Editing DC-to-DC converter

{{Short description|Type of electronic circuit}}
{{Power engineering}}
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 conversion|electric power converter]]. Power levels range from very low (small batteries) to very high (high-voltage power transmission).

==History==
{{See also|Antique radio#Car radios}}
Before the development of power semiconductors, one way to convert the voltage of a DC supply to a higher voltage, for low-power applications, was to convert it to AC by using a [[vibrator (electronic)|vibrator]], then by a step-up [[transformer]], and finally a [[rectifier]].<ref name=vib>{{cite web |url=http://www.radioremembered.org/vpwrsup.htm |title=Vibrator Power Supplies |newspaper=Radioremembered.org |access-date= 18 January 2016}}</ref><ref name="Brorein2012">{{Cite web
| title = Watt's Up?: What Is Old is New Again: Soft-Switching and Synchronous Rectification in Vintage Automobile Radios
| author = Ed Brorein 
| work = Keysight Technologies: Watt's Up? 
| date = 2012-05-16
| access-date = 2016-01-19
| url = http://powersupply.blogs.keysight.com/2012/05/what-is-old-is-new-again-soft-switching.html
}}</ref> Where higher power was needed, a [[motor–generator]] unit was often used, in which an electric motor drove a generator that produced the desired voltage. (The motor and generator could be separate devices, or they could be combined into a single "dynamotor" unit with no external power shaft.) These relatively inefficient and expensive designs were used only when there was no alternative, as to power a car radio (which then used thermionic valves (tubes) that require much higher voltages than available from a 6 or 12&nbsp;V car battery).<ref name=vib/>

The introduction of power semiconductors and integrated circuits made it economically viable by use of techniques described below. For example, first is converting the DC power supply to high-frequency AC as an input of a transformer - it is small, light, and cheap due to the high frequency — that changes the voltage which gets rectified back to DC.<ref>There is at least one example of a very large (three refrigerator-size cabinets) and complex pre-transistor switching regulator using thyratron gas-filled tubes, although they appear to be used as regulators rather than for DC-to-DC conversion as such. This was the 1958 power supply for the IBM&nbsp;704 computer, using 90&nbsp;kW of power.[http://www.mirrorservice.org/sites/www.bitsavers.org/pdf/ibm/704/223-6818_704_CE_Manual/736_741_746_PwrSupply_CE_Oct58.pdf]</ref> Although by 1976 transistor car radio receivers did not require high voltages, some [[amateur radio]] operators continued to use vibrator supplies and dynamotors for mobile [[transceiver]]s requiring high voltages although transistorized power supplies were available.<ref name=arrl1976>[https://archive.org/details/RadioAmateurHandbook1976 Radio Amateur's Handbook 1976], pub. [[ARRL]], p331-332</ref>

While it was possible to derive a ''lower'' voltage from a higher with a [[linear regulator]] or even a resistor, these methods dissipated the excess as heat; energy-efficient conversion became possible only with solid-state switch-mode circuits.

== Uses ==
{{See also|High-voltage direct current}}
DC-to-DC converters are used in portable electronic devices such as [[cellular phone]]s and [[laptop computer]]s, which are supplied with power from [[Battery (electricity)|batteries]] primarily. Such electronic devices often contain several sub-[[Electrical network|circuits]], each with its own voltage level requirement different from that supplied by the battery or an external supply (sometimes higher or lower than the supply voltage).  Additionally, the battery voltage declines as its stored energy is drained.  Switched DC to DC converters offer a method to increase voltage from a partially lowered battery voltage thereby saving space instead of using multiple batteries to accomplish the same thing.

Most DC-to-DC converter circuits also regulate the output voltage. Some exceptions include high-efficiency [[LED power sources]], which are a kind of DC to DC converter that regulates the current through the LEDs, and simple [[charge pump]]s which double or triple the output voltage.

DC-to-DC converters which are designed to maximize the energy harvest for [[photovoltaic systems]] and for [[wind turbine]]s are called [[power optimizer]]s.

Transformers used for voltage conversion at mains frequencies of 50–60&nbsp;Hz must be large and heavy for powers exceeding a few watts. This makes them expensive, and they are subject to energy losses in their windings and due to eddy currents in their cores. DC-to-DC techniques that use transformers or inductors work at much higher frequencies, requiring only much smaller, lighter, and cheaper wound components. Consequently these techniques are used even where a mains transformer could be used; for example, for domestic electronic appliances it is preferable to rectify mains voltage to DC, use switch-mode techniques to convert it to high-frequency AC at the desired voltage, then, usually, rectify to DC. The entire complex circuit is cheaper and more efficient than a simple mains transformer circuit of the same output. DC-to-DC converters are widely used for DC microgrid applications, in the context of different voltage levels.

