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How would i get this circuit to oscillate correctly?

How would i get the tank circuit in this schematic to oscillate correctly, and to provide a high frequency sine wave to the load, as shown in the circuit...I know the cap and inductor values are incorrect, but would these be feasible? What the idea behind it is that when the cap and inductor circuit starts to slow down, the transistor pumps in a little more juice into it, making it fully oscillate. I don't know if i have the circuit even set up right, any advice or pointers to my idea would be greatly appreciated. thank you. :D http://s497.photobucket.com/albums/rr335/jaredmist...

4 Answers

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  • 1 decade ago
    Favorite Answer

    That circuit is not an oscillator. Find the circuit for a real oscillator.

    This is just a common emitter circuit with a tuned circuit in the base. But there it nothing to make it oscillate, which requires a circuit with a gain of +1 at some frequency.

    .

  • Bob D1
    Lv 7
    1 decade ago

    The circuit very likely will not oscillate in its current configuration unless there are enough stray capacitance between base/collector junction to sustain appropriate feedback.

    With a 1 uf cap and a 10 mh coil, natural operating frequency is about 1.6 KHz.

    Fr = 1 / (6.28 x sqr(L x C))

    What you have to have in order to make the circuit oscillate is a circuit gain of at least 1 at the desired operating frequency. Then you also need a feedback path from the collector back to the base LC tuned circuit that will shift collector signal by 180 degrees (invert the signal) and feed that inverted voltage back to the tuned circuit in the base. The transistor should be biased beyond cutoff (class C) operation.

    The two standard transistor oscillator circuits configurations that comes the closest to your design is the Colpitts LC Oscillator and the Clapp Oscillator.

    ----------------------------

    See: Electronic Tutorials

    http://www.electronics-tutorials.ws/oscillator/col...

    Circuit Simulator: Colpitts Oscillator

    http://www.indiabix.com/electronics-circuits/colpi...

    Good luck

    Source(s): self
  • 1 decade ago

    I am not disagreeing with the other answer. I will just add that you must have a controlled amount of positive (in phase) feed back at the desired frequency to maintain stable oscillations. Almost any high gain amplifier will amplify the random noise frequencies that are always present on it`s input enough to start oscillations.. The trick is to feed back from the amplifier`s output a portion of only the desired frequency while avoiding feeding back all other frequencies. Of course the desired frequency ac Voltage fed back must be in phase with the input other wise it will retard oscillations rather than sustaining them. You will need to review the theory of operation on proven oscillator circuits and then decide which one you want to use as a guide to building your own.

    Your circuit as is has zero feed back not even negative (out of phase) feed back.

  • 5 years ago

    Yes; the same formula applies as two parallel resistors. In either case (circuit with two parallel resistors or two parallel reactors) the values can be written in terms of impedance, Z. For example: if you have an inductor with reactance (jXL) of 10 ohm, in parallel to a capacitor of reactance (jXC) of 5 ohm, the equation would be: Z(equivalent) = (0 + j10) * (0 -j5) / [(0 + j10) + (0 -j5)] Z = 50 / (0 + j5) Z = (0 -10)

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