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Rectifier

A rectifier is an electrical Electricity

Electricity is a general term for the variety of phenomena resulting from the presence and flow of electric charge [i] ... 

 device Machine

A machine is any mechanical [i] or organic [i] device that transmits or modif ... 

, comprising one or more semiconductive Semiconductor

A semiconductor is a material with electrical conductivity [i] that is intermediate between that of an ... 

 devices or vacuum tube Vacuum tube

In electronics [i], a vacuum tube or valve is a device generally used to amplify [i], ... 

s arranged for converting alternating current Alternating current

An alternating current is an electrical current [i] whose magnitude [i] and direction vary c ... 

 to direct current Direct current

Direct current is the constant flow of electrons [i] from low to high potential [i]. ... 

. When just one diode is used to rectify AC the difference between the term diode and the term rectifier is merely one of usage, e.g., the term rectifier describes a diode that is being used to convert AC to DC. Rectification is a process whereby alternating current Alternating current

An alternating current is an electrical current [i] whose magnitude [i] and direction vary c ... 

  is converted into direct current Direct current

Direct current is the constant flow of electrons [i] from low to high potential [i]. ... 

 . Almost all rectifiers comprise a number of diodes in a specific arrangement for more efficiently converting AC to DC than is possible with just a single diode.

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Encyclopedia



A rectifier is an electrical Electricity

Electricity is a general term for the variety of phenomena resulting from the presence and flow of electric charge [i] ... 

 device Machine

A machine is any mechanical [i] or organic [i] device that transmits or modif... 

, comprising one or more semiconductive Semiconductor

A semiconductor is a material with electrical conductivity [i] that is intermediate between that of an ... 

 devices or vacuum tube Vacuum tube

In electronics [i], a vacuum tube or valve is a device generally used to amplify [i], ... 

s arranged for converting alternating current Alternating current

An alternating current is an electrical current [i] whose magnitude [i] and direction vary c ... 

 to direct current Direct current

Direct current is the constant flow of electrons [i] from low to high potential [i]. ... 

. When just one diode is used to rectify AC the difference between the term diode and the term rectifier is merely one of usage, e.g., the term rectifier describes a diode that is being used to convert AC to DC. Rectification is a process whereby alternating current Alternating current

An alternating current is an electrical current [i] whose magnitude [i] and direction vary c ... 

  is converted into direct current Direct current

Direct current is the constant flow of electrons [i] from low to high potential [i]. ... 

 . Almost all rectifiers comprise a number of diodes in a specific arrangement for more efficiently converting AC to DC than is possible with just a single diode. Rectification is commonly performed by semiconductor diode Diode

In electronics [i], a diode is a component [i] that restricts the direction of mov... 

s. Before the development of solid state rectifiers, vacuum tube Vacuum tube

In electronics [i], a vacuum tube or valve is a device generally used to amplify [i], ... 

 diodes and copper oxide or selenium rectifier stacks were used. Early radios, called crystal set Crystal radio receiver

[i] consisting of a variable [[LC circuit|LC]... 

s, used a "cat's whisker" of fine wire pressing on a crystal of galena Galena

Galena is a lead [i] ore [i]. ... 

  to serve as a point contact rectifier or "crystal detector". In gas heating systems "flame rectification" can be used to detect a flame. Two metal electrodes in the outer layer of the flame provide a current path and rectification of an applied alternating voltage, but only while the flame is present.

Half-wave rectification

A half wave rectifier is a special case of a clipper Clipper

A clipper was a very fast multiple-masted sailing ship [i] of the 19th century [i]. ... 

. In half wave rectification, either the positive or negative half of the AC wave is passed easily while the other half is blocked, depending on the polarity of the rectifier. Because only one half of the input waveform reaches the output, it is very inefficient if used for power transfer. Half wave rectification can be achieved with a single diode in a one phase supply.


Full-wave rectification

Full-wave rectification converts both polarities of the input waveform to DC, and is more efficient. However, in a circuit with a non-center tapped transformer, four rectifiers are required instead of the one needed for half-wave rectification. This is due to each output polarity requiring 2 rectifiers each, for example, one for when AC terminal 'X' is positive and one for when AC terminal 'Y' is positive. The other DC output requires exactly the same, resulting in four individual junctions . Four rectifiers arranged this way are called a bridge rectifier Diode bridge

A diode bridge or bridge rectifier is an arrangement of four diode [i]s connected in a bridge circuit [i] ... 

:



A full wave rectifier converts the whole of the input waveform to one of constant polarity at its output by reversing the negative portions of the alternating current waveform. The positive portions thus combine with the reversed negative portions to produce an entirely positive voltage/current waveform.

For single phase AC, if the AC is center-tapped, then two diodes back-to-back form a full wave rectifier.




A very common vacuum tube Vacuum tube

In electronics [i], a vacuum tube or valve is a device generally used to amplify [i], ... 

 rectifier configuration contained one cathode and twin anodes inside a single envelope; in this way, the two diodes required only one vacuum tube. The 5U4 and 5Y3 were popular examples of this configuration.


For three phase AC, six diodes are used. Typically there are three pairs of diodes, each pair, though, is not the same kind of double diode that would be used for a full wave single phase rectifier. Instead the pairs are in series . Typically, commercially available double diodes have four terminals so the user can configure them as single phase split supply use, for half a bridge, or for three phase use.


Most devices that generate alternating current generate three phase AC. For example, an automobile alternator has six diodes inside it to function as a full wave rectifier for battery charge applications.

