Remember, you are not required to read or participate in this thread.

Ratch

 

[Tony Stewart]

If you consider the given design is a current buffered Zener, it helps to reduce the loading effects on the zener which changes voltage due to ESR of the zener and changing current thru the zener which gets drawn by the load
With the advent of integrated regulators, this design is obsolete but for academic understanding the Re=40R is the useful load of the circuit to be driven from this regulator. THis load on the zener of hFE*Re from the base-emitter, so as current is amplified from base to emitter, the input impedance is multiplied by the same hfe amount and AS WELL, the emitter output impedance is reduced by the same hFE gain from the input Zener ESR impedance.

For example if the Zener operating point offers an ESR of 15 Ohms and the hFE is 100, now the output impedance of the emitter is effectively 0.15 Ohm and the 40 Ohm emitter resistance appears to be 4000 Ohms across the zener.
..

Does that help you?

 

[Ratchit]

If you consider the given design is a current buffered Zener, it helps to reduce the loading effects on the zener which changes voltage due to ESR of the zener and changing current thru the zener which gets drawn by the load
With the advent of integrated regulators, this design is obsolete but for academic understanding the Re=40R is the useful load of the circuit to be driven from this regulator. THis load on the zener of hFE*Re from the base-emitter, so as current is amplified the input impedance is multiplied by the same amount and the emitter ouput impedance is reduced by the same hFE gain from the input..

Does that help you?

No, it does not. The reason is that I don't know what the problem is that you are addressing. If you could be a little more specific, and perhaps include a schematic, I could give you a more cogent response.

Ratch

 

[crutschow]

I never said or assumed a voltage and large resistor was the one and only way to produce a current source. Whomever said I did?

Whomever would be you:
"The current source is a voltage source with a relatively large resistor. Therefore, anytime you hook up a current source to the base of a BJT you are making a transistor circuit by adding the external resistor of the current source." (Emphasis mine).

I don't see a lot of wiggle room in that statement (but I'm sure you'll find some).

But, no matter how a current source is made, it is still equivalent to a voltage in series with a resistor.

I don't see how that's true for the superconducting inductor. That device acts as a pure current source.

A circuit driven by a differently constructed current source will still behaves the same way as a voltage in series with a large resistor. No matter how the input resistance changes, the same current will be present in the input terminals.

If you can make a current source of out those two items, then they will act in the circuit like they have a large resistor.

Name 50 more examples and the equivalency is the same. A current source, no matter how it is constructed, will possess a large internal resistance.

How about if I name 51?
Ratch, I have you give you credit for being a good debater (in the political sense of that term). You are an expert at deflecting arguments that disprove your point by going off on red-herring arguments and I took the (red-herring) bait with a completely tangent discussion about current sources and whether an equivalent resistance constitutes a circuit.

Exactly how the base current is generated (it could even be from a voltage source) has absolutely nothing to do with the original point I made about how a BJT appears to be a black-box current-controlled current-source. If you want to address that issue directly without obfuscation, fine. But if experience is any indication, you won't.

 

[Ratchit]

Whomever would be you:
"The current source is a voltage source with a relatively large resistor. Therefore, anytime you hook up a current source to the base of a BJT you are making a transistor circuit by adding the external resistor of the current source." (Emphasis mine).

I don't see a lot of wiggle room in that statement (but I'm sure you'll find some).

I already did. Did you read my answer to you, "I never said or assumed a voltage and large resistor was the one and only way to produce a current source. Whomever said I did?" There is a difference between stating there is an equivalency and saying that one way is the only way.

I don't see how that's true for the superconducting inductor. That device acts as a pure current source.

Do you mean putting a fully energized coil into the base circuit of a BJT? And having the collapsing field send a high voltage pulse through the base-emitter circuit? That would be a transient action that would send the BJT out of its active region.

How about if I name 51?

Won't work, same problem.

Ratch, I have you give you credit for being a good debater (in the political sense of that term). You are an expert at deflecting arguments that disprove your point by going off on red-herring arguments and I took the (red-herring) bait with a completely tangent discussion about current sources and whether an equivalent resistance constitutes a circuit.

I deal with facts. If they pertain to the discussion, then I readily put them on the table. A current source does contain a equivalent resistance, otherwise it would not be a current source, would it?

