Question

Explain the use of P-N junction diode as full wave rectifier on the basis of the following points.
(i) Labelled circuit diagram
(ii) Working method
(iii) Graph between input and output potential with the variation of time.

Answer 1

(i) The figure shows the full wave rectifier. In this figure $D_1$ and $D_2$ are the two P-N junction diodes the input alternating voltage is applied across the terminals of primary coil $L_1$ of the transformer (step up) T and ends A and B of it's secondary coil $L_2$ are connected with the P terminals of both the diodes $D_1$ and $D_2$. The N terminals of both the diodes are connected by them A Load resistance $R_L$ is connected between the midpoint (E) of the secondary coil $L_2$ of the transformers and the N-terminal to obtain output D coil across it.
(ii) Working: When alternating voltage is applied on primary coil of step up transformer. Then alternating voltage is induced in the secondary coil.
During the positive half cycle of the input alternating voltage end A is a positive and B is at negative potential with respect to E. Therefore the diode $D_1$ is forward biased and diode $D_2$ is reversed biased, so $D_1$ is in conducting state and $D_2$ is in non conducting state and the current flows in the load resistance $R_L$ from C to D.
Now during the negative half cycle of the input signal, end A is at negative and end B is at positive potential. Thus the potential of A becomes negative with respect to the potential E and B, therefore the diode $D_2$ is powered biased and $D_1$ is reversed biased. So the diode $D_2$ is in conducting state and $D_1$ is in non conducting state. As a result the current again flows from C and D. Through the load resistance $R_L$.
In this way in both the half cycles the current flows through the load resistant and diode behaves as full wave rectifier.