Editing Rectifier (section)

== Rectification technologies ==

=== Electromechanical ===
Before about 1905 when tube-type rectifiers were developed, power conversion devices were purely electro-mechanical in design. [[Mechanical rectifier]]s used some form of rotation or resonant vibration driven by electromagnets, which operated a switch or commutator to reverse the current.

These mechanical rectifiers were noisy and had high maintenance requirements, including lubrication and replacement of moving parts due to wear. Opening mechanical contacts under load resulted in electrical arcs and sparks that heated and eroded the contacts. They also were not able to handle AC [[frequencies]] above several thousand cycles per second.

==== Synchronous rectifier ====
{{main|Synchronous rectification}}
To convert alternating into direct current in [[electric locomotive]]s, a synchronous rectifier may be used.{{Citation needed|date=October 2009}} 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 at an instant when the sinusoidal current goes through a zero-crossing. The contacts do not have to ''switch'' a large current, but they must be able to ''carry'' a large current to supply the locomotive's DC [[traction motor]]s.

==== {{anchor|Vibrator}}Vibrating rectifier ====
{{Main|Mechanical rectifier}}
[[File:Vibrator rectifier battery charger.jpg|thumb|A [[vibrator (electronic)|vibrator]] battery charger from 1922.  It produced 6 A DC at 6 V to charge automobile batteries.]]
These consisted of a resonant [[reed switch|reed]], vibrated by an alternating magnetic field created by an AC [[electromagnet]], with contacts that reversed the direction of the current on the negative half cycles. They were used in low power devices, such as [[battery charger]]s, to rectify the low voltage produced by a step-down transformer. Another use was in battery power supplies for portable vacuum tube radios, to provide the high DC voltage for the tubes.  These operated as a mechanical version of modern solid state switching [[inverter]]s, with a transformer to step the battery voltage up, and a set of vibrator contacts on the transformer core, operated by its [[magnetic field]], to repeatedly break the DC battery current to create a pulsing AC to power the transformer. Then a second set of [[mechanical rectifier|rectifier contacts]] on the [[vibrator (electronic)|vibrator]] rectified the high AC voltage from the transformer secondary to DC.
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==== Motor-generator set ====
{{Main|Motor-generator|Rotary converter}}
[[File:Rotierender Umformer.jpg|thumb|A small motor-generator set]]
A ''motor-generator set'', or the similar ''rotary converter'', is not strictly a rectifier as it does not actually ''rectify'' current, but rather ''generates'' DC from an AC source. In an "M-G set", the shaft of an AC motor is mechanically coupled to that of a DC [[Electrical generator|generator]]. The DC generator produces multiphase alternating currents in its [[armature (electrical engineering)|armature]] windings, which a [[commutator (electric)|commutator]] on the armature shaft converts into a direct current output; or a [[homopolar generator]] produces a direct current without the need for a commutator. M-G sets are useful for producing DC for railway traction motors, industrial motors and other high-current applications, and were common in many high-power DC uses (for example, carbon-arc lamp projectors for outdoor theaters) before high-power semiconductors became widely available.
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=== Electrolytic ===
The [[electrolytic]] rectifier<ref name="Hawkins1914">{{cite book|first=Nehemiah|last=Hawkins|title=Hawkins Electrical Guide: Principles of electricity, magnetism, induction, experiments, dynamo|chapter-url=https://archive.org/details/hawkinselectric02hawkgoog|year=1914|publisher=T. Audel|location=New York|chapter=54. Rectifiers}}</ref> was a device from the early twentieth century that is no longer used. A home-made version is illustrated in the 1913 book ''The Boy Mechanic''<ref>{{cite web|url=http://chestofbooks.com/crafts/popular-mechanics/The-Boy-Mechanic-700-Things-for-Boys-to-Do/How-To-Make-An-Electrolytic-Rectifier.html |title=How To Make An Electrolytic Rectifier |publisher=Chestofbooks.com |access-date=2012-03-15}}</ref> but it would be suitable for use only at very low voltages because of the low [[breakdown voltage]] and the risk of [[electric shock]]. A more complex device of this kind was patented by G. W. Carpenter in 1928 (US Patent 1671970).<ref>{{cite patent| country = US| number = 1671970| status = patent| title = Liquid Rectifier| gdate = 1928-06-05| fdate = 1921-06-07| invent1 = Glenn W. Carpenter}}</ref>

When two different metals are suspended in an electrolyte solution, direct current flowing one way through the solution sees less resistance than in the other direction. Electrolytic rectifiers most commonly used an aluminum anode and a lead or steel cathode, suspended in a solution of triammonium orthophosphate.

