Common emitter vs. common collector power amplification

  • Thread starter kthouz
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  • #1
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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 [tex]\beta[/tex] (the current gain factor) to give an output collector current Ic=[tex]\beta[/tex]Ib while as far as common collector configuration concerned, the input base current is multiplied by (1+[tex]\beta[/tex]) giving an output emitter current Ie=(1+[tex]\beta[/tex])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+[tex]\beta[/tex])Ib[tex]\geq[/tex]c=[tex]\beta[/tex]Ib . Am I right?
 

Answers and Replies

  • #2
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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
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Then the great part of power is from the voltage. Now i understand.Thank you!
 
  • #4
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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
 

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