BJT basic amplifier problem

Discussion in 'General Electronics Chat' started by Abhinavrajan, Oct 6, 2016.

  1. Abhinavrajan

    Thread Starter Member

    Aug 7, 2016
    77
    1
    Hi all.

    Please have a look at the two attachments.

    The first one is a biasing circuit.
    In this circuit, I have to find the value of Rb1.
    I have calculated that value which turns out to be 46.24k ohms.
    But, it seems to be wrong.
    I can't understand what mistake I am making.
    If that answer is wrong, please help me with the approach to find the right answer.



    The second ,attachment consists of a CE BJT amplifier.
    I need to find the collector current and Midband gain of the amplifier.
    Please tell me the correct method to approach to find the collector current and midband gain and help me solve it.

    Thanks.
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,767
    1,102
    Since this is 'Homework Help' you are expected to show your efforts so far. Show how you got the value 46.24k.
    Use Ohm's Law to calculate the circuit voltages and currents.
     
  3. Abhinavrajan

    Thread Starter Member

    Aug 7, 2016
    77
    1
    Since, we know the value of Vb, Vcc and Rb2, I found the value of Rb1 using the voltage divider formula.

    3.65=((12)(Rb1))/(105.8k+Rb1). I solved for Rb1 and found it to be 46.24k ohms.
     
  4. Abhinavrajan

    Thread Starter Member

    Aug 7, 2016
    77
    1
    Please, explain a bit more clearer.

    Thanks.
     
  5. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    Last edited: Oct 6, 2016
  6. Abhinavrajan

    Thread Starter Member

    Aug 7, 2016
    77
    1
  7. Veracohr

    Well-Known Member

    Jan 3, 2011
    549
    75
    You're given the emitter current & the transistor gain. That's all you need to calculate the DC base current.
     
    Abhinavrajan likes this.
  8. hp1729

    Well-Known Member

    Nov 23, 2015
    1,938
    218
    When calculating the current through RB1 you need to subtract the base current from the current through RB2.
     
    Abhinavrajan likes this.
  9. Abhinavrajan

    Thread Starter Member

    Aug 7, 2016
    77
    1
    Thank you all. Got the answer! :)
     
Loading...