Can i test my base bias circuit in this way?

Discussion in 'Homework Help' started by simpsonss, Oct 7, 2010.

  1. simpsonss

    Thread Starter Active Member

    Jul 8, 2008
    173
    0
    hi,

    I'm learning on base biasing for BJT. Below is the circuit. Can i test my biasing in this way?which i input a signal and have a look on the output to conclude whether it is properly bias or not. I do it in this way because i'm not sure what value should i go for the resistors. And i get this result from the Vo. And it seems like it works fine. So can i do it in this way?

    Untitled.jpg Untitled1.jpg


    thank you.
     
  2. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    If you got this output by feeding the maximum expected signal amplitude you are good to go. If signal of larger amplitude may be used on the input, try it and observe the output again.

    But if you are interested in some theory on how to bias that layout in general, other members could help you better than me.
     
  3. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    If you want max output swing the you should always aim to set Vce = 0.5*Vcc.
    And Rc << Rload
    So for RL =1K CE amplifier is not the bast chose.
    Rc = 0.1*RL = 100Ω
    Ic = 6V/100 = 60mA
    Rb = β*(Vcc - Vbe) / Ic ≈ 134 * (12V - 0.79V)/ 60mA = 25KΩ
    The voltage gain
    Au ≈ gm* Rc||RL = 40* Ic * Rc||RL ≈ 219
    And this type of bias circuit does not work good in practice.
    In practice we use voltage divider and RE resistor.
    http://forum.allaboutcircuits.com/showthread.php?p=222975#post222975

    http://forum.allaboutcircuits.com/showthread.php?p=229316#post229316

    And in your simulation set "step Celiling" to 1u
     
    Last edited: Oct 7, 2010
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