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Common Collector BJT configuration

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ABEL DANIEL

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How can we justify the fact that,collector when made common to both input and output,it is either tied to ground or to power supply rail?I understood,collector tied to ground-which means output and input is taken with respect to collector(ground).But i didn't understand ,why collector can even be connected to power supply??
 

The term "common collector" means that the collector node is common for input and output SIGNALS (of course, not for DC).
And for signals the DC supply has a negligible internal resistance. To further reduce this signal resistance, the DC supply often is bypassed with capacitors.
 

Thanks for the reply.Ya ,you are right,collector is common to the i/p signal and o/p signal(not DC)..But if we consider ,emitter follower circuit(which is cc configuration),collector is not grounded(if it has to be common to both i/p and o/p),rather it is connected to Vcc,right?
 

Ground and Vcc are the same to a signal because the power supply has a very low resistance and is bypassed with a capacitor.
 

ABEL DANIEL said:
if we consider ,emitter follower circuit(which is cc configuration),collector is not grounded(if it has to be common to both i/p and o/p),rather it is connected to Vcc,right?
Click to expand...

It is grounded - as far as signals are concerned!
 

ABEL DANIEL said:
But if we consider ,emitter follower circuit(which is cc configuration),collector is not grounded(if it has to be common to both i/p and o/p),rather it is connected to Vcc,right?
Click to expand...
Not always. Here's two emitter follower circuits with the collector connected to ground.

 

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