Question

What is rectification? Explain the working of bridge rectifier. Draw the input and output signals.

Answer 1

Rectifier : The process in which alternating voltage or alternating current is converted into direct voltage or direct current is known as rectification. The device used for this process is called rectifier.
Working of a Bridge rectifier :
A bridge rectifier is shown in figure. There are four diodes $D_1,D_2,D_3$ and $D_4$ used in the circuit, which are connected to form a network. The input ends $A$ and $C$ of the network are connected to the secondary ends $S_1$ and $S_2$ of the transformer. The output ends $B$ and $D$ are connected to the load resistance $R_L$.
During positive input half cycle of the arc voltage, the point $A$ is positive with respect to $C$. The diodes $D_1$ and $D_3$ are forward biased and conduct, whereas the diodes $D_2$ and $D_4$ are reverse biased and do not conduct.
Hence, current flows along $S_{1}ABCD{S}_2$ through $RL$. During negative half cycle, the point $C$ is positive with respect to $A$. The diodes $D_2$ and $D_4$ are forward biased and conduct, whereas the diodes $D_1$ and $D_3$ are reverse biased and they do not conduct. Hence, current flows along $S_{2}CBAD{S}_1$ through $R_L$. The same process is repeated for subsequent half cycles. It can be seen that current flows through $R_L$ in the same direction, during both half cycles of the input a.c. signals. The output signal corresponding to the input signal is shown in figure. The efficiency of the bridge rectifier is approximately $81.2$%.
Advantages of bridge rectifier : (i) Centre tap on the secondary of the transformer is not necessary, (ii) Smaller transformer can be used and (iii) It is suited for high voltage applications.