Multiple-Output DC–DC Converters: Applications and Solutions

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Citation: Litrán, S.P.; Durán, E.;

Semião, J.; Díaz-Martín, C.

Multiple-Output DC–DC Converters:

Applications and Solutions.

Electronics 2022, 11, 1258. https://

doi.org/10.3390/electronics11081258

Academic Editor: Kai Fu

Received: 10 March 2022

Accepted: 13 April 2022

Published: 15 April 2022

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electronics

Review

Multiple-Output DC–DC Converters: Applicationsand SolutionsSalvador P. Litrán 1,2 , Eladio Durán 2,3,* , Jorge Semião 4 and Cristian Díaz-Martín 2

1 Department of Electrical and Thermal Engineering, Design and Projects, University of Huelva,21007 Huelva, Spain; [email protected]

2 Centro Científico-Tecnológico de Huelva (CCTH), University of Huelva, 21007 Huelva, Spain;[email protected]

3 Department of Electronic Engineering, Computer Systems and Automation, University of Huelva,21007 Huelva, Spain

4 Instituto Superior de Engenharia (ISE), Universidade do Algarve, 8005-139 Faro, Portugal/INESC-ID,1000 Lisboa, Portugal; [email protected]

* Correspondence: [email protected]; Tel.: +34-959217655

Abstract: Multiple-output DC–DC converters are essential in a multitude of applications wheredifferent DC output voltages are required. The interest and importance of this type of multiportconfiguration is also reflected in that many electronics manufacturers currently develop integratedsolutions. Traditionally, the different output voltages required are obtained by means of a transformerwith several windings, which are in addition to providing electrical isolation. However, the currenttrend in the development of multiple-output DC–DC converters follows general aspects, such aslow losses, high-power density, and high efficiency, as well as the development of new architecturesand control strategies. Certainly, simple structures with a reduced number of components andpower switches will be one of the new trends, especially to reduce the size. In this sense, theincorporation of devices with a Wide Band Gap (WBG), particularly Gallium Nitride (GaN) andSilicon Carbide (SiC), will establish future trends, advantages, and disadvantages in the developmentand applications of multiple-output DC–DC converters. In this paper, we present a review of the mostimportant topics related to multiple-output DC–DC converters based on their main topologies andconfigurations, applications, solutions, and trends. A wide variety of configurations and topologiesof multiple-output DC–DC converters are shown (more than 30), isolated and non-isolated, singleand multiple switches, and based on soft and hard switching techniques, which are used in manydifferent applications and solutions.

Keywords: DC–DC converters; multiple outputs; applications; solutions

1. Introduction

Multiple-output DC–DC converters are fundamental in electric power supply, distri-bution, management, and power delivery systems. They are essential in applications suchas: Intermediate Bus Architecture (IBA), Distributed Power Architectures (DPA), DynamicBus Architecture (DBA), Central Control Architecture (CCA), Datacom and Telecom, Light-Emitting Diodes (LEDs), consumer electronics products, battery chargers, or even ElectricVehicles (EV). These converters are used for USB power delivery, I/O, CPUs, FPGAs, ASICs,and other low-voltage devices, applications where controllability, efficiency, reliability, andminiaturization are critical.

Undoubtedly, the development of power switch semiconductor technologies has alsocontributed significantly to more efficient switching and has facilitated a higher frequencyoperation. This has allowed the development of applications where multiple-outputDC–DC converters are used, considering mainly three aspects: high-power density, highefficiency, and small size. The increase in the rating of power devices, such as Insulated

Electronics 2022, 11, 1258. https://doi.org/10.3390/electronics11081258 https://www.mdpi.com/journal/electronics

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Electronics 2022, 11, 1258 2 of 34

Gate Bipolar Transistors (IGBT) and Metal-Oxide-Semiconductor Field-Effect Transistor(MOSFET) technologies, has allowed innumerable applications to be addressed in thelast 40 years. They have helped to improve energy efficiency and CO2 reductions, incommercial, residential, transportation systems, industrial, military, aerospace, computersystems, lighting, and vehicle applications. MOSFET and IGBT, either as power modules orwithin discrete devices, have been the preferred technologies for high and medium powerapplications. IGBTs are used in applications of high-current, with voltages over 1 kV andup to 10 kVA, while MOSFETs are used in applications below 1 kV, but they are the mostsuitable in applications of high switching frequency, between 10–100 kHz.

Although silicon-based technologies have improved enormously in the recent years,and still continue to improve, this development will be restricted, ultimately, by silicontechnology limitations [1]. Among the semiconductor materials with the greatest futurepotential are those with a Wide Band Gap (WBG), particularly Gallium Nitride (GaN) andSilicon Carbide (SiC). The physical properties of WBG materials make them especiallysuitable for high switching frequency and high-power applications, also giving them highresistance to high temperatures, lower switching losses, with low reverse recovery and lowon-resistance, a better relationship between breakdown voltage (VBD) and on-resistance(RDS(ON)), lower cooling requirements, and with low parasitic inductance. Applicationswhere broadband technology is experiencing a considerable growth are: in the lightingsector (using GaN based LEDs); in the generation (transmission and distribution of electricalenergy, where SiC devices present significant improvements in energy efficiency of theelectrical network); and hybrid and fully electric vehicles (where GaN and SiC-baseddevices are essential elements, both in the propulsion and energy distribution systems ofthe vehicle).

The interest in DC–DC converters with multiple outputs is reflected in the sub-citedanalysis and numerous publications, both from the academic, research, and economic/business world [2–11], as well as from industry and manufacturer publications [12–17].The most recent forecasts estimate that the market for DC–DC converters is expected toincrease at a CAGR (Compound Annual Growth Rate) of 12.1% in the next five years, from$9.9 billion in 2021 to $17.6 billion in 2026, and that the market for industrial power supplyis expected to increase at a CAGR of 6.9% in the same period, from $7.0 billion in 2021 to$9.7 billion in 2026, with multiple-output DC–DC converters being one of the segments withthe highest growth rate during the same period [18–30]. This growth is due to very differentsectors and applications, such as storage and servers, battery management, healthcare andmedical equipment, railway traction, beverage and food, information technology andtelecom, transportation, consumer electronics, energy and utilities, defense and aerospace,machine tools, and security systems. Mobile Phone Industry and Internet of Things (IoT)are applications where DC–DC converters help to extend battery life. Also, the lightingsector through technology Light-Emitting Diode (LED) and Organic LED (OLED), whichhas provided more reliable and efficient light sources, is also an important sector. Moreover,the demand for DC–DC converters with multiple outputs in the automotive industryis driven by electric vehicles, such as Fuel Cell Electric Vehicle (FCEV), Battery ElectricVehicles (BEV), Plug-in Hybrid Vehicles (PHEV), and Hybrid Electric Vehicle (HEV).

All these applications contemplate various aspects and types of DC–DC converters,such as output number (dual-output, bipolar output, three- and four-output-type convert-ers), power (<1 kW, 1–10 kW, 10–20 kW, and >20 kW) including low, medium, and highpower, input voltage (<40 V, 40–70 V, and >70 V), output voltage (24 V, 15 V, 12 V, 5 V, and3.3 V), isolated (one switch, two switches, and four switches converters) and non-isolated(one switch or several switches) DC–DC converters. In low-power applications, the twomain trends are related to high-power density and low voltage, while in high power, withhigh efficiency and reliability. But the main trend is related to miniaturization for integra-tion. Small size and weight, together with high-power density are very important itemsin power supplies for small format applications, mobile electronic systems, and onboardsystems, driven by applications with facilities with space restrictions such as More-Electric

Electronics 2022, 11, 1258 3 of 34

Aircraft (MEA), Electric Vehicle (EV), Robotics, Electric Ship (ES), Robotics, Solid-StateLighting, Integrated DC–DC Power Supply and Monolithic Power Systems, IntelligentDC–DC Power Distribution (micro or nano grids), On-chip Power Supply, Wireless RemoteSensing Node and Power Transfer, New Transport Technologies, Energy Harvesting, andIoT. In these applications, multiple or single power systems are used, which distributeenergy to different loads, with converters operating in power ranging from hundreds ofkilowatts to a few watts. This focus on multiple-output DC–DC converter applicationshas also led to the development and commercialization of integrated solutions by manyelectronic manufacturers [31–42], and to different tutorials, webinars, on-line publica-tions, white papers and some surveys, reviews, and overviews papers being reported inthe literature.

