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Rectifier is an electronic device that uses one or more P-N junction diodes to convert alternating current into direct current.
- This process is generally called rectification since it is known to "straighten" the direction of the current.
- P-N junction diode only allows current in the forward bias condition and blocks the current in the reverse bias condition.
- If one polarity of alternating current is utilized to generate a pulsating direct current, then the procedure is called half-wave rectification.
- While, if both polarities are used, yielding a continuous train of pulses, then the procedure is known as full-wave rectification.
Rectifiers have a wide range of applications, but they are most commonly seen as components of DC power supplies and high-voltage direct-current power transmission systems. They can take the shape of various physical forms like solid-state diodes, vacuum tube diodes, silicon-controlled rectifiers, and other silicon-based semiconductor switches.
| Table of Content |
Key Terms: Rectifier, Diode, Half-wave Rectifier, P-n Junction, Semiconductors, Uncontrolled Rectifiers, Full-wave Rectifier, LED, DC Power, switches, AC Voltage, alternating current, direct current
What is Rectifier?
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A rectifier converts alternating current into direct current. The operation of many electrical circuits is based on DC voltage. A p-n junction diode is a device that can quickly convert AC voltage or current into DC voltage or current. Rectifier can be defined as:
| “An electrical device that converts alternating current into direct current by enabling current to flow via it in only one direction.” |
Rectifier
A rectifier can be found in numerous physical forms like,
- Solid-state diodes
- Vacuum tube diodes
- Mercury-arc valves
- Silicon-controlled rectifiers, and more.
In forward bias, a p-n junction diode permits electric current to pass, but in reverse bias, the current is blocked. Simply said, a diode enables just one direction of electric current to pass. The diode's unique characteristic allows it to function as a rectifier.
A diode functions as a one-way valve, allowing current to flow in just one direction. This is referred to as the correction. Rectifiers can be classified under different waveforms, like:
- Half-Wave Rectifier
- Full-Wave Rectifier
- Single-Phase AC
- Three-Phase AC
Also read:
| Topic Related Links | ||
|---|---|---|
| Transistor as Switch Amplifier | Application of Junction Diode as a Rectifier | Integrated Circuits |
| Intrinsic Semiconductor | Junior Transistor | Extrinsic Semiconductor |
Principle of Rectifier
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In forward bias, the resistance of a p-n junction diode is extremely low, while in reverse bias, the resistance is extremely high. Because of this condition, a p-n junction diode only enables the current to travel in one direction.
Principle of Rectifier
When an alternating voltage is applied across a diode, current flows during the forward-biased portion of the cycle. A rectifier is a circuit that uses the p-n junction diode's ability to correct alternating voltages.
Where are Rectifiers used?Rectifiers can be used in many devices, such as:
What is the principle of a rectifier?Rectifiers are devices which are able to convert alternating current into a unidirectional or pulsating type of direct current. This procedure of conversion of alternating currents into a form of direct current is termed rectification. Define centre-tap rectifier.A Center-tap Full-wave rectifier circuit is a type of rectifier circuit whose transformer secondary is tapped in order to obtain the desired output voltage to rectify the complete cycle by means of using two diodes alternatively. What is Forward and Reverse Bias?Forward biasing can be expressed as putting a voltage across a diode which enables current to flow easily. Whereas, reverse biasing can be expressed as putting a voltage across a diode in the opposite direction.
Forward and Reverse Bias |
Types of Rectifiers
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Rectifiers are divided into two categories:
- Uncontrolled Rectifier
- Controlled Rectifier
Uncontrolled Rectifier
The input of this rectifier is rectified using diodes. This diode is a unidirectional device, which means it only enables electricity to travel in one direction.
Uncontrolled Rectifier
The rectifier's diode arrangement prevents the power from varying based on the load requirement. Uncontrolled rectifiers are further subdivided into the following categories:
- Half-wave Rectifier
- Full-wave Rectifier
A half-wave rectifier converts only the half-cycle of alternating current into direct current. A full-wave rectifier, on the other hand, converts both the positive and negative half cycles of the AC. Bridge rectifier is an example of this. It is made up of four diodes coupled in a Wheatstone bridge.
Controlled Rectifier
The output voltage of a controlled rectifier can be changed, unlike the fixed output voltage in uncontrolled rectifiers.
- To control it, we use SCRs, MOSFETs, and IGBTs.
- Half Wave Controlled Rectifier and Full Wave Controlled Rectifier are the two types of controlled rectifiers.
- The half-wave controlled rectifier is similar to the half-wave uncontrolled rectifier except that the diode is replaced with an SCR.
Working of Half-wave Rectifier
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Half-wave Rectifier allows the passing of one half-cycle of an AC voltage waveform, blocking the other half-cycle.
