Talking about the circuit in post #8

1. GND is required for the circuit to function.
2. The collector is the node which is common to both the input and the output
3. The output signal is taken from the junction between the emitter and the load resistor. You can measure it from emitter to ground, or you can measure it from emitter to V+. Since there is a fixed relationship between V+ and ground it does not matter which one you choose.
4. The input goes to the base in the circuit of post #8 and it can be measured with respect to either node because there is a fixed relationship between the nodes.
5. Reread the section on AC analysis, where you set all DC sources to zero. That is because DC sources have no effect on the AC behavior of a circuit.

Talking about your original circuit, the identification of input and output nodes is complicated by having an AC source in place of the usual DC source. It would make more sense to have a DC source in series with an AC source if you are trying to understand the operation of a voltage regulator. Standard transistor configurations apply to amplifiers, and a voltage regulator is NOT an amplifier. It is a different kind of species.

I have 4 questions about this.

1. The output signal is taken from the junction between the emitter and the load resistor. You can measure it from emitter to ground, or you can measure it from emitter to V+. Since there is a fixed relationship between V+ and ground it does not matter which one you choose.

Why I can measure the output signal from emitter to ground ? Doesn't it imply that emiter is the common node ?

I mean we have then input collector - base and output emiter - ground (emiter - emiter) something like that.
Which doesn't make sense for me.

1. The input goes to the base in the circuit of post #8 and it can be measured with respect to either node because there is a fixed relationship between the nodes.

Either node ? Which exactly ? If I have common collector then one node must be collector.
So I believe the next input node must be base or emiter ?

Output node also must be collector as I understand. Because there must be 2 nodes that are used for input/output.
And output that uses emiter and ground doesn't use collector node so why I can use it?

• Reread the section on AC analysis, where you set all DC sources to zero. That is because DC sources have no effect on the AC behavior of a circuit.

I can understand that DC has no effect on AC.

Talking about your original circuit, the identification of input and output nodes is complicated by having an AC source in place of the usual DC source. It would make more sense to have a DC source in series with an AC source if you are trying to understand the operation of a voltage regulator. Standard transistor configurations apply to amplifiers, and a voltage regulator is NOT an amplifier. It is a different kind of species.

As I understand, if it's not and amplifier or voltage regulator then indentyfing which is the configuration is a lot harder ?

What If I added DC source instead of AC source ?

 

You left out common base, where the base can be connected to GND or to V+.

OP is already confused. Didn't see the need to comment on something he wasn't asking about.

 

There is output. The examples are poor because we don't know the operating points and they're more likely to be saturation mode.

For common emitter circuits, the output is taken from the collector. For common collector, the output is taken from the emitter.

You left out common base, where the base can be connected to GND or to V+.

So this example :



Doesn't show what is the configuration ?

If I want common emiter on the left then I should put input in base - emiter or collector - emiter and output must be emiter so emiter - ground.

and if I want common collector on the left then input must be collector - base ? and output must be collector - emiter or collector - ground ?

 

OP is already confused. Didn't see the need to comment on something he wasn't asking about.

In fact it was part of his original question.

 

So this example :

View attachment 270967

Doesn't show what is the configuration ?

If I want common emiter on the left then I should put input in base - emiter or collector - emiter and output must be emiter so emiter - ground.

and if I want common collector on the left then input must be collector - base ? and output must be collector - emiter or collector - ground ?

The problem with circuit fragments is that they leave out critical details. In the left drawing of post #23, the input would be applied to the base with respect to ground thru R1, and the output would be taken from the collector with resepect to ground ground.

In the right drawing of post #23 the input would be applied to the base with respect to ground through R1 and the output would be taken from the emitter

 

You are confusing the expressions "common emitter", "common collector" with circuit "common" and circuit "GND".

The expressions "common base", "common emitter" and "common collector" were coined to distinguish the three types of configurations for bipolar junction transistors or BJT. Do not interpret this to have any reference to circuit "common" or "ground".



Reference: https://www.electronics-tutorials.ws/transistor/tran_1.html

 

It's a simple common emitter configuration SE voltage amplifier. The bias is set by the voltage of the zener diode and the current through the stage is roughly (Vzener-0.7v)/500Ω

I'd say it was a common collector configuration, with a resistor in the collector to limit the current or reduce transistor power dissipation. It looks like a series-pass voltage regulator to me. Vout = Vzener - Vbe, and the 500Ω resistor is the load.

 

Also keep in mind that a BJT (Bipolar Junction Transistor) is NOT a voltage device, It is an input current that control an output current.

I am sorry to say but this statement is wrong.
There is not a single proof for current control - however, there are many for voltage control (experimental and theoretical).
Even from the energy point of view - it is impossible that a small quantity could directly "control" a larger quantity of the same kind.

