Monday, November 24, 2014

Transistor as Feedback Oscillator

Generally a transistor can act like an amplifier and when you give a consistent input, it will amplify and give a consistent output. But here we are looking for a kind of amplifier which can give a consistent output without even giving a continuous input. This kind of the feet can be achieved by taking a portion of the output and connecting it back to the input transistor.This kind of the circuit is called feedback circuit. The very purpose of the feedback circuit is to pass the portion of the output that is taken back to the input without any serious loso at the output level.This can be achieved by the concept of the mutual inductance as well as the LCR circuit network of alternate currents.

The LCR circuit is being designed in such a way that, for a certain frequency of the alternate current their opposition to the flow of the current which is being called as an impedance is minimum and hence they are able to pass the best possible current to the circuit back and it is the most effective way of working. 

Therefore there is no loss of the output that has to be pass it to the input and the consistent output is automatically amplified with the consistent supply of the feedback circuit.

The LCR circuit consists of a inductor, capacitor and resister. Though they are connected in series the flow of the current is going to have different phases when alternate current is passing through them. We know that alternate current will go in phase both in terms of voltage and current when it is passing through a resister. In the case of a resister current and voltage go hand-in-hand such that between them there is no phase difference in an alternate current is passing through it.

When the alternate current is passing through a inductor voltage leads by 90° when compared with the current. When alternate current is passing through a capacitor voltage lacks by 90°. Hence it referred as inductor and capacitor are having a phase difference of 180°. The opposition to the flow of the current by the inductor is called inductive reactance and by the capacitor is called capacity reactance. They are having a phase difference of 180° between them. The resultant of this is perpendicular to resistance and the total opposition of all these things together is called impedance. The impedance of the circuit will be minimum when capacity reactance is equal to the inductive reactance,so that both of them cancels each other and the impedance is equal to the resistance of the resister itself.

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