Rectifiers: Circuit Diagram and Working

What is Rectifier?


A Rectifier is an electronic circuit or device that offers a low resistance path (ideally zero resistance path) to current in one direction and high resistance path (ideally infinite resistance path) in opposite direction.


This property allows the rectifier to convert a bidirectional waveform, such as sinusoidal waveform (AC signal), whose average value is zero, into a unidirectional waveform, which has non-zero average value and a constantly changing magnitude.


Rectifier

The constantly changing magnitude of the output waveform of the rectifier indicates the presence of the AC component and the non zero average value of this waveform indicates the presence of the DC component. Therefore, this waveform is referred to as a pulsating DC waveform and can be further filtered out as a pure DC signal with the help of different kinds of filters and freewheeling diode.


Thus, a rectifier is most commonly known as an AC to DC converter.



Importance of Rectifier

Rectifiers are the fundamental circuits in electronics because most of the electronics circuit or device operates on DC power, while the universal supply of electricity is AC in nature, as it is less expensive and safer. Therefore, the conversion of AC to DC is the fundamental need of those electronic devices. Although, there are various DC power sources available but these sources are limited and not economical. 



What is Rectification?


The process of conversion of a bidirectional waveform into a unidirectional waveform is known as rectification or in simple words we can say that the process of conversion of AC waveform into DC signal is known as rectification.


There are two types of rectification i.e. half wave rectification and full wave rectification

 

Half wave rectification means the conversion of half of the AC waveform into DC signal and the rectifier that offers half wave rectification is called half wave rectifier.

 

Full wave rectification means the conversion of the full waveform of AC signal into DC signal and the rectifier that offers full wave rectification is called full wave rectifier.

 



Rectifier's Circuit Diagram


In rectifier circuits, we use semiconductor switches that allow the conduction of current in one direction only such as Diodes, SCRs, MOSFETs etc. As mentioned earlier, a rectifier itself allows the conduction of current in one direction only. These semiconductor switches are connected in different circuit configurations for half wave rectification as well as full wave rectification.


Let us explore the circuit configurations for both half wave rectifiers and full wave rectifiers separately.


Rectifier circuits can be either single phase or three phase, depending on the nature of supply. Since the universal supply is either single phase or three phase AC. 


Further in this article, we will discuss the concept of rectifiers by using single phase rectifiers because it is easier to understand. 



Half Wave Rectifier Circuit


Half wave rectifier circuit employs only one semiconductor switch to convert half of the AC waveform into DC signal. The circuit diagram for the half wave rectifier is shown in the given figure.

Rectifier Circuit Diagram




Full wave Rectifier Circuit


For full wave rectification, we use two types of circuit configuration i.e. Centre tapped rectifier circuit and bridge rectifier circuit


Centre Tapped Rectifier Circuit


A center tapped rectifier uses two semiconductor switches and a center tapped transformer, connected as shown in the given figure.

Rectifier Circuit Diagram



Bridge Rectifier Circuit


A bridge rectifier circuit configuration uses four switches connected in a bridge-like arrangement. The circuit diagram of the bridge rectifier is shown in the given figure.

Rectifier Circuit Diagram



Note :- The above classifications of rectifiers are based on the rectification and circuit configuration. Additionally, rectifiers are further classified as controlled rectifiers, un-controlled rectifiers and semi-controlled rectifiers on the basis of controlling the output or the switch used.

 


We have created a dedicated article on the types of rectifiers. You can check it out for detailed information on Rectifiers and their types.


 


Working of Rectifier


The working of the Rectifier depends on the biasing of the switch used in its circuit. 


As we discussed above, a rectifier circuit uses semiconductor switches that have unidirectional current conduction property such as diodes, SCRs, MOSFETs, etc. So according to the biasing of these switches, we ensure the direction of current flow in the rectifier circuit. This allows us to effectively convert the bidirectional waveform such as AC signal into a unidirectional waveform such as pulsating DC signal.

 

Let us understand the above discussed working of rectifiers in detail for both half wave rectification as well as full wave rectification separately.

 


To make it easy to understand, we'll use rectifier circuits with diodes only.


Half Wave Rectification


As we discussed above, for half wave rectification a rectifier circuit employs only one semiconductor switch (diode). In this circuit the diode is connected in such a way that it only conducts for the desired half of the AC supply. 

 

Typically, it is desired that only the positive half of the AC supply is converted into DC signal. So, we will focus on the working of half wave rectifiers for converting the positive half of AC supply into DC signal. 

 

However, you can also convert the negative half of AC supply as well. To convert the negative half of the AC supply, you can simply reverse the orientation of the switch used in this circuit.

 

The figure given below shows the rectifier circuit using a diode for half wave rectification.  

