I have a feeling that this is not an easy subject.

But I don't know what is active load.

Maybe I used the wrong word. Maybe I should have said preferential load.



If R3 and R4 are equal, what would you call this?
This is neither common emitter nor common collector.
Don't get hung up on the name of a certain configuration.

 

I have a feeling that this is not an easy subject.

But I don't know what is active load.

I'm being completely serious about taking a step back. Trying to assimilate and process a large volume of information in a short period of time is exhausting and frustrating. When this happens, I often take a step back and try to go after bite sized chunks of information to build a foundation. It does work for me and maybe it will work for you.

You didn't ask, but my current quest is to understand Orbital Mechanics at a deep level. It can't be done in an evening of "light" reading.

 

Aaaa cool so if I do something like this :

View attachment 271059

So it is now a common collector. If I'm right here of course.
Then cool and now I think I get it.

thats the basic 1/4 watt transistor tester.

 

Maybe I used the wrong word. Maybe I should have said preferential load.

View attachment 271080

If R3 and R4 are equal, what would you call this?
This is neither common emitter nor common collector.
Don't get hung up on the name of a certain configuration.

Hmmm
I know for certain that many sites and books says about 3 configurations, but if this one doesn't have any then It gets really confusing.
So active load you mean the one I pick with Vout ?

I'm being completely serious about taking a step back. Trying to assimilate and process a large volume of information in a short period of time is exhausting and frustrating. When this happens, I often take a step back and try to go after bite sized chunks of information to build a foundation. It does work for me and maybe it will work for you.

You didn't ask, but my current quest is to understand Orbital Mechanics at a deep level. It can't be done in an evening of "light" reading.

You might be right but I tried to understand it way before, and I get really tired to understand it at the same time thinking that transistors and other electrical stuff are getting even more harder. Like I'm studying electronics, and I want to try to do something with my knowledge. But I don't understand why some circuits are done in some way like some random capacitance etc.

It's hard for me to learn alone so I like to talk with people about it. And I know I am annoying for many people. Also some sites are saying this like "it must be grounded" or something similar on websites so it's hard to find a "legit" information.

 

Hmmm
I know for certain that many sites and books says about 3 configurations, but if this one doesn't have any then It gets really confusing.
So active load you mean the one I pick with Vout ?

You might be right but I tried to understand it way before, and I get really tired to understand it at the same time thinking that transistors and other electrical stuff are getting even more harder. Like I'm studying electronics, and I want to try to do something with my knowledge. But I don't understand why some circuits are done in some way like some random capacitance etc.

It's hard for me to learn alone so I like to talk with people about it. And I know I am annoying for many people. Also some sites are saying this like "it must be grounded" or something similar on websites so it's hard to find a "legit" information.

You are still hung up on labeling a node Vout. Don't worry about the label.
Try to understand the flow of current within a circuit and how this current presents itself as a voltage across a resistor.

I think your problem is you are attempting to learn about a topic by jumping into the middle the course. You skipped over the introductory parts of the course. For example, you cannot apply BJT to circuit applications if you have not covered how the PN semiconduction junction works, much less how a BJT works.

Have you covered DC and AC circuits yet?

Start with Direct Current from the Education tab at the top of this page.
Master one chapter before moving on the next.

 

You are still hung up on labeling a node Vout. Don't worry about the label.
Try to understand the flow of current within a circuit and how this current presents itself as a voltage across a resistor.

I think your problem is you are attempting to learn about a topic by jumping into the middle the course. You skipped over the introductory parts of the course. For example, you cannot apply BJT to circuit applications if you have not covered how the PN semiconduction junction works, much less how a BJT works.

Have you covered DC and AC circuits yet?

Start with Direct Current from the Education tab at the top of this page.
Master one chapter before moving on the next.

I mean I know some basics how to calculate DC or AC circuits, using complex numbers.

For transistors I know some basics for NPN. That it need 0,7 Volts or 0,5 to make the transistor work (0,7 V for V_be)

I just don't see it in transistor how it flows or how should I look at it.
I just read some rules that, load must be connected to emitter to make common collector or connect load to collector for it to make a common emitter.

