All Topics  
Rectifier

 

   Email Print
   Bookmark   Link






 

Rectifier



 
 
For other uses see Rectifier (disambiguation)
Rectifier (disambiguation)

The word Rectifier refers to the general act of straightening.Articles include:...


A rectifier is an electrical device that converts alternating current
Alternating current

In alternating current the movement of electric charge periodically reverses direction. An electric charge would for instance move forward, then backward, then forward, then backward, over and over again....
 (AC) to direct current
Direct current

Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as battery , thermocouples, solar cells, and commutator-type electric machines of the dynamo type....
 (DC), a process known as rectification. Rectifiers have many uses including as components of power supplies
Power supply

Power supply is a reference to a source of electrical power. A device or system that supplies electrical or other types of energy to an output External electric load or group of loads is called a power supply unit or PSU....
 and as detector
Detector (radio)

A detector is a device that recovers information of interest contained in a modulated wave. The term dates from the early days of radio when all transmissions were in Morse Code, and it was only necessary to detect the presence of a radio wave using a device such as a coherer without necessarily making it audible....
s of radio
Radio

Radio is the transmission of signals, by modulation of electromagnetic radiation with frequency below those of visible light.Electromagnetic radiation radio propagation by means of oscillating electromagnetic fields that pass through the air and the vacuum of space....
 signals. Rectifiers may be made of solid state
Solid state (electronics)

Solid-state electronic components, devices, and systems are based entirely on the semiconductor, such as transistors, microprocessor chips, and the bubble memory....
 diode
Diode

In electronics, a diode is a two-terminal device .Diodes have two active electrodes between which the signal of interest may flow, and most are used for their unidirectional electric current property....
s, vacuum tube
Vacuum tube

In electronics, a vacuum tube, electron tube , thermionic valve, or just valve is a device used to amplifier, switch, otherwise modify, or create an Electricity signal by controlling the movement of electrons in a low-pressure space....
 diodes, mercury arc valve
Mercury arc valve

A mercury arc valve is a type of electrical rectifier which converts alternating current into direct current. Rectifiers of this type were used in electric motor power supplies for industry, in Railway electrification system,...
s, and other components.

A device which performs the opposite function (converting DC to AC) is known as an inverter
Inverter (electrical)

An inverter is an electrical or electro-mechanical device that converts direct current to alternating current ; the resulting AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits....
.

When only one diode is used to rectify AC (by blocking the negative or positive portion of the wave
Wave

A wave is a disturbance that propagates through space and time, usually with transference of energy. While a mechanical wave exists in a medium , waves of electromagnetic radiation can travel through vacuum, that is, without a medium....
form), the difference between the term diode and the term rectifier is merely one of usage, i.e., the term rectifier describes a diode that is being used to convert AC to DC.






Discussion
Ask a question about 'Rectifier'
Start a new discussion about 'Rectifier'
Answer questions from other users
Full Discussion Forum



Recent Posts









Encyclopedia


For other uses see Rectifier (disambiguation)
Rectifier (disambiguation)

The word Rectifier refers to the general act of straightening.Articles include:...


A rectifier is an electrical device that converts alternating current
Alternating current

In alternating current the movement of electric charge periodically reverses direction. An electric charge would for instance move forward, then backward, then forward, then backward, over and over again....
 (AC) to direct current
Direct current

Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as battery , thermocouples, solar cells, and commutator-type electric machines of the dynamo type....
 (DC), a process known as rectification. Rectifiers have many uses including as components of power supplies
Power supply

Power supply is a reference to a source of electrical power. A device or system that supplies electrical or other types of energy to an output External electric load or group of loads is called a power supply unit or PSU....
 and as detector
Detector (radio)

A detector is a device that recovers information of interest contained in a modulated wave. The term dates from the early days of radio when all transmissions were in Morse Code, and it was only necessary to detect the presence of a radio wave using a device such as a coherer without necessarily making it audible....
s of radio
Radio

Radio is the transmission of signals, by modulation of electromagnetic radiation with frequency below those of visible light.Electromagnetic radiation radio propagation by means of oscillating electromagnetic fields that pass through the air and the vacuum of space....
 signals. Rectifiers may be made of solid state
Solid state (electronics)

Solid-state electronic components, devices, and systems are based entirely on the semiconductor, such as transistors, microprocessor chips, and the bubble memory....
 diode
Diode

In electronics, a diode is a two-terminal device .Diodes have two active electrodes between which the signal of interest may flow, and most are used for their unidirectional electric current property....
s, vacuum tube
Vacuum tube

In electronics, a vacuum tube, electron tube , thermionic valve, or just valve is a device used to amplifier, switch, otherwise modify, or create an Electricity signal by controlling the movement of electrons in a low-pressure space....
 diodes, mercury arc valve
Mercury arc valve

A mercury arc valve is a type of electrical rectifier which converts alternating current into direct current. Rectifiers of this type were used in electric motor power supplies for industry, in Railway electrification system,...
s, and other components.

