q-point of a transistor ..help

Discussion in 'Homework Help' started by herbgriffin, Feb 17, 2011.

  1. herbgriffin

    Thread Starter New Member

    Feb 14, 2011
    we are tasked to make a bjt amplifier, and i don't know what values of Ic,Vce ..Rb and Rc and other values....because i don't know how to find the operating point of the transistor....
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
  3. hobbyist

    Distinguished Member

    Aug 10, 2008
    Please give all the parameters you need to work under,
    such as load impedance, or signal voltage, power supply, ect....
  4. herbgriffin

    Thread Starter New Member

    Feb 14, 2011
    we are given an input of 50mVpeak and expected output of 10Vpeak to peak
    and beta is 69.28 ....
  5. Audioguru

    AAC Fanatic!

    Dec 20, 2007
    You cannot buy a transistor that has a specific beta of 69.28. So we design circuits for a transistor that has a typical beta of 69 but could have beta from 35 to 140. Then any transistor with that part number will work.

    You need a voltage gain of 200 so the load resistance must be very high or use more than one transistor.
    Last edited: Feb 18, 2011
  6. Adjuster

    Well-Known Member

    Dec 26, 2010
    It may be easier to obtain the required voltage gain and output swing if you use a rather bigger supply voltage than you might at first think necessary. The voltage would of course need to be suitable for the transistor used.

    An adequate supply voltage will allow you to use a big enough collector load to obtain the required gain. If possible, it might be better to use an even larger load resistance so that somewhat more voltage gain is available, and then to set the gain to the required level by inserting a small additional (undecoupled) emitter resistance.