In this paper, an overview of the most important topics related to multiple-outputDC–DC converters based on their main topologies and configurations, applications, so-lutions, and trends are presented. The work is organized as follows: Section 2 reviewsmultiple-output DC–DC converters: topologies and configurations and some of their maincharacteristics are analyzed. Section 3 presents some of the most important applicationsand solutions of multiple-output DC–DC converters. Finally, in Section 4 some conclusionsare presented.

2. Multiple-Output DC–DC Converters: Topologies and Configurations

The main objective of DC–DC power conversion is to transfer electric power from a DCsource into another DC source, which can be a load, with the highest efficiency and thereforelowest losses. The DC–DC converters are widely used at all power levels (from mW to kW),current levels (from nA to hundreds of amps) and voltage levels (from mV to kV) and havebeen very popular for the last three decades, they can invert the polarity of the DC voltageand increase or decrease its magnitude. The topologies and properties of DC–DC convertersare reported in the literature and are well known. Topology describes how source, load,inductive and capacitive elements, and switches are interconnected in the converter, whilethe configuration establishes the DC conversion relation between the input and outputcurrent/voltage and according to the operating mode and the converter topology. Efficiencydepends on how close converter elements are to ideal condition; assuming that the sameelements are available, efficiency is related to the converter topology. Switch electricalstress (current and voltage) decides the choice of semiconductor devices used to implementthe switches. For lower losses on parasitic resistances, lower generated noise, and moreefficient filtering, it is preferred that input and output waveforms be continuous (ideally,DC only). Complexity of a converter is measured by the number of inductors, capacitors,and switches. Efficiency and density (watts/volume) have long been the metrics used tocompare the performance of power converters.

DC–DC converters can be classified depending on the number of inputs as Multiple-Input and Single-Output (MISO), or Single-Input and Single-Output (SISO), dependingon the number of outputs as Single-Input and Multiple-Output (SIMO), or Multiple-Inputand Multiple-Output (MIMO). In all cases, they can provide one or more output voltages,from one or more input voltages. Multiple-output DC–DC converters are of interest inapplications that require several outputs, from one or more input voltages, which includeconfigurations MIMO [43–46] and SIMO [47–51].

As it is showed in Figure 1, SIMO DC–DC converters can be classified into isolated andnon-isolated, depending on whether they are implemented with or without an electrical iso-lation, by means of a transformer, generally operated at high frequency. The output/inputpower range is often used as the main aspect when selecting a topology. However, thereare many other factors that influence the topology selection for an isolated multi-outputDC–DC power converter, such as: electrical stress, size, cost, input voltage range, andoutput noise. The size of an isolated multi-output power converter mainly depends on thetransformer size and the number of active switches employed, while for a non-isolatedconverter depends on the number of active switches employed. The utilization of the

Electronics 2022, 11, 1258 4 of 34

power transformer affects the size of the power converter. A high-frequency transformerprovides galvanic isolation between input and output, and allows increasing the step-upconversion ratio, while coupled inductors can also be used to increase the step-up ratio in aDC conversion and provide different output voltages from several secondary windings.

Electronics 2022, 11, x FOR PEER REVIEW 4 of 35

lated multi-output DC–DC power converter, such as: electrical stress, size, cost, input

voltage range, and output noise. The size of an isolated multi-output power converter

mainly depends on the transformer size and the number of active switches employed,

while for a non-isolated converter depends on the number of active switches employed.

The utilization of the power transformer affects the size of the power converter. A high-

frequency transformer provides galvanic isolation between input and output, and allows

increasing the step-up conversion ratio, while coupled inductors can also be used to in-

crease the step-up ratio in a DC conversion and provide different output voltages from

several secondary windings.

Single-Input Multiple-Output

DC-DC Converters

Single-Input Single-Output

DC-DC Converters

DC-DC Converters

Multiple-Input Single-Output

DC-DC Converters

Multiple-Input Multiple-Output

DC-DC Converters

Multiple-SwitchSingle-Switch

Forward

Converter

Flyback

Converter

SIMO DC-DC Converters

Non-Isolated

SIMO DC-DC Converters

Isolated

MIMO DC-DC Converters

Non-Isolated

MIMO DC-DC Converters

Isolated

Two-Switch Forward

Converter

Two-Switch Flyback

Converter

Fly-Buck

Converter

Active Clamp Forward

Converter

Push-Pull Converter Full-Bridge ConverterHalf-Bridge Converter

Resonant Converters

LLC, LCC, LCL, CLC

Converters

Single-Switch

Multiple-Switch

Multiple-Switch Multiple-Switch

The most common multiple-output converters

Figure 1. Multiple-Output DC–DC Converters Classification.

Control over DC conversion relation can be obtained by PWM (Pulse-Width Modu-

lation) technique, usually using a Constant Frequency (CF). D (Duty Cycle) is the ratio

between TON (Conduction Time) of switch/es and TS (Switching Period). In PWM, the

output voltage regulation is corrected (adjusted) by changing the TON of the switching

element in the converter. Other control strategies used in DC–DC converters are: Varia-

ble Frequency and Constant on-Time (VF-C-on-T), Variable Frequency and Constant off-

Time (VF-C-off-T), and variable frequency and variable pulse width. In VF-C-on-T, the

operating frequency varies as a function of the input and load current. In VF-C-off-T

conduction, the operating frequency varies (implying variable on-time conduction) as a

function of the input and load current. CF is usually preferred over VF control since fil-

tering components can be optimized to suppress voltage and current ripples at switch-

ing frequency and its harmonics. Also, noise generated by VF converters is more diffi-

cult to handle, and, in some applications, it cannot be tolerated. There is a wide variety

of modes, techniques (linear and nonlinear), and types of controllers used for DC–DC

converters: Voltage Mode Control (VMC), Current Mode Control (CMC), Sliding Mode

(SM) or Hysteretic Mode (HM), and Band-Band Control (BBC), and controllers such as

PID (Proportional-Integral-Derivative), Fuzzy Logic (FL), and Neural Network (NN) in

different variants and their advantages and disadvantages are well understood and de-

scribed in the literature.

Figure 1. Multiple-Output DC–DC Converters Classification.

Control over DC conversion relation can be obtained by PWM (Pulse-Width Modu-lation) technique, usually using a Constant Frequency (CF). D (Duty Cycle) is the ratiobetween TON (Conduction Time) of switch/es and TS (Switching Period). In PWM, theoutput voltage regulation is corrected (adjusted) by changing the TON of the switchingelement in the converter. Other control strategies used in DC–DC converters are: VariableFrequency and Constant on-Time (VF-C-on-T), Variable Frequency and Constant off-Time(VF-C-off-T), and variable frequency and variable pulse width. In VF-C-on-T, the operatingfrequency varies as a function of the input and load current. In VF-C-off-T conduction,the operating frequency varies (implying variable on-time conduction) as a function of theinput and load current. CF is usually preferred over VF control since filtering componentscan be optimized to suppress voltage and current ripples at switching frequency and itsharmonics. Also, noise generated by VF converters is more difficult to handle, and, in someapplications, it cannot be tolerated. There is a wide variety of modes, techniques (linearand nonlinear), and types of controllers used for DC–DC converters: Voltage Mode Control(VMC), Current Mode Control (CMC), Sliding Mode (SM) or Hysteretic Mode (HM), andBand-Band Control (BBC), and controllers such as PID (Proportional-Integral-Derivative),Fuzzy Logic (FL), and Neural Network (NN) in different variants and their advantages anddisadvantages are well understood and described in the literature.

