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Designing Circuit by BC546

Discussion in 'Electronics Homework Help' started by Mobin, Nov 9, 2017.

  1. Mobin

    Mobin

    13
    0
    May 1, 2017
    Hello every body.
    I have an assignment requesting the followings:
    Design a circuit using BC546 that gives us the gain of 1500
    R(in)=2.5KΩ
    R(out)=3.3KΩ
    R(source)=50Ω
    R(load)=3.3KΩ
    Vcc=15 volt
    and assume ro=infinite

    the problem is I don't actually know how to start solving it if you can help me I would be very grateful.

    in addition I have questions before starting :
    1- How many stages should I use?
    2- is common emitter configuration proper for all of the stages? and what is the reason?
     
    Last edited: Nov 9, 2017
  2. Alec_t

    Alec_t

    2,658
    700
    Jul 7, 2015
    Were you paying attention in class :)?
    Revise what you have been taught. Start by considering which transistor configurations give reasonable gain and what their input and output impedances are likely to be. Post your best effort at a solution.
     
    Harald Kapp and Mobin like this.
  3. Mobin

    Mobin

    13
    0
    May 1, 2017
    thanks
    I did it mostly by using 2 stage winch both have common emitter configuration but I'm still stuck with R(out)=3.3KΩ
    in the second stage below you can see if I want R(out)=3.3KΩ while RL is already equal to 3.3KΩ then R6 will be so great that almost no current will flow through the collector. meanwhile I need a cuurent between 1 to 10 mA for collector to get to a suitable beta according to datasheets and if it goes around μA or less then I would have no idea about the amount of beta
    can you help me with this last problem?
    el.PNG
     
  4. duke37

    duke37

    5,211
    718
    Jan 9, 2011
    RL is not part of the amplifier, it is the load.

    Looking in to the amplifier, you will see R6 and the transistor are effectively in parallel. The output impedance of Q2 will be very high so you are left with R6 as the output resistance, assuming C1 has a low impedance at the frequency of interest.
     
    Mobin likes this.
  5. Mobin

    Mobin

    13
    0
    May 1, 2017
    thank you very much
    as the last question::)
    How can I determine the amount of resistor on the collector the stage before the last one?
    in fact I have all the parameters of the last stage
    but I to determine R7 and R8 I can't
    because I have 4 unknown parameter about the transistor "Q2":
    R7 , R8 , Ic , Vce
    and there is only 3 equations:
    AC load line equation , DC load line equation , Gain equation
    so what am I missing here? what should I do? photo_2017-11-11_18-02-45.jpg
     
  6. Audioguru

    Audioguru

    2,570
    580
    Sep 24, 2016
    Your assignment says that "ro is infinite". Isn't ro your RL? Then remove your RL.

    I think you must learn about transistors because your resistor values appear to be selected at random.
    Here is the operation of your second transistor:
     

    Attached Files:

  7. Alec_t

    Alec_t

    2,658
    700
    Jul 7, 2015
    Your capacitor values appear to be 1 FARAD ! Re-think those.
     
  8. Audioguru

    Audioguru

    2,570
    580
    Sep 24, 2016
    The parts were selected at random without any circuit design.
     
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