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The Cockcroft–Walton (CW) generator, or multiplier, is an electric circuit that generates a high DC voltage from a low voltage AC or pulsing DC input. It was named after the British and Irish physicists John Douglas Cockcroft and Ernest Thomas Sinton Walton, who in 1932 used this circuit design to power their particle accelerator, performing the first artificial nuclear disintegration in history. They used this voltage multiplier cascade for most of their research, which in 1951 won them the Nobel Prize in Physics for "Transmutation of atomic nuclei by artificially accelerated atomic particles". Less well known is the fact that the circuit was discovered much earlier, in 1919, by Heinrich Greinacher, a Swiss physicist. For this reason, this doubler cascade is sometimes also referred to as the Greinacher multiplier. Cockcroft-Walton circuits are still used in particle accelerators. They also are used in everyday electronic devices that require high voltages, such as x-ray machines, television sets, and photocopiers. ==Design== The CW is a voltage multiplier that converts AC or pulsing DC electrical power from a low voltage level to a higher DC voltage level. It is made up of a voltage multiplier ladder network of capacitors and diodes to generate high voltages. Unlike transformers, this method eliminates the requirement for the heavy core and the bulk of insulation/potting required. Using only capacitors and diodes, these voltage multipliers can step up relatively low voltages to extremely high values, while at the same time being far lighter and cheaper than transformers. The biggest advantage of such circuits is that the voltage across each stage of the cascade is equal to only twice the peak input voltage in a half wave rectifier. In a full wave rectifier it is three times the input voltage. It has the advantage of requiring relatively low cost components and being easy to insulate. One can also tap the output from any stage, like a multitapped transformer. To understand the circuit operation, see the diagram of the two-stage version at right. Assume the circuit is powered by an alternating voltage ''V''i with a peak value of ''V''p. After the input voltage is turned on *When the input voltage ''V''i reaches its negative peak −''V''p, current flows through diode ''D1'' to charge capacitor ''C1'' to a voltage of ''V''p. *When ''V''i reverses polarity and reaches its positive peak +''V''p, it adds to the capacitor's voltage to produce a voltage of 2''V''p on ''C1''s righthand plate. Since ''D1'' is reverse-biased, current flows from ''C1'' through diode ''D2'', charging capacitor ''C2'' to a voltage of 2''V''p. *When ''V''i reverses polarity again, current from ''C2'' flows through diode ''D3'', charging capacitor ''C3'' also to a voltage of 2''V''p. *When ''V''i reverses polarity again, current from ''C3'' flows through diode ''D4'', charging capacitor ''C4'' also to a voltage of 2''V''p. With each change in input polarity, current flows up the "stack" of capacitors through the diodes, until they are all charged. All the capacitors are charged to a voltage of 2''V''p, except for ''C1'', which is charged to ''V''p. The key to the voltage multiplication is that, while the capacitors are charged in parallel, they are connected to the load in series. Since ''C2'' and ''C4'' are in series between the output and ground, the total output voltage (under no-load conditions) is ''V''o = 4''V''p. This circuit can be extended to any number of stages. The output voltage is twice the peak input voltage multiplied by the number of stages ''N'' : or equivalently the peak-to-peak input voltage swing ''V''pp times the number of stages. The number of stages is equal to the number of capacitors in series between the output and ground. One way to look at the circuit is that it functions as a charge "pump", pumping electric charge in one direction, up the stack of capacitors. The CW circuit, along with other similar capacitor circuits, are often called charge pumps. For substantial loads, the charge on the capacitors is partially depleted, and the output voltage drops according to the output current divided by the capacitance. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cockcroft–Walton generator」の詳細全文を読む スポンサード リンク
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