 

The problem with circuit fragments is that they leave out critical details. In the left drawing of post #23, the input would be applied to the base with respect to ground thru R1, and the output would be taken from the collector with resepect to ground ground.

In the right drawing of post #23 the input would be applied to the base with respect to ground through R1 and the output would be taken from the emitter

I can undestand that the output from the left image can be taken from the collector with respect to the ground.
Because there is emiter and they are common node for input and output.

But what about right circuit ? Input is connected to the base - ground, but emiter is grounded not collector.
And output is connecter to emiter and where then ?

You said that common is when both input and output have common node. I don't see it.

You are confusing the expressions "common emitter", "common collector" with circuit "common" and circuit "GND".

The expressions "common base", "common emitter" and "common collector" were coined to distinguish the three types of configurations for bipolar junction transistors or BJT. Do not interpret this to have any reference to circuit "common" or "ground".

View attachment 270976

Reference: https://www.electronics-tutorials.ws/transistor/tran_1.html

In the tutorial they say for CC, collector has to be grounded but emiter is grouned there.



I still don't get it. In every sites they say that common is when both input and output has the same 1 node. But i don;t see it ...
Also here :


Input/Output common collector node and here also common collector :



I'm a little bit dumb here ... Can I get a pictures with marked places where I should focus on when it comes to "common" configuration ?

 

I said emphatically, ignore reference to common and ground.

The input is on base, output on emitter. This is Common Collector configuration.
Learn to recognize the configuration, not where is ground. You can remove the GND symbol and place it anywhere in the circuit diagram. It still is Common Collector.

 

I said emphatically, ignore reference to common and ground.

The input is on base, output on emitter. This is Common Collector configuration.
Learn to recognize the configuration, not where is ground. You can remove the GND symbol and place it anywhere in the circuit diagram. It still is Common Collector.
View attachment 271016

Ok so the rule is that when the input is on base, not in collector or emiter but in base then the output must be on emiter for it to be a common collector ?

If I put input on base and output on collector then it is common collector ?

Edit;

I know you said to ignore common or GND but why in the tutorial about config this is written in this tutorial :

 

Ok so the rule is that when the input is on base, not in collector or emiter but in base then the output must be on emiter for it to be a common collector ?

If I put input on base and output on collector then it is common collector ?

The "common" is the one where there is no signal.
common emitter - input on base, output on collector
common collector - input on base, output on emitter
common base - input on emitter, output on collector.
You'll generally find that the "common" terminal is connected to a power supply, or some point that is heavily decoupled to ground.

You will aslo find "common collector" referred to as an "emitter follower", because, unlike the other two configurations, the gain is always just below 1, so the emitter signal is almost the same as the base signal so it "follows" it.

 

Common Collector configuration


Does this make you happy now?

 

The "common" is the one where there is no signal.
common emitter - input on base, output on collector
common collector - input on base, output on emitter
common base - input on emitter, output on collector.
You'll generally find that the "common" terminal is connected to a power supply, or some point that is heavily decoupled to ground.

You will aslo find "common collector" referred to as an "emitter follower", because, unlike the other two configurations, the gain is always just below 1, so the emitter signal is almost the same as the base signal so it "follows" it.

Okey I think I get the rule now

Common Collector configuration
View attachment 271026

Does this make you happy now?

I'm really sorry, I didn't mean to annoy you.
I just thought that if the output must be linked to emiter. But the definition on the website said that collector is grounded but it doesn't have to be

By the way even if I add a resistor on this collector it is still common collector ?

Edit :



Still common collector even if I add resistor to the collector ?

 

Yes, it is still common collector.

 

Yes, it is still common collector.

Okey

And here it is hard to say because there is no Vout like before :




Normally I would say the left is common emiter when Vout is from collector but it is not

 

Left schematic is common emitter. The load is on the collector.
Right schematic is common collector. The load is on the emitter.

 

Here, just the location of the bypass capacitor changes the AC response of the circuit.
Hence the BJT circuit configuration is different.

I intentionally did not draw supply voltages or ground because they are irrelevant.

 

Left schematic is common emitter. The load is on the collector.
Right schematic is common collector. The load is on the emitter.

Shouldn't it be that the load should look like that ?



Because there is no Vout node which indicates the config like you said before.

View attachment 271041
Here, just the location of the bypass capacitor changes the AC response of the circuit.
Hence the BJT circuit configuration is different.

I intentionally did not draw supply voltages or ground because they are irrelevant.

Like here I can say which config is which by looking at the Vout. But from the above I can't say because there is no Vout.

 

The load is LED1 + R2.
That represents your output.
In terms of current and voltage, the output is the current flowing through LED1 + R2.
The voltage is the voltage across LED1 + R2.

Where you connect GND is irrelevant.