When several outputs must be regulated it appears a mutual Cross Regulation (CR)effect, and this is one of the critical challenges in multi-output converters, when there is aload change in any one or more of its outputs. Among the different techniques implementedto regulate multiple DC outputs, cross regulation technique is very used by its simplicity. Inthis technique, one of the output voltages is directly sensed by the controller and regulatedto the desired value. The other output voltages are indirectly regulated (quasi-regulated) by

Electronics 2022, 11, 1258 5 of 34

the main inductor and switch. Of course, the non-controlled outputs have lower regulationcapacity and can present a variation with respect to their nominal values (CR =4Voi/4Ioj).On the other hand, cross regulation allows the reduction in size, weight, and cost, andcircuitry simplicity in several applications since it shows many advantages in terms offlexibility and integration in power-management systems. To suppress cross regulation,some methods have been reported in the literature [52,53].

2.1. SIMO DC–DC Converters Isolated

Isolated SIMO DC–DC converter topologies can be denominated as either double-ended or single-ended, based on the use of the magnetization curve (B-H curve, flux densityversus magnetic field strength), as shown in Figure 2. During the operation, if the fluxoscillates in two quadrants of the B-H curve (Figure 2a), then the topology is called asdouble-ended. While, if the flux oscillates in only one quadrant of the B-H curve (Figure 2b),then the topology is called as single-ended. In general, for given operating conditions, asingle-ended topology requires a greater core than a double-ended topology and needs anadditional reset winding.


When several outputs must be regulated it appears a mutual Cross Regulation (CR)

effect, and this is one of the critical challenges in multi-output converters, when there is

a load change in any one or more of its outputs. Among the different techniques imple-

mented to regulate multiple DC outputs, cross regulation technique is very used by its

simplicity. In this technique, one of the output voltages is directly sensed by the control-

ler and regulated to the desired value. The other output voltages are indirectly regulated

(quasi-regulated) by the main inductor and switch. Of course, the non-controlled out-

puts have lower regulation capacity and can present a variation with respect to their

nominal values (CR = △Voi/△Ioj). On the other hand, cross regulation allows the reduc-

tion in size, weight, and cost, and circuitry simplicity in several applications since it

shows many advantages in terms of flexibility and integration in power-management

systems. To suppress cross regulation, some methods have been reported in the litera-

ture [52,53].

2.1. SIMO DC–DC Converters Isolated

Isolated SIMO DC–DC converter topologies can be denominated as either double-

ended or single-ended, based on the use of the magnetization curve (B-H curve, flux

density versus magnetic field strength), as shown in Figure 2. During the operation, if

the flux oscillates in two quadrants of the B-H curve (Figure 2a), then the topology is

called as double-ended. While, if the flux oscillates in only one quadrant of the B-H

curve (Figure 2b), then the topology is called as single-ended. In general, for given oper-

ating conditions, a single-ended topology requires a greater core than a double-ended

topology and needs an additional reset winding.

( )B t

m

Bm L

H

= =

( )H t

Core Saturation

Bidirectional Core Excitation

(Quadrants I and III)

maxB .

Hmax .

Core Saturation

Quadrant I

Quadrant III

maxB− .

H− max .

( )B t

m

Bm L

H

= =

( )H t

Core Saturation

Unidirectional Core Excitation

(Quadrant I)

maxB .

Hmax .

Core Saturation

Quadrant I

Quadrant III

maxB− .

H− max .

(a) (b)

Figure 2. B-H Curve (without hysteresis) of Transformer Core. (a) Bidirectional Core Excitation.

(b) Unidirectional Core Excitation.

Among Buck and Buck–Boost derived DC–DC converters, the most popular single-

switch are Forward and Flyback converter, while those employing multiple switches in-

clude Full-Bridge, Half-Bridge, and Push–Pull converter. Figures 3–5, show the basic iso-

lated SIMO DC–DC converters. The conversion relations for DCM (Discontinuous Con-

duction Mode) and CCM (Continuous Conduction Mode) are summarized in Table 1.

The output filter inductor in Full-Bridge, Half-Bridge, and Push–Pull converters acts as

the inductance in a Buck converter, and thus the equation for critical inductance for the

Buck is valid for these Buck-Derived converters, as long as the appropriate transfor-

mation of the input voltage due to the transformer turns ratio and topology is applied.

Figure 2. B-H Curve (without hysteresis) of Transformer Core. (a) Bidirectional Core Excitation.(b) Unidirectional Core Excitation.

Among Buck and Buck–Boost derived DC–DC converters, the most popular single-switch are Forward and Flyback converter, while those employing multiple switchesinclude Full-Bridge, Half-Bridge, and Push–Pull converter. Figures 3–5, show the basicisolated SIMO DC–DC converters. The conversion relations for DCM (DiscontinuousConduction Mode) and CCM (Continuous Conduction Mode) are summarized in Table 1.The output filter inductor in Full-Bridge, Half-Bridge, and Push–Pull converters acts asthe inductance in a Buck converter, and thus the equation for critical inductance for theBuck is valid for these Buck-Derived converters, as long as the appropriate transformationof the input voltage due to the transformer turns ratio and topology is applied. As aresult, Isolated Buck (Fly-Buck) converter is used in applications below 15 W, Flyback, andBuck-Derived converters in 10–100 W, Forward in 50–300 W, Half-Bridge, and Push–Pullconverters in more than 500 W, while Full-Bridge is used in applications with a power rangeof 1 to 5 kW. Table 2 summarizes some features of the converters shown in Figures 3–5.

Electronics 2022, 11, 1258 6 of 34


As a result, Isolated Buck (Fly-Buck) converter is used in applications below 15 W, Fly-

back, and Buck-Derived converters in 10–100 W, Forward in 50–300 W, Half-Bridge, and

Push–Pull converters in more than 500 W, while Full-Bridge is used in applications with

a power range of 1 to 5 kW. Table 2 summarizes some features of the converters shown

in Figures 3–5.

gV

1N( )1i t

1mL

( )1i t

( )1V t

PWM Q

( )gi t ( )21V t

2N ( )21i t

1R

1oI

1oV1oC1D

( )2NV t

NN ( )2Ni t

NR

oNI

oNVoNCND

( )21V t

2N ( )21i t

1R

1oI

1oV1oC1D

( )2NV t

NN ( )2Ni t

NR

oNI

oNVoNCND

gV

1N

( )1i t

1mL

( )1i t

( )1V t

( )gi t

PWM

1Q

2Q

(a) (b)

(c) (d)

Figure 3. Multiple-Output Isolated DC–DC Converters Topologies. (a) Single-Switch Flyback

Converter. (b) Two-Switch Flyback Converter. (c) Single-Switch Forward Converter. (d) Two-

Switch Forward Converter.

