280px, Villard cascade voltage multiplier.
A voltage multiplier is an
electrical circuit
An electrical network is an interconnection of electrical components (e.g., batteries, resistors, inductors, capacitors, switches, transistors) or a model of such an interconnection, consisting of electrical elements (e.g., voltage sources, ...
that converts AC electrical power from a lower
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
to a higher DC voltage, typically using a network of
capacitor
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.
The effect of ...
s and
diode
A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other.
A diode ...
s.
Voltage multipliers can be used to generate a few volts for electronic appliances, to 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 (but actually invented by
Heinrich Greinacher
Heinrich Greinacher (May 31, 1880 in St. Gallen – April 17, 1974 in Bern) was a Swiss physicist. He is regarded as an original experimenter and is the developer of the magnetron and the Greinacher multiplier.
Greinacher was the only child of ...
).
Operation
Assuming that the peak voltage of the AC source is +U
s, and that the C values are sufficiently high to allow, when charged, that a current flows with no significant change in voltage, then the (simplified) working of the cascade is as follows:
# negative peak (−U
s): The C
1 capacitor is charged through diode D
1 to U
s V (
potential difference
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
between left and right plate of the capacitor is U
s)
# positive peak (+U
s): the potential of C
1 adds with that of the source, thus charging C
2 to 2U
s through D
2
# negative peak: potential of C
1 has dropped to 0 V thus allowing C
3 to be charged through D
3 to 2U
s.
# positive peak: potential of C
2 rises to 2U
s (analogously to step 2), also charging C
4 to 2U
s. The output voltage (the sum of voltages under C
2 and C
4) rises until 4U
s is reached.
In reality more cycles are required for C
4 to reach the full voltage. Each additional stage of two diodes and two capacitors increases the output voltage by twice the peak AC supply voltage.
Voltage doubler and tripler
![Cockcroft Walton voltage multiplier circuit](https://upload.wikimedia.org/wikipedia/commons/7/7b/Cockcroft_Walton_voltage_multiplier_circuit.svg)
A voltage doubler uses two stages to approximately double the DC voltage that would have been obtained from a single-stage
rectifier
A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The reverse operation (converting DC to AC) is performed by an Power ...
. An example of a voltage doubler is found in the input stage of
switch mode power supplies
A switched-mode power supply (switching-mode power supply, switch-mode power supply, switched power supply, SMPS, or switcher) is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently.
Lik ...
containing a SPDT switch to select either 120 V or 240 V supply. In the 120 V position the input is typically configured as a full-wave voltage doubler by opening one AC connection point of a bridge rectifier, and connecting the input to the junction of two series-connected filter capacitors. For 240 V operation, the switch configures the system as a full-wave bridge, re-connecting the capacitor center-tap wire to the open AC terminal of a bridge rectifier system. This allows 120 or 240 V operation with the addition of a simple SPDT switch.
A voltage tripler is a three-stage voltage multiplier. A tripler is a popular type of voltage multiplier. The output voltage of a tripler is in practice below three times the peak input voltage due to their high
impedance, caused in part by the fact that as each
capacitor
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.
The effect of ...
in the chain supplies power to the next, it partially discharges, losing voltage doing so.
Triplers were commonly used in color television receivers to provide the high voltage for the
cathode ray tube
A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms ( oscilloscope), pictu ...
(CRT, picture tube).
Triplers are still used in
high voltage
High voltage electricity refers to electrical potential large enough to cause injury or damage. In certain industries, ''high voltage'' refers to voltage above a certain threshold. Equipment and conductors that carry high voltage warrant spec ...
supplies such as
copier
A photocopier (also called copier or copy machine, and formerly Xerox machine, the generic trademark) is a machine that makes copies of documents and other visual images onto paper or plastic film quickly and cheaply. Most modern photocopiers u ...
s,
laser printer
Laser printing is an electrostatic digital printing process. It produces high-quality text and graphics (and moderate-quality photographs) by repeatedly passing a laser beam back and forth over a negatively-charged cylinder called a "drum" to d ...
s,
bug zapper
A bug zapper, more formally called an electrical discharge insect control system, electric insect killer or (insect) electrocutor trap, is a device that attracts and kills flying insects that are attracted by light. A light source attracts insect ...
s and
electroshock weapon
An electroshock weapon is a less-lethal weapon that utilizes an electric shock to incapacitate a target by either temporarily disrupting voluntary muscle control and/or through pain compliance. There are several different types of electroshock w ...
s.