== Electronic conversion ==
{{See also|Switched-mode power supply}}

[[File:Commutation_cell_in_converters.svg|thumb|421x421px|Comparison of non-isolated switching DC-to-DC converter topologies: [[Buck converter|buck]], [[Boost converter|boost]], [[Buck–boost converter|buck-boost]], and [[Ćuk converter|Ćuk]]. The input is on the left, the output with load (rectangle) is on the right. The switch is typically a [[MOSFET]], [[IGBT]], or [[BJT]].]]

'''Switching converters''' or switched-mode DC-to-DC converters store the input energy temporarily and then release that energy to the output at a different voltage, which may be higher or lower. The storage may be in either magnetic field storage components (inductors, transformers) or electric field storage components (capacitors). This conversion method can increase or decrease voltage. Switching conversion is often more power-efficient (typical efficiency is 75% to 98%) than linear voltage regulation, which dissipates unwanted power as heat. Fast semiconductor device rise and fall times are required for efficiency; however, these fast transitions combine with layout parasitic effects to make circuit design challenging.<ref name="Howard2015">{{Cite web
| title = How to Design DC-to-DC Converters
| author = Andy Howard
| work = YouTube
| date = 2015-08-25
| access-date = 2015-10-02
| url = https://www.youtube.com/watch?v=LwPJi3jyfw0
}}</ref> The higher efficiency of a switched-mode converter reduces the heatsinking needed, and increases battery endurance of portable equipment. Efficiency has improved since the late 1980s due to the use of power [[Field-effect transistor|FETs]], which are able to switch more efficiently with lower {{ill|switching loss|lt=switching losses|de|Schaltverluste}} at higher frequencies than power [[bipolar transistors]], and use less complex drive circuitry.
Another important improvement in DC-DC converters is replacing the [[flyback diode]] with [[synchronous rectification]]<ref name="Sangwine2007">{{cite book
|author=Stephen Sangwine
|title=Electronic Components and Technology, Third Edition
|url=https://books.google.com/books?id=vVHvBQAAQBAJ&pg=PA73
|date=2 March 2007
|publisher=CRC Press
|isbn=978-1-4200-0768-8
|page=73}}</ref> using a power FET, whose "on resistance" is much lower, reducing conduction losses. Before the wide availability of power semiconductors, low-power DC-to-DC synchronous converters consisted of an electro-mechanical vibrator followed by a voltage step-up transformer feeding a vacuum tube or semiconductor rectifier, or synchronous rectifier contacts on the vibrator.

Most DC-to-DC converters are designed to move power in only one direction, from dedicated input to output. However, all switching regulator topologies can be made bidirectional and able to move power in either direction by replacing all diodes with independently controlled [[active rectification]]. A bidirectional converter is useful, for example, in applications requiring [[regenerative brake|regenerative braking]] of vehicles, where power is supplied ''to'' the wheels while driving, but supplied ''by'' the wheels when braking.

Although they require few components, switching converters are electronically complex. Like all high-frequency circuits, their components must be carefully specified and physically arranged to achieve stable operation and to keep switching noise ([[Radio frequency interference|EMI / RFI]]) at acceptable levels.<ref>{{cite web |url=http://www.eetimes.com/document.asp?doc_id=1279232 |title=Understand and reduce DC/DC switching-converter ground noise |newspaper=Eetimes.com |date=21 November 2011 |author=Jeff Barrow of Integrated Device Technology, Inc.|access-date= 18 January 2016}}</ref> Their cost is higher than linear regulators in voltage-dropping applications, but their cost has been decreasing with advances in chip design.

DC-to-DC converters are available as [[integrated circuit]]s (ICs) requiring few additional components. Converters are also available as complete [[hybrid circuit]] modules, ready for use within an electronic assembly.

[[Linear regulator]]s which are used to output a stable DC independent of input voltage and output load from a higher but less stable input by [[Joule heating|dissipating excess volt-amperes as heat]], could be described literally as DC-to-DC converters, but this is not usual usage. (The same could be said of a simple [[voltage drop]]per resistor, whether or not stabilised by a following [[voltage regulator]] or [[Zener diode]].)

There are also simple [[#Capacitive|capacitive]] [[voltage doubler]] and [[Dickson multiplier]] circuits using diodes and capacitors to multiply a DC voltage by an integer value, typically delivering only a small current.