And then I see an example that doesn't have load added to so I can't figure out the rules.

Also I know that time can't make me figure things out I don't know why I just get more and more stressed out when I can't understand something, so I know overtime I will get more stressed. So I want to understand at least configurations, how to solve the Voltage in certain resistors in transistor will come later but now I just want to know the configurations because specific configurations have specific way to solve all voltages in BJT.

I'm sorry for being insistive

 

I just read some rules that, load must be connected to emitter to make common collector or connect load to collector for it to make a common emitter.

For now, just forget the labels "common collector" and "common emitter" since it just adds to your confusion and frustration.
For the moment, the labels are not important.

Learn how to properly bias a BJT circuit.
https://www.allaboutcircuits.com/textbook/semiconductors/chpt-4/biasing-calculations/

 

Hello everybody !


I'm confused by many thing lately, but the transistors configuration is one of them.

I can't understand how to identify in which configuration the transistor is working on.

For example this one :

View attachment 270958

I can't say which configuration is that with this photo :

View attachment 270959

In some websites they say that common emiter is then when we ground the emiter and common collector is when collector is grounded but then I've this picture that says it is common collector while emiter is grounded.

View attachment 270960

I don't know how to identify the configuration.

Thanks for any advice

I think you may be referring to a base class known as amplifiers but let's explore this a little more.

Going by that exact diagram with dark background and green 'wires' it can be one of two things (or maybe both but probably not both)...
1. A voltage regulator/clipper that regulates the voltage to the 500 Ohm resistor.
2. A current regulator/rectifier that regulates the current in the 100 Ohm resistor.

The main idea is that the zener regulates the voltage across the 500 Ohm resistor and so that regulates the current through the 100 Ohm resistor to a decent degree of accuracy although not perfect and still a bit temperature dependent. This means it can be applied to be either a voltage regulator for the 500 Ohm resistor or a current regulator for the 100 Ohm resistor. This would be if there was a DC supply voltage and also AC with one more catch.
Because there is an AC supply shown, it could also be a clipper for the voltage across the 500 Ohm resistor and a clipper/rectifier for the current through the 100 Ohm resistor.

To classify this as to some canonical transistor circuit form:
If the output is the 500 Ohm resistor then it could be called a common collector also known as an emitter follower but with current limiting.
If the output is at the 100 Ohm resistor then it could be called a common emitter although that might be a stretch.

However, sometimes it is not a good idea to try to classify transistor circuits within the bounds of these strict forms. Better to just state what the circuit does. Amplifiers are a little different you can usually classify them without stretching the definitions.

 

I think your problem is you are attempting to learn about a topic by jumping into the middle the course. You skipped over the introductory parts of the course. For example, you cannot apply BJT to circuit applications if you have not covered how the PN semiconduction junction works, much less how a BJT works.

Yes - I only can underline this recommendation.
1) At first - try to understand the fundamental working principle of a transistor:
A DC voltage of app. Vbe=(0.6...0.7) volts will "open" the transistor (that means: It allows a current Ic to flow between C and E (if there is a DC voltage of some volts between C and E).
2) Any signal voltage at the base (swinging around the DC bias) will cause variations of Ic (signal current ic), which can be transferred into a corresponding signal voltage using a resistor in the collector or/and emitter path.

 

So I want to understand at least configurations, how to solve the Voltage in certain resistors in transistor will come later but now I just want to know the configurations because specific configurations have specific way to solve all voltages in BJT.

Why do you think that you need a "specific way" for a certain configuration? This is NOT the case.
All you need is the following
(a) basic rules for analyzing electrical circuits (laws from Ohm and Kirchhoff)
(b) the fundamental expression describing the relation between voltage and current for a pn junction (applicable for diodes and bipolar transistors):
I=Is*[exp(Vf/Vt)-1] with Vf=forward voltage and Vt=temperature voltage (app. 26mV)

Comment: The last equation is important for calculating the gain because the slope of this function gives delta(I)=f[delta(V)] and is simply given as

d(I)/d(V)=gm=Ic/Vt.
Hence, the transconductance gm is proportional to the DC current Ic.