gV1N

( )1i t

1mL

( )1i t

( )1V t( )gi t

PWM 2Q

cC

PWM 1Q

( )2Ni t

( )2NV t

2NN

NR

oNI

oNVoNC1ND

2ND

NL

( )NLi t

( )21V t

21N

1R

1oI

1oV1oC11D

21D

1L

( )1Li t( )21i t

gV

1N( )1i t

1mL

( )1i t

( )1V t

PWM Q

( )gi t

( )2Ni t

( )2NV t

2NN

NR

oNI

oNVoNC2ND

NL

( )NLi t

( )21V t

21N

1R

1oI

1oV1oC21D

1L

( )1Li t( )21i t2C

2CV

2NC

2NCV

(a) (b)

gV1N

( )1i t

( )2Ni t

1mL

( )1i t

( )1V t

PWM Q

3N

( )3V t

( )3i t

3D

( )2NV t

2NN

NR

oNI

oNVoNC1ND

2ND

NL

( )NLi t

( )21V t

21N

1R

1oI

1oV1oC11D

21D

1L

( )1Li t( )21i t

gV

3D

1N

( )1i t

1mL

( )1i t

( )1V t

PWM

4D

1Q

2Q

( )2Ni t

( )2NV t

2NN

NR

oNI

oNVoNC1ND

2ND

NL

( )NLi t

( )21V t

21N

1R

1oI

1oV1oC11D

21D

1L

( )1Li t( )21i t

Figure 3. Multiple-Output Isolated DC–DC Converters Topologies. (a) Single-Switch Flyback Con-verter. (b) Two-Switch Flyback Converter. (c) Single-Switch Forward Converter. (d) Two-SwitchForward Converter.


As a result, Isolated Buck (Fly-Buck) converter is used in applications below 15 W, Fly-

back, and Buck-Derived converters in 10–100 W, Forward in 50–300 W, Half-Bridge, and

Push–Pull converters in more than 500 W, while Full-Bridge is used in applications with

a power range of 1 to 5 kW. Table 2 summarizes some features of the converters shown

in Figures 3–5.

gV

1N( )1i t

1mL

( )1i t

( )1V t

PWM Q

( )gi t ( )21V t

2N ( )21i t

1R

1oI

1oV1oC1D

( )2NV t

NN ( )2Ni t

NR

oNI

oNVoNCND

( )21V t

2N ( )21i t

1R

1oI

1oV1oC1D

( )2NV t

NN ( )2Ni t

NR

oNI

oNVoNCND

gV

1N

( )1i t

1mL

( )1i t

( )1V t

( )gi t

PWM

1Q

2Q

(a) (b)

(c) (d)

Figure 3. Multiple-Output Isolated DC–DC Converters Topologies. (a) Single-Switch Flyback

Converter. (b) Two-Switch Flyback Converter. (c) Single-Switch Forward Converter. (d) Two-

Switch Forward Converter.

gV1N

( )1i t

1mL

( )1i t

( )1V t( )gi t

PWM 2Q

cC

PWM 1Q

( )2Ni t

( )2NV t

2NN

NR

oNI

oNVoNC1ND

2ND

NL

( )NLi t

( )21V t

21N

1R

1oI

1oV1oC11D

21D

1L

( )1Li t( )21i t

gV

1N( )1i t

1mL

( )1i t

( )1V t

PWM Q

( )gi t

( )2Ni t

( )2NV t

2NN

NR

oNI

oNVoNC2ND

NL

( )NLi t

( )21V t

21N

1R

1oI

1oV1oC21D

1L

( )1Li t( )21i t2C

2CV

2NC

2NCV

(a) (b)

gV1N

( )1i t

( )2Ni t

1mL

( )1i t

( )1V t

PWM Q

3N

( )3V t

( )3i t

3D

( )2NV t

2NN

NR

oNI

oNVoNC1ND

2ND

NL

( )NLi t

( )21V t

21N

1R

1oI

1oV1oC11D

21D

1L

( )1Li t( )21i t

gV

3D

1N

( )1i t

1mL

( )1i t

( )1V t

PWM

4D

1Q

2Q

( )2Ni t

( )2NV t

2NN

NR

oNI

oNVoNC1ND

2ND

NL

( )NLi t

( )21V t

21N

1R

1oI

1oV1oC11D

21D

1L

( )1Li t( )21i t

Figure 4. Cont.

Electronics 2022, 11, 1258 7 of 34Electronics 2022, 11, x FOR PEER REVIEW 7 of 35

(c) (d)

Figure 4. Multiple-Output Isolated DC–DC Converters Topologies. (a) Active Clamp Forward

Converter. (b) Isolated Zeta Converter. (c) Isolated SEPIC Converter. (d) Isolated Ćuk Converter.

gV

( )gi t

1N( )1i t

1mL

( )1i t

( )1V tPWM

2Q

1R

1oI

1oV1oC

1D

( )21V t

2N ( )21i t

2R

2oI

2oV2oC

( )2NV t

NN ( )2Ni t

NR

oNI

oNVoNCND

2D

1N

1mL( )1PV t

1R

1oI

1oV1oC

1D

2D

1L

( )1Li t

( )1SV t

2N

2N

( )2SV t

( )1i t

( )2i t

Q

( )1i t

( )2i t

gV

( )gi t

C

C

gV

2gV

2gV

PWM 1Q

PWM 2Q

NR

oNI

oNVoNC

1ND

2ND

NL

( )LNi t

( )1S NV t

NN

NN

( )2S NV t

( )1Ni t

( )2Ni t

(a) (b)

(c) (d)

Figure 5. Multiple-Output Isolated DC–DC Converters Topologies. (a) Isolated Buck (Fly-Buck)

Converter. (b) Half-Bridge Converter. (c) Push–Pull Converter. (d) Full-Bridge Converter.

1N1Li1C

1CV

gV

gi

1L

1LV

( )1i t

1VPWM Q ( )21V t

2N ( )21i t

1R

1oI

1oV1oC1D

( )2NV t

NN ( )2Ni t

NR

oNI

oNVoNCND

1N1Li1C

1CVgi

1L

1LV

( )1i t

1VPWM Q ( )2Ni t

( )2NV t

2NN

NR

oNI

oNVoNC2ND

NL

( )NLi t

( )21V t

21N

1R

1oI

1oV1oC21D

1L

( )1Li t( )21i t2C

2CV

2NC

2NCV

gV

1R

1oI

1oV1oC

1D

2D

1L

( )1Li t

( )1SV t

2N

2N

( )2SV t

( )1i t

( )2i t

NR

oNI

oNVoNC

1ND

2ND

NL

( )LNi t

( )1S NV t

NN

NN

( )2S NV t

( )1Ni t

( )2Ni t

1N

( )2i t

1mL

( )2PV t

1N

( )1i t

( )1PV t

Q

gV

( )gi t

PWM 2Q

PWM

1Q

1R

1oI

1oV1oC

1D

2D

1L

( )1Li t

( )1SV t

2N

2N

( )2SV t

( )1i t

( )2i t

NR

oNI

oNVoNC

1ND

2ND

NL

( )LNi t

( )1S NV t

NN

NN

( )2S NV t

( )1Ni t

( )2Ni t

gV

1N

1mL( )1PV t

( )gi t

gV

Q2

3

( )1i t

( )2i t

Q Q1PWM1 1Q PWM2 2Q

Q Q1PWM2 3Q PWM1 4Q

Figure 4. Multiple-Output Isolated DC–DC Converters Topologies. (a) Active Clamp ForwardConverter. (b) Isolated Zeta Converter. (c) Isolated SEPIC Converter. (d) Isolated Cuk Converter.


