I don't understand transistors in combinations .... Or maybe basics ....

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Discussion Overview

The discussion revolves around the understanding of transistors, particularly in complex circuit configurations. Participants explore the basic principles of transistor operation, the effects of resistors on current and voltage, and the challenges of analyzing circuits involving multiple transistors.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses confusion about how voltage dividers affect the base voltage (Vb) when connected to a transistor, noting that Vb changes unexpectedly.
  • Another participant emphasizes that R1 and R2 should not be too high in value to avoid affecting the current drawn by the transistor base.
  • Some participants argue that the fundamental principle of transistor operation is based on current rather than voltage, suggesting that a small base current controls a larger collector-emitter current.
  • There is a discussion about the importance of understanding internal currents in BJTs, with one participant suggesting that VBE can be treated as near zero for circuit understanding.
  • One participant proposes simplifying the analysis by using a basic model of the transistor before moving to more complex configurations.
  • Another participant notes that the emitter voltage will rise due to emitter current, which will feedback to limit the emitter current, raising questions about how this feedback mechanism works in practice.
  • Several participants express uncertainty about how to analyze circuits with multiple transistors, particularly regarding the interactions between base and emitter voltages and currents.

Areas of Agreement / Disagreement

Participants generally agree on the importance of current in transistor operation, but there is no consensus on how to effectively analyze complex circuits involving multiple transistors. Multiple competing views on the role of voltage and current in these circuits remain unresolved.

Contextual Notes

Participants highlight limitations in their understanding of how changing resistor values and voltages affect transistor behavior, particularly in more complex configurations. There is also mention of the need for feedback mechanisms to limit currents, which remains a point of confusion.

  • #61
Xenon02 said:
So not limited Base can drain as much current it wants
Please explain your thinking here so maybe we can get you on track. What you've said is quite simply wrong.
 
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  • #62
Xenon02 said:
Yea I tried to think of the upper resistor as an Rb. The thing is that the current is splitting into two pieces.
One piece is going into base which doesn't have Rb and the other piece is going into R2. So not limited Base can drain as much current it wants
It would help us if you could say about which circuit you are speaking (drawing).
Otherwise, misunderstandings are unavoidable.
 
  • #63
Averagesupernova said:
Please explain your thinking here so maybe we can get you on track. What you've said is quite simply wrong.

Sure thing I'll use pictures to visualize my vision of it.

1664723863530.png

Basically I see it like that. There is Rb that limits the current from voltage source that is going into transistor because he himself cannot.
When I see the divider that has this current flow :

1664724036431.png

And the current is splitted into transistor that doesn't have Rb and it splits also to R2.

Transistor without Rb look like that in my eyes :

1664724314770.png

Of course the part only with transistor that doesn't have Rb. Because here in this picture the transistor can take any amount of current.
 
  • #64
LvW said:
It would help us if you could say about which circuit you are speaking (drawing).
Otherwise, misunderstandings are unavoidable.

I'm sorry I was talking about the circuit with LEDs.
But I would like to stick with your recomendation and start with basics and using these basics understand the further. For example I've made an analize in Post#10 you can check if it's correct.
Because my mind set is stuck in the analizys in post#10 which transistor needs to have Rb and struggles to understand why the divider works when transistor doesn't have this Rb. Or combinations with many transistors.
Let's try from the very beginning and progress.
 
  • #65
I've looked at your diagrams in post #63. Equating the second and third diagrams would be flat out wrong.
-
Take the first diagram and add a resistor tied to the base and emitter. Why is it you think that somehow by doing that it is the equivalent of having no resistors at all?
 
  • #66
Averagesupernova said:
Take the first diagram and add a resistor tied to the base and emitter. Why is it you think that somehow by doing that it is the equivalent of having no resistors at all?
Add resistor you mean the add it to the 1st picture in post#63 ?
If yes then it would look like that :

1664726009601.png

Which there is a limit and the transistor that has no limit and another resistor.
Why is it like that ? I don't know because it wasn't covered in any tutorial nor in basics from websites. I just know that Rb there is direct limit for transistor.
 
  • #67
Xenon02 said:
I'm sorry I was talking about the circuit with LEDs.
But I would like to stick with your recomendation and start with basics and using these basics understand the further. For example I've made an analize in Post#10 you can check if it's correct.
Because my mind set is stuck in the analizys in post#10 which transistor needs to have Rb and struggles to understand why the divider works when transistor doesn't have this Rb. Or combinations with many transistors.
Let's try from the very beginning and progress.
Xenon02 - sorry to say, but it is not easy to discuss with you because you are not very "systematic".
You have agreed to analyze one particular circuit - and what is the result?
Again three different circuits - two of them without any practical relevance.
More than that, you continue to speak very often about a resistor Rb - and we only can guess what you mean. I cannot see any Rb in your drawings.
 
  • #68
Xenon02 said:
Add resistor you mean the add it to the 1st picture in post#63 ?
If yes then it would look like that :

View attachment 314904
Which there is a limit and the transistor that has no limit and another resistor.
Why is it like that ? I don't know because it wasn't covered in any tutorial nor in basics from websites. I just know that Rb there is direct limit for transistor.
Rc limits current no matter what. Are you able to see the schematic that you drew on a resistor is the same as the original with the push button as far as base associated components?
 
  • #69
Thread closed for Moderation...

UPDATE -- I'm in a PM conversation with the OP about learning resources right now...
 
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