=== Magnetic===

In these DC-to-DC converters, energy is periodically stored within and released from a [[magnetic field]] in an [[inductor]] or a [[transformer]], typically within a frequency range of 300&nbsp;kHz to 10&nbsp;MHz. By adjusting the [[duty cycle]] of the charging voltage (that is, the ratio of the on/off times), the amount of power transferred to a load can be more easily controlled, though this control can also be applied to the input current, the output current, or to maintain constant power. Transformer-based converters may provide isolation between input and output.  In general, the term ''DC-to-DC converter'' refers to one of these switching converters. These circuits are the heart of a [[switched-mode power supply]]. Many topologies exist. This table shows the most common ones.

{| class="wikitable"
|-
! width="10%" |
! width="45%" | Forward (energy transfers through the magnetic field)
! width="45%" | Flyback (energy is stored in the magnetic field)
|-
! rowspan=3 | No transformer (non-isolated)
| {{unbulleted list
 | [[buck converter|Step-down (buck)]] - The output voltage is lower than the input voltage, and of the same polarity.
 }}
| {{unbulleted list
 | Non-inverting: The output voltage is the same [[electric polarity]] as the input.{{unbulleted list
  | style=margin-left:1.6em;
  | [[boost converter|Step-up (boost)]] - The output voltage is higher than the input voltage.
  | [[SEPIC converter|SEPIC]] - The output voltage can be lower or higher than the input.
  }}
 | Inverting: the output voltage is of the opposite polarity as the input.{{unbulleted list
  | style=margin-left:1.6em;
  | [[buck-boost converter|Inverting (buck-boost)]].
  | [[Ćuk converter|Ćuk]] - Output current is continuous.
  }}
 }}
|-
| colspan=2 align="center" | {{unbulleted list
 | [[buck-boost converter|True buck-boost]] - The output voltage is the same polarity as the input and can be lower or higher.
 }}
|-
| colspan=2 align="center" | {{unbulleted list
 | [[Split-pi|Split-pi (boost-buck)]] - Allows bidirectional voltage conversion with the output voltage the same polarity as the input and can be lower or higher.
 }}
|-
! With transformer (isolatable)
| {{unbulleted list
 | [[Forward converter|Forward]] - 1 or 2 transistor drive.
 | [[Push–pull converter|Push-pull (half bridge)]] - 2 transistors drive.
 | [[H-bridge|Full bridge]] - 4 transistor drive.<ref>{{cite journal|url=https://ieeexplore.ieee.org/document/9265771|title=11kW, 70kHz LLC Converter Design for 98% Efficiency|date=November 2020 |pages=1–8 |doi=10.1109/COMPEL49091.2020.9265771 |s2cid=227278364 |url-access=subscription }}</ref>
 }}
| {{unbulleted list
 | [[Flyback converter|Flyback]] - 1 transistor drive.
 }}
|}

In addition, each topology may be:
; Hard switched: Transistors switch quickly while exposed to both full voltage and full current
; Resonant: An [[LC circuit]] shapes the voltage across the transistor and current through it so that the transistor switches when either the voltage or the current is zero

Magnetic DC-to-DC converters may be operated in two modes, according to the current in its main magnetic component (inductor or transformer):
; Continuous: The current fluctuates but never goes down to zero
; Discontinuous: The current fluctuates during the cycle, going down to zero at or before the end of each cycle
A converter may be designed to operate in continuous mode at high power, and in discontinuous mode at low power.

The [[H-Bridge|half bridge]] and [[flyback converter|flyback]] topologies are similar in that energy stored in the magnetic core needs to be dissipated so that the core does not saturate. Power transmission in a flyback circuit is limited by the amount of energy that can be stored in the core, while forward circuits are usually limited by the I/V characteristics of the switches.

Although [[MOSFET]] switches can tolerate simultaneous full current and voltage (although thermal stress and [[electromigration]] can shorten the [[MTBF]]), bipolar switches generally can't so require the use of a [[snubber]] (or two).

High-current systems often use multiphase converters, also called interleaved converters.<ref>
Damian Giaouris et al.
[http://onlinelibrary.wiley.com/doi/10.1002/cta.1906/abstract "Foldings and grazings of tori in current controlled interleaved boost converters"].
{{doi | 10.1002/cta.1906}}.
</ref><ref>
Ron Crews and Kim Nielson.
[http://powerelectronics.com/power-management/interleaving-good-boost-converters-too "Interleaving is Good for Boost Converters, Too"].
2008.
</ref><ref>
Keith Billings.
[http://powerelectronics.com/content/advantages-interleaving-converters "Advantages of Interleaving Converters"].
2003.
</ref>
Multiphase regulators can have better ripple and better response times than single-phase regulators.<ref>
John Gallagher
[http://powerelectronics.com/passive-components/coupled-inductors-improve-multiphase-buck-efficiency "Coupled Inductors Improve Multiphase Buck Efficiency"].
2006.
</ref>

