On my mobile here so its hard to get a schematic. And this isn't really a coursework question but its about my Cw so...
I've been busy learning to calculating all these values for a basic bjt which is good. Never really took the time to say well what is this thing? So I went and found out about transistors.
If I learned the purpose correctly it was to achieve a transformative / resistive output signal - at the emitter.
Yet every dang circuit I've calculated the emitter is connected to the ground. Like wt....? Seriously what would be the purpose of that? Isn't the emitter the point of the thing? Yet its grounded
And the 'voltmeter' (least i think thats what it is) the lil bare horizontal wire is always slapped on to the end of the collector signal. Labelled VCE... Hmmm... Think I might have just thought of something there... But ill leave my rant up anyways... incase I'm wrong...hmm...

 

A transistor can be thought of several different ways, depending on how it is being used. In analog electronics, it is generally either thought of as a current amplifier (the collector current is some fairly large constant (beta) times the base current) or as a voltage-controlled current source (the collector current is an exponential function of the base-emitter voltage). In most circuits, some type of feedback is used to make the circuit's behavior reliable and relatively insensitive to variations in the transistor's specific parameters.

The name comes from "trans-resistor" and one way of thinking about it is that the effective resistance between the collector and the emitter is controlled by the signal between the base and emitter. Nearly all electrical concepts require two (or more) points in order to be meaningful -- it makes no sense to talk about the resistance at the emitter. What does the resistance at a single point mean?

 

Thanks Wbahm. A trans-resistor is what it is! I love the way nobody tells me these things. Instead its, here's a series of equations, learn how to calculate that. Which is good too I suppose. That has its uses. But really, the basics would be nice!

 

Yet every dang circuit I've calculated the emitter is connected to the ground. Like wt....? Seriously what would be the purpose of that? Isn't the emitter the point of the thing? Yet its grounded

Sometimes you want to use the transistor as a switch, either ON or OFF. In those cases, the emitter of an NPN transistor will often be grounded.


If you're using a transistor as an amplifier, e.g. class A, it will have emitter and collector resistors because the ratio of the two resistors will determine gain.

 

If you're using a transistor as an amplifier, e.g. class A, it will have emitter and collector resistors because the ratio of the two resistors will determine gain.

The emitter resistor also stabilizes the operating (bias) point.

 

Thanks Wbahm. A trans-resistor is what it is! I love the way nobody tells me these things. Instead its, here's a series of equations, learn how to calculate that. Which is good too I suppose. That has its uses. But really, the basics would be nice!

Hello,

That's where the name "transistor" came from: "trans"+"resistor" => "transistor".

The main idea is that as you apply more base current, the resistance between the collector and emitter decreases. Because of the unipolar junctions involved it also has to be biased properly.
It's not hard to comprehend in this manner, but the analysis itself is usually based on the ideas either of:
1. Current controlled current source (with limited operating regions).
2. Voltage controlled current source (also with externally enforced limitations).
3. Two back to back diodes and a current controlled current source (limitations are inherent to the model itself).
4. Small signal models (limitations are implied).

Of these three, #1 gets you there the quickest, while #2 is usually needed for special circumstances. #3 is the most accurate but also the most difficult to analyze because it's so very non linear. #4 is obviously for certain applications.

If you first study dependent sources this gets 1000 times easier to comprehend.

 

Thanks guys. Most of this has confirmed what I was thinking. I still have a complaint.

 

Opps that posted itself. That's not my complaint btw. Looking at the two poorly drawn schematics up there - A is the ones we've being calculating. Where Vp = The purpose of the signal. Some type of amped signal or whatever.
Now B is what my limited brain would like to see. That lil leg there with the arrow that's the emitter part, right? Isn't an emitter supposed to emit something. Like output something? Yet there it is going to ground with no useful purpose in life

 

The emitter, as the name suggest, emits the "electrons" and collector collect them.

https://forum.allaboutcircuits.com/...r-amp-doubts-and-questions.91084/#post-663195

 

..........Isn't an emitter supposed to emit something. Like output something? Yet there it is going to ground with no useful purpose in life

It does, but it does it internally.
Externally it needs to be connected to provide a path for the transistor current.
For some circuits that path goes directly to ground.

You need to read and understand how the transistor works, to understand how the circuits using them work.

 

Hmmm... I think I will take the time to do that in summer. I've still more calculations to study for big exam come Monday. So ill have to propone. I've enough knowledge to get me through for the mo

 

Thanks guys. Most of this has confirmed what I was thinking. I still have a complaint.

Hello,

That terminal is called the 'emitter' but if you want to follow the electron flow it goes INTO the emitter terminal in those diagrams.

You're thinking of an emitter that emits something to the outside world, like coffee from a coffee pot being poured into a cup, but this emitter emits inside the device package, so the emission goes from external to internal, not from internal to external like the coffee pot, so it's like we are filling the coffee pot with coffee from some other source. Recall that a PNP emitter looks like it is pointing INTO the device not out of it. Dont worry so much about the names of the terminals though, just learn how it works from a math point of view.

Very often it is not possible to deduce the correct operation of something just from it's simple external description. You have to learn how the guts work, then how that relates to the outside world.

 

Ahaa I see said the blind man. Thats it MrAi, the lightbulb goes on.