 

I think you may be referring to a base class known as amplifiers but let's explore this a little more.

Going by that exact diagram with dark background and green 'wires' it can be one of two things (or maybe both but probably not both)...
1. A voltage regulator/clipper that regulates the voltage to the 500 Ohm resistor.
2. A current regulator/rectifier that regulates the current in the 100 Ohm resistor.

The main idea is that the zener regulates the voltage across the 500 Ohm resistor and so that regulates the current through the 100 Ohm resistor to a decent degree of accuracy although not perfect and still a bit temperature dependent. This means it can be applied to be either a voltage regulator for the 500 Ohm resistor or a current regulator for the 100 Ohm resistor. This would be if there was a DC supply voltage and also AC with one more catch.
Because there is an AC supply shown, it could also be a clipper for the voltage across the 500 Ohm resistor and a clipper/rectifier for the current through the 100 Ohm resistor.

To classify this as to some canonical transistor circuit form:
If the output is the 500 Ohm resistor then it could be called a common collector also known as an emitter follower but with current limiting.
If the output is at the 100 Ohm resistor then it could be called a common emitter although that might be a stretch.

However, sometimes it is not a good idea to try to classify transistor circuits within the bounds of these strict forms. Better to just state what the circuit does. Amplifiers are a little different you can usually classify them without stretching the definitions.

I've been thinking about DC, If there was DC supply instead of AC what could it change ?
Could it change the way we see 100 ohm and 500 ohm ? I mean the configuration ?
I know that only one can be here as an output.

However, sometimes it is not a good idea to try to classify transistor circuits within the bounds of these strict forms. Better to just state what the circuit does. Amplifiers are a little different you can usually classify them without stretching the definitions.

Why do you think that you need a "specific way" for a certain configuration? This is NOT the case.
All you need is the following
(a) basic rules for analyzing electrical circuits (laws from Ohm and Kirchhoff)
(b) the fundamental expression describing the relation between voltage and current for a pn junction (applicable for diodes and bipolar transistors):
I=Is*[exp(Vf/Vt)-1] with Vf=forward voltage and Vt=temperature voltage (app. 26mV)

Comment: The last equation is important for calculating the gain because the slope of this function gives Delta(I)=f[Delta(V)] and is simply given as

Delta(I)/Delta(V)=gm=Ic/Vt.
Hence, the transconductance gm is proportional to the DC current Ic.

I though that specific configuration give specific equations (for amplifying voltage or current) Because CC amplifies current CE amplifies Voltage. So I thought is it essential to know how it works.

 

I though that specific configuration give specific equations (for amplifying voltage or current) Because CC amplifies current CE amplifies Voltage. So I thought is it essential to know how it works.

No. That is not a good approach. Voltage and current go together according to Ohm's Law.

What you need to remember are the basic characteristics between common collector and common emitter configuration.
Regardless of the which configuration is used you still need to learn how to conduct the DC and AC analysis for each configuration.

You need to learn how to do a transistor load line analysis.


Reference: https://www.tutorialspoint.com/amplifiers/transistor_load_line_analysis.htm

 

I though that specific configuration give specific equations (for amplifying voltage or current) Because CC amplifies current CE amplifies Voltage. So I thought is it essential to know how it works.

To make it more clear: Of course, it is essentiell to kow HOW IT (the BJT) WORKS.

But this does not mean that you need "specific equations".
Everythig can be done with the tools I have mentioned.
Perhaps I should add that you need the given exponential equation only to verify the value of Vbe=(0.6..0.7) V.
But very important is the SLOPE of this funktion because it contains the amplifying properties of the BJT: The transconductance gm=Ic/Vt.
A small change of input voltage causes a change in output current - which in turn will cause a corresponding change in output voltage when this current goes through a resstor.

 

I've been thinking about DC, If there was DC supply instead of AC what could it change ?
Could it change the way we see 100 ohm and 500 ohm ? I mean the configuration ?
I know that only one can be here as an output.

I though that specific configuration give specific equations (for amplifying voltage or current) Because CC amplifies current CE amplifies Voltage. So I thought is it essential to know how it works.

