Question

Name two important processes involved in the formation of a p-n junction diode. With the help of a circuit diagram, explain the working of junction diode as a full wave rectifier. Draw its input and output waveforms. State the characteristic property of a junction diode that makes it suitable for rectification.

Answer 1

p-n junction formation

p-n junction is formed either when a p-type semiconductor is grown in n-type or n-type is grown in p-type semiconductor.

The p-n junction is formed due to diffusion of charge carriers.

The two main process in p-n junction formation are

(1) Diffusion of charge carriers

(2) Drifting of charge Carriers

Full wave Rectifier:

As diode has unique property that it allow the current in one direction and offer large (ideally infinite) resistance in other direction. This property makes suitable to use diode in a rectifier circuit.

The schematic diagram of a full wave centre tap rectifier is shown in the figure (a).

(a)

 

(b)

(C)

Consider the input voltage to A with respect to the centre tap at any instant is positive then at that instant, voltage at B will be negative and vice-versa.

During the positive half-cycle of the input voltage sine wave, the diode D₁ is forward-biased and diode D₂ is reverse-biased, and the current flows in the direction shown in the figure. During the negative half-cycle, the diode D₂ is forward-biased and diode D₁ is reverse-biased. Hence, during this time also, a current flows through R_L in the same direction as in the previous half-cycle. Thus, the current flows (in the same direction) through R_L during the positive as well as the negative half-cycles of the input ac voltage. Hence, the dc voltage shape across R, is as shown in figure (c). This process is known as full-wave rectification.