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The magnetic amplifier (colloquially known as the "mag amp") is an electromagnetic
Electromagnetism

Electromagnetism is the physics of the electromagnetic field, a field which exerts a force on Elementary particles with the property of electric charge and which is reciprocally affected by the presence and motion of such particles....
 device for amplifying electrical signals. The magnetic amplifier was invented early in the 20th century, and was used as an alternative to 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....
 amplifiers where robustness and high current capacity were required. World War II
World War II

World War II, or the Second World War , was a global military conflict which involved a Participants in World War II, including all of the great powers, organised into two opposing military alliances: the Allies of World War II and the Axis powers....
 Germany
Germany

Germany , officially the Federal Republic of Germany , is a country in Central Europe. It is bordered to the north by the North Sea, Denmark, and the Baltic Sea; to the east by Poland and the Czech Republic; to the south by Austria and Switzerland; and to the west by France, Luxembourg, Belgium, and the Netherlands....
 perfected this type of amplifier, and it was used for instance in the V-2 rocket
V-2 rocket

The V-2 rocket was the first ballistic missile and first man-made object to achieve sub-orbital spaceflight, the progenitor of all modern rockets....
. The magnetic amplifier has now been largely superseded by the transistor
Transistor

In electronics, a transistor is a semiconductor device commonly used to Electronic amplifier or switch Electronics signals. A transistor is made of a solid piece of a semiconductor material, with at least three terminals for connection to an external circuit....
-based amplifier, except in a few safety critical, high reliability or extremely demanding applications.

ally a mag amp device may resemble a transformer
Transformer

A transformer is a device that transfers electrical energy from one electrical network to another through inductive coupling conductors — the transformer's coils or "windings"....
 but the operating principle is quite different from a transformer - essentially the mag amp is a saturable reactor
Saturable reactor

A saturable reactor in electrical engineering is a special form of inductor where the magnetic core can be deliberately saturation by means of a direct current electric current flowing in a control winding....
.






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Encyclopedia


The magnetic amplifier (colloquially known as the "mag amp") is an electromagnetic
Electromagnetism

Electromagnetism is the physics of the electromagnetic field, a field which exerts a force on Elementary particles with the property of electric charge and which is reciprocally affected by the presence and motion of such particles....
 device for amplifying electrical signals. The magnetic amplifier was invented early in the 20th century, and was used as an alternative to 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....
 amplifiers where robustness and high current capacity were required. World War II
World War II

World War II, or the Second World War , was a global military conflict which involved a Participants in World War II, including all of the great powers, organised into two opposing military alliances: the Allies of World War II and the Axis powers....
 Germany
Germany

Germany , officially the Federal Republic of Germany , is a country in Central Europe. It is bordered to the north by the North Sea, Denmark, and the Baltic Sea; to the east by Poland and the Czech Republic; to the south by Austria and Switzerland; and to the west by France, Luxembourg, Belgium, and the Netherlands....
 perfected this type of amplifier, and it was used for instance in the V-2 rocket
V-2 rocket

The V-2 rocket was the first ballistic missile and first man-made object to achieve sub-orbital spaceflight, the progenitor of all modern rockets....
. The magnetic amplifier has now been largely superseded by the transistor
Transistor

In electronics, a transistor is a semiconductor device commonly used to Electronic amplifier or switch Electronics signals. A transistor is made of a solid piece of a semiconductor material, with at least three terminals for connection to an external circuit....
-based amplifier, except in a few safety critical, high reliability or extremely demanding applications.

Principle of operation

Visually a mag amp device may resemble a transformer
Transformer

A transformer is a device that transfers electrical energy from one electrical network to another through inductive coupling conductors — the transformer's coils or "windings"....
 but the operating principle is quite different from a transformer - essentially the mag amp is a saturable reactor
Saturable reactor

A saturable reactor in electrical engineering is a special form of inductor where the magnetic core can be deliberately saturation by means of a direct current electric current flowing in a control winding....
. It makes use of magnetic saturation
Saturation (magnetic)

Seen in some magnetic materials, saturation is the state reached when an increase in applied external magnetizing field H cannot increase the magnetization of the material further, so the total magnetic field B levels off....
 of the core, a non-linear property of a certain class of transformer cores. For controlled saturation characteristics the magnetic amplifier employs core materials that have been designed to have a specific B-H curve
Hysteresis

A system with hysteresis can be summarized as a system that may be in any number of states, independent of the inputs to the system. To be exact, a system with hysteresis exhibits path-dependence, or "rate-independent memory"....
 shape that is highly rectangular, in contrast to the slowly tapering B-H curve of softly saturating core materials that are often used in normal transformers.

The typical magnetic amplifier consists of two physically separate but similar transformer magnetic cores, each of which has two windings - a control winding and an AC winding. A small DC current from a low impedance source is fed into the series-connected control windings. The AC windings may be connected either in series or in parallel, the configurations resulting in different types of mag amps. The amount of control current fed into the control winding sets the point in the AC winding waveform at which either core will saturate. In saturation, the AC winding on the saturated core will go from a high impedance state ("off") into a very low impedance state ("on") - that is, the control current controls at which voltage the mag amp switches "on".

A relatively small DC current on the control winding is able to control or switch large AC currents on the AC windings. This results in current amplification.

Applications


Magnetic amplifiers were used extensively as the switching element in early switched-mode (SMPS
SMPS

SMPS may refer to:*Switched-mode power supply*Single member plurality system*Society for Marketing Professional Services...
) power supplies, as well as in lighting control. They have been largely superseded by semiconductor based solid-state switches, though recently there has been some regained interest in using mag amps in compact and reliable switching power supplies. PC ATX power supplies often use mag amps for secondary side voltage regulation.

Magnetic amplifiers are still used in some arc welders.

Magnetic amplifier transformer cores designed specifically for switch mode power supplies are currently manufactured by several large electromagnetics companies, including Metglas and Mag-Inc.

Magnetic amplifiers can be used for measuring high DC-voltages without direct connection to the high voltage and are therefore still used in the HVDC-technique.

Another small book on the subject of Magnetic amplifiers by the US Navy (1951)

Misnomer uses

Late in the 20th century, Robert Carver designed and produced several high quality high powered audio amplifiers, calling them magnetic amplifiers. In fact, they were in most respects conventional audio amplifier designs with an unusual power supply circuit. They were not magnetic amplfiers in the sense of this article.

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