What is Rectifier? How do Rectifiers work?
A complete Guide on all types of Rectifiers.
All of us are familiar with the name Rectifier but beginners and new students are so curious to know what do Rectifiers do?
When they know about rectifiers then many new questions come in mind and got curious to know all about it. So here is a complete guide on all types of Rectifiers.
Here we are going to study some important topics about Rectifiers which all beginners must know. So here are some points which we will discuss in this article.
- What do Rectifiers do?
- How do Rectifiers work?
- What are the types of Rectifiers?
- How to find out the DC output voltage of any rectifier?
- Comparison of all the types.
- What type is preferable?
Before starting the study about rectifiers, you must know basics, therefore, read about what is DC Regulated Power Supply?. Block diagram of DC Regulated Power Supply and functions of each part used in it.
Let us discuss here all types of Rectifiers construction, circuit diagram, working details.
What do Rectifier do?
The process of converting Bi-directional AC voltage into the Unidirectional DC voltage is called as Rectification.
An electronic circuit consists of a crystal diode/ PN junction Diode which converts Bidirectional AC voltage into DC voltage is called as a Rectifier circuit. The rectifier eliminates the use of the battery, therefore, it is also called a “Battery Eliminator”.
Generally, three circuits are used for the Rectification so following are the three types of rectifiers.
- Half-wave Rectifier.
- Center tap Full-wave Rectifier.
- Bridge Full-wave Rectifier.
The Half wave rectifier is a simple and low cost rectifier circuit. It is used when high quality DC is not required. Following circuit diagram shows the half wave rectifier.
It consists of a diode connected in series with the load resistor RL and the output voltage is taken across the load resistor RL.
During the positive half cycle of AC the secondary terminal of transformer A is positive with respect to the terminal B the diode becomes in forward bias condition and the diode is conducting. The current flowing from terminal A through diode D and RL to terminal B as shown in circuit diagram. Thus output voltage is developed across RL similar to the positive half cycle of AC.
During the negative half cycle of AC the secondary terminal of transformer A is negative with respect to the terminal B the diode becomes in reverse bias condition and the diode is non conducting. So the current flowing is not possible from terminal A to B. Thus the diode will conduct only for positive half cycle of AC so called as half wave rectifier
Average DC voltage Vdc = Vp/π
The PIV rating of diode is Vp = Vp
Ripple Frequency Fo = Fin
Efficiency of HWR =40.8%
Ripple factor: –
It is an Important factor which decides the quality of the rectifier.
The ratio of RMS value of AC component to the DC component in the rectifier output is known as a ripple factor.
Ripple factor = RMS value of AC component / DC component = 1.21
% Ripple = Ripple factor × 100 %
Advantages and Disadvantages of Half wave Rectifier
1. The half wave rectifier is simple and low cost circuit.
2. It requires normal transformer and only one diode.
1. It converts only positive half cycle of input AC wave therefore less output voltage obtained.
2. It cannot use negative half cycle therefore its efficiency is 40.6% only.
3. As its ripple frequency is less therefore it produces poor quality of DC.
Center tap Full wave Rectifier
To utilize to the negative half cycle of Ac supply to Diodes are connected with a special type of Transformer called as centre tap Transformer. In this transformer middle terminal is tapped so that the upper terminal A and lower terminal B becomes opposite in phase.
The centre tap full wave rectifier consist of a centre tap transformer and two diodes D1 & D2 connected with centre tap transformer as shown in circuit diagram and the output is taken across the load resistance RL. The Diode D1 utilizes the ac voltage across the upper half CA of the secondary winding while Diode D2 uses lower half CB of the secondary winding.
In the center tap full wave rectifier the diodes are conducting in alternate cycle so that current through the load resistance RL flows in the same direction for both half cycle.
During the positive half cycle of AC supply terminal A becomes positive and terminal B becomes negative with respect to common terminal C. The Diode D1 becomes forward biased and Diode D2 becomes reverse biased. Hence only Diode D1 conducts and acts as a closed switch. So the current flows from terminal A – D1 and through load resistance RL towards the center tap terminal C. As the current flows through the load resistance RL output voltage is developed across RL.
During the negative half cycle of Ac supply the polarity of terminal A & B get changed. The terminal B becomes positive and terminal A becomes negative with respect to common terminal C. The Diode D2 becomes forward biased and Diode D1 becomes reverse biased. Hence only Diode D2 conducts and acts as a closed switch. So the current flows from terminal B – D2 and through load resistance RL towards the center tap terminal C. As the current flows through the load resistance RL output voltage is developed across RL. The direction of current is in same direction of positive half cycle so we get unidirectional output voltage.
The output voltage is given by V dc = 2Vp/π
The PIV rating of diode is Vp + Vp = 2 Vp
Ripple Frequency Fo = 2 Fin
1. It is difficult to locate the centre tap winding.
2. The cost of centre tap Transformer is more than normal type of transformer.
3. PIV rating of Diode is 2VP therefore cost of Diode is more.
4. The DC output voltage is smaller as each diode utilizes only one half of sec.voltage.
Bridge full - wave Rectifier
The center tap transformer is eliminated in the bridge rectifier by using four diodes connected in the form of bridge. As four diodes are connected in bridge this rectifier is called as a bridge full wave rectifier.
The diodes D1, D2 , D3, & D4 are used to form the bridge circuit as shown in the circuit diagram. The secondary of transformer is connected diagonally opposite end of the bridge. The load resistance RL is connected between other two ends of bridge.
During the positive half cycle of AC, the secondary terminal of A is positive with respect to the terminal B. The diodes D1 & D3 becomes in forward biased and the diodes D2 & D4 are in reverse biased. Therefore only diodes D1 & D3 are conducts and working as a closed switch. The conventional current flows from terminal A through diode D1 then through load resistance RL, and through diode D3 to terminal B. We get output voltage developed across RL.
During the negative half cycle of AC the secondary terminal of transformer B is positive with respect to the terminal A. The diode D2 & D4 becomes forward biased and the diodes D1 & D3 becomes reverse biased. Therefore only diode D2 & D4 are conducts and working as a closed switch. The conventional current flows from terminal B through diode D2, then through load resistance RL, and through diode D4 to terminal A. We get output voltage developed across RL.
The direction of current through the load resistor RL is in same direction of positive half cycle so we get unidirectional output voltage across load resistance RL.
The Average output voltage is given by V dc = 2Vp/π
The PIV rating of diode = Vp
Efficiency of FWR =81.2%
Ripple Frequency = 2Fin
Ripple factor = 0.48
Advantages and Disadvantages
- It does not require center tap transformer, hence it is low cost rectifier.
- Peak Inverse voltage of each diode is only peak voltage of secondary. PIV = Vp.
- The output voltage is twice that of center tap rectifier for same secondary voltage of transformer.
- It requires four diodes.
- As during each half cycle of AC input two diodes are conducting therefore internal voltage drop is 1.4V that reduces output voltage.
Comparison of all Rectifiers
| Half wave |
|Center Tap Full |
|Bridge Full wave Rectifier|
|1.||No. of Diodes||One||Two||Four|
|2.||Type of Transformer||Normal||Center Tap||Normal|
|3.||PIV Rating of Diode||Vp||2Vp||Vp|
|4.||Average DC output Voltage||Vp/π||2Vp/π||2Vp/π|
|5.||Ripple Frequency||F in||2 F in||2 F in|
|8.||DC Diode Current||Idc||0.5 Idc||0.5 Idc|
From above comparison table we can easily decide that, which type of Rectifier we need to select for construction of DC Regulated Power Supply and it is nothing but the Bridge full wave Rectifier.
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