Class B push-pull amplifier (question)

Discussion in 'General Electronics Chat' started by Shayan22h, Aug 14, 2013.

  1. Shayan22h

    Thread Starter Member

    Oct 24, 2012
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    3
    hey guys i have made a Class B push-pull amplifier where the current is supposed to be amplified but in fact there is no increment in the output current .
    i have 2V input ac voltage so at the end i get 2V voltage between the two transistors obviously whatever load i place there the current will be 2v/RL,, so my question is we could get the same current with placing the RL in series with input ac voltage 2v so what is the point of this Class B push-pull amplifier ???
    and i know as it is shown on the green graph the current going through the transistors have been amplified but this cant help the output current since the voltage difference between the two transistors is always equal with the input voltage !
    cheers and thanks for ur time !
     
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  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    Shayan22h likes this.
  3. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    I also noticed a error in your diagram, look at Q2.
     
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  4. Shayan22h

    Thread Starter Member

    Oct 24, 2012
    30
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    thanks for ur reply :) well i don't see anything wrong with Q2 it is a PNP transistor
    i chose my transistors based on this page, the designer has recommended these 2 transistors :)
    could u tell me what wrong is with Q2 plz ?
     
  5. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    A tip
    Q2 emitter should be connected to the output not to Vee.
     
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  6. studiot

    AAC Fanatic!

    Nov 9, 2007
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    It's a bit difficult to follow your circuit, the way you have drawn it, but one of your transistors is the wrong way round. If you look D1, D2 and the base -emitter diode of Q1 clamp the collector-base voltage of Q2 to three diode drops max.
     
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  7. Shayan22h

    Thread Starter Member

    Oct 24, 2012
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    woow thank u so much what a stupid mistake i made :)))

    ok now one more question please, as it is shown on the oscilloscope i measured the current on the base of the NPN transistor and it is not fluctuating now and it is constant 1mA, why is it the case ? the current is fluctuating all over the circuits and it makes sens for me to also fluctuate in the base of the transistors and it was also fluctuating before u would give me hint to correct Q2
     
  8. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    Change scope setting, set "scale" for channel A current 50mV/Div.
     
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  9. Shayan22h

    Thread Starter Member

    Oct 24, 2012
    30
    3
    wow amazing u re such a life saver Jony , u really made my day, I wish ur day would be made ;)
     
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