The LC oscillating circuit refers to an oscillating circuit composed of a frequency-selective network composed of an inductor L and a capacitor C for generating a high-frequency sine wave signal. A common LC sine wave oscillating circuit has a transformer feedback LC oscillating circuit and an inductor three-point LC oscillating circuit. And capacitor three-point LC oscillator circuit. The radiated power of the LC oscillating circuit is proportional to the fourth power of the oscillating frequency. To allow the LC oscillating circuit to radiate sufficiently strong electromagnetic waves outward, the oscillating frequency must be increased and the circuit must be open.
The LC oscillating circuit uses the energy storage characteristics of the capacitor and the inductor to alternate the electromagnetic energy. That is to say, the energy and the magnetic energy have a maximum and minimum value, and there is oscillation. However, this is only an ideal situation. In fact, all electronic components will have losses. Energy is either lost during the mutual conversion between the capacitor and the inductor, or it leaks out of the outside, and the energy is continuously reduced. Therefore, the actual LC oscillation circuit is An amplifying component, either a triode or an integrated operational amplifier, is used. This amplifying component is used to cause the continuously consumed oscillating signal to be amplified by feedback through various signal feedback methods, thereby finally outputting an amplitude and frequency. More stable signal. The frequency calculation formula is f=1/[2π√(LC)],
Where f is the frequency in Hertz (Hz); L is the inductance in Henry (H); C is the capacitance in Farads (F).
The LC electromagnetic oscillation process involves a large amount of physical quantities, and the changes in physical quantities are also complicated. In the actual analysis process, if you notice the asynchronous change of the electric field quantity (electric field energy, voltage, electric field strength) and magnetic field quantity (magnetic field energy, current intensity, magnetic induction intensity), the electric field quantity and the magnetic field quantity each change synchronously, make full use of the electric field. The conservation of energy, energy and magnetic energy, and other physical changes by energy changes, can quickly understand the changes in physical quantities and determine the state of the circuit.
The LC oscillating circuit uses the energy storage characteristics of the capacitor and the inductor to alternate the electromagnetic energy. That is to say, the energy and the magnetic energy have a maximum and minimum value, and there is oscillation. Since all electronic components are depleted, energy is either lost during the conversion between the capacitor and the inductor. Therefore, the actual LC oscillator circuit requires an amplifying component, either a triode or an integrated operational amplifier. By using this amplifying element, the continuously consumed oscillating signal is amplified by feedback through various signal feedback methods, thereby finally outputting a signal whose amplitude is relatively stable with frequency.
The common-emitter transformer-coupled oscillator has high power gain and is easy to start. However, since the common-emitter current amplification factor B decreases sharply with the increase of the operating frequency, the common oscillation amplitude is easily affected by the oscillation frequency, so it is often used for fixing. Frequency oscillator.
LC oscillation circuit analysis methodThe LC electromagnetic oscillation process involves a large amount of physical quantities, and the changes in physical quantities are also complicated. In the actual analysis process, if the amount of electric field (electric field energy, charge amount, voltage, electric field strength) and the amount of magnetic field (magnetic field energy, current intensity, magnetic induction) are changed asynchronously, the synchronous changes of the electric field amount and the magnetic field amount are sufficient. By using energy conservation including electric field energy and magnetic field energy, and radiating other physical changes by energy changes, it is possible to quickly understand the changes in physical quantities and determine the state of the circuit.
1. The resistance of the whole circuit is R=0 (including coils and wires). From the energy point of view, there is no other form of inward energy conversion, that is, the heat loss is zero.
2. The inductor L concentrates the inductance of all the circuits, and the capacitor C concentrates the capacitance of all the circuits, and no submerged capacitor exists.
3. The LC oscillating circuit does not radiate electromagnetic waves to the external space when electromagnetic oscillation occurs. It is a closed circuit in a strict sense. Only the mutual conversion between the magnetic field energy of the coil and the electric field energy of the capacitor occurs inside the LC circuit, even if the change occurs in the capacitor. The electric field, the changing magnetic field generated in the coil, does not excite the corresponding magnetic field and electric field according to Maxwell's electromagnetic field theory, and radiates electromagnetic waves to the surrounding space.
A current that produces a change in magnitude and direction with a period is called an oscillating current. A circuit that generates an oscillating current is called an oscillating circuit The simplest oscillating circuit is called the LC loop.
The oscillating current is an alternating current, which is a high-frequency alternating current. It cannot be generated by the rotation of a coil in a magnetic field, but can only be generated by an oscillating circuit.
Charging is completed (charging starts): the electric field energy reaches the maximum, the magnetic field energy is zero, and the induced current i=0 in the loop.
The discharge is completed (discharge start): the electric field energy is zero, the magnetic field can reach the maximum, and the induced current in the loop reaches the maximum.
Charging process: The electric field energy is increasing, the magnetic field energy is decreasing, the current in the loop is decreasing, and the electric quantity on the capacitor is increasing. From the perspective of energy: the magnetic field can be converted into electric field energy.
Discharge process: The electric field energy is decreasing, the magnetic field energy is increasing, the current in the loop is increasing, and the amount of electricity on the capacitor is decreasing. From the perspective of energy: the electric field can be converted into a magnetic field.
In the process of generating an oscillating current in the oscillating circuit, the electric charge on the plate of the capacitor, the current passing through the coil, and the magnetic field and electric field associated with the current and the electric charge are periodically changed. This phenomenon is called electromagnetic oscillation.
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