Hi again,

Well until we know what the application is we dont know what the output is, if it is one or the other or both. It was up to the designer and their end goal.

If the circuit was run on just DC, it would just mean the output(s) are constant rather than pulsing once every half cycle of the AC input.
This would mean a constant voltage or current output that would not change because the input goes up and down with time.

You are right that specific configurations give specific equations for amplifying, but because of the number of pins on each component the number of possible circuits goes far beyond the canonical configurations. This is generally known as topology and that is much more general then "common emtter" or "common collector" or "common base".
I think you are looking for a set procedure to solve a circuit with a transistor and the only way to do that is with a complete analysis rather than trying to squeeze the circuit into some preset form. Amplifiers are classified in certain ways, but more general circuits only have a classification according to what they do and that can be something other than just amplification.

So for some circuits you will have to forget about the "common emitter", "common collector", etc., and just go with a full analysis using something like Nodal Analysis.

Also, we dont usually start with a configuration like "common emitter" and then try to fit the circuit into that frame of thought, we do the opposite; we do an analysis and then decide later if it fits into a certain form like "common emitter". So when you see a circuit you dont understand it is best to do an analysis with a technique like Nodal Analysis and then later you can decide if you think it is in a certain amplifier form if you think that is necessary.

The best thing you could probably do now it look into Nodal Analysis it is very general. You will have to learn a few other things too along with that but in the end you'll be in a much better place to understand circuits like this with little doubt as to what it does or can do.

 

I think this might be pretty off what I will ask right now.

But I have a question.
I've read here that AC "Output voltage is the measure of potential difference between two points.
Where you place your reference voltage is irrelevant with respect to AC analysis. "
Why ?

And why does those configuration won't effect on DC but effect on AC ? I don't get it.

 

Where you place your reference voltage is irrelevant with respect to AC analysis.

It's not quite true. The reference doesn't matter provided that it is an AC earth, in other words, it is connected to earth by something that is a low impedance at the frequencies in question.
Generally, that includes any power supply voltage, because they are at a low impedance, and anything that is decoupled to a supply voltage with a large capacitor.

Having sorted that out, then the position of the reference is immaterial because for AC analysis we are discounting any DC component of the signal - if there is net DC voltage between the two points, we are ignoring it.

 

Having sorted that out, then the position of the reference is immaterial because for AC analysis we are discounting any DC component of the signal - if there is net DC voltage between the two points, we are ignoring it.

I don't know If I get it.
If we are doing AC analysis we ignore DC voltage supply as a short circuit. But if we have for example capacitor. We can't ignore capacitor in AC analysis even if it has DC voltage and AC voltage in this capacitor.

 

I don't know If I get it.
If we are doing AC analysis we ignore DC voltage supply as a short circuit. But if we have for example capacitor. We can't ignore capacitor in AC analysis even if it has DC voltage and AC voltage in this capacitor.

You can if it is big enough! If you are analysing at 20kHz, then a 100uF capacitor has an impedance of 0.08Ω - it's a short circuit.

 

Then it must be a high frequency.
But if it is 60Hz then I must use smaller capacitor to say it is short circuit. And instead of 0,08 ohm then I can just ignore it in calculations.

But usually I have to take every component at some consideration if it's AC analysis but change DC voltage into short circuit.

I also wonder why those configurations doesn't effect on DC but effect on AC.

 

I don't know If I get it.
If we are doing AC analysis we ignore DC voltage supply as a short circuit. But if we have for example capacitor. We can't ignore capacitor in AC analysis even if it has DC voltage and AC voltage in this capacitor.

Hi,

You have to be careful how you look at these things.
If you have a capacitor then the DC voltage across it can be anything, 0, 1, 2, 3, 100, 3000 volts etc., while the AC voltage across it will depend on other things in the circuit, and the 'output' if it is used as a coupling capacitor will usually reflect the input AC voltage because in general a capacitor passes AC current and blocks DC. The 'output' DC voltage would be zero referenced to ground.
Usually an AC measurement drops the DC offset voltage and just measures something like the peak to peak AC voltage.

But all this stuff is kind of skipping over the real analysis because the situations can vary widely. It is always best to do a full analysis.