The rectification action is due to a thin coating of [[aluminium hydroxide]] on the aluminum electrode, formed by first applying a strong current to the cell to build up the coating. The rectification process is temperature-sensitive, and for best efficiency should not operate above 86&nbsp;°F (30&nbsp;°C). There is also a [[breakdown voltage]] where the coating is penetrated and the cell is short-circuited. Electrochemical methods are often more fragile than mechanical methods, and can be sensitive to usage variations, which can drastically change or completely disrupt the rectification processes.

Similar electrolytic devices were used as [[lightning arrester]]s around the same era by suspending many aluminium cones in a tank of triammonium orthophosphate solution. Unlike the rectifier above, only aluminium electrodes were used, and used on A.C., there was no polarization and thus no rectifier action, but the chemistry was similar.<ref name="Society1920">{{cite book|author=American Technical Society|title=Cyclopedia of applied electricity|url=https://books.google.com/books?id=PcN-AAAAMAAJ|volume=2|year=1920|publisher=American technical society|page=487}}</ref>

The modern [[electrolytic capacitor]], an essential component of most rectifier circuit configurations was also developed from the electrolytic rectifier.

=== Plasma type ===
The development of [[vacuum tube]] technology in the early 20th century resulted in the invention of various tube-type rectifiers, which largely replaced the noisy, inefficient mechanical rectifiers.

==== Mercury-arc ====
{{Main|Mercury-arc valve}}

{{multiple image
| align = right
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| header   = 
| image1   = Quecksilberdampfgleichrichter in Betrieb.JPG
| caption1 = Early [[3-phase]] industrial [[mercury vapor]] rectifier tube 
| width1   = 150
| image2   = Mercury Arc Valve, Radisson Converter Station, Gillam MB.jpg
| caption2 = 150&nbsp;kV [[mercury-arc valve]] at [[Manitoba Hydro]] power station, Radisson, Canada converted AC [[hydropower]] to DC for transmission to distant cities.
| width2   = 150
| footer   =
}}

A rectifier used in high-voltage direct current (HVDC) power transmission systems and industrial processing between about 1909 to 1975 is a ''mercury-arc rectifier'' or ''mercury-arc valve''. The device is enclosed in a bulbous glass vessel or large metal tub. One electrode, the [[cathode]], is submerged in a pool of liquid mercury at the bottom of the vessel and one or more high purity graphite electrodes, called [[anode]]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 (in principle, this is a higher-power counterpart to [[flame rectification]], which uses the same one-way current transmission properties of the plasma naturally present in a flame).

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 been replaced by silicon semiconductor rectifiers and high-power [[thyristor]] circuits in the mid-1970s. The most powerful mercury-arc rectifiers ever built were installed in the [[Manitoba Hydro]] [[Nelson River Bipole]] HVDC project, with a combined rating of more than 1 GW and 450 kV.<ref>Pictures of a mercury-arc rectifier in operation can be seen here: [http://www.subbrit.org.uk/sb-sites/sites/b/belsize_park_deep_shelter/index14.shtml Belsize Park deep shelter rectifier 1], [http://www.subbrit.org.uk/sb-sites/sites/b/belsize_park_deep_shelter/index13.shtml Belsize Park deep shelter rectifier 2]</ref><ref name=sood1>{{cite book
|url=https://www.amazon.com/gp/reader/1402078900/ref=sib_fs_top?ie=UTF8&p=S00T&checkSum=kIuBlcbI0cpOJz1UiVfSKdIqFhPcDOXQ98WG3SabLpA%3D#reader-link
| title= HVDC and FACTS Controllers: Applications of Static Converters in Power Systems
| last=Sood
| first=Vijay K
| page=1
| publisher=[[Springer-Verlag]]
| isbn=978-1-4020-7890-3
| quote= The first 25 years of HVDC transmission were sustained by converters having mercury arc valves till the mid-1970s. The next 25 years till the year 2000 were sustained by line-commutated converters using thyristor valves. It is predicted that the next 25 years will be dominated by force-commutated converters [4]. Initially, this new force-commutated era has commenced with Capacitor Commutated Converters (CCC) eventually to be replaced by self-commutated converters due to the economic availability of high-power switching devices with their superior characteristics.| date= 31 May 2004
}}</ref>
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===={{anchor|Tungar}} Argon gas electron tube ====
[[File:Tungar bulbs.jpg|thumb|upright=0.7|Tungar bulbs from 1917, 2 ampere ''(left)'' and 6 ampere]]

The [[General Electric]] Tungar rectifier was a [[Mercury (element)|mercury vapor]] (ex.:5B24) or [[argon]] (ex.:328) [[gas-filled tube|gas-filled electron tube]] device with a tungsten filament cathode and a carbon button anode. It operated similarly to the thermionic vacuum tube diode, but the gas in the tube ionized during forward conduction, giving it a much lower forward voltage drop so it could rectify lower voltages. It was used for battery chargers and similar applications from the 1920s until lower-cost [[metal rectifier]]s, and later semiconductor diodes, supplanted it. These were made up to a few hundred volts and a few amperes rating, and in some sizes strongly resembled an [[incandescent lamp]] with an additional electrode.