Breakdown voltage
While the multiplier can be used to produce thousands of volts of output, 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 that some safety margin is needed across the relative range of voltage 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.
Other circuit topologies
![Full-wave Villard cascade](https://upload.wikimedia.org/wikipedia/commons/c/ca/Full-wave_Villard_cascade.svg)
;Stacking:
![Stacked Villard cascade](https://upload.wikimedia.org/wikipedia/commons/b/ba/Stacked_Villard_cascade.svg)
An even number of diode-capacitor cells is used in any column so that the cascade ends on a smoothing cell. If it were odd and ended on a clamping cell the
ripple
Ripple may refer to:
Science and technology
* Capillary wave, commonly known as ripple, a wave traveling along the phase boundary of a fluid
** Ripple, more generally a disturbance, for example of spacetime in gravitational waves
* Ripple (electri ...
voltage would be very large. Larger capacitors in the connecting column also reduce ripple but at the expense of charging time and increased diode current.
Dickson charge pump
![Dickson voltage multiplier](https://upload.wikimedia.org/wikipedia/commons/1/12/Dickson_voltage_multiplier.svg)
The Dickson charge pump, or Dickson multiplier, is a modification of the
Greinacher/Cockcroft–Walton multiplier. Unlike that circuit, however, the Dickson multiplier takes a DC supply as its input so is a form of
DC-to-DC converter
A DC-to-DC converter is an electronic circuit or electromechanical device that converts a source of direct current (DC) from one voltage level to another. It is a type of electric power converter. Power levels range from very low (small batteries) ...
. Also, unlike Greinacher/Cockcroft–Walton which is used on high-voltage applications, the Dickson multiplier is intended for low-voltage purposes. In addition to the DC input, the circuit requires a feed of two
clock pulse
In electronics and especially synchronous digital circuits, a clock signal (historically also known as ''logic beat'') oscillates between a high and a low state and is used like a metronome to coordinate actions of digital circuits.
A clock signa ...
trains with an amplitude swinging between the DC supply rails. These pulse trains are in antiphase.
To describe the ideal operation of the circuit, number the diodes D1, D2 etc. from left to right and the capacitors C1, C2 etc. When the clock
is low, D1 will charge C1 to ''V''
in. When
goes high the top plate of C1 is pushed up to 2''V''
in. D1 is then turned off and D2 turned on and C2 begins to charge to 2''V''
in. On the next clock cycle
again goes low and now
goes high pushing the top plate of C2 to 3''V''
in. D2 switches off and D3 switches on, charging C3 to 3''V''
in and so on with charge passing up the chain, hence the name
charge pump
A charge pump is a kind of DC-to-DC converter that uses capacitors for energetic charge storage to raise or lower voltage. Charge-pump circuits are capable of high efficiencies, sometimes as high as 90–95%, while being electrically simple c ...
. The final diode-capacitor cell in the cascade is connected to ground rather than a clock phase and hence is not a multiplier; it is a
peak detector
The precision rectifier is a configuration obtained with an operational amplifier in order to have a circuit behave like an ideal diode and rectifier.Paul Horowitz and Winfield Hill, ''The Art of Electronics''. 2nd ed. Cambridge University Press, ...
which merely provides
smoothing
In statistics and image processing, to smooth a data set is to create an approximating function (mathematics), function that attempts to capture important patterns in the data, while leaving out noise or other fine-scale structures/rapid phenomena ...
.
There are a number of factors which reduce the output from the ideal case of ''nV''
in. One of these is the threshold voltage, ''V''
T of the switching device, that is, the voltage required to turn it on. The output will be reduced by at least ''nV''
T due to the volt drops across the switches.
Schottky diode
The Schottky diode (named after the German physicist Walter H. Schottky), also known as Schottky barrier diode or hot-carrier diode, is a semiconductor diode formed by the junction of a semiconductor with a metal. It has a low forward voltage ...
s are commonly used in Dickson multipliers for their low forward voltage drop, amongst other reasons. Another difficulty is that there are
parasitic capacitance
Parasitic capacitance is an unavoidable and usually unwanted capacitance that exists between the parts of an electronic component or circuit simply because of their proximity to each other. When two electrical conductors at different voltages a ...
s to ground at each node. These parasitic capacitances act as voltage dividers with the circuit's storage capacitors reducing the output voltage still further. Up to a point, a higher clock frequency is beneficial: the ripple is reduced and the high frequency makes the remaining ripple easier to filter. Also the size of capacitors needed is reduced since less charge needs to be stored per cycle. However, losses through stray capacitance increase with increasing clock frequency and a practical limit is around a few hundred kilohertz.
