What is Rectifier?

 
Rectifier
Rectifier


A Rectifier is a device which converts an oscillating two directional alternating current (AC) into a single directional direct current (DC).

Why rectifier is needed?

 
Need of Rectifier
Need of Rectifier


Most of the electronic appliances which we use in our daily lives and also in the industries use direct current (DC), but the power supply available is alternating current(AC). 

So some device is needed to convert alternating current(AC) to direct current(DC). Diode with junction P type and N type is used for rectification, since it allows current to flow in only forward bias and blocks current in reverse bias.

Function of the rectifier:

 
Function of the Rectifier
Function of the Rectifier


The biasing is in the form of alternating current (AC). This AC current is in the form of sinusoidal wave, it is not constant but it varies with time. 

The upper part of the wave is the positive side and it is the current during forward bias. The lower part of the sinusoidal wave is the negative side and it is the current due to reverse bias.

The current during forward bias, that is the positive side of the wave is alone allowed to pass through the rectifier. The output of the rectifier is not pure DC current, but it contains some ripples. These ripples can be removed by connecting filter to the rectifier.

Working of the Rectifier:


 
To know the working of the rectifier we should understand the working of the PN junction diode.

Forward bias of PN Junction diode
Forward bias of PN Junction diode


When the PN junction diode is forward biased, the P type is connected to the positive terminal and the N type is connected to the negative terminal. So the holes which is the majority carrier in the P type get repelled by the positive charged voltage at the P side and it moves towards the N type. 

In the same way the electrons which is the majority carrier in the N type moves towards the P type. The movement of the majority charge carriers forms the current. Thus during the forward bias current is allowed to flow.
 
Reverse bias of PN Junction diode
Reverse bias of PN Junction diode


When the PN Junction diode is reverse biased the P type is connected to the negative terminal and the N type is connected to the positive terminal. 

The holes which is the majority carrier in the P type gets attracted to the negative terminal and the electrons gets attracted to the positive terminal. So the depletion layer increases and the current does not flow.
 
Thus the PN Junction allows the current only during the positive cycle of the alternating current (AC).