Editing DC-to-DC converter (section)

== 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.