Construction of Half-wave Rectifier
The construction of a half-wave rectifier is:
- The figure given below is a half-wave rectifier. An appropriate step-down transformer's primary coil P receives the AC input voltage.
- The transformer's secondary coil S is coupled to a load resistance RL and a semiconductor p-n junction diode D.
Half and Full Wave Rectifier
Working Principle of Half-wave Rectifier
The working principle of a half-wave rectifier is:
- During the first half of the AC input cycle, end A of the secondary S of the transformer is at positive potential and end B to be at negative potential.
- The diode is forward-biased in this case and current flows across the circuit.
- As a result, an output voltage is obtained across load RL.
- The end A of the secondary S of the transformer is at negative potential during the second half of the AC input, and diode D is in reverse bias.
- As a result, no current flows through load RL, and no output voltage is present across RL.
- We obtain the output again in the next positive half-cycle of AC input, and so on.
- The output voltage is considered to be rectified when it is confined to only one direction, even though it still varies in magnitude.
- The device is known as a half-wave rectifier because the rectified output of the circuit is only achieved for half of the input AC wave.
Working of Full-wave Rectifier
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A full-wave rectifier converts the complete cycle of alternating current into pulsating direct current.
Construction of Full-wave Rectifier
The construction of a full-wave rectifier is:
- In a full-wave rectifier, two semiconductor diodes in complementary mode are used.
- The AC input is connected to the primary coil P of a centre tap transformer.
- The p-ends of the diodes D1 and D2 are connected to the two ends A and B of the secondary S of the transformer, respectively.
- A load resistance (RL) is connected between the center tap (O) of the secondary winding and the n-terminals of both diodes.
- The DC output is obtained by passing the current through the load resistance RL.
Working Principle of Full-wave Rectifier
The working principle of full-wave rectifier is:
- Terminal A is positive for O during the first half cycle of the input voltage, whereas terminal B is negative for O. The current flows through RL from D to O because the first diode is forward biased and conducts, while the second diode is reverse biassed and does not conduct.
- A is negative and B is positive for O during the second half cycle, therefore diode one is reverse-biased and diode two is forward-biased. The current flowing through RL is the same as it was throughout the first half of the cycle. A continuous series is produced.
- The rectifier is called a full-wave rectifier because it produces output in both the positive and negative halves of the AC input cycle. This is a more efficient circuit than a half-wave rectifier for obtaining rectified voltage or current.
The video below explains this:
Full Wave Rectifier Detailed Video Explanation:
Limitations of Rectifier
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There are a few limitations of a Rectifier. Some of them include:
- Although a full-wave rectifier produces a continuous output voltage/current in one direction, the rectified voltage is in the form of half sinusoidal pulses.
- The output voltage is unidirectional but not constant.
- Such a pulsating output has some AC ripple mixed in with a pure DC voltage, and we must filter out the AC ripple using an extra filter configuration to produce pure DC voltage output.
Applications of Rectifier
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Rectifiers are used in a variety of ways, including:
- Rectifiers are used to provide polarised voltage in electric welding.
- Mosquitoes are repelled by half-wave rectifiers.
- In AM radio, half-wave rectifiers are used as signal peak detectors.
- Modulation, demodulation, and voltage multipliers all employ rectifiers.
Things to Remember
- Rectifiers transform an AC input voltage into a DC voltage supply to power electronic circuits.
- Rectification is the process of converting alternating current (AC) to direct current (DC) by only allowing current to flow in one direction.
- When forward biased, a junction diode has a low resistance to current in one direction and high resistance when reverse biased.
- The ripple factor is a measurement of a rectifier's efficiency.
- A half-wave rectifier can be defined as a type of rectifier that converts only the half-cycle of alternating current into a direct current.
- A full-wave rectifier converts both the positive and negative half cycles of the AC.
Also read:
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Sample Questions
Ques. What is a rectifier? (1 Mark)
Ans. A rectifier is an electronic device that converts an alternating current into a direct current by using one or more semiconductor diodes.
Ques. What is the rectification of an alternating current? (1 Mark)
Ans. Rectification is the process of converting an alternating current (AC) into a direct current (DC).
Ques. Define an uncontrolled Rectifier. (2 Marks)
Ans. The circuit converter which converts AC to DC is known as a rectifier. Using diodes the rectifier circuit only is called the uncontrolled rectifier circuit. Unlike the diodes, SCR does not become or behave like this after conducting immediately after its voltage becomes positive. It gets triggered using the gate pulse signals.
