A gain and capacitor question

Discussion in 'General Electronics Chat' started by Atakan Şişman, Oct 17, 2017.

  1. Atakan Şişman

    Thread Starter New Member

    Dec 17, 2016
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    0
    Ekran Alıntısı.PNG
    Hello everyone,
    given me informations are Vcc, Re, Rc Rl Rsig R1 R2, ( ß, Vbe, Vt in transistor).
    wanted: 1.mid band gain Vo/Vsig and Vo/Vi.
    2.C1 , C2, C3 a 3-dB low freq of fl= 100Hz.

    My question is that , is it important r1 and r2 in this circuit for V0/Vsig , Vo/Vi
    How can i find Vi ?
     
  2. MrChips

    Moderator

    Oct 2, 2009
    16,874
    5,183
    Usually, one would assume that Rsig is small compared with Ri.
    Hence Vi is the same as Vsig.

    R1 and R2 are critical since they set up the bias point, i.e. the Q-point.
     
  3. ian field

    AAC Fanatic!

    Oct 27, 2012
    6,207
    1,117
    Essentially; R1 & R2 are a voltage divider providing a rudimentary Vref for the base. With the emitter resistor, it plays a part in the quiescent collector current. that part of the circuit is an emitter follower - the transistor will try to keep Vre at vr1/r2 less Vbe. Since Re is constant; the collector current to maintain the set voltage is also constant.

    Your input signal varies the notional Vref at r1/r2 to upset the balance just described and cause collector current to vary in accordance to device gain. The higher you make r1/r2; the less it loads the signal - but making them too high causes other problems.
     
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