Voltage doubler
A voltage doubler is an electronic circuit which charges capacitors from the input voltage and switches these charges in such a way that, in the ideal case, exactly twice the voltage is produced at the output as at its input.
The simplest of these circuits is a form of rectifier which take an AC voltage as input and outputs a doubled DC voltage. The switching elements are simple diodes and they are driven to switch state merely by the alternating voltage of the input. DC-to-DC voltage doublers cannot switch in this way and require a driving circuit to control the switching. They frequently also require a switching element that can be controlled directly, such as a transistor, rather than relying on the voltage across the switch as in the simple AC-to-DC case.
Voltage doublers are a variety of voltage multiplier circuits. Many, but not all, voltage doubler circuits can be viewed as a single stage of a higher order multiplier: cascading identical stages together achieves a greater voltage multiplication.
Voltage doubling rectifiers
Villard circuit
The Villard circuit, conceived by
Greinacher circuit
The Greinacher voltage doubler is a significant improvement over the Villard circuit for a small cost in additional components. The ripple is much reduced, nominally zero under open-circuit load conditions, but when current is being drawn depends on the resistance of the load and the value of the capacitors used. The circuit works by following a Villard cell stage with what is in essence a
This circuit was first invented by
Delon circuit
The Delon circuit uses a
The circuit consists of two half-wave peak detectors, functioning in exactly the same way as the peak detector cell in the Greinacher circuit. Each of the two peak detector cells operates on opposite half-cycles of the incoming waveform. Since their outputs are in series, the output is twice the peak input voltage.
Switched capacitor circuits
It is possible to use the simple diode-capacitor circuits described above to double the voltage of a DC source by preceding the voltage doubler with a chopper circuit. In effect, this converts the DC to AC before application to the voltage doubler.[8] More efficient circuits can be built by driving the switching devices from an external clock so that both functions, the chopping and multiplying, are achieved simultaneously. Such circuits are known as switched capacitor circuits. This approach is especially useful in low-voltage battery-powered applications where integrated circuits require a voltage supply greater than the battery can deliver. Frequently, a clock signal is readily available on board the integrated circuit and little or no additional circuitry is needed to generate it.[9]
Conceptually, perhaps the simplest switched capacitor configuration is that shown schematically in figure 5. Here two capacitors are simultaneously charged to the same voltage in parallel. The supply is then switched off and the capacitors are switched into series. The output is taken from across the two capacitors in series resulting in an output double the supply voltage. There are many different switching devices that could be used in such a circuit, but in integrated circuits MOSFET devices are frequently employed.[10]
Another basic concept is the charge pump, a version of which is shown schematically in figure 6. The charge pump capacitor, CP, is first charged to the input voltage. It is then switched to charging the output capacitor, CO, in series with the input voltage resulting in CO eventually being charged to twice the input voltage. It may take several cycles before the charge pump succeeds in fully charging CO but after steady state has been reached it is only necessary for CP to pump a small amount of charge equivalent to that being supplied to the load from CO. While CO is disconnected from the charge pump it partially discharges into the load resulting in ripple on the output voltage. This ripple is smaller for higher clock frequencies since the discharge time is shorter, and is also easier to filter. Alternatively, the capacitors can be made smaller for a given ripple specification. The practical maximum clock frequency in integrated circuits is typically in the hundreds of kilohertz.[11]
Dickson charge pump
The Dickson charge pump, or