Ques. Explain the reduction of 12 pulse Rectifiers Harmonics. (2 Marks)
Ans. A 12-pulse rectifier utilizes two 6-pulse rectifiers connected in parallel to feed a common DC bus. An open primary and two secondary winding which are present in the 12-phase rectifier create a 30-degree phase shift between the two current waveforms, which starts to eliminate the 7th and the 5th harmonics and reduces current THD to between 10 and 15th percent.
Ques. Draw the output waveform across the resistor (figure). (2 Marks)
Ans. It is a half-wave rectifier, therefore only the positive cycle will be rectified. Thus the output waveform is as shown.
Ques. Draw a labeled circuit diagram of a full-wave rectifier using a p-n junction. (2 Marks)
Ans. The circuit diagram of a full wave rectifier is shown below.
Ques. What is rectification? Explain the working of a full-wave rectifier. (4 Marks)
Ans. Rectifiers can be single-phase or multi-phase. Usually, for domestic purposes, single-phase rectifiers are used and for industrial purposes, multiphase rectifiers are used. Half-wave rectification and full-wave rectification are possible for a single-phase rectifier.
A full Wave Rectifier converts the whole of the input waveform into pulsating direct current (DC). It converts both polarities of the input waveform, unlike half-wave rectifiers which convert only one of the two polarities. This also shows that the average output of the full-wave rectifier will be greater than that of a half-wave rectifier.
Note: Two diodes are connected to a center-tapped secondary winding of the transformer. When an alternating current enters the full-wave rectifier, in the first half cycle one diode will be forward biased and the other will be reverse biased and vice versa for the other half cycle. During the positive half cycle, the diode D1 is provided with the positive cycle and, therefore will be in forwarding bias. During the negative half cycle, the diode D2 is provided with the positive cycle and, therefore will be in forwarding bias.
Ques. In a full-wave rectifier in which input voltage is represented by V = VM sinωt then the peak inversion voltage of the non-conducting diode will be: (2 Marks)
a. −VM
b. VM/2
c. 2VM
d. 0
Ans. Half-wave rectifiers use only half-wave of the input alternating current cycle, and full-wave rectifiers utilize full-wave.
The entire secondary voltage appears across the non-conducting diode, therefore the peak inverse voltage for the full-wave rectifier is 2VM.
By using a full-wave rectifier with a center-tapped transformer, it generates the voltages that are in phase with each other.
According to the question V = VMsinωt,
So we can say that the peak inversion voltage is 2VM
The full-wave rectifier has more efficiency compared to that of a half-wave rectifier; there is no loss in the output power.
There will be no loss in the input voltage signal in the full-wave rectifier.
The ripple factor in the full-wave rectifier is less compared to that of the half-wave rectifier.
Hence the correct option is (C).
Ques. Draw the circuit diagram of a full-wave rectifier by the use of two p-n junction diodes and describe its working. Represent the input and output waveforms. (5 Marks)
Ans. The AC input voltage across the secondary S1 and S2 varies the polarity after each half cycle. Let us assume during the first half cycle of the input AC signal, terminal S1 is the positive relative to center tap O and S2 is the negative relative to O.
Then diode D1 will be in forwarding bias and diode D2 will be in reverse biased. Hence, the diode D1 conducts while diode D2 will not conduct.
In the next half-cycle, the terminal S1 will be negative for the center tap O, and S2 will be positive relative to O. Then diode D2 is forward biased and diode D1 is reverse biased. Therefore diode D2 conducts while diode D1 does not. The direction of current in the load resistance RL will be the same from A to B for both the half cycles. Hence for the input AC signal, the output current will be a continuous series of unidirectional pulses.
Ques. Using the necessary circuit diagrams, show how the V – l characteristics of a p-n junction are obtained in
(a) Forward biasing
(b) Reverse biasing
How these characteristics are made use of in rectification? (5 Marks)
Ans. (a) p-n junction diode under forwarding bias: The p-side is connected to the positive terminal and the n-side to the negative terminal. Applied voltage drops across the depletion region. Electrons in the n-region move towards the p-n junction and holes in the p-region move towards the junction.
The width of the depletion layer decreases and hence, it offers less resistance. Diffusion of majority carriers takes place across the junction. This leads to the forward current.
(b) p-n junction diode under reverse bias: The positive terminal of the battery is connected to the n-side and the negative terminal to the p-side. Reverse bias supports the potential barrier. Therefore, the barrier height increases, and the width of the depletion region also increases.
Due to the majority of carriers, there is no conduction across the junction. A few minority carriers cross the junction after being accelerated by the high reverse bias voltage. This constitutes a current that flows in opposite directions, which is called reverse current.
For V-l curves
A p-n junction diode is used as a half-wave rectifier. Its work is based on the fact that the resistance of the p-n junction becomes low when forward-biased and becomes high when reverse-biased. These characteristics of the diode are used in rectification.
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