Type of transistor configuration on a circuit

In summary, the transistor configuration on a circuit is determined by the terminal that is common to both the input and output of the circuit. The terminal that is common to both the input and output of the circuit defines the description (common-emitter, common-collector, common-base).
  • #1
jonnathan_andre
1
0
OK, I need some help here. I can´t really recognize the type of transistor configuration on a circuit (common emitter, common base, common colector).
I`ll some tips that help me identify the configuration.

Check the circuit attached.
 

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  • #2
Assuming you already know how to identify (convention for naming) each transistor terminal, the terminal that is common to both the input and output of the circuit defines the description (common-emitter, common-collector, common-base).

illustration ---> http://people.deas.harvard.edu/~jones/es154/lectures/lecture_3/bjt_amps/bjt_amps.html

With that in mind, it should be straight forward deciding how T1 and T2 are used in your circuit.
 
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  • #3
Although you can have common emitter, common base, and common collector you NEVER input a signal on a collector. I have never seen it anyway, and that is what is being attempted in this circuit.
 
  • #4
Averagesupernova said:
Although you can have common emitter, common base, and common collector you NEVER input a signal on a collector. I have never seen it anyway, and that is what is being attempted in this circuit.
I believe the fellow in the bjt_amps reference just wanted to illustrate the naming of these three kinds of circuits (without adding too many additional circuit elements).

I agree with you, in practise you would not find a input (Vin) directly attached to the collector (often a DC supply Vdc is connected),
however in the AC analysis the collector would be common to both Vin and Vout nodes.
The following reference illustrates this idea.
---> http://www.allaboutcircuits.com/vol_3/chpt_4/6.html

Also in practise, the common-emmitter may have impedance or Vdc in series with the emitter before reaching a common Vin, Vout node. Similarly for common-base, there may be impedance or Vdc in series with the base before reaching a common Vin, Vout node. (you can see this illustrated at some of the links on the above reference).
 
  • #5
The word 'common"

This word ONLY applies to the circuit equivalent of a single transistor and it means your reference point for voltages ( i.e that point is considered at voltage zero ) .
In a more complex circuits with several devices the common point is usually what is referred to as Ground ( often - ve supply ) but not always .
Generally the 'common point ' is simply the zero voltage reference point
by which all others are measured .
The reference point in no way effects what is occurring in a circuit so 'common emitter' 'common collector' or 'common base ' in no way changes the behaviour -- it only has to do with the way YOU see things if you consider such a point as a reference .
Example all the usual oscillator configurations are actually the same but viewed with different reference points .
As an example in the Sun / planets system , it is a lot simpler to consider the Sun as a reference as opposed to the Earth .
So 'common collector ' means viewing a specific collector as zero voltage
and everything measured with respect to this -- that's all -- for ONE transistor this is not too complex but you would not wish to do this for a whole circuit .
Ray --- it's usually the English as opposed to the science which is confusing
Ray.
 

Related to Type of transistor configuration on a circuit

1. What is a transistor configuration on a circuit?

A transistor configuration on a circuit refers to the specific arrangement of transistors within a circuit. This arrangement can affect the performance and functionality of the circuit, and there are three main types of configurations: common emitter, common base, and common collector.

2. What is the difference between a common emitter and a common base configuration?

In a common emitter configuration, the input signal is applied to the base of the transistor, while the output is taken from the collector. In a common base configuration, the input is applied to the emitter and the output is taken from the collector. Additionally, the common emitter configuration has high voltage gain and low current gain, while the common base configuration has low voltage gain and high current gain.

3. How does a common collector configuration differ from common emitter and common base configurations?

In a common collector configuration, the input is applied to the base of the transistor, while the output is taken from the emitter. This configuration is also known as an emitter follower, as the output voltage follows the input voltage with a small voltage drop. It has high current gain and low voltage gain, making it useful for impedance matching and signal buffering.

4. Which transistor configuration is most commonly used in amplifiers?

The common emitter configuration is the most commonly used in amplifiers because it provides high voltage gain and can amplify both AC and DC signals. It also has good linearity and can drive low impedance loads. However, the choice of configuration ultimately depends on the specific application and desired performance.

5. Can a transistor configuration be changed after a circuit is built?

Yes, a transistor configuration can be changed after a circuit is built, but it may require additional components or modifications to the circuit. It is important to carefully consider the desired performance and functionality of the circuit before choosing a transistor configuration, as it can be difficult to change once the circuit is built.

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