Many laptop and desktop [[motherboard]]s include interleaved buck regulators, sometimes as a [[voltage regulator module]].<ref>
Juliana Gjanci.
[http://www.ece.uic.edu/~masud/Juliana_MS_THESIS_final.pdf "On-Chip Voltage Regulation for Power Management inSystem-on-Chip"] {{webarchive|url=https://web.archive.org/web/20121119013307/http://www.ece.uic.edu/~masud/Juliana_MS_THESIS_final.pdf |date=2012-11-19 }}.
2006.
p. 22-23.
</ref>

=== Bidirectional DC-to-DC converters ===
Specific to these converters is that the energy flows in both directions of the converter. These converters are commonly used in various applications and they are connected between two levels of DC voltage, where energy is transferred from one level to another.<ref>[https://palawanboard.com/chapter-1-introduction-bidirectional-dc-dc-converters/ CHAPTER 1 INTRODUCTION Bidirectional DC-DC Converters palawanboard.com]</ref>

* Boost bidirectional DC-to-DC converter 
* Buck bidirectional DC-to-DC converter 
* Boost-buck non-inverting bidirectional DC-to-DC converter
* Boost-buck inverting bidirectional DC-to-DC converter
* SEPIC bidirectional DC-to-DC converter
* CUK bidirectional DC-to-DC converter

Multiple isolated bidirectional DC-to-DC converters are also commonly used in cases where [[galvanic isolation]] is needed.<ref>[https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8811451&tag=1/ Topologies and Control Schemes of Bidirectional DC–DC Power Converters: An Overview https://ieeexplore.ieee.org]</ref>

* Bidirectional flyback 
* Isolated Ćuk & SEPIC/ZETA
* Push-pull
* Forward
* Dual-active bridge (DAB)
* Dual-half bridge
* Half-full bridge
* Multiport DAB

=== Capacitive ===

{{main|Charge pump}}
Switched capacitor converters rely on alternately connecting capacitors to the input and output in differing topologies.  For example, a switched-capacitor reducing converter might charge two capacitors in series and then discharge them in parallel. This would produce the same output power (less that lost to efficiency of under 100%) at, ideally, half the input voltage and twice the current. Because they operate on discrete quantities of charge, these are also sometimes referred to as [[charge pump]] converters. They are typically used in applications requiring relatively small currents, as at higher currents the increased efficiency and smaller size of switch-mode converters makes them a better choice.<ref>{{Cite book|title = Control of Parallel Converters for Load Sharing with Seamless Transfer between Grid Connected and Islanded Modes|url = http://eprints.qut.edu.au/14216/|website = eprints.qut.edu.au|date = 2008|access-date = 2016-01-19|first1 = Ritwik|last1 = Majumder|first2 = Arindam|last2 = Ghosh|first3 = Gerard F.|last3 = Ledwich|first4 = Firuz|last4 = Zare| isbn=9781424419067 }}</ref> They are also used at extremely high voltages, as magnetics would break down at such voltages.

==Electromechanical conversion==
{{Main|Motor–generator}}
[[File:Rotierender Umformer.jpg|thumb|right|A motor generator with separate motor and generator.]]
A motor–generator set, mainly of historical interest, consists of an [[electric motor]] and generator coupled together. A ''[[dynamotor]]'' combines both functions into a single unit with coils for both the motor and the generator functions wound around a single rotor; both coils share the same outer field coils or magnets.<ref name=arrl1976/> Typically the motor coils are driven from a [[commutator (electric)|commutator]] on one end of the shaft, when the generator coils output to another commutator on the other end of the shaft. The entire rotor and shaft assembly is smaller in size than a pair of machines, and may not have any exposed drive shafts.

Motor–generators can convert between any combination of DC and AC voltage and phase standards. Large motor–generator sets were widely used to convert industrial amounts of power while smaller units were used to convert battery power (6, 12 or 24 V DC) to a high DC voltage, which was required to operate [[vacuum tube]] (thermionic valve) equipment.

For lower-power requirements at voltages higher than supplied by a vehicle battery, vibrator or "buzzer" power supplies were used. The vibrator oscillated mechanically, with contacts that switched the polarity of the battery many times per second, effectively converting DC to [[Square wave (waveform)|square wave]] AC, which could then be fed to a transformer of the required output voltage(s).<ref name=vib/> It made a characteristic buzzing noise.

== Electrochemical conversion==
A further means of DC to DC conversion in the kilowatts to megawatts range is presented by using [[Flow battery|redox flow batteries]] such as the [[vanadium redox battery]].