Working of Rectifier

In this circuit : 

  • During the positive half-cycle of the AC input, the diode D is forward-biased and conducts current, allowing the positive half of the AC waveform to pass through the load

  • During the negative half-cycle, the diode D is reverse-biased and does not conduct current, blocking the negative half of the AC waveform.

This results in a pulsating DC output that consists only of the positive half-cycles of the input AC signal.

The working and the output waveform for the half wave rectifier can be visualized with help of the given figure.




Full Wave Rectification


As we mentioned earlier, for full wave rectification, there are two types of rectifier circuit configurations used that are center-tapped circuit and bridge rectifier circuit

 

Let us understand the working of both circuits of full wave rectifiers separately.

 


Center Tapped Full Wave Rectifier Working


The circuit diagram for center-tapped full wave rectifier using diodes is shown in the given figure.

Working of Rectifier

In this circuit: 

  • During the positive half-cycle of the AC input supply, the terminal A is positive with respect to B, therefore the Diode D1 is forward biased and it allows the conduction of current and D2 is reverse biased and it does not allow the conduction of current. In this condition the current flows through the diode D1, the load and the center taping of the transformer and the output voltage across the load is the same as the input waveform.


  • During the negative half-cycle of the AC input supply, the terminal A is negative with respect to B, therefore the Diode D2 is forward biased and it allows the conduction of current and D1 is reverse biased and it does not allow the conduction of current. In this condition the current flows through the diode D2, the load and the center taping of the transformer and the output voltage across the load is the negative of the input waveform.

 

The working and the output waveform for the center tap full wave rectifier can be visualized with help of the given figure.





Bridge Rectifier Working


The circuit diagram for bridge rectifier using diodes is shown in the given figure.

Working of Rectifier

In this circuit the two diagonally opposite diodes conduct for each half cycle of AC input supply.


  • For the positive half cycle of the AC input supply, diodes D1 and D3 are forward biased, therefore these diodes conduct the current, and the diodes D2 and D4 are reverse biased, therefore these diodes will not conduct the current. During this condition the voltage across the load is the same as that of the input supply.


  • For the negative half cycle of the AC input supply, diodes D2 and D4 are forward biased, therefore these diodes conduct the current, and the diodes D1 and D3 are reverse biased, therefore these diodes will not conduct the current. During this condition the voltage across the load is the negative of the input supply.

The working and the output waveform for the bridge rectifier can be visualized with help of the given figure.


The working of the rectifiers typically involves converting the AC waveform into DC signal. But what happens when we put DC supply through a rectifier? This question was asked several times on different online platforms on the internet and deserves some attention, so we have taken this question into consideration. 

 



Working of Rectifier on DC Supply


Let us understand what happens when DC supply is given to different rectifiers separately.

 

Working of Half Wave Rectifier on DC Supply


Consider the half wave rectifier circuit discussed previously.

Working of Rectifier


In this circuit if we apply the DC voltage, then the diode either conducts continuously or blocks the conduction of current continuously until the supply is given. The conduction and blocking of current depend on the polarity of supply and the orientation of the diode used.


You can visualize this phenomenon by the help of the given figure.


Working of Rectifier



Working of Full Wave Rectifier on DC Supply

 

Working of Center Tapped Rectifier on DC Supply


Consider the same center tapped rectifier circuit using diode that was discussed previously.

Working of Rectifier on DC Supply

If we apply DC to this circuit, the transformer used in this circuit for center tapping will not function correctly. In this conduction, the rated current will flow through the primary winding of the transformer, causing the winding of the transformer to burn out and the saturation of the transformer core. 

 


Working of Bridge Rectifier on DC Supply

Consider the same bridge rectifier circuit that was discussed previously.


Working of Rectifier on DC Supply


In this circuit if we apply the DC voltage of positive polarity (polarity that is shown in the given figure) then the diodes D1 and D3 become forward biased and they will conduct the current continuously to the load until the supply is given. The polarity of the voltage across the load terminals is equal to the supply voltage.


Working of Rectifier on DC Supply

And if the DC supply of negative polarity is applied, then the diodes D2 and D4 become forward biased and they will conduct the current continuously to the load until the supply is given and the polarity of voltage across the load terminals is reversed.


Working of Rectifier on DC Supply
If we reverse the orientation of the switches used in this circuit then the flow of the current and the polarity of the output voltage changes vice versa.

 



Output waveform of rectifier


In the above discussion of the working of the rectifier, we see that the output waveform for half wave rectifier and full wave rectifier is shown as the given figure.


Output Waveform of Rectifier
Half Wave Rectifier Output Waveform


Output Waveform of Rectifier
Full Wave Rectifier Output Waveform


If we observe the output waveform of the both types of rectifiers, we will find that these are not the pure DC waveform. They are unidirectional waveforms that constantly change their magnitude. 

 

As we discussed previously in the definition of rectifier, these waveforms contain both DC and AC components of voltage, and therefore referred to as pulsating DC. 






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