The 0Z4 was a gas-filled rectifier tube commonly used in [[vacuum tube]] car radios in the 1940s and 1950s. It was a conventional full-wave rectifier tube with two anodes and one cathode, but was unique in that it had no filament (thus the "0" in its type number). The electrodes were shaped such that the reverse breakdown voltage was much higher than the forward breakdown voltage. Once the breakdown voltage was exceeded, the 0Z4 switched to a low-resistance state with a forward voltage drop of about 24 V.
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=== Diode vacuum tube (valve) ===
{{See also|List of vacuum tubes}}
[[File:FRec var.jpg|thumb|Vacuum tube diodes]]

The [[thermionic]] [[vacuum tube]] [[diode]], originally called the [[Fleming valve]], was invented by John Ambrose Fleming in 1904 as a detector for radio waves in radio receivers, and evolved into a general rectifier.  It consisted of an evacuated glass bulb with a [[electrical filament|filament]] heated by a separate current, and a metal plate [[anode]].  The filament emitted [[electron]]s by [[thermionic emission]] (the Edison effect), discovered by [[Thomas Edison]] in 1884, and a positive voltage on the plate caused a current of electrons through the tube from filament to plate.  Since only the filament produced electrons, the tube would only conduct current in one direction, allowing the tube to rectify an alternating current.

Thermionic diode rectifiers were widely used in power supplies in vacuum tube consumer electronic products, such as phonographs, radios, and televisions, for example the [[All American Five]] radio receiver, to provide the high DC plate voltage needed by other vacuum tubes.  "Full-wave" versions with two separate plates were popular because they could be used with a center-tapped transformer to make a full-wave rectifier.  Vacuum tube rectifiers were made for very high voltages, such as the high voltage power supply for the CRT of [[television]] receivers, and the '''kenotron''' used for power supply in [[X-ray]] equipment.  However, compared to modern semiconductor diodes, vacuum tube rectifiers have high internal resistance due to [[space charge]] and therefore high voltage drops, causing high power dissipation and low efficiency.  They are rarely able to handle currents exceeding 250&nbsp;mA owing to the limits of plate power dissipation, and cannot be used for low voltage applications, such as battery chargers. Another limitation of the vacuum tube rectifier is that the heater power supply often requires special arrangements to insulate it from the high voltages of the rectifier circuit.

=== Solid state ===

==== Crystal detector ====
{{Main|Crystal detector}}
[[File:CatWhisker.jpg|thumb|Galena cat's whisker [[crystal detector]]]]

The [[crystal detector]], the earliest type of [[semiconductor diode]], was used as a [[detector]] in some of the earliest [[radio receiver]]s, called [[crystal radio]]s, to rectify the radio [[carrier wave]] and extract the [[modulation]] which produced the sound in the earphones.   Invented by [[Jagadish Chandra Bose]] and [[Greenleaf Whittier Pickard|G. W. Pickard]] around 1902, it was a significant improvement over earlier detectors such as the [[coherer]].  One popular type of crystal detector, often called a ''cat's whisker detector'', consists of a crystal of some [[semiconducting]] [[mineral]], usually [[galena]] (lead sulfide), with a light springy wire touching its surface. Its fragility and limited current capability made it unsuitable for power supply applications. It was used widely in radios until the 1920s when [[vacuum tube]]s replaced it.  In the 1930s, researchers [[Diode#Solid-state diodes|miniaturized and improved]] the crystal detector for use at microwave frequencies, developing the first semiconductor diodes.
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==== Selenium and copper oxide rectifiers ====
{{Main|Metal rectifier}}
[[File:Selenium Rectifier.jpg|thumb|upright=0.7|[[Selenium rectifier]]]]
Once common until replaced by more compact and less costly silicon solid-state rectifiers in the 1970s, these units used stacks of oxide-coated metal plates and took advantage of the [[semiconductor]] properties of [[selenium]] or copper oxide.<ref>H. P. Westman et al., (ed), ''[http://lccn.loc.gov/43014665 Reference Data for Radio Engineers, Fifth Edition]'', 1968, Howard W. Sams and Co., no ISBN, Library of Congress Card No. 43-14665 chapter 13</ref> While [[selenium rectifier]]s were lighter in weight and used less power than comparable vacuum tube rectifiers, they had the disadvantage of finite life expectancy, increasing resistance with age, and were only suitable to use at low frequencies. Both selenium and copper oxide rectifiers have somewhat better tolerance of momentary voltage transients than silicon rectifiers.

