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Wien-Bridge Oscillator using BJT's

Discussion in 'The Projects Forum' started by fmadero, May 4, 2010.

  1. fmadero

    Thread Starter New Member

    May 4, 2010
    I can't get the attached circuit schematic in OrCAD to oscillate, I have had a gain of >= 3 and no oscillations occur.
  2. JDT

    Well-Known Member

    Feb 12, 2009
    For starters, I'm slightly worried about some of your component values. Is the emitter resistor of Q2 really 7 ohms? in that case you have got 0.58A flowing through this transistor! A real 2N2222 would be getting rather hot (2.6W)!

    A real wien-bridge oscillator requires some white noise in the system to get it going. This noise is amplified, filtered and fed back. The feed-back increases until the oscillation is established*. Don't know if Orcad can simulate this.

    * In fact the oscillation amplitude increases forever until something limits the increase. Usually clipping or some other non-linearity. A real wien-bridge oscillator has an automatic gain controlling device - often a thermistor.

    Find a circuit diagram (google) and build the real thing.