In electronic circuits, make full use of the switching role of transistors, use the inductive energy storage and the capacitor charge and discharge principle, the stored electrical energy into the inductive magnetic energy, and then turn the magnetic energy into electrical energy.
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The transistor replaces the switch in the circuit to supplement the energy, and the time to supplement the energy is determined by the feedback part of the LC oscillation itself, so that it can be rhythmically supplemented to obtain the resonance.
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The generation of LC oscillation must have the following three conditions in the final analysis;
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(1) There is an LC oscillation loop, which is the main internal cause of oscillation and determines the frequency of the resonance.
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(2) Energy supplement with positive feedback control, and the positive feedback should be large enough to ensure that the added energy is not less than the energy consumed in the first oscillation.
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(3) The use of nonlinear component transistor as a switch, when the oscillation is strong, the feedback is weak, and the automatic adjustment amplitude is small. On the contrary, when the oscillation is weak, the positive feedback generated by the transistor is stronger, and the amplitude is automatically adjusted to be larger, so that the constant amplitude oscillation can be maintained.
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The basic circuits of commonly used LC oscillators are transformer coupled LC oscillator, inductor three-point LC oscillator, capacitor three-point LC oscillator.
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If the need is not high-frequency oscillation, but low-frequency oscillation, or even ultra-low frequency oscillation, this time the LC oscillator is not suitable. This is because, when the frequency is very low, it is necessary to have the inductance of LC and the capacity of the capacitor is very large, for example, to produce a low frequency of 16Hz, according to the calculation formula of f=1\/2π√LC, this time the inductance will be 1H, and the capacitance will be 100uf. If the oscillation period is greater than one second, the volume of the inductance capacitor is considerable. Therefore, RC oscillators should be used at low frequencies.