(c) (d)

Figure 4. Multiple-Output Isolated DC–DC Converters Topologies. (a) Active Clamp Forward

Converter. (b) Isolated Zeta Converter. (c) Isolated SEPIC Converter. (d) Isolated Ćuk Converter.

gV

( )gi t

1N( )1i t

1mL

( )1i t

( )1V tPWM

2Q

1R

1oI

1oV1oC

1D

( )21V t

2N ( )21i t

2R

2oI

2oV2oC

( )2NV t

NN ( )2Ni t

NR

oNI

oNVoNCND

2D

1N

1mL( )1PV t

1R

1oI

1oV1oC

1D

2D

1L

( )1Li t

( )1SV t

2N

2N

( )2SV t

( )1i t

( )2i t

Q

( )1i t

( )2i t

gV

( )gi t

C

C

gV

2gV

2gV

PWM 1Q

PWM 2Q

NR

oNI

oNVoNC

1ND

2ND

NL

( )LNi t

( )1S NV t

NN

NN

( )2S NV t

( )1Ni t

( )2Ni t

(a) (b)

(c) (d)

Figure 5. Multiple-Output Isolated DC–DC Converters Topologies. (a) Isolated Buck (Fly-Buck)

Converter. (b) Half-Bridge Converter. (c) Push–Pull Converter. (d) Full-Bridge Converter.

1N1Li1C

1CV

gV

gi

1L

1LV

( )1i t

1VPWM Q ( )21V t

2N ( )21i t

1R

1oI

1oV1oC1D

( )2NV t

NN ( )2Ni t

NR

oNI

oNVoNCND

1N1Li1C

1CVgi

1L

1LV

( )1i t

1VPWM Q ( )2Ni t

( )2NV t

2NN

NR

oNI

oNVoNC2ND

NL

( )NLi t

( )21V t

21N

1R

1oI

1oV1oC21D

1L

( )1Li t( )21i t2C

2CV

2NC

2NCV

gV

1R

1oI

1oV1oC

1D

2D

1L

( )1Li t

( )1SV t

2N

2N

( )2SV t

( )1i t

( )2i t

NR

oNI

oNVoNC

1ND

2ND

NL

( )LNi t

( )1S NV t

NN

NN

( )2S NV t

( )1Ni t

( )2Ni t

1N

( )2i t

1mL

( )2PV t

1N

( )1i t

( )1PV t

Q

gV

( )gi t

PWM 2Q

PWM

1Q

1R

1oI

1oV1oC

1D

2D

1L

( )1Li t

( )1SV t

2N

2N

( )2SV t

( )1i t

( )2i t

NR

oNI

oNVoNC

1ND

2ND

NL

( )LNi t

( )1S NV t

NN

NN

( )2S NV t

( )1Ni t

( )2Ni t

gV

1N

1mL( )1PV t

( )gi t

gV

Q2

3

( )1i t

( )2i t

Q Q1PWM1 1Q PWM2 2Q

Q Q1PWM2 3Q PWM1 4Q

Figure 5. Multiple-Output Isolated DC–DC Converters Topologies. (a) Isolated Buck (Fly-Buck)Converter. (b) Half-Bridge Converter. (c) Push–Pull Converter. (d) Full-Bridge Converter.

Electronics 2022, 11, 1258 8 of 34

Table 1. Conversion relations for Multiple-Output Isolated DC–DC Converters.

Converter CCM DCM

FlybackConverter

(Figure 3a,b)

Vo1 = Vg · N2N1· D

1−D , . . . ,

VoN = Vg · NNN1· D

1−D

Vo1 = D ·Vg

√Req.1·Ts2·Lm1

, . . . , VoN = D ·Vg

√Req.N ·Ts2·Lm1

With : 1Req.1

= 1R1

+ 1R2

(N3N2

)2+ · · ·+ 1

RN

(NN+1

N2

)2, . . .

. . . , 1Req.N

= 1R1

(N2

NN+1

)2+ 1

R2

(N3

NN+1

)2· · ·+ 1

RN

0 < D < 1

Isolated BuckConverter(Figure 5a)

Vo1 = D · VgVo2 = N2

N1·Vo1, . . . , VoN = NN

N1· Vo1

Vo1 =2·Vg(

1+√

1+ 8·Lm1R1 ·D2 ·Ts

)Vo2 = N2

N1·Vo1, . . . , VoN = NN

N1· Vo1

0 < D < 1

ForwardConverter

(Figure 3c,d)

Vo1 = N21N1· D · Vg, . . . , VoN = N2N

N1· D · Vg Vo1 =

(N21N1

)·2·Vg(

1+√

1+ 8·L1R1 ·D2 ·Ts

) , . . . , VoN =

(N2NN1

)·2·Vg(

1+√

1+ 8·LNRN ·D2 ·Ts

)0 < D < 0.5 f or N1 = N3

Active ClampForward Converter

(Figure 4a)

Vo1 = N21N1· D · Vg, . . . , VoN = N2N

N1· D · Vg Vo1 =

(N21N1

)·2·Vg(

1+√

1+ 8·L1R1 ·D2 ·Ts

) , . . . , VoN =

(N2NN1

)·2·Vg(

1+√


)0 < D < 0.5

Push–Pull Converter(Figure 5c)

Vo1 = 2 · N21N1· D · Vg, . . . ,

VoN = 2 · N2NN1· D · Vg

Vo1 =

(N21N1

)·4·Vg(

1+√

1+ 8·L1R1 ·D2 ·Ts

) , . . . , VoN =

(N2NN1

)·4·Vg(

1+√


)0 < D < 0.5

Half-Bridge Converter(Figure 5b)

Vo1 = N21N1· D · Vg, . . . , VoN = N2N

N1· D · Vg

Vo1 =

(N21N1

)·2·Vg(

1+√

1+ 8·L1R1 ·D2 ·Ts

) , . . . , VoN =

(N2NN1

)·2·Vg(

1+√


)0 < D < 0.5

Full-Bridge Converter(Figure 5d)

Vo1 = N21N1· D · Vg, . . . , VoN = N2N

N1· D · Vg Vo1 =

(N21N1

)·4·Vg(

1+√

1+ 8·L1R1 ·D2 ·Ts

) , . . . , VoN =

(N2NN1

)·4·Vg(

1+√


)0 < D < 0.5

Buck–Boost-DerivedIsolated Converters

(Figure 4b–d)

Vo1 = Vg · N2N1· D

1−D , . . . ,

VoN = Vg · NNN1· D

1−D

Vo1 = D ·Vg

√Req.1·Ts2·Lm1

, . . . , VoN = D ·Vg

√Req.N ·Ts2·Lm1

With : 1Req.1

= 1R1

+ 1R2

(N3N2

)2+ · · ·+ 1

RN

(NN+1

N2

)2, . . .

. . . , 1Req.N

= 1R1

(N2

NN+1

)2+ 1

R2

(N3

NN+1

)2· · ·+ 1

RN

0 < D < 1

Nomenclature:Vg: Source voltage

N: Winding turn numberD: Duty cycle

R: Load resistanceL: Inductance

Ts: Switching period

Other classification of isolated multiple-output DC–DC converters can be realized de-pending on the switching technique: hard-switching (PWM converters) and soft-switching(resonant converters) [54–56]. They are traditionally used in applications such as veryhigh frequency power supplies, induction heating, ballasts for fluorescent lamps, sonartransmitters, ultrasonic generators, and power supplies for laser cutting machines. Isolatedresonant converters can be defined as converter networks to which resonant (L and C)

Electronics 2022, 11, 1258 9 of 34

elements are added. In contrast to square wave switch waveforms in PWM converters,resonant topologies exhibit smooth quasi-sinusoidal waveforms and, therefore, reducedswitching losses. The incentive to increase the frequency at which DC–DC converters areoperated is motivated by the fact that correspondingly smaller values and, hence, weightsand sizes of energy storage components should result in lighter and smaller converters.However, the inevitable increase in power losses due to switching establishes a practicalupper limit in the frequency range. Resonant isolated converter topologies overcome someof the switching loss mechanisms attributed to PWM converters and offer the possibility ofextending the usable frequency range toward higher frequencies (typically 100 to 500 kHz).In contrast to sharp transitions in current and voltage waveforms of PWM converters, theresonant converters operate with smooth, quasi-sinusoidal, resonant waveforms, leadingto reduced losses ascribed to switching transitions. Soft-switching converters can exhibitreduced switching loss, at the expense of increased conduction loss.

