Undamped Oscillations from Tank Circuit
As discussed before, a tank circuit produces damped oscillations. However, in practice, we need continuous undamped oscillations for the successful operation of electronics equipment.
In order to make the oscillations in the tank circuit undamped,
it is necessary to supply correct amount of energy to the tank circuit at the proper time intervals to meet the losses.
Thus referring back to Fig-1, any energy which would be apply to the circuit must have a polarity conforming to the existing polarity at the instant of application of energy.
If the applied energy is of opposite polarity,
it would oppose the energy in the tank circuit, causing stoppage of oscillations.
Therefore, in order to make the oscillations in the tank circuit undamped, the following conditions must be fulfill :
(i) The amount of energy supplied should be such so as to meet the losses in the tank circuit and the a.c. energy removed from the circuit by the load.
For instance, if losses in LC circuit amount to 5 mW and a.c. output being take is 100 mW, then power of 105 mW should be continuously supply to the circuit.
(ii) The applied energy should have the same frequency as that of the oscillations in the tank circuit.
(iii) The apply energy should be in phase with the oscillations set up in the tank circuit i.e.
It should aid the tank circuit oscillations.
If these conditions are fulfill, the circuit will produce continuous undamped output as shown in Fig-1.
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