The Dickson multiplier is frequently employed in integrated circuits where the supply voltage (from a battery for instance) is lower than that required by the circuitry. It is advantageous in integrated circuit manufacture that all the semiconductor components are of basically the same type. MOSFETs are commonly the standard logic block in many integrated circuits. For this reason the diodes are often replaced by this type of transistor, but wired to function as a diode - an arrangement called a diode-wired MOSFET. Figure 8 shows a Dickson voltage doubler using diode-wired n-channel enhancement type MOSFETs.[13]
There are many
As an example, an alkaline battery cell has a nominal voltage of 1.5 V. A voltage doubler using ideal switching elements with zero voltage drop will output double this, namely 3.0 V. However, the drain-source voltage drop of a diode-wired MOSFET when it is in the on state must be at least the gate threshold voltage which might typically be 0.9 V.[15] This voltage "doubler" will only succeed in raising the output voltage by about 0.6 V to 2.1 V. If the drop across the final smoothing transistor is also taken into account the circuit may not be able to increase the voltage at all without using multiple stages. A typical Schottky diode, on the other hand, might have an on state voltage of 0.3 V.[16] A doubler using this Schottky diode will result in a voltage of 2.7 V, or at the output after the smoothing diode, 2.4 V.[17]
Cross-coupled switched capacitors
Cross-coupled switched capacitor circuits come into their own for very low input voltages. Wireless battery driven equipment such as pagers, bluetooth devices and the like may require a single-cell battery to continue to supply power when it has discharged to under a volt.[18]
When clock is low transistor Q2 is turned off. At the same time clock is high turning on transistor Q1 resulting in capacitor C1 being charged to Vin. When goes high the top plate of C1 is pushed up to twice Vin. At the same time switch S1 closes so this voltage appears at the output. At the same time Q2 is turned on allowing C2 to charge. On the next half cycle the roles will be reversed: will be low, will be high, S1 will open and S2 will close. Thus, the output is supplied with 2Vin alternately from each side of the circuit.[19]
The loss is low in this circuit because there are no diode-wired MOSFETs and their associated threshold voltage problems. The circuit also has the advantage that the ripple frequency is doubled because there are effectively two voltage doublers both supplying the output from out of phase clocks. The primary disadvantage of this circuit is that stray capacitances are much more significant than with the Dickson multiplier and account for the larger part of the losses in this circuit.[20]
See also
- Boost converter
- Buck-boost converter
- DC to DC converter
- Flyback converter
References
- ^ Kind & Feser 2001, p. 28
- ^ a b
- Earl Gates (2011). Introduction to Electronics. Cengage Learning. pp. 283–284. ISBN 978-1-111-12853-1.
- James F. Cox (2002). Fundamentals of Linear Electronics: Integrated and Discrete. Cengage Learning. pp. 42–43. ISBN 0-7668-3018-7.
- Robert Diffenderfer (2005). Electronic Devices: Systems and Applications. Cengage Learning. p. 135. ISBN 1-4018-3514-7.
- Earl Gates (2011). Introduction to Electronics. Cengage Learning. pp. 283–284.
- ^ Mehra, p. 284
- ^ Kind & Feser 2001, p. 29
- ^ Kind & Feser 2001, p. 30
- ^ Ryder 1970, p. 107
- ^ Kories and Schmidt-Walter, p.615
Millman and Halkias, p. 109
Wharton and Howorth, pp. 68–69 - ^ McComb, pp.148-150
- ^ Liu 2006, pp. 225–226
- ^ Ahmed, p.164
- ^ Zumbahlen, p.741
- ^ Liu 2006, p. 226
Yuan, pp.13-14 - ^ Liu 2006, p. 226
Yuan, p.14 - ^ Liu 2006, pp. 228–232
Yuan, 14-21 - ^ Liou et al., p.185
- ^ Bassett & Taylor 2003, p. 17/27
- ^ Yuan, p.17
- ^ Peluso et al., pp.36-37
Liu 2006, pp. 232–234 - ^ Campardo et al., p.377
Peluso et al., p.36
Liu 2006, p. 234 - ^ Peluso et al., p.36
Liu 2006, p. 234
Bibliography
- Ahmed, Syed Imran Pipelined ADC Design and Enhancement Techniques, Springer, 2010 ISBN 90-481-8651-X.
- Bassett, R. J.; Taylor, P. D. (2003), "17. Power Semiconductor Devices", Electrical Engineer's Reference Book, Newnes, pp. 17/1–17/37, ISBN 0-7506-4637-3
- Campardo, Giovanni; Micheloni, Rino; Novosel, David VLSI-design of Non-volatile Memories, Springer, 2005 ISBN 3-540-20198-X.
- Kind, Dieter; Feser, Kurt (2001), translator Y. Narayana Rao (ed.), High-voltage Test Techniques, Newnes, )
- Kories, Ralf; Schmidt-Walter, Heinz Taschenbuch der Elektrotechnik: Grundlagen und Elektronik, Deutsch Harri GmbH, 2004 ISBN 3-8171-1734-5.