Table 2. Comparative summary of SIMO Isolated DC–DC Converters.

TypeConverter

NumberSwitches

NumberComponents

VoltageStress

TransformerUtility

FloatingSwitches

Input/OutputFeature

Single-SwitchFlyback Low Low High Moderate No Discontinuous input current

Discontinuous output currents

Two-SwitchFlyback Medium Low Medium Moderate Yes Discontinuous input current


Single-SwitchForward Low Medium High Moderate No Discontinuous input current

Continuous output currents

Two-SwitchForward Medium Medium Medium Moderate Yes Discontinuous input current


Active ClampForward Medium High Medium Moderate Yes Discontinuous input current


Isolated Zeta Low Medium High Moderate No Discontinuous input currentContinuous output currents

Isolated SEPIC Low Medium High Moderate No Continuous input currentDiscontinuous output currents

Isolated Cuk Low Medium High Moderate No Continuous input currentContinuous output currents

Isolated Buck(Fly–Buck) Low Low Medium Moderate Yes Discontinuous input current


Half-Bridge Medium Medium Medium Good Yes Continuous input currentContinuous output currents

Push–Pull Medium High Medium Good No Continuous input currentContinuous output currents

Full-Bridge High High Low Good Yes Continuous input currentContinuous output currents

Resonant converters use resonant L-C elements that cause sinusoidal variation ofvoltage and current waveforms in order to reduce switching losses. They were developed asan alternative to simple rectangular switching, the power devices switch at high frequency,maintaining acceptable converter efficiency by minimizing the significant switching lossesassociated with hard-switching. In these converters, the size and weight are reduced(mainly, magnetic and filtering components) and the power density is increased, with lowstress on the switching devices. In addition, the soft-switching technique utilizes VariableFrequency (VF) for regulation, with constant on-time or constant off-time, which createsan oscillating circuit that allows power device transitions to occur at zero voltage (ZeroVoltage Switching, ZVS) or zero current (Zero Current Switching, ZCS), eliminating or

Electronics 2022, 11, 1258 10 of 34

reducing the switching losses in the converter, higher-frequency operation and reducingthe size of magnetic and filter components. Both resonant techniques are widely used inmany applications.

In isolated multiple-output DC–DC converters, the resonant components can be placedeither on the primary or on the secondary side. When a resonant capacitor is placed onin some winding, the leakage inductance and magnetizing inductance of the transformercan be used as a resonant element in order to reduce the number of discrete magneticcomponents and, therefore, increase the power density of the converter.

Although there is a wide variety of isolated multiple-output resonant converter topolo-gies, the most widely used are those based on three reactive elements, being LLC and LCC,shown in Figure 6, the most popular. The conversion relations for these topologies aresummarized in Table 3 [56]. Table 4 shows some features of the LLC and LCC converters.


1N

1mL( )PV t

RLRC

( )1mLi t

( )RLV t ( )

RCV t

( )RLi t

( )2QV t

gVgV

( )gi t

VF-COT 1Q

2QVF-COT

1R

1oI

1oV1oC

1D

2D

( )1SV t

2N

2N

( )2SV t

( )1i t

( )2i t

NR

oNI

oNVoNC

1ND

2ND

( )1S NV t

NN

NN

( )2S NV t

( )1Ni t

( )2Ni t

(a)

RLRC

( )pi t

( )RLV t ( )

RCV t

( )RLi t

( )2QV t

( )PV t

1N

1mLpC

( )gi t

1Q

2Q

gVgV

VF-COT

VF-COT

1R

1oI

1oV1oC

1D

2D

( )1SV t

2N

2N

( )2SV t

( )1i t

( )2i t

NR

oNI

oNVoNC

1ND

2ND

( )1S NV t

NN

NN

( )2S NV t

( )1Ni t

( )2Ni t

(b)

Figure 6. Three-element Multiple-Output Isolated Resonant DC–DC Converters: LLC and LCC. (a)

LLC Resonant DC–DC Converter. (b) LCC Resonant DC–DC Converter.

Figure 6. Three-element Multiple-Output Isolated Resonant DC–DC Converters: LLC and LCC.(a) LLC Resonant DC–DC Converter. (b) LCC Resonant DC–DC Converter.

Electronics 2022, 11, 1258 11 of 34

Table 3. Conversion relations for Multiple-Output Isolated Resonant DC–DC Converters.

Converter Output Voltages

LLC ResonantDC–DC Converter

(Figure 6a)

Vo1 =N2N1· Vg

2√[(Ln+1)− 1

f 2n

]2

· 1L2

n+(

fn− 1fn

)2·Q2

, . . . , VoN =NNN1· Vg

2√[(Ln+1)− 1

f 2n

]2

· 1L2

n+(

fn− 1fn

)2·Q2

VoN = NNN1· Vg

2 ← Mode I ( fS = fR1

).

VoN = NNN1· Vg

2 ← Mode II ( fS > fR1

).

VoN > / < NNN1· Vg

2 ← Mode III ( fS < fR1

).

fs = Switching Frequency, fR1 =1

2π√

LRCRand fR2 =

12π√(LR+Lm1 )CR

fn =fS

fR1, Ln = LR

Lm1, Q = π2

8Req.·√

LRCR

and 1Req.

= 1R1

(N2N1

)2+ · · ·+ 1

RN

(NN+1

N1

)2

LCC ResonantDC–DC Converter

(Figure 6b)

Vo1 =N2N1· Vg

2√[ Cn+1

Cn− f 2

n ]2·C2

n+(

fn− 1fn

)2·Q2

, . . . , VoN =NNN1· Vg

2√[ Cn+1

Cn− f 2

n ]2·C2

n+(

fn− 1fn

)2·Q2

VoN = NNN1· Vg

2 ← Mode I ( fS = fR1

).

VoN = NNN1· Vg

2 ← Mode II ( fS < fR1

).

VoN > / < NNN1· Vg

2 ← Mode III ( fS > fR1

).

fs = Switching Frequency, fR1 =1

2π√

LRCRand fR2 =

1

2π

√LR

(CR ·CP

CR+CP

)fn =

fSfR1

, Cn = CPCR

, Q = π2

8Req.·√

LR(CR+CP)CR ·CP

and 1Req.

= 1R1

(N2N1

)2+ · · ·+ 1

RN

(NN+1

N1

)2

Nomenclature:Vg: Source voltage

N: Winding turn numberD: Duty cycle

R: Load resistance

L: Inductancefs: Switching frequencyfR: Resonance frequency

Q = Quality factor

Table 4. Comparative summary of SIMO Isolated DC–DC Resonant Converters.

TypeConverter

NumberSwitches

NumberComponents

VoltageStress

TransformerUtility

FloatingSwitches

Input/OutputFeature

LLC Resonant Medium Medium Medium Good Yes Discontinuous input currentContinuous output currents

LCC Resonant Medium High Medium Good Yes Discontinuous input currentContinuous output currents

2.2. SIMO DC–DC Converters Non-Isolated

Multiple-output converters without transformers are an alternative in applicationswhere galvanic isolation is not required. In this sense, non-isolated multiple-output convert-ers can be implemented with single switch or multiple switches, with their advantages anddisadvantages. As an example, multiple switches require several control switches, whichincreases the cost, losses, and number of gate drivers in the converter, while single-switchconverters cause higher stress in terms of voltage and current.