Exactly how the base current is generated (it could even be from a voltage source) has absolutely nothing to do with the original point I made about how a BJT appears to be a black-box current-controlled current-source. If you want to address that issue directly without obfuscation, fine. But if experience is any indication, you won't.

I have no problem with you averring that a transistor circuit can be thought as a black box. But when you refer to the transistor by itself as a current amplifier instead of a transconductance amplifier, then my correction circuit takes over.

Ratch

 

[audioguru]

Hi Willen,
A 5.1V to 6.8v zener diode operating at its spec'd current makes a pretty good voltage regulator. The emitter-follower transistor at its output ruins its voltage regulation because its base-emitter voltage changes when its current and temperature change.
The datasheet for a zener diode shows that a low voltage one regulates its voltage poorly and its voltage drops when it gets warm.

 

[Tony Stewart]

Empirical models show what a device does, but not how a device works, unless the model is based on the actual physical parameters of the device. I don't understand what you mean by reversible. For instance, if I apply 0.59 volts to the base-emitter and read 10 ma collector current, will I get 0.59 volts on the base-emitter if I somehow force 10 ma through the CE?

Ratch

It seems I need to be more explicit to improve your understanding.
The Input VI response is known so BJT can be defined as either Voltage controlled or Current control. This reciprocity is what I intended but current control is far more linear.

 

[Tony Stewart]

No, it does not. The reason is that I don't know what the problem is that you are addressing. If you could be a little more specific, and perhaps include a schematic, I could give you a more cogent response.

Ratch

It was you that wanted me to respond to the OP's schematic. Remember? too bad this thread is getting derailed by your incessant contradictions.

 

[Ratchit]

It seems I need to be more explicit to improve your understanding.
The Input VI response is known so BJT can be defined as either Voltage controlled or Current control. This reciprocity is what I intended but current control is far more linear.

Yes, I am familiar with those curves, where several instances are shown at various base currents. Load lines may be plotted and the Early effect observed from those curves. Linearity is not the issue. Neither is the convenience of having those curves. What I am saying is that those curves show a transistor circuit, not the transistor by itself. This is because the base is driven by a current source which introduces an external resistor from the current source. In other words, those curves do not prove that a lone transistor can be regarded as a current amplifier.

Ratch

 

[Ratchit]

It was you that wanted me to respond to the OP's schematic. Remember? too bad this thread is getting derailed by your incessant contradictions.

Look back through this thread again. Nowhere did I ask you for an analysis of the OP's schematic. I did contradict you when you derailed the discussion by talking about switches, but that was a valid contradiction.

Ratch

 

[atferrari]

I found this to be a practical demo of how to use bipolar transistors.

Concise and to the point. All his videos are of similar good quality.

 

[kinarfi]

Don't think about polarity, think about current direction.
Just remember that the normal current direction in a BJT goes in the direction of the emitter arrow.
Thus it flows from base to emitter (also collector to emitter) in an NPN, and flows from emitter to base (also emitter to collector) in a PNP.
Similarly the current direction is from source to drain in an N-MOSFET, and from drain to source in a P-MOSFET.
(The arrow direction on a MOSFET can be a little confusing since it shows the substrate diode direction, which is normally reverse biased. Thus the drain-source current direction in opposite to the arrow direction).
If you follow those rules then you will always be able to determine the relative voltage polarities across the transistor connections when operating normally.

Has the general community settled on which direction flow of current is standard or normal? crutschow appears to favor Conventional current flow (+ to -). I had to stop for a moment and think about it because I favor Electron flow (- to +). I have often thought that when anyone says current flows, they should state conventional or electron to prevent any confusion.

 

[JimB]

Has the general community settled on which direction flow of current is standard or normal? crutschow appears to favor Conventional current flow (+ to -). I had to stop for a moment and think about it because I favor Electron flow (- to +). I have often thought that when anyone says current flows, they should state conventional or electron to prevent any confusion.

As a general rule when I am considering current, I prefer to think of conventional current flowing from +ve to -ve.
However when considering thermionic valves (yes, I do from time to time) I prefer to think in terms of electron flow.

