[SOLVED] How this circuit is common collector ?

How this circuit is common collector , how to identify ?

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d123 said:

**broken link removed**

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this is copied from this link , m i correct or correct ? well you have even seen my circuit diagram.
http://www.evalidate.in/lab1/pages/bjt/BJTAmplifier/BJTAmplifier_T.html

@RAHUL, The above configuration is common collector since the output is in the emitter and the input is in the base; if we replaced the transistor with a black box with 4 pins (eg transistor hybrid model), 2 of the pins would be in the collector.

@d123, let's agree that the figure representing the comom collector in the cited link, is at least unusual, since it is supposedly placing the GND rail at the bottom side of the drawing, otherwise the NPN transistor itself would be wrongly chosen, being the PNP the correct option.

andre_teprom said:

@RAHUL, The above configuration is common collector since the output is in the emitter and the input is in the base; if we replaced the transistor with a black box with 4 pins (eg transistor hybrid model), 2 of the pins would be in the collector.

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sir , m nt getting clear picture. got what u said about hybrid model

RAHUL_KUMAR said:

sir , m nt getting clear picture. got what u said about hybrid model

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This is just a formal way of understanding why the above circuit "topology" is so called, once it indicates the path that a small signal would have to take to be amplified within the black-box (e.g, the above mentioned model), and get out form it.

In other words, more simplified, once the device has 3 pins, if the signal enters at one pin and leaves from the other, the remaining pin is common to both the input and output, since it is the common reference of the signal. Take a search on the web for the keywords "bipolar-transistor-hybrid-pi-model" for more details.

i agree wt u said , but the image i posted , the collector is not common to base and emitter. collector is shared with emitter only and not base. that is where i am stuck.

the input is between base and emitter ,and not between base and collector. plz refer the image i send

Hi Rahul,

...Sorry about that: The text definition (which I made into the link for the page it comes from) is a good, clear description so I thought it would be helpful - I didn't focus on the "fascinating" schematic interpretation which is either confusingly drawn upside down or is just wrong, so I guess they drew it upside down, maybe. Thanks for pulling me up on that, gentlemen.

I used the quote as a professional will far better distil the concept than my amateurish attempts and interpretations.

Looking at your last post Rahul, personally, with cc cb ce, I just suspend doubt and accept the conventional descriptions. I appreciate your interpretation "the input is between base and emitter, and not between base and collector" - doesn't it just look that way?! However, an alternative way of reading the multitude of identical descriptions for cc ce cb, in my case, is that - in a sense - common whatever BJT pin is describing the "unused"/"less relevant" pin regarding the transfer from in to out.

I think Andre's post #6 is a fine explanation, common is just a convenient term to describe what appears to be understood.

Or - as Andre eluded to in his hybrid representation: the pin that isn't the input or the output is the 'common' pin.

Brian.

RAHUL_KUMAR said:

but the image i posted , the collector is not common to base and emitter

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You are missing an important detail: Whenever you see the suffix L in some component designator, the term "Load" is implied, which has the same function as what would be called as an "Output", the input of the circuit is at Vin, which obviously refers to the input, then both Base and Emitter are being used, therefore using the above Andre's simple rule (sorry, I could not resist), the remaining pin defines its circuit topology.

andre_teprom said:

You are missing an important detail: Whenever you see the suffix L in some component designator, the term "Load" is implied, which has the same function as what would be called as an "Output", the input of the circuit is at Vin, which obviously refers to the input, then both Base and Emitter are being used, therefore using the above Andre's simple rule (sorry, I could not resist), the remaining pin defines its circuit topology.

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sir, how can this method be applied in this image below: common base , i this if the rule satisfy this one too , i would be able to get exact idea and will be thankful to you.

You need to study more on transistor AC and DC circuit analysis, because just answering random questions will not be productive. Note that the circuit you are presenting is wrong because the polarization resistors are missing, otherwise the transistor will burn due to the power source being short-circuited throught the transistor. This circuit is likely a simplified representation, but even so the author forgot to indicate the input and output nodes of the signal, which by guessing, given its orientation with emitter on the left side and collector on the right side, should be common base, as stated on its subtitle.

"Common XXX" term comes form the AC signal path.Since the Collector is short circuited by supply here, this amplifier is called Common Collector.DC Biasing has no effect on amplifier's topology.

Thanks. I think understand the diagram clearly. There is a voltage input at the base of a NPN transistor. Meaning a plus sign (1) and forward bias through the resistor. Negative would be the emitter. Conventional flow of electric. Positive to negative battery terminals.