Common Collector BJT configuration

[ABEL DANIEL]

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??

 

[LvW]

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.

 

[ABEL DANIEL]

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?

 

[Audioguru]

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

 

[LvW]

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?

It is grounded - as far as signals are concerned!

 

[godfreyl]

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?

Not always. Here's two emitter follower circuits with the collector connected to ground.