Transistor as an Oscillator : By using transistor as an oscillator we can convert d.c. into a.c. of desired frequency. It consists of Tank circuit which consists of an inductor ‘L’ and capacitor ‘C’ in parallel with each other producing the LC oscillations of charge with frequency v = 1/2π√LC
By changing the value of L,C or both oscillations of any frequency can be obtained. Transistor Amplifier: The oscillations occurring in LC circuit are applied to input of transistor amplifier. Due to amplifying action of transistor, we get amplified output of these oscillations. A suitable fraction of the output of transistor is fed to LC circuit to meet the losses in LC circuit.
Feedback circuit: It is a circuit which receives the output of transistor amplifier and supplies correct amount of energy to LC circuit. When the key K is closed, the collector current IC in the circuit starts increasing. The changing current through inductance L1 induces an emf across the inductor L, which further increases the base current IB and hence the emitter current IE .The upper plate of capacitor gets positively charged.
As the current through inductor L1 becomes steady, the mutual induction stops and induced emf across inductor L becomes zero and capacitor starts getting discharged through inductor L, thereby decreasing the base current IB and hence emitter current IE and collector current IC till IC becomes zero. Again the collector, base and emitter currents starts increasing and after attaining a maximum value starts decreasing. In this way collector current oscillates between maximum and zero values. In the oscillator, energy is supplied by the battery B2 to the LC circuit at proper time and in proper phase, therefore the battery B2 gets consumed in the oscillator. This means that in oscillator d.c. is converted into a.c
