Why circuits oscillate

Click to expand You should confirm the following: 1 It is an amplifier or an OP amplifier. You can make the bandwith and gain of amplifier a vety large value. The best is to post the circuit. I have attached the circuit. The transistor in the shown circuit won't oscillate for the simple reason, that it misses a DC bias.

In this case, you don't need to think further about fulfillling the oscillation condition. The other point is that a transistor isn't an ideal inverting amplifier. It has additional parameters, e. Thus I won't exclude, that the circuit can possibly oscillate after adding a bias network. But if so, it's not due the RLC feedback allone. BradtheRad Super Moderator Staff member. The bias level needs to be adjustable, hence a potentiometer is handy for this purpose. It is distinguished by having a coil and cap in series.

Operational circuits have a few more components added. You may be able to get your setup to work, if you can fulfil all the conditions. Don't be surprised if it requires some reconfiguring. See if you can jolt it into operation somehow. There may be a few oscillations afterward, even if they decay quickly.

I recognize you are using Falstad's simulator. For the circuit, , the total electromagnetic energy U is.

For the mass-spring system, , the total mechanical energy E is. The equivalence of the two systems is clear. Now x t is given by. Finally, the current in the LC circuit is found by taking the time derivative of q t :. The time variations of q and I are shown in Figure e for. At all of the energy is stored in the capacitor, which has charge C. Strategy The angular frequency of the LC circuit is given by Figure. To find the maximum current, the maximum energy in the capacitor is set equal to the maximum energy in the inductor.

The time for the capacitor to become discharged if it is initially charged is a quarter of the period of the cycle, so if we calculate the period of the oscillation, we can find out what a quarter of that is to find this time. Lastly, knowing the initial charge and angular frequency, we can set up a cosine equation to find q t.

This result can also be found by an analogy to simple harmonic motion, where current and charge are the velocity and position of an oscillator. Since the time taken for the capacitor to become fully discharged is The capacitor is completely charged at so Using Figure , we obtain Thus, and. Significance The energy relationship set up in part b is not the only way we can equate energies. At most times, some energy is stored in the capacitor and some energy is stored in the inductor.

We can put both terms on each side of the equation. By examining the circuit only when there is no charge on the capacitor or no current in the inductor, we simplify the energy equation. What is the value of c A second identical capacitor is connected in parallel with the original capacitor. To keep it going, you have to add a little bit of energy on each cycle.

In a pendulum clock, the energy that keeps the pendulum moving comes from the spring. The pendulum gets a little push on each stroke to make up for the energy it loses to friction. See How Pendulum Clocks Work for details. Energy needs to move back and forth from one form to another for an oscillator to work. You can make a very simple oscillator by connecting a capacitor and an inductor together. A capacitor stores energy in the form of an electrostatic field, while an inductor uses a magnetic field.

If you charge up the capacitor with a battery and then insert the inductor into the circuit, here's what will happen:. It will oscillate at a frequency that depends on the size of the inductor and the capacitor. It is connected to an antenna and ground like this:. Thousands of sine waves from different radio stations hit the antenna.

The capacitor and inductor want to resonate at one particular frequency. The sine wave that matches that particular frequency will get amplified by the resonator, and all of the other frequencies will be ignored. It doesn't matter that the signal might be attenuated by 20dB, there will still be enough signal left to be amplified and generate a sinewave. Sign up to join this community. The best answers are voted up and rise to the top.

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