# Common emitter vs. common collector power amplification

1. Apr 9, 2009

### kthouz

Hello everybody!
I was studying stuff about transistor and i got stuck somewhere. In lecture they said that The common emitter is the more likely configuration used to amplify signals because it produces more power than other configurations. But when i tried to understand it clearly if found that in a common emitter configuration the input base current Ib is multiplied by $$\beta$$ (the current gain factor) to give an output collector current Ic=$$\beta$$Ib while as far as common collector configuration concerned, the input base current is multiplied by (1+$$\beta$$) giving an output emitter current Ie=(1+$$\beta$$)Ib. As we know the power is directly dependent on the current (P=UI), so i can conclude saying that the power due to a common collector configuration is higher than the one due to a common emitter configuration since the Ie=(1+$$\beta$$)Ib$$\geq$$c=$$\beta$$Ib . Am I right?

2. Apr 9, 2009

### cabraham

The *current* gain is nearly equal for CC & CE. But the *voltage* gain is >> 1 for CE, but just under 1 for CC. The *power* gain is the product of current gain & voltage gain. The CE has greater *power* gain than the CC.

Claude

3. Apr 9, 2009

### kthouz

Then the great part of power is from the voltage. Now i understand.Thank you!

4. Apr 9, 2009

### cabraham

Well, as far as power goes, it's the product of both current & voltage. One is not "greater". For a CB stage, the current gain is just under 1, while the voltage gain >> 1. So with the CB & CC stages, power gain is less than that of the CE stage. The CE has a current gain >> 1, as well as a voltage gain >> 1. This is why the CE has such great power gain.

The current gain & voltage gain are equally important as far as power gain is concerned.

Claude