![Dickson MOSFET voltage multiplier](https://upload.wikimedia.org/wikipedia/commons/7/76/Dickson_MOSFET_voltage_multiplier.svg)
Dickson multipliers are frequently found in
integrated circuit
An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...
s (ICs) where they are used to increase a low-voltage battery supply to the voltage needed by the IC. It is advantageous to the IC designer and manufacturer to be able to use the same technology and the same basic device throughout the IC. For this reason, in the popular
CMOS
Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss", ) is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSFE ...
technology ICs the transistor which forms the basic building block of circuits is the
MOSFET
The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...
. Consequently, the diodes in the Dickson multiplier are often replaced with MOSFETs wired to behave as diodes.
![Dickson multiplier with 2nd transistor](https://upload.wikimedia.org/wikipedia/commons/e/e9/Dickson_multiplier_with_2nd_transistor.svg)
The diode-wired MOSFET version of the Dickson multiplier does not work very well at very low voltages because of the large drain-source volt drops of the MOSFETs. Frequently, a more complex circuit is used to overcome this problem. One solution is to connect in parallel with the switching MOSFET another MOSFET biased into its linear region. This second MOSFET has a lower drain-source voltage than the switching MOSFET would have on its own (because the switching MOSFET is driven hard on) and consequently the output voltage is increased. The gate of the linear biased MOSFET is connected to the output of the next stage so that it is turned off while the next stage is charging from the previous stage's capacitor. That is, the linear-biased transistor is turned off at the same time as the switching transistor.
An ideal 4-stage Dickson multiplier (5× multiplier) with an input of would have an output of . However, a diode-wired MOSFET 4-stage multiplier might only have an output of . Adding parallel MOSFETs in the linear region improves this to around . More complex circuits still can achieve an output much closer to the ideal case.
Many other variations and improvements to the basic Dickson circuit exist. Some attempt to reduce the switching threshold voltage such as the Mandal-Sarpeshkar multiplier or the Wu multiplier. Other circuits cancel out the threshold voltage: the Umeda multiplier does it with an externally provided voltage and the Nakamoto multiplier does it with internally generated voltage. The Bergeret multiplier concentrates on maximising power efficiency.
Modification for RF power
![Modified Dickson multiplier](https://upload.wikimedia.org/wikipedia/commons/9/91/Modified_Dickson_multiplier.svg)
In CMOS integrated circuits clock signals are readily available, or else easily generated. This is not always the case in
RF integrated circuits, but often a source of RF power will be available. The standard Dickson multiplier circuit can be modified to meet this requirement by simply grounding the normal input and one of the clock inputs. RF power is injected into the other clock input, which then becomes the circuit input. The RF signal is effectively the clock as well as the source of power. However, since the clock is injected only into every other node the circuit only achieves a stage of multiplication for every second diode-capacitor cell. The other diode-capacitor cells are merely acting as peak detectors and smoothing the ripple without increasing the multiplication.
Cross-coupled switched capacitor
![Cross-coupled voltage multiplier](https://upload.wikimedia.org/wikipedia/commons/d/db/Cross-coupled_voltage_multiplier.svg)
A voltage multiplier may be formed of a cascade of voltage doublers of the
cross-coupled switched capacitor type. This type of circuit is typically used instead of a Dickson multiplier when the source voltage is or less. Dickson multipliers have increasingly poor power conversion efficiency as the input voltage drops because the voltage drop across the diode-wired transistors becomes much more significant compared to the output voltage. Since the transistors in the cross-coupled circuit are not diode-wired the volt-drop problem is not so serious.
The circuit works by alternately switching the output of each stage between a voltage doubler driven by
and one driven by
. This behaviour leads to another advantage over the Dickson multiplier: reduced ripple voltage at double the frequency. The increase in ripple frequency is advantageous because it is easier to remove by filtering. Each stage (in an ideal circuit) raises the output voltage by the peak clock voltage. Assuming that this is the same level as the DC input voltage then an ''n'' stage multiplier will (ideally) output ''nV''
in. The chief cause of losses in the cross-coupled circuit is parasitic capacitance rather than switching threshold voltage. The losses occur because some of the energy has to go into charging up the parasitic capacitances on each cycle.
Applications
280px, TV cascade (green) and (blue).">flyback transformer (blue).
