PSPICE help needed: plotting load voltage of a Class-B amp

Discussion in 'Homework Help' started by random_digit, Apr 21, 2007.

  1. random_digit

    Thread Starter New Member

    Apr 21, 2007
    8
    0
    Hello,

    I'm having trouble getting the right output graph for the following circuit (class-b amplifier w/ darlington pair).

    The correct output is supposed to be a nice sin wave with some distortion (the problems objective is to show it to you visually)... but I'm not getting the right plot. I've attached my results also.

    I'm not sure where my slip-up is :confused: -- I've checked everything so I'm assuming that it's something very minor and involves PSPICE (I'm still getting accustomed to it).

    Can anybody help me out? I'd REALLY appreciate it. Thank you for your time.

    --
    Best Regards,
    Arthur
     
  2. antseezee

    Active Member

    Sep 16, 2006
    45
    0
    I got the following error when I put the circuit in exactly as shown:

    Expecting keyword STIMULUS, saw V.|

    STIMULUS has to do with the configuation files so...crap.
     
  3. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    656
    You need a base bias resistor from the bases of Q1 and Q3 to GND.
     
  4. Distort10n

    Active Member

    Dec 25, 2006
    429
    1
    The dreaded input bias return path.
     
  5. antseezee

    Active Member

    Sep 16, 2006
    45
    0
    The bias resistor fixed it. Neat, although, the value of my bias resistor seems to have tuned some loss to the circuit.
     
  6. random_digit

    Thread Starter New Member

    Apr 21, 2007
    8
    0
    So it's not supposed to be a sin wave?

    I'm still getting a transient looking wave, like a capacitor type output, and not a sin wave which I thought was the correct output.

    Thanks for your replies!
     
  7. antseezee

    Active Member

    Sep 16, 2006
    45
    0
    Check your print step rate. I didn't really zoom in on the output. It "kind of" looked sinusoidal. But it wasn't a smooth wave by any means.
     
  8. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,157
    You are suppose to see a crossover distortion during each half cycle. The answer to why this occurs and how to solve that problem will appear on later tests.
     
  9. random_digit

    Thread Starter New Member

    Apr 21, 2007
    8
    0
    Okay! Thanks I got it to work... I just overlooked zooming it out >_>

    But thank you everybody
     
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