Voltage Multiplier

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Villard cascade voltage multiplier. A voltage multiplier multiplier is an electrical circuit that converts AC electrical power from a lower voltage to a higher DC voltage by means of  capacitors and diodes combined into a network. Voltage multipliers can be used to generate bias voltages of a few volts or tens of  volts or millions of volts for purposes such as high-energy physics experiments and lightning safety testing. The most common type of voltage multiplier is the half-wave series multiplier, also called the Villard cascade. Such a circuit is shown opposite. Assum Assuming ing that the peak voltage voltage of the AC sourc sourcee is +U s we can descri describe be the the (simplified) working of the cascade as follows:

1. 2. 3.

negative peak (−U s): The C1 capacitor is charged through diode D 1 to 0V (potential difference between left and right plate of the capacitor is U s) positive peak (+U s): the potential of C1 adds with that of the source, thus charging C2 to 2Us through D2 negative peak: potential of C 1 drops to 0V thus allowing C 3 to be charged through D3 to 2Us.

4.

posit positiv ivee peak: peak: potent potential ial of C 1 rise risess to 2Us (analo (analogo gousl usly y to step step 2), 2), also also charging C4 to 2Us. The output voltage (the sum of voltages under C 2 and C4) raises till 4Us.

In reality more cycles are required for C 4 to reach the full voltage. Adding more segments analogous to C 1-D1-D2-C2, we can increase output voltage by 2U s.

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1 Break Breakdown down Voltage 2 Alter Alternativ nativee diagr diagrams ams 3 App Applic licati ations ons 4 Se Seee al also so

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5 Ext Extern ernal al lin links ks

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[edit edit]] Breakdown Voltage While While the the multi multipli plier er can be used used to produc producee thou thousan sands ds of volts volts of outpu output, t, the individual components do not need to be rated to withstand the entire voltage range. Each component only needs to be concerned with the relative voltage differences directly across its own terminals and of the components immediately adjacent to it. Typically a voltage multiplier will be physically arranged like a ladder, so that the progressively increasing voltage potential is not given the opportunity to arc across to the much lower potential sections of the circuit. Note Note that that some some safet safety y marg margin in is neede needed d acro across ss the rela relativ tivee range range of voltag voltagee differences in the multiplier, so that the ladder can survive the shorted failure of at least one diode or capacitor component. Otherwise a single-point shorting failure could successively over-voltage and destroy each next component in the multiplier, potentially destroying the entire multiplier chain.

[edit edit]] Alternative diagrams Alternatives: T The images in this article show the diodes at right angles to the capacitors, stressing that stray capacity between the columns should be minimized. W The diodes are arranged diagonally, this stresses that the diodes hold DCvoltage.

Z Sometimes the capacitors of the two columns are drawn next to each other (no shift shift), ), bu butt this this make makess less less sense sense,, as the capac capacito itors rs are are on diffe differe rent nt potential. X Two cascades can be driven by a single center-tapped transformer to get fullwave rectification leading to less ripple. Stack  A second cascade can be stacked onto the first one driven by a high voltage isolated second secondary winding connected with 180° phase shift to get full wave rectification. A single secondary winding of a transformer can drive two cascades of different polarity at the same time. Two of these can in turn be stacked. The goal is to reduce the ripple and the capacity at the same time. To further reduce ripple, an even number of stages is used and the connecting column gets bigger capacitors.

[edit edit]] Applications The high-voltage supplies for cathode ray tubes often use voltage multipliers with the final-stage smoothing capacitor formed by the interior and exterior aquadag coatings on the CRT itself. A common type of voltage multiplier used in high-energy physics is the CockcroftWalton generato generatorr (which (which was designed designed by John Douglas Cockcro Cockcroft ft and Ernest Thomas Sinton Walton for a particle accelerator, accelerator , for use in research that won them the Nobel Prize in Physics in 1951 1951). ).