The high-voltage supplies for
cathode-ray tube
A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms (oscilloscope), pictur ...
s (CRTs) in TVs often use voltage multipliers with the final-stage smoothing capacitor formed by the interior and exterior
aquadag Aquadag is a trade name for a water-based colloidal graphite coating commonly used in cathode ray tubes (CRTs). It is manufactured by Acheson Industries, a subsidiary of ICI. The name is a shortened form of "Aqueous Deflocculated Acheson Graphite" ...
coatings on the CRT itself. CRTs were formerly a common component in television sets. Voltage multipliers can still be found in modern TVs,
photocopier
A photocopier (also called copier or copy machine, and formerly Xerox machine, the generic trademark) is a machine that makes copies of documents and other visual images onto paper or plastic film quickly and cheaply. Most modern photocopiers u ...
s, and
bug zapper
A bug zapper, more formally called an electrical discharge insect control system, electric insect killer or (insect) electrocutor trap, is a device that attracts and kills flying insects that are attracted by light. A light source attracts insect ...
s.
[McGowan, p. 87]
High voltage multipliers are used in spray painting equipment, most commonly found in automotive manufacturing facilities. A voltage multiplier with an output of about 100kV is used in the nozzle of the paint sprayer to electrically charge the atomized paint particles which then get attracted to the oppositely charged metal surfaces to be painted. This helps reduce the volume of paint used and helps in spreading an even coat of paint.
A common type of voltage multiplier used in high-energy physics is the
Cockcroft–Walton generator
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 Tho ...
(which was designed by
John Douglas Cockcroft
Sir John Douglas Cockcroft, (27 May 1897 – 18 September 1967) was a British physicist who shared with Ernest Walton the Nobel Prize in Physics in 1951 for splitting the atomic nucleus, and was instrumental in the development of nuclea ...
and
Ernest Thomas Sinton Walton
Ernest Thomas Sinton Walton (6 October 1903 – 25 June 1995) was an Irish physicist and Nobel laureate. He is best known for his work with John Cockcroft to construct one of the earliest types of particle accelerator, the Cockcroft–Walton ge ...
for a
particle accelerator
A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams.
Large accelerators are used for fundamental research in particle ...
for use in research that won them the
Nobel Prize in Physics
)
, image = Nobel Prize.png
, alt = A golden medallion with an embossed image of a bearded man facing left in profile. To the left of the man is the text "ALFR•" then "NOBEL", and on the right, the text (smaller) "NAT•" then " ...
in 1951).
See also
*
Marx generator
A Marx generator is an electrical circuit first described by Erwin Otto Marx in 1924. Its purpose is to generate a high-voltage pulse from a low-voltage DC supply. Marx generators are used in high-energy physics experiments, as well as to simulate ...
(a device that uses
spark gap
A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the potential difference between the conductor ...
s instead of diodes as the switching elements and can deliver higher peak currents than diodes can).
*
Boost converter
A boost converter (step-up converter) is a DC-to-DC power converter that steps up voltage (while stepping down current) from its input (supply) to its output (load). It is a class of switched-mode power supply (SMPS) containing at least two semi ...
(a DC-to-DC power converter that steps up voltage, frequently using an inductor)
Notes
Bibliography
*Campardo, Giovanni; Micheloni, Rino; Novosel, David ''VLSI-design of Non-volatile Memories'', Springer, 2005 .
*Lin, Yu-Shiang ''Low Power Circuits for Miniature Sensor Systems'', Publisher ProQuest, 2008 .
*Liu, Mingliang ''Demystifying Switched Capacitor Circuits'', Newnes, 2006 .
*McGowan, Kevin, ''Semiconductors: From Book to Breadboard'', Cengage Learning, 2012 .
*Peluso, Vincenzo; Steyaert, Michiel; Sansen, Willy M. C. ''Design of Low-voltage Low-power CMOS Delta-Sigma A/D Converters'', Springer, 1999 .
*Yuan, Fei ''CMOS Circuits for Passive Wireless Microsystems'', Springer, 2010 .
*Zumbahlen, Hank ''Linear Circuit Design Handbook'', Newnes, 2008 .
External links
{{Commons category, Voltage doubler
Basic multiplier circuitsCockcroft Walton multipliersSchematic of Kadette brand (International Radio Corp.) model 1019 A 1937
radio
Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmit ...
with a
vacuum tube
A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied.
The type kn ...
(25Z5) voltage multiplier rectifier.
Electrical circuits
Electric power conversion
Rectifiers