Typically these rectifiers were made up of stacks of metal plates or washers, held together by a central bolt, with the number of stacks determined by voltage; each cell was rated for about 20 V. An automotive battery charger rectifier might have only one cell: the high-voltage power supply for a [[vacuum tube]] might have dozens of stacked plates. Current density in an air-cooled selenium stack was about 600 mA per square inch of active area (about 90 mA per square centimeter).
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==== Silicon and germanium diodes ====
{{Main|Diode}}
[[File:Dioden.JPG|thumb|A variety of silicon diodes of different current ratings. At left is a [[bridge rectifier]]. On the 3 center diodes, a painted band identifies the cathode terminal]] 
[[Silicon]] diodes are the most widely used rectifiers for lower voltages and powers, and have largely replaced other rectifiers.   Due to their substantially lower forward voltage (0.3V versus 0.7V for silicon diodes) germanium diodes have an inherent advantage over silicon diodes in low voltage circuits.  
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==== High power: thyristors (SCRs) and newer silicon-based voltage sourced converters ====
{{main|Silicon controlled rectifier}}
[[File:Manitoba Hydro-BipoleII Valve.jpg|thumb|200px|Two of three high-power [[thyristor]] valve stacks used for long-distance transmission of power from [[Manitoba Hydro]] dams. Compare with mercury-arc system from the same dam-site, above.]]

In high-power applications, from 1975 to 2000, most mercury valve arc-rectifiers were replaced by stacks of very high power [[thyristor]]s, silicon devices with two extra layers of semiconductor, in comparison to a simple diode.

In medium-power transmission applications, even more complex and sophisticated [[voltage sourced converter]] (VSC) silicon semiconductor rectifier systems, such as [[IGBT transistor|insulated gate bipolar transistors (IGBT)]] and [[Gate turn-off thyristor|gate turn-off thyristors (GTO)]], have made smaller high voltage DC power transmission systems economical. All of these devices function as rectifiers.

{{As of|2009}} it was expected that these high-power silicon "self-commutating switches", in particular IGBTs and a variant thyristor (related to the GTO) called the [[integrated gate-commutated thyristor]] (IGCT), would be scaled-up in power rating to the point that they would eventually replace simple thyristor-based AC rectification systems for the highest power-transmission DC applications.<ref>{{cite book|first1=Jos|last1=Arrillaga|first2=Yonghe H|last2=Liu|first3=Neville R|last3=Watson|first4=Nicholas J|last4=Murray|title=Self-Commutating Converters for High Power Applications|publisher=John Wiley & Sons|isbn=978-0-470-68212-8|date=12 January 2010}}</ref>

====Active rectifier====
{{main|Active rectification}}
[[Image:Diode mosfet.svg|thumb|250px|Voltage drop across a diode and a [[power MOSFET|MOSFET]].  The low on-resistance property of a MOSFET reduces ohmic losses compared to the diode rectifier (below 32&nbsp;A in this case), which exhibits a significant voltage drop even at very low current levels.  Paralleling two MOSFETs (pink curve) reduces the losses further, whereas paralleling several diodes won't significantly reduce the forward-voltage drop.]]

Active rectification is a technique for improving the efficiency of rectification by replacing [[diode]]s with actively controlled switches such as [[transistor]]s, usually [[power MOSFET]]s or [[power BJT]]s.<ref name="emadi"/> Whereas normal semiconductor diodes have a roughly fixed voltage drop of around 0.5 to 1 volts, active rectifiers behave as resistances, and can have arbitrarily low voltage drop.

Historically, [[vibrator (electronic)|vibrator]]-driven switches or motor-driven [[commutator (electric)|commutator]]s have also been used for [[mechanical rectifier]]s and synchronous rectification.<ref>
{{cite book
 | title = Standard polyphase apparatus and systems
 | edition = 5th
 | author = Maurice Agnus Oudin
 | publisher = Van Nostrand
 | date = 1907
 | page = [https://archive.org/details/standardpolypha00oudigoog/page/n248 236]
 | url = https://archive.org/details/standardpolypha00oudigoog
 | quote = synchronous rectifier commutator.
 }}</ref>

Active rectification has many applications. It is frequently used for arrays of photovoltaic panels to avoid reverse current flow that can cause overheating with partial shading while giving minimum power loss.