- Liou, Juin J.; Ortiz-Conde, Adelmo; García-Sánchez, F. Analysis and Design of MOSFETs, Springer, 1998 ISBN 0-412-14601-0.
- Liu, Mingliang (2006), Demystifying Switched Capacitor Circuits, Newnes, ISBN 0-7506-7907-7
- McComb, Gordon Gordon McComb's gadgeteer's goldmine!, McGraw-Hill Professional, 1990 ISBN 0-8306-3360-X.
- ISBN 0-387-95179-2.
- Millman, Jacob; Halkias, Christos C. Integrated Electronics, McGraw-Hill Kogakusha, 1972 ISBN 0-07-042315-6.
- Peluso, Vincenzo; Steyaert, Michiel; Sansen, Willy M. C. Design of Low-voltage Low-power CMOS Delta-Sigma A/D Converters, Springer, 1999 ISBN 0-7923-8417-2.
- Ryder, J. D. (1970), Electronic Fundamentals & Applications, Pitman Publishing, ISBN 0-273-31491-2
- Wharton, W.; Howorth, D. Principles of Television Reception, Pitman Publishing, 1971 ISBN 0-273-36103-1.
- Yuan, Fei CMOS Circuits for Passive Wireless Microsystems, Springer, 2010 ISBN 1-4419-7679-5.
- Zumbahlen, Hank Linear Circuit Design Handbook, Newnes, 2008 ISBN 0-7506-8703-7.
Primary sources
- . Villard's voltage booster appears in Fig. 1 on p. 31.
- ^ Greinacher, H. (1914), "Das Ionometer und seine Verwendung zur Messung von Radium- und Röntgenstrahlen" [The ionometer and its application to the measurement of radium- and Röntgen rays], Physikalische Zeitschrift (in German), 15: 410–415. Greinacher's voltage doubler appears in Fig. 4 on p. 412. He used chemical (electrolytic) rectifiers, which are denoted "Z" (Zellen, cells).
- S2CID 119816536
- ^ In 1919, a year before Greinacher published his voltage multiplier, the German Moritz Schenkel published a multi-stage voltage multiplier.
- Schenkel, Moritz (July 10, 1919), "Eine neue Schaltung für die Erzeugung hoher Gleichspannungen" [A new circuit for the creation of high d.c. voltages], Elektrotechnische Zeitschrift (in German), 40 (28): 333–344
- A condensed version of Schenkel's article — with an illustration of the circuit — appeared in: "Eine neue Schaltung für die Erzeugung hoher Gleichspannungen," Polytechnische Schau, 334 : 203-204 (1919). Available on-line at: Polytechnisches Journal.
- ^ Jules Delon (1876-1941) was an engineer for the French company Société française des câbles électriques Berthoud-Borel. He used a mechanical rectifier, which was based on a rotating commutator (contact tournant).
- His apparatus was exhibited at the 1908 Exposition d'électricité in Marseille, France: Georges Tardy (August 15, 1908) "Contact tournant de la Société française des câbles électriques Systeme Berthoud-Borel", L'Electricien: Revue Internationale de l'Electricité et de ses Applications, 2nd series, 36 (920) : 97-98. (Article includes photograph of machine.) The equipment was used to test insulation on high-voltage commercial power lines.
- The operation of Delon's bridge rectifier is also explained (with schematic) in: E. von Rziha and Josef Seidener, Starkstromtechnik: Taschenbuch für Elektrotechniker (High-current technology: A Pocket book for Electrical Engineers), 5th ed., vol. 1, (Berlin, Germany: Wilhelm Ernst & Sohn, 1921), pages 710-711.
- Delon's name and dates appear in: Friedrich Heilbronner, Internationale Liste von Elektrotechnikern (2013), pp. 14-15. Brief obituary of Jules Delon, Technica (Journal of the Association des anciens eleves de l'ecole centrale Lyonnaise (Association of the Alumni of the Central School of Lyon)), 2nd series, no. 25, page 24 (December 1941). Available on-line at: Technica. See also Delon's U.S. patents no. 1,740,076, no. 1,837,952, and no. 1,995,201.