Rectifiers

Rectifiers

Key Point : A rectifier is a device which converts a.c. voltage to pulsating d.c. voltage, using one or more p-n junction diodes.

• The p-n junction diode conducts only in one direction. It conducts when forward biased while practically it does not conduct when reverse biased. Thus if an alternating voltage is applied across a p-n junction diode, during positive half cycle the diode will be forward biased and will conduct successfully. While during the negative half cycle it will be reversed biased and will not conduct at all. Thus the conduction occurs only during positive half cycle. If the resistance is connected in series with the diode, the output voltage across the resistance will be unidirectional i.e. d.c. Thus p-n junction diode subjected to an a.c. voltage acts as a rectifier converting alternating voltage to a pulsating d.c. voltage.

1. The Important Characteristics of a Rectifier Circuit

• The important points to be studied while analysing the various rectifier circuits are,

a) Waveform of the load current : As rectifier converts a.c. to pulsating d.c., it is important to analyze the nature of the current through load which ultimately determines the waveform of the load voltage.

b) Regulation of the output voltage : As the load current changes, load voltage changes. Practically load voltage should remain constant. So concept of regulation is to study the effect of change in load current on the load voltage.

c) Rectifier efficiency : It signifies, how efficiently the rectifier circuit converts a.c. power into d.c. power.

d) Peak value of current in the rectifier circuit : The peak value is the maximum value of an alternating current in the rectifier circuit. This decides the rating of the rectifier circuit element which is diode.

e) Peak value of voltage across the rectifier element in the reverse direction (PIV) : When the diode is not conducting, the reverse voltage gets applied across the diode. The peak value of such voltage decides the peak inverse voltage i.e. PIV rating of a diode.

f) Ripple factor : The output of the rectifier is of pulsating d.c. type. The amount of a.c. content in the output can be mathematically expressed by a factor called ripple factor. Less is the ripple factor, better is the performance of the circuit.

• Using one or more diodes, following rectifier circuits can be designed.

1. Half wave rectifier

2. Full wave rectifier

3.Bridge rectifier.

Review Questions

1. What is rectifier ?

2. Which are the important characteristics of a rectifier circuit ?