== Chaotic behavior ==
DC-to-DC converters are subject to different types of [[Chaos theory|chaotic]] dynamics such as [[bifurcation theory|bifurcation]],<ref>{{cite conference |last= Tse |first= Chi K. |author2= Bernardo, Mario Di |title= Complex behavior in switching power converters| publisher= Proceedings of the IEEE |year=2002 |pages=768–781}}</ref> [[crisis (dynamical systems)|crisis]], and [[intermittency]].<ref>{{cite conference |chapter= Study of bifurcation and chaos in dc-dc boost converter using discrete-time map |last= Iqbal |first= Sajid |title= 2014 International Conference on Mechatronics and Control (ICMC) |display-authors=etal |year= 2014|pages= 1813–1817 | doi=10.1109/ICMC.2014.7231874 |publisher= IEEE International Conference on Mechatronics and Control (ICMC'2014) 2014|isbn= 978-1-4799-2538-4 }}</ref><ref>{{cite journal |last= Fossas |first= Enric |author2= Olivar, Gerard |title= Study of chaos in the buck converter |publisher=  Circuits and Systems I: Fundamental Theory and Applications, IEEE Transactions on |year=1996 |pages=13–25}}</ref>

== Terminology ==
; Step-down
: A converter where the output voltage is lower than the input voltage (such as a [[buck converter]]).
; Step-up
:A converter that outputs a voltage higher than the input voltage (such as a [[boost converter]]).
; Continuous current mode
:Current and thus the magnetic field in the inductive energy storage never reaches zero.
;Discontinuous current mode
:Current and thus the magnetic field in the inductive energy storage may reach or cross zero.
;Noise
:Unwanted electrical and electromagnetic [[signal noise]], typically switching artifacts.
;RF noise
:Switching converters inherently emit [[radio waves]] at the switching frequency and its harmonics. Switching converters that produce triangular switching current, such as the [[Split-pi topology|split-pi]], [[forward converter]], or [[Ćuk converter]] in continuous current mode, produce less harmonic noise than other switching converters.<ref name="hoskins" /> RF noise causes [[electromagnetic interference]] (EMI). Acceptable levels depend upon requirements, e.g. proximity to RF circuitry needs more suppression than simply meeting regulations.
;Coil-integrated DC/DC converters
:These may include a power control IC, coil, capacitor, and resistor; decreases mounting space with a small number of components in a single integrated solution.
;Input noise
:The input voltage may have non-negligible noise. Additionally, if the converter loads the input with sharp load edges, the converter can emit RF noise from the supplying power lines. This should be prevented with proper filtering in the input stage of the converter.
;Output noise
:The output of an ideal DC-to-DC converter is a flat, constant output voltage. However, real converters produce a DC output upon which is superimposed some level of electrical noise. Switching converters produce switching noise at the switching frequency and its harmonics. Additionally, all electronic circuits have some [[thermal noise]]. Some sensitive radio-frequency and analog circuits require a power supply with so little noise that it can only be provided by a linear regulator.<ref>{{Cite web|last=Bhimsen|date=2021-10-30|title=Linear voltage regulator and its application|url=https://electronics-fun.com/linear-voltage-regulator-and-its-application/|access-date=2021-10-30|website=electronics fun|language=en-US}}</ref> Some analog circuits which require a power supply with relatively low noise can tolerate some of the less-noisy switching converters, e.g. using continuous triangular waveforms rather than square waves.<ref name="hoskins">[http://www.linear.com/docs/4173 Making -5V 14-bit Quiet, section of Linear Technology Application Note 84, Kevin Hoskins, 1997, pp 57-59]</ref>{{Failed verification|date=January 2016|reason=application note is about the excellent PSRR of a particular ADC}}

==See also==
* [[Buck–boost converter]]
* [[Combined Charging System]]
* [[Switched-mode power supply]]
* [[Battery_charger#DC–DC_charger|DC-to-DC charger]]

==References==
{{Reflist}}

==External links==
* [https://web.archive.org/web/20121105123653/http://www.powerguru.org/2012/07/02/dc-dc-converter-technologies-for-electrichybrid-electric-vehicles/ DC-DC Converter Technologies for Electric/Hybrid Electric Vehicles]
* [https://web.archive.org/web/20181017192712/http://www.smpstech.com/books/books.htm Power Electronics Books]
* [https://web.archive.org/web/20071012131943/http://sii-ic.com/en/app_crct.jsp Switching regulator application note for LCD power supply]

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[[Category:DC-to-DC converters| ]]
[[Category:Electric power conversion]]
[[Category:Power supplies]]