Peak loss

An aspect of most rectification is a loss from peak input voltage to the peak output voltage, caused by the threshold voltage of the diodes . Half wave rectification and full wave rectification using two separate secondaries will have a peak voltage loss of one diode drop. Bridge rectifcation will have a loss of two diode drops. This may represent significant power loss in very low voltage supplies. In addition, the diodes will not conduct below this voltage, so the circuit is only passing current through for a portion of each half-cycle, causing short segments of zero voltage to appear between each "hump".

Rectifier output smoothing

While half- and full-wave rectification suffices to deliver a form of DC output, neither produces constant voltage DC. In order to produce steady DC from a rectified AC supply, a smoothing circuit is required. In its simplest form this can be what is known as a reservoir capacitor Reservoir capacitor

The pulsating DC from an AC rectifier [i] sometimes needs to be smoothed to be useful. ... 

 or smoothing capacitor, placed at the DC output of the rectifier. There will still remain an amount of AC ripple voltage where the voltage is not completely smoothed.

Sizing of the capacitor represents a tradeoff. For a given load, a larger capacitor will reduce ripple but will cost more and will create higher peak currents in the transformer secondry and in the supply feeding it. In extreme cases where many rectifiers are loaded onto a power distribution circuit, it may prove difficult for the power distribution authority to maintain a correctly shaped sinusoidal voltage curve.

To further reduce this ripple, a capacitor-input filter Capacitor-input filter

The capacitor-input filter is a type of filter circuit [i]. ... 

 can be used. This complements the reservoir capacitor with a choke and a second filter capacitor, so that a steadier DC output can be obtained across the terminals of the filter capacitor. The choke presents a high impedance to the ripple current.

If the DC load is very demanding of a smooth supply voltage, a voltage regulator will be used either in addition to the capacitor-input filter, both to remove the last of the ripple and to deal with variations in supply and load characteristics.

Applications


The primary application of rectifiers is to derive usable DC power from an AC supply. Virtually all electronics requires a DC supply but mains power is AC so rectifiers find uses inside the power supplies of virtually all electronic equipment.

Converting DC voltage from one level to another is much more complicated but rectifiers are usually involved. One method of such DC-to-DC conversion is to first convert to AC , then use a transformer to change the voltage, and finally rectify it back to DC.

Rectifiers also find a use in detection of amplitude modulated Amplitude modulation

Amplitude modulation is a technique used in electronic communication, most commonly for transmitting au... 

 radio signals. The signal may or may not be amplified before detection but if unamplified a very low voltage drop diode must be used. In this case the capacitor and load resistance must be carefully matched. Too low a capacitance will result in the high frequency carrier passing to the output and too high will result in the capacitor just charging and staying charged.

High power rectification

Vacuum tubes, metal oxide rectifier stacks and semiconductor diodes are useful in the range of milliamperes to a few hundred amperes of current. In order to handle thousands of amperes at hundreds of volts or hundreds of amperes at thousands of volts, some interesting solutions have been devised. For example, to convert AC current into DC current in electric locomotive Electric locomotive

An electric locomotive is a locomotive [i] powered by electric motor [i]s that are supplied with electricity [i] ... 

s, a synchronous rectifier may be used. It consists of a synchronous motor driving a set of heavy-duty electrical contacts. The motor spins in time with the AC frequency and periodically reverses the connections to the load just when the sinusoidal current goes through a zero-crossing. The contacts do not have to switch a large current, but they need to be able to carry a large current to supply the locomotive's DC traction motors. In recent years semiconductor synchronous rectifiers have been designed, although they still cannot compete with the low losses offered by the older electromechanical synchronous rectifiers.

Another type of rectifier used in high voltage power transmission systems and industrial processing since about 1909 is a mercury arc rectifier or mercury arc valve Mercury arc valve

A mercury arc valve is a type of electrical rectifier [i] which converts alternating current into direct current [i] ... 

. The device is enclosed in a bulbous glass vessel or large metal tub. One electrode, the cathode Cathode

A cathode is the electrode [i] at which electrons [i] go into a cell, tube or diode, whether dr ... 

, is submerged in a pool of liquid mercury at the bottom of the vessel and one or more high purity graphite electrodes, called anode Anode

An anode is the electrode [i] in a device that electrons flow out of to return to the circuit. ... 

s, are suspended above the pool. There may be several auxiliary electrodes to aid in starting and maintaining the arc. When an electric arc is established between the cathode pool and suspended anodes, a stream of electrons flows from the cathode to the anodes through the ionized mercury, but not the other way. These devices can be used at power levels of hundreds of kilowatts, and may be built to handle one to six phases of AC current. Mercury arc rectifiers have largely been replaced by silicon semiconductor rectifiers from the mid 1970s onward.

A third type of rectifier, a motor-generator set Motor-generator

A motor-generator is a device for converting electrical power [i] to another form. ... 

, is not a rectifier in the strict sense. Here, an AC motor is mechanically coupled to a DC generator Electrical generator

An electrical generator is a device that produces electrical [i] energy [i] from a mechanica... 

. The DC generator produces a multiphase alternating current in its windings, but a commutator is used to convert the alternating currents into a direct current output. Such devices are useful for producing hundreds of amperes of direct current at tens to hundreds of volts.

Patents

 — Copper oxide rectifiers

See also

  • Mercury arc valve Mercury arc valve

    A mercury arc valve is a type of electrical rectifier [i] which converts alternating current into direct current [i] ... 

  • Diode Diode

    In electronics [i], a diode is a component [i] that restricts the direction of mov... 

  • Metal rectifier
  • Inverter
  • Precision rectifier Precision rectifier

    The super diode or precision rectifier is a configuration obtained with an operational amplifier [i] ... 

  • Voltage_multiplier Voltage multiplier

    A voltage multiplier is an electrical circuit [i] that converts AC electrical power from a lower voltage [i] ...