Thankyou MikeML. You are undoubtedly correct. But could you relate the statements of your immediately previous message to the original 2 questions which started this thread (see start of thread) ?

 

To which I say again:

"I believe that the independent variable (input?) of this problem is the pot wiper position, and the dependent variables are the various node voltages and device currents"

Thankyou MikeML. You are without doubt correct. But what is the relation of these statements to the two questions which started this thread ?

 

Forgot to thank you for your comprehensive and clear exposition Jony. I am still studying this...

 

Why is the transistor input voltage considered to be between the potentiometer wiper and ground and not between Q1's base terminal and ground ? Diagram from Vol VI, Chapt 5 - Voltage Follower. Does the above definition not include Rbase as part of a separate component, ie the transistor ? Help please.

hi dan,
Your first question will get different answers from different people, unfortunately there are different naming terms used for the same thing.
I was taught to measure and name the transistor voltages relative to its own terminals, if you start including external components as a part of the transistor, when do you stop.??
Obviously they must be included in the overall circuit function and its operational description.

The second question is answered partly in the first answer, ' is the Rbase resistor really a part of the transistor or is its purpose to set the operating state of the transistor.?
Using your idea Rbase as part of a separate component, ie the transistor, you would also have to include the potentiometer.

'Common usage' terminology causes many misunderstandings, for example: 'Ground', there is no ground on your circuit.!

When you say Ground, you mean a Common reference measuring point on your circuit. [I guess you know that]
Some people use Ground to mean Earth.

Eric

 

Why is the transistor input voltage considered to be between the potentiometer wiper and ground and not between Q1's base terminal and ground ?

As I said before, IMHO the circuit input is the position of the pot wiper. It can take any position from 0 (at the bottom) to 1 (at the top). Refer back to the simulation I posted in #18 of this thread. The pot wiper position (pos = 0 to 1 in steps of 0.01) is the independent variable, and is plotted along the X-axis of the plot pane.

Now you can ask all kinds of questions about the circuit, like:

What is the voltage at the pot wiper relative to ground=V(w) Green Trace ?

What is the voltage at the base relative to ground = V(b) Red Trace ?

What is the voltage at the emitter relative to ground = V(e) Lt. Blue Trace?

What is the emitter current of Q1 = Ie(Q1) Gray Trace?

What is the base current of Q1 = Ib(Q1) Dk. Blue Trace?

These are all plotted along the Y-axes (right and left, depending if they are voltages or currents) as a function of the pot wiper position.

Note the difference between the Green Trace and Red Trace. Since they almost fall on top of each other for all pot positions, that implies that the voltage drop across Rbase (R1 in my circuit) is negligable, as would be predicted by multiplying Ib(Q1) by 1000...

Note that Jony analyzed the circuit for just one pot position, namely where the pot is 0.1342 up from the bottom. The simulation I posted happens to do it for lots of pot positions between 0 and 1.... To close that loop, I repeat my sim for just that one pot position = 0.1342 as shown below:



If you look at the plots at pot position = 0.13, note that there is good agreement between what Jony showed and the plotted values...

Diagram from Vol VI, Chapt 5 - Voltage Follower. Does the above definition not include Rbase as part of a separate component, ie the transistor ?

I take Rbase as being a physical resistor external to the transistor. In a practical circuit, perhaps it was added to limit the peak current out of the pot wiper (to protect it from being destroyed) in the event that the output V(e) was inadvertently shorted to ground???

 

hi dan,
Your first question will get different answers from different people, unfortunately there are different naming terms used for the same thing.
I was taught to measure and name the transistor voltages relative to its own terminals, if you start including external components as a part of the transistor, when do you stop.??
Obviously they must be included in the overall circuit function and its operational description.

The second question is answered partly in the first answer, ' is the Rbase resistor really a part of the transistor or is its purpose to set the operating state of the transistor.?
Using your idea Rbase as part of a separate component, ie the transistor, you would also have to include the potentiometer.

'Common usage' terminology causes many misunderstandings, for example: 'Ground', there is no ground on your circuit.!

When you say Ground, you mean a Common reference measuring point on your circuit. [I guess you know that]
Some people use Ground to mean Earth.

Eric

hi dan,
Your first question will get different answers from different people, unfortunately there are different naming terms used for the same thing.
I was taught to measure and name the transistor voltages relative to its own terminals, if you start including external components as a part of the transistor, when do you stop.??
Obviously they must be included in the overall circuit function and its operational description.

The second question is answered partly in the first answer, ' is the Rbase resistor really a part of the transistor or is its purpose to set the operating state of the transistor.?
Using your idea Rbase as part of a separate component, ie the transistor, you would also have to include the potentiometer.

'Common usage' terminology causes many misunderstandings, for example: 'Ground', there is no ground on your circuit.!

When you say Ground, you mean a Common reference measuring point on your circuit. [I guess you know that]
Some people use Ground to mean Earth.

Eric

Eric, thankyou for your very clear and for me, very satisfying explanation. Your reasoning with regard to my initial "input" question gels precisely with my own thinking, thinking which prompted the original question. Likewise for my question re the base resistor's significance. For me both questions have now been resolved.
Thank you again.

 

As I said before, IMHO the circuit input is the position of the pot wiper. It can take any position from 0 (at the bottom) to 1 (at the top). Refer back to the simulation I posted in #18 of this thread. The pot wiper position (pos = 0 to 1 in steps of 0.01) is the independent variable, and is plotted along the X-axis of the plot pane.

Now you can ask all kinds of questions about the circuit, like:

What is the voltage at the pot wiper relative to ground=V(w) Green Trace ?

What is the voltage at the base relative to ground = V(b) Red Trace ?

What is the voltage at the emitter relative to ground = V(e) Lt. Blue Trace?

What is the emitter current of Q1 = Ie(Q1) Gray Trace?

What is the base current of Q1 = Ib(Q1) Dk. Blue Trace?

These are all plotted along the Y-axes (right and left, depending if they are voltages or currents) as a function of the pot wiper position.

Note the difference between the Green Trace and Red Trace. Since they almost fall on top of each other for all pot positions, that implies that the voltage drop across Rbase (R1 in my circuit) is negligable, as would be predicted by multiplying Ib(Q1) by 1000...

Note that Jony analyzed the circuit for just one pot position, namely where the pot is 0.1342 up from the bottom. The simulation I posted happens to do it for lots of pot positions between 0 and 1.... To close that loop, I repeat my sim for just that one pot position = 0.1342 as shown below:

View attachment 73698

If you look at the plots at pot position = 0.13, note that there is good agreement between what Jony showed and the plotted values...



I take Rbase as being a physical resistor external to the transistor. In a practical circuit, perhaps it was added to limit the peak current out of the pot wiper (to protect it from being destroyed) in the event that the output V(e) was inadvertently shorted to ground???

Mike, thank you for your time & trouble in answering my questions. Unfortunately, I'm limited to a mobile phone while participating in this thread (on vacation in Spain) and must await studying your plots on a PC when I return home (chart sizes too large and text too small for easy viewing). Jony130, ericgibbs & Mr Chips have the advantage here. I can see their message content easily & clearly. Nevertheless I can see & read enough to realise that your message content is in approximate agreement with them and so both my questions have been resolved to my satisfaction. Thank you again.