Rectifier

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Introduction

An electric device that converts alternating current (AC), which periodically reverses direction, to (DC) direct current, which flows in only one direction is known as a rectifier. The process of doing this is known as rectification as it straightens the direction of current . physically describing rectifiers, take a number of forms including diode and vacuum tubes, wet chemical cells, mercury arc valves, stocks of cotton and selenium oxide plates, semiconductor diode, silicon controlled rectifiers and other silicon based semiconductor switches.  rectifiers have many uses but more often they are seen serving as components of DC supply of power and high voltage direct current power transmission system.


Bridge Rectifier

An important part of electronic power supply is the bridge rectifier. Different types of electronic power circuits also require the DC power supply for powering the various electronic components available in AC mains supply. Rectifiers are also found in various wide variety of electronics, AC power devices like the home appliances, modulation process, motor controllers, welding applications etc.

A bridge rectifier is a converter of alternating current (AC) to direct current (DC) that rectifies main AC input to main DC output.  These rectifiers are used in power supply that provide necessary DC voltage for electronics devices or components. Bridge rectifiers are of different types: 

Single Phase and Three Phase Rectifier 

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The nature of supply is dependent on the single phase or three phase rectifiers. A single phase rectifier consists of four bodies for converting the AC current into DC. on the other hand a three phase rectifier uses six diodes, as presented by the figure. 

Uncontrolled Bridge Rectifier

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This rectifier uses diodes for rectifying the input. As the name shows that this diode is a unidirectional device so it allows the current to flow in one direction only. With this diode configuration in the rectifier it does not allow the power to vary depending on the load requirement. 

Controlled Bridge Rectifier

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This is called an AC/DC converter or rectifier instead of uncontrolled diode controlled solid state devices like SCR, IGBT are used to vary output power at varying voltage.

Full Wave Rectifier

It is one of the methods to improve the cycle of conversions. Two bodies are used in the full wave rectifiers one for each half of the cycle. Multiple winding transformers are used whose secondary winding is equally split into two halves with a common center taped connection. 

This configuration results in each diode conducting in turn when it’s anode terminal is positive with respect to the center of the transformer which is producing output during both half cycles, twice for the half rectifier so it’s 100% efficient. 

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Half Wave Rectifier

A rectifier converts AC current to DC. It is done with the help of a diode or group of diodes, but a half wave rectifier uses only one diode whereas a full wave uses multiple diodes. It is the simplest form of rectifier available. Its working is: when a standard waveform is passed through it only half of the AC waveforms remain. It only allows half cycle of AC voltage through and it blocks the other half cycle on the DC side. 

Only one diode is required to initial a half wave cycle. As we know that the DC system is designed in such a manner that the current can flow in one direction only, putting a waveform from negative and positive cycles through a DC device may result in destructive consequences. So we use the half wave rectifier to convert the AC input to the DC output. 

The complete half circuit consists of three main components that are:

A transformer, resistive load, diode. 


Some Applications of Rectifiers

The primary use of a rectifier is to derive DC power from an AC supply. Inside the power supplies of the virtually electronic equipment. DC\AC power supplies are divided into two parts that are linear power supply and switch mode power supplies. The rectifier in such power supply will be in series following the transformer and be filled by a smoothing filter and a voltage regulator. From one volt converting the DC power into another is much more complicated. DC-to-DC first converts power to AC then to change a voltage used by the transformer. And finally rectifies power back to DC. 

For the detection of amplitude modulated radio signals also rectifiers are used. The signal may get amplified before detection. 

Polarised voltage is supplied by rectifiers for welding purposes; in such circuits the output current is controlled, this is achieved sometimes by replacing the diode in a bridge rectifier with thyristors, diodes whose voltage output can be regulated.

FAQ (Frequently Asked Questions)

Q1. Define an uncontrolled Rectifier?

Ans: The circuit converter which converts AC current to DC current is known as a rectifier. Using diodes the rectifier circuit only is called the uncontrolled rectifiers circuit. Unlike the diodes, SCR does not become or behave like this after conducting immediately after it’s voltage becomes positive. It gets triggered by means of gate pulse signals.

Q2. Explain the reduction of 12 pulse Rectifiers Harmonics?

Ans: A two 6 plus rectifier is used by the 12 pulse rectifier in parallel to feed a common DC bus. An open primary and two secondary winding which is present in the 12 phase rectifier creates a 30 degree phase shift between the two currents waveforms, which starts to eliminate the 7th and the 5th harmonics and reduces current THD to between 10 and 15th percent.

Q3. Mention the components of a Rectifier.

Ans: A rectifier consists of a transformer, a stack and a cabinet. The transformers function is to safely separate the incoming AC voltage that is the primary side, from the secondary side, which is then adjusted to control the output voltage of the rectifier.

Q4. Define 6 plus Rectifiers.

Ans: The down to earth theory for this is: the 6 plus rectifier is used in both the rectifier and inverter as well and for the first time we are with the frying alpha. It has a plus number of 6 and so it can be thought of as a 6 phase or half wave circuit.