A device which performs the opposite function (converting DC to AC) is known as an inverter
Inverter (electrical)

An inverter is an electrical or electro-mechanical device that converts direct current to alternating current ; the resulting AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits....
.

When only one diode is used to rectify AC (by blocking the negative or positive portion of the wave
Wave

A wave is a disturbance that propagates through space and time, usually with transference of energy. While a mechanical wave exists in a medium , waves of electromagnetic radiation can travel through vacuum, that is, without a medium....
form), the difference between the term diode and the term rectifier is merely one of usage, i.e., the term rectifier describes a diode that is being used to convert AC to DC. Almost all rectifiers comprise a number of diodes in a specific arrangement for more efficiently converting AC to DC than is possible with only one diode. Before the development of silicon semiconductor rectifiers, vacuum tube
Vacuum tube

In electronics, a vacuum tube, electron tube , thermionic valve, or just valve is a device used to amplifier, switch, otherwise modify, or create an Electricity signal by controlling the movement of electrons in a low-pressure space....
 diodes and copper(I) oxide
Copper(I) oxide

Copper oxide or cuprous oxide is an oxide of copper. It is insoluble in water and organic solvents. Copper oxide dissolves in concentrated ammonia solution to form the colorless complex [Cu2]+, which easily redox in air to the blue [Cu42]2+....
 or selenium
Selenium

Selenium is a chemical element with the atomic number 34, represented by the chemical symbol Se, an atomic mass of 78.96. It is a nonmetal, chemically related to sulfur and tellurium, and rarely occurs in its elemental state in nature....
 rectifier stacks were used.

Early radio receivers, called crystal radios, used a "cat's whisker" of fine wire pressing on a crystal of galena
Galena

Galena is the natural mineral form of lead sulfide. It is the most important lead ore mineral.Galena is one of the most abundant and widely distributed sulfide minerals....
 (lead sulfide) 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

In half wave rectification, either the positive or negative half of the AC wave is passed, while the other half is blocked. 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, or with three diodes in a three-phase supply.

Halfwave

Full-wave rectification


A full-wave rectifier converts the whole of the input waveform to one of constant polarity (positive or negative) at its output. Full-wave rectification converts both polarities of the input waveform to DC (direct current), and is more efficient. However, in a circuit with a non-center tap
Center tap

In electronics, a center tap is a connection made to a point half way along a winding of a transformer or inductor, or along the element of a resistor or a potentiometer....
ped transformer, four diodes are required instead of the one needed for half-wave rectification. (See semiconductor
Semiconductor

A semiconductor is a material that has electrical conductivity between those of a Electrical conductor and an electrical insulation; it can vary over that wide range either permanently or dynamically....
s, diode
Diode

In electronics, a diode is a two-terminal device .Diodes have two active electrodes between which the signal of interest may flow, and most are used for their unidirectional electric current property....
). Four rectifiers arranged this way are called a diode bridge
Diode bridge

A diode bridge or bridge rectifier is an arrangement of four diode in a bridge circuit configuration that provides the same Polarity of output volt for either polarity of input voltage....
 or bridge rectifier:

Gratz
For single-phase AC, if the transformer is center-tapped, then two diodes back-to-back (i.e. anodes-to-anode or cathode-to-cathode) form a full-wave rectifier (in this case, the voltage is half of that for the non-tapped bridge circuit above, and the diagram voltages are not to scale).

Fullwave


Vacrect2e
A very common vacuum tube
Vacuum tube

In electronics, a vacuum tube, electron tube , thermionic valve, or just valve is a device used to amplifier, switch, otherwise modify, or create an Electricity signal by controlling the movement of electrons in a low-pressure space....
 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.

