We use sinusoidal a.c. voltage in our house. A.C sinusoidal voltage changes its polarity continuously. Many electronic appliances we use in d.c voltage in our house like audio, amplifier, radio, tape, recorder etc. To operate those D.C. electronic appliance we need D.C. voltage but we are using a.c. voltage. We can solve the problem using p-n junction diode which rectifies A.C. voltage to D.C. voltage.
Converting a.c. voltage to unidirectional D.C. voltage by which process is called rectification. By which circuit the rectification is made called rectifier or A.C to D.C rectifier.
Rectifier is classified into two types (i) Half-wave rectifier and (ii) Full-wave rectifier.
A simple circuit diagram is shown on figure as half-wave rectifier. A step up or step down transformer is used in the circuit depending on the requirement. Here a.c. voltage is applied to the terminal p1 and p2 of a transformer. This is called primary side of the transformer. And the other secondary side of the transformer s1 and s2 points are gained a.c. on attending voltage. S1 Point is connected with p-region of a p-n junction diode and s2 point is connected n-region of the diode through a load resistance R. The resistance R will give the D.C. output voltage in figure (a) and (b) input and output diagrams are shown of the diode.
One half a.c. cycle end s1 of the transformer secondary is positive with respect to the end s2. Here the diode is forward biased, so a strong current flows from p to n through the diode in the direction of the arrow as shown in figure. The next n-region and the diode gets reverse biased. So, no current flows through the load resistance R. Here, output voltage will be zero as shown in figure. The next positive half a.c. cycle the output voltage is obtained and the next negative one half cycle voltage will give no output and so on. Since one half of the a.c. input is utilized in this case to produce output current the rectification is called half-wave rectification and the device is called half-wave rectifier.
In full-wave rectifier two diodes are used with the transformer. (a) Shows the input and (b) shows the output in the figure. The anodes of the two diodes D1 and D2 are connected with the two ends of the secondary side of the transformer. For the half of the A.C input the terminal A positive and the terminal B is negative. Diode D1 becomes the forward biased and the current flows through the direction arrow. As diode D2 is reversed biased. So no current flows through it. Current flows from the load R2 with the direction from C to D. For the second half cycle D1 diode becomes reverse biased and D2 diode is forward biased. As D1 is reversed no current flows through it. For the diode D2 current flows with the direction C to D. Hence for both diodes D1 & D2 Current flows with same direction C to D. So, the output shows the complete cycle on full-wave. As the rectifier shows full cycles output, so the rectifier is full-wave rectifier.