When explaining something related to current flow to someone who may be confused by conventional current or electron flow, I will state which I am using to explain the problem.

JimB

 

[crutschow]

Do you mean putting a fully energized coil into the base circuit of a BJT? And having the collapsing field send a high voltage pulse through the base-emitter circuit? That would be a transient action that would send the BJT out of its active region.

The inductance would send a constant current through the base emitter junction equal to its circulating current. The voltage would be equal to the normal Vbe of the transistor. There would not be a high voltage pulse (assuming ideal switches of course). That current slowly decays as the inductive energy is dissipated in the base-emitter junction.

I deal with facts. If they pertain to the discussion, then I readily put them on the table. A current source does contain a equivalent resistance, otherwise it would not be a current source, would it?

Facts? Then why do you continue to talk about the nature of a current source when that has nothing to do with whether a BJT appears as a black-box current-controlled current source.

I have no problem with you averring that a transistor circuit can be thought as a black box. But when you refer to the transistor by itself as a current amplifier instead of a transconductance amplifier, then my correction circuit takes over.

Then your correction circuit is faulty.
From a black-box view a BJT transistor, by itself, meets the standard criteria for a current-controlled current-source. (The black-box input port does appear to have a diode in series but that has no effect on its current-controlled behavior). The black-box behavior has absolutely nothing to do with how the transistor works internally.
But I understand why you can't ever agree with me. That would kill all the fun.

 

[Ratchit]

Has the general community settled on which direction flow of current is standard or normal? crutschow appears to favor Conventional current flow (+ to -). I had to stop for a moment and think about it because I favor Electron flow (- to +). I have often thought that when anyone says current flows, they should state conventional or electron to prevent any confusion.

It will cause you a lot of grief if you worry about the polarity of the charge carriers before you do the network calculation. Always assume the charge flow goes from the positive terminal of the voltage source to the negative terminal. This is a mathematical convention, not necessarily the charge flow of the real charge carriers. Then, if you really care about the direction of flow of the real charge carriers, reverse the flow direction for electrons and negative ions. Otherwise the direction is correct for positive charge carriers like holes and positive ions. You will notice that ammeters and diodes are marked in accordance with the mathematical convention, and not the true direction of the real charge carriers. Perhaps if you submit some examples, we can show you how that works.

Ratch

 

[Ratchit]

The inductance would send a constant current through the base emitter junction equal to its circulating current. The voltage would be equal to the normal Vbe of the transistor. There would not be a high voltage pulse (assuming ideal switches of course). That current slowly decays as the inductive energy is dissipated in the base-emitter junction.

The collapsing field of the inductor will send a pulse through the transistor and probably destroy it. For practical purposes, how does a coil made out of a superconductor material differ that much from a coil with very little resistance? What do you mean by circulating current? Current does not circulate in a coil unless it is part of a resonant circuit. Perhaps you want to give a different example of a current source.

Facts? Then why do you continue to talk about the nature of a current source when that has nothing to do with whether a BJT appears as a black-box current-controlled current source.

Because the model tells you what the BJT will do under particular circumstances, but not how the transistor works. I said that before. You can make a transistor do just about anything electrical if you add the proper circuit components and wire them up correctly. But then you are not talking about a transistor by itself.

Then your correction circuit is faulty.
From a black-box view a BJT transistor, by itself, meets the standard criteria for a current-controlled current-source. (The black-box input port does appear to have a diode in series but that has no effect on its current-controlled behavior). The black-box behavior has absolutely nothing to do with how the transistor works internally.
But I understand why you can't ever agree with me. That would kill all the fun.

A black box view is am empirical model which does not tell you how a transistor works, only what it does. I am sure they are useful, but not for understanding how a transistor works. I do agree with you on a lot of things, But not on whether a lone BJT is anything other than a transconductance amplifier.

 

[kubeek]

... What I am saying is that those curves show a transistor circuit, not the transistor by itself. This is because the base is driven by a current source which introduces an external resistor from the current source. In other words, those curves do not prove that a lone transistor can be regarded as a current amplifier.
Ratch

Why does it matter whether the current is going through a resistor or not? It still is current, and current in a series circuit is the same everywhere. Regardless whether it is coming from a voltage source, current source or potato battery.