SIMO non-isolated with multiple switches converters have been developed for manyapplications and in different configurations and topologies [57–64]. They can providespace savings, while maintaining high efficiency. They are generally based on traditionalSingle-Input Single-Output (SISO) structures such as Buck, Boost, Buck–Boost and cascadeBuck–Boost, as shown in Figure 7. Each output voltage is a function of a fraction of the duty

Electronics 2022, 11, 1258 12 of 34

cycle of the switch to which it is connected. By having several switches, different switchingstrategies (time sequencing [65] and time-multiplexing [66]) and operation modes (CCMand DCM) are applicable.


Table 4. Comparative summary of SIMO Isolated DC–DC Resonant Converters.

Type

Converter

Number

Switches

Number

Components

Voltage

Stress

Transformer

Utility

Floating

Switches

Input/Output

Feature

LLC Resonant Medium Medium Medium Good Yes Discontinuous input current


LCC Resonant Medium High Medium Good Yes Discontinuous input current


2.2. SIMO DC–DC Converters Non-Isolated

Multiple-output converters without transformers are an alternative in applications

where galvanic isolation is not required. In this sense, non-isolated multiple-output con-

verters can be implemented with single switch or multiple switches, with their ad-

vantages and disadvantages. As an example, multiple switches require several control

switches, which increases the cost, losses, and number of gate drivers in the converter,

while single-switch converters cause higher stress in terms of voltage and current.

SIMO non-isolated with multiple switches converters have been developed for

many applications and in different configurations and topologies [57–64]. They can pro-

vide space savings, while maintaining high efficiency. They are generally based on tradi-

tional Single-Input Single-Output (SISO) structures such as Buck, Boost, Buck–Boost and

cascade Buck–Boost, as shown in Figure 7. Each output voltage is a function of a fraction

of the duty cycle of the switch to which it is connected. By having several switches, dif-

ferent switching strategies (time sequencing [65] and time-multiplexing [66]) and opera-

tion modes (CCM and DCM) are applicable.

Within SIMO non-isolated with multiple-switch converters, special attention should

be paid to Single Input Dual Output (SIDO), Symmetric Outputs DC–DC Converters or

Bipolar Output DC–DC Converters, as shown in Figure 8. Not only because of the inter-

est of its applications, but also because of the different topologies that have been devel-

oped [67–77]. The conversion relations SIDO Boost and Buck–Boost converters based are

summarized in Table 5 [67].

Controller

D

1oV

1oD

1oC

1oi

1R

NoV

NoD

NoC

Noi

NR

LiL

LV

1S

gV

gi

1oi

NoS

gi

1oS

D

1Li 1L

1LV

1S

gV

gi

1C1oV

1D1oC

1oi

1R1oS

2L

2LV

NoVND

NoCNoi

NRNoSNLV

NC

NL

Controller

(a)

1oV

1oi

1R

NoV

Noi

NRgV

gi

1S

1oS

LiL

LV

1oD

NoD

NoS

1oC

NoC

Controller

gV

gi

1C1o

V1o

C1o

i

1R

NoVNoC

Noi

NRNC

1S

1Li 1L

1LV

1D

2L

2LV

NLV

NL

NoS

Controller

1oD

NoD

1oS

(b)


Li

LLV

1oV

1oD

C

1oi

1R

1S

NoV

NoD

C

Noi

NRgV

gi

1oS

NoS

Controller

1S

gV

gi

1C1oV

1oC1oi

1R1oS

NoVNoC

Noi

NRNoSNC

1Li

1L1LV

1D 2D

ND

NLVNL

2L2LV

Controller

(c)

Figure 7. Single Input Multiple-Output (SIMO) non-isolated multiple switches DC–DC converters.

(a) SIMO Buck Converter versions [57]. (b) SIMO Boost Converter versions. (c) SIMO Buck–Boost

Converter versions.

1oC

2oC

2oi

1oi

LR−

LR+

LRoV

1oV

2oV

cc

oi1D

gi

gV

L

LVLi

2D

2S

1S

Controller

1oC

2oC

2oi

1oi

LR−

LR+

LRoV

1oV

2oV

cc

oi

1D

gi

gV

2D

2S

1S

1L

1LV1Li

2L

2LV2Li

Controller

(a) (b)

(c) (d)

1oC

2oC

2oi

1oi

LR−

LR+

LRoV

1oV

2oV

cc

oi2Dgi

L

LVLi

3D

2SgV

c

1S

1D

Controller

(e)

1oC

2oC

2oi

1oi

LR−

LR+

LRoV

1oV

2oV

cc

oi

2L2LV

2Li

c

2S

1L1LV

1Li

c

gi

gV

Controller

1S

3S

4S

1

1oC

2oC

2oi

1oi

LR−

LR+

LRoV

1oV

2oV

cc

oi1Dgi

1L

1LV1Li

2D

1SgV

2L2LV

2Li

2S

c

c

Controller

Figure 7. Single Input Multiple-Output (SIMO) non-isolated multiple switches DC–DC converters.(a) SIMO Buck Converter versions [57]. (b) SIMO Boost Converter versions. (c) SIMO Buck–BoostConverter versions.

Electronics 2022, 11, 1258 13 of 34

Within SIMO non-isolated with multiple-switch converters, special attention should bepaid to Single Input Dual Output (SIDO), Symmetric Outputs DC–DC Converters or BipolarOutput DC–DC Converters, as shown in Figure 8. Not only because of the interest of itsapplications, but also because of the different topologies that have been developed [67–77].The conversion relations SIDO Boost and Buck–Boost converters based are summarized inTable 5 [67].


Li

LLV

1oV

1oD

C

1oi

1R

1S

NoV

NoD

C

Noi

NRgV

gi

1oS

NoS

Controller

1S

gV

gi

1C1oV

1oC1oi

1R1oS

NoVNoC

Noi

NRNoSNC

1Li

1L1LV

1D 2D

ND

NLVNL

2L2LV

Controller

(c)

Figure 7. Single Input Multiple-Output (SIMO) non-isolated multiple switches DC–DC converters.

(a) SIMO Buck Converter versions [57]. (b) SIMO Boost Converter versions. (c) SIMO Buck–Boost

Converter versions.

1oC

2oC

2oi

1oi

LR−

LR+

LRoV

1oV

2oV

cc

oi1D

gi

gV

L

LVLi

2D

2S

1S

Controller

1oC

2oC

2oi

1oi

LR−

LR+

LRoV

1oV

2oV

cc

oi

1D

gi

gV

2D

2S

1S

1L

1LV1Li

2L

2LV2Li

Controller

(a) (b)

(c) (d)

1oC

2oC

2oi

1oi

LR−

LR+

LRoV

1oV

2oV

cc

oi2Dgi

L

LVLi

3D

2SgV

c

1S

1D

Controller

(e)

1oC

2oC

2oi

1oi

LR−

LR+

LRoV

1oV

2oV

cc

oi

2L2LV

2Li

c

2S

1L1LV

1Li

c

gi

gV

Controller

1S

3S

4S

1

1oC

2oC

2oi

1oi

LR−

LR+

LRoV

1oV

2oV

cc

oi1Dgi

1L

1LV1Li

2D

1SgV

2L2LV

2Li

2S

c

c

Controller

Figure 8. Single Input Dual Output (SIDO) DC–DC Converters. (a) Three-level Single-inductorBoost Converter [69]. (b) Three-level Two-inductors Boost Converter [70]. (c) Dual-output DC–DCBoost Converter [71]. (d) Series-combined Boost and Buck–Boost Converter [72]. (e) Single-inductorBuck–Boost Converter [73].

