common collector push pull design

Discussion in 'General Electronics Chat' started by serhatkisa, Dec 12, 2011.

  1. serhatkisa

    Thread Starter New Member

    May 15, 2011
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    hi.i just made the calculation for this amplifier, but i suspect that it is not correct because the simulation wasnt work.please help me.
     
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  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    Increase the C1 capacitor size from 1nF to 100uF.
     
  3. serhatkisa

    Thread Starter New Member

    May 15, 2011
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    i tried but the output signal is still too weak.voltage gain is small than 1
     
  4. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    But the push-pull stage voltage gain is always smaller then 1.
    The push-pull stage is a "current amplifier" not a voltage.
    And additional your design is very poor because R2 and R3 further reduce the voltage gain.
     
  5. serhatkisa

    Thread Starter New Member

    May 15, 2011
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    but its not my design.its a project that given by teacher.see that
     
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I don't see any power supply in your simulation. It should be +12V.
    A 10 ohm load will cause a lot of attenuation. Try 10kohms. You will still get crossover distortion, because the voltage between the bases is only 1.18V.
     
  7. serhatkisa

    Thread Starter New Member

    May 15, 2011
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    i have fixed the problem about simulation. it works now as you see below but when i tried to set up the circuit on the breadboard, the output signal is clipped somehow. i drawed it in red line.(clipped part is under red line) i can not get the reason of this problem. i have to fix that circuit until tomorrow. please help me.

    (i put the screen shots from the circuit simulation operating normally. and the ossiloscope screen when i set up the circuit on board.)
     
  8. Audioguru

    New Member

    Dec 20, 2007
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    The BD140 pulls down the output signal. Its pins are connected wrong or it is defective.
     
  9. serhatkisa

    Thread Starter New Member

    May 15, 2011
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    i tried two bd140 transistors but none of them fix the problem. if you think that the bd140 is defective can you suggest a transistor model instead of it
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    I don't use old European BD139 and BD140 transistors. I use American TIP31 and TIP32 instead which are almost the same but they are in a modern TO-220 case.
     
  11. Ron H

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    Apr 14, 2005
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    You almost certainly have a wiring error.
     
  12. serhatkisa

    Thread Starter New Member

    May 15, 2011
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    i fix the problem about graph that cilipped negative alternation by changing the transistors to Tip31-32. now occure another problem. the output voltage value is too weak. push pull amplifiers have a voltage gain about 1 they have current gain. but on my circuit Vav is nearly 0.3 how can i fix this problem. i cannot change the load resistance value because push pull amps have small valued resistance
     
  13. serhatkisa

    Thread Starter New Member

    May 15, 2011
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    is there noone to help me? when i use tip31 and 32 transistors i cant see crossover distortion.please help me because i will complete this project before tuesday.
     
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