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Transistor, AC amplification

Discussion in 'General Electronics Discussion' started by newuser, Feb 20, 2013.

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  1. newuser

    newuser

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    Dec 16, 2012
    Hi,

    i would like to see the output of this circuit, but i cant start the simulation...am i missing something?

    what i tried to start the simulation:
    simulation -> time domain

    error:
    solver returned no data

    any ideas whats missing?
     
  2. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    I see no circuit here.

    Bob
     
  3. newuser

    newuser

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    0
    Dec 16, 2012
  4. BobK

    BobK

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    1,688
    Jan 5, 2010
    You have two voltages driving the same net, V2 and V3.

    Also the circuit is not very good even if you decoupled with a capacitor. You need two resistors to bias the base, one to ground and one to V+. And you need a capacitor to couple the input so the base is not absolutely driven by the voltage source.

    Bob
     
  5. newuser

    newuser

    9
    0
    Dec 16, 2012
    dont i need a dc voltage to bias the transistor and a ac volatge source for my input signal?
    EDIT: ive added another resistor for the base and changed the ac input sources node
     
    Last edited: Feb 20, 2013
  6. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    This is what a typical common emittter transistor amplifier looks like.
     
  7. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    Add a capacitor between the AC source and the base. Otherwise your DC biasing resistors will simply be overridden by the AC voltage.

    Bob
     
  8. newuser

    newuser

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    0
    Dec 16, 2012
    just realised that i didnt saved my changes from post #5, sry. now they are in.
     
  9. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Now that should work.
    Where's the problem there?
     
  10. newuser

    newuser

    9
    0
    Dec 16, 2012
    im expecting a sinus wave as output, but i only get +15v. have to work some more with the program itself.

    what BobK said: why would the AC voltage source override the DC biasing resistors?
    isnt the capacitor at the input to block DC voltage coming from the source for the input which might not be a perfect sinus wave power source?
     
  11. BobK

    BobK

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    Jan 5, 2010
    The two biasing resistors should be chosen such the the voltage on the collector is 1/2 the supply voltage. With the resistors you have chosen, I expect the transistor to be fully on and stay there, so the output should remain close to 0. The blocking capacitor is fine as you have it.

    Bob
     
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