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Common emitter vs. common collector power amplification

  1. Apr 9, 2009 #1
    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?
     
  2. jcsd
  3. Apr 9, 2009 #2
    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
     
  4. Apr 9, 2009 #3
    Then the great part of power is from the voltage. Now i understand.Thank you!
     
  5. Apr 9, 2009 #4
    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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