3 Fase Bridge Rectifier
For three-phase AC
Three-phase electric power

Three-phase electric power is a common method of Alternating-current electric power electric power electric power transmission. It is a type of polyphase system, and is the most common method used by electric power distribution grids worldwide to distribute power....
, 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 (anode
Anode

An anode is an electrode through which electric charge flows into a polarized electrical device. Mnemonic: ACID . Electrons flow in the opposite direction to the positive electric current....
 to cathode
Cathode

A cathode is an electrode through which electric charge flows out of a polarized electrical device. Mnemonic: CCD .From an electrochemical point of view, positively charged ion invariably move toward the cathode and/or negatively charged ion move away from it to balance the electrons arriving from external circuitry....
). 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.

Getting Behind the Tridge Rectifier
Most devices that generate alternating current (such devices are called alternator
Alternator

An alternator is an generator that converts mechanical energy to alternating current electrical energy. Most alternators use a rotating magnetic field but linear alternators are occasionally used....
s) generate three-phase AC. For example, an automobile alternator has six diodes inside it to function as a full-wave rectifier for battery charging applications.

Peak loss

An aspect of most rectification is a loss from peak input voltage to the peak output voltage, caused by the built-in voltage of the diodes (around 0.7 V for ordinary silicon p-n-junction diodes and 0.3 V for Schottky diode
Schottky diode

The Schottky diode is a semiconductor diode with a low forward voltage drop and a very fast switching action.The cat's-whisker detectors used in the early days of wireless#History can be considered as primitive Schottky diodes....
s). Half-wave rectification and full-wave rectification using two separate secondaries will have a peak voltage loss of one diode drop. Bridge rectification 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-wave and full-wave rectification suffice 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, sometimes called a filter
Electronic filter

Electronic filters are electronic circuits which perform signal processing functions, specifically to remove unwanted frequency components from the signal and/or to enhance wanted ones....
, is required. In its simplest form this can be what is known as a reservoir capacitor
Reservoir capacitor

A reservoir capacitor is a capacitor that is used to smooth the pulsating DC from an AC rectifier....
, filter capacitor 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 secondary 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.

For a given tolerable ripple the required capacitor size is proportional to the load current and inversely proportional to the supply frequency and the number of output peaks of the rectifier per input cycle. The load current and the supply frequency are generally outside the control of the designer of the rectifier system but the number of peaks per input cycle can be affected by the choice of rectifier design.

A half-wave rectifier will only give one peak per cycle and for this and other reasons is only used in very small power supplies. A full wave rectifier achieves two peaks per cycle and this is the best that can be done with single-phase input. For three-phase inputs a three-phase bridge will give six peaks per cycle and even higher numbers of peaks can be achieved by using transformer networks placed before the rectifier to convert to a higher phase order.

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

The capacitor-input filter, also called "Pi" filter due to its shape that looks like the Greek alphabet pi , is a type of electronic filter. Filter circuits are used to remove unwanted or undesired frequencies from a signal....
 can be used. This complements the reservoir capacitor with a choke
Choke (electronics)

A choke is an inductor designed to have a high Reactance to a particular frequency when used in a signal-carrying circuit....
 and a second filter capacitor
Filter capacitor

Filter capacitors are any capacitors used for filtering. Filter capacitors are common in electrical and electronic work, and cover a number of applications, such as:...
, so that a steadier DC output can be obtained across the terminals of the filter capacitor. The choke presents a high impedance
Electrical impedance

Electrical impedance, or simply impedance, describes a measure of opposition to a sinusoidal alternating current . Electrical impedance extends the concept of Electrical resistance to AC circuits, describing not only the relative amplitudes of the voltage and Electric current, but also the relative Phase ....
 to the ripple current.

If the DC load is very demanding of a smooth supply voltage, a voltage regulator
Voltage regulator

A voltage regulator is an electricity regulator designed to automatically maintain a constant voltage level.It may use an electromechanical mechanism, or passive or active electronic components....
 will be used either instead of or 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.

Voltage-doubling rectifiers

The simple half wave rectifier can be built in two versions with the diode pointing in opposite directions, one version connects the negative terminal of the output direct to the AC supply and the other connects the positive terminal of the output direct to the AC supply. By combining both of these with separate output smoothing it is possible to get an output voltage of nearly double the peak AC input voltage. This also provides a tap in the middle, which allows use of such a circuit as a split rail supply.

A variant of this is to use two capacitors in series for the output smoothing on a bridge rectifier then place a switch between the midpoint of those capacitors and one of the AC input terminals. With the switch open this circuit will act like a normal bridge rectifier with it closed it will act like a voltage doubling rectifier. In other words this makes it easy to derive a voltage of roughly 320V (+/- around 15%) DC from any mains supply in the world, this can then be fed into a relatively simple switched mode power supply.