Electronics 2022, 11, 1258 14 of 34

SIMO non-isolated with single-switch converters [78–80] try to avoid some of the dis-advantages of using multiple controlled switches. They are also based on the combinationof SISO structures, using their front end, as shown in Figures 9 and 10. In these cases, eachoutput voltage is a function of the duty cycle of the single switch, operation modes (CCMand DCM) and of the combined configuration.

Table 5. Conversion relations for SIDO DC–DC Converters.

Converter CCM DCM

Boost Converter(Figure 8a) Vo =

Vg1−D = 2Vo1 = 2Vo2

Ig = Io1−D

Vo =Vg2

(1 +

√1 + 2RL ·D2·Ts

L

)Ig = Io

2

(1 +

√1 + 2RL ·D2·Ts

L

)Buck–Boost Converter

(Figure 8e) Vo =Vg D1−D = 2Vo1 = 2Vo2

Ig = Io D1−D

Vo = D ·Vg

√RL ·TS

2·L

Ig = D · Io

√RL ·TS

2·L

Nomenclature:Vg: Source voltageIg: Source curren

D: Duty cycle

R: Load resistanceL: Inductance

Ts: Switching period


Boost–SEPIC

combination Low Low High No

Continuous input current


Buck–Boost–Zeta

combination Low Low High Yes

Discontinuous input current

Discontinuous/Continuous

output currents

SEPIC–Ćuk

combination Low Low High No



output currents

Three-output-type

converter

for six loads

Low Medium High No



output currents

2oV

D

C

2oi

2R

1C

1CV

2Li

D

2L2LV

2C

1oi

1oV1R

( )

( )

1

2

1

1

1

o g

o g

DV V CCM

D

V V CCMD

=−

=−

S

1Li

gV

gi

1L

1LV

PWM

(a) (b)

(c) (d)

Figure 9. Two-output-type converter combinations. (a) Boost–Ćuk converter combination. (b)

Boost–SEPIC converter combination. (c) Buck–Boost–Zeta converter combination. (d) SEPIC–Ćuk

converter combination.

1C

2oV

D2oi

2R

2Li2L

1oVD

2LV

1oC

1oi

1R1CV

2oC( )

( )

1

2

1

1

1

o g

o g

DV V CCM

D

V V CCMD

=−

=−

S

1Li

gV

gi

1L

1LV

PWM

( )1 2 1

o o g

DV V V CCM

D= =

−

2Li 2L

1Li

1L1LV

1C

1oVD

2LV

2C

1oi

1R1CV

2oV

D

C

2oi

2R

S

gV

gi

PWM

1C

D

2oi

2oV

2Li2L

1oVD

2LV

1oC

1oi

1R1CV

2R3LV

3L2oC

2C

2CV

3Li

( )

( )

1

2

1

1

o g

o g

DV V CCM

D

DV V CCM

D

=−

=−

S

1Li

gV

gi

1L

1LV

PWM

Figure 9. Two-output-type converter combinations. (a) Boost–Cuk converter combination. (b) Boost–SEPIC converter combination. (c) Buck–Boost–Zeta converter combination. (d) SEPIC–Cuk con-verter combination.

Electronics 2022, 11, 1258 15 of 34

Table 6 summarizes some features of the converters shown in Figures 7–10.


( )

( )

1 3

1 2

2 3

2

1

1

1

o g

o g

o g

DV V CCM

D

DV V CCM

D

V V

−

−

−

=−

+=

−

=

gVgi

1Li

1LV1L

S

3LV3L

3oC2CV

3Li

2C

3D

2Li2L

1D

2LV

1oC1CV

1C

2oC

2D

2oV

3oi

1oi

2oi

1 3R −

1R1 2oV− 1oV

2R

3R

1 2R −

2 3R −

2 3oV− 3oV

1 3oV−

2oV

3oV

1oV

( )

( )

1 3

2

1

1

1

o o g

o g

DV V V CCM

D

V V CCMD

= =−

=−

PWM

Figure 10. Three-output-type converter combination for six loads.

2.3. MIMO DC–DC Converters Isolated

In the same way, MIMO DC–DC converters for combining various output loads

and input sources, they have become an interesting alternative in recent years, especially

because they allow the integration of different sources, such as: Rectifiers, Photovoltaic

Systems, Fuel Cells, Batteries, Supercapacitors, and, in some cases, Wind Energy Sys-

tems. Fundamentally, MIMO converters are implemented according with two struc-

tures: sharing a high voltage or low voltage common DC bus; and sharing one or more

transformers; or both architectures are also possible.

MIMO isolated configurations use a multi-winding transformer to transfer the en-

ergy from the primary side to the secondary side and to couple the different sources and

loads, with several power switches and centralized or distributed control signals. Sever-

al configurations can be derived from Full-Bridge, Half-Bridge Push–Pull Forward and

Flyback topologies, and other such as those shown in Figure 11 [81,82]. These converters

consist of Boost, Half-Bridge, or the called Boost–Dual-Half-Bridge (BDHB) topologies.

In these converters, the conversion ratio and output voltages depend on the control

strategy of the power switches, operation modes, and the turns ratio between the trans-

former windings. Normally, the power switches are controlled by phase-shifted PWM

operating at 50% duty cycle, in CCM and DCM. Table 7 shows some features of the

MIMO isolated converters.

1gV

1gi

1

´S

1Li 1L

1LV

1S

2gV

2gi

2

´S

2Li 2L

2LV

2S

gNV

gNi

´

NS

LNi L

LNV

NS

C

C

1N1

´

oS

1oS

1oC

1oC2N

1R

1oI

1oV

´

oNS

oNS

oNC

oNCNN

NR

oNI

oNV

Controller

Controller

Controller

(a)


Table 6. Comparative summary of SIMO DC–DC Converters Non-Isolated.

TypeConverter

NumberSwitches

NumberComponents

VoltageStress

FloatingSwitches

Input/OutputFeature

SIMO Buck Medium Medium High Yes Discontinuous input currentDiscontinuous output currents

SIMO Boost Medium Medium High Yes Continuous input currentDiscontinuous output currents

SIMO Buck–Boost Medium Medium High Yes Discontinuous input currentDiscontinuous output currents

Three-level Single-inductor Boost Medium Low Medium Yes Continuous input current


Three-level Two-inductors Boost Medium Low Medium Yes Continuous input current


Dual-outputDC–DC Boost Medium Low Medium No Continuous input current


Series-combined Boostand Buck–Boost Medium Low Medium Yes Continuous input current


Single-inductorBuck–Boost Medium Medium Medium Yes Discontinuous input current


Boost–Cukcombination

Low Low High NoContinuous input current

Discontinuous/Continuousoutput currents

Electronics 2022, 11, 1258 16 of 34

Table 6. Cont.

TypeConverter

NumberSwitches

NumberComponents

VoltageStress

FloatingSwitches

Input/OutputFeature

Boost–SEPICcombination Low Low High No Continuous input current


Buck–Boost–Zetacombination Low Low High Yes

Discontinuous input currentDiscontinuous/Continuous

output currents

SEPIC–Cukcombination

Low Low High NoContinuous input current

Discontinuous/Continuousoutput currents

Three-output-typeconverter

for six loadsLow Medium High No

Continuous input currentDiscontinuous/Continuous

output currents


In the same way, MIMO DC–DC converters for combining various output loadsand input sources, they have become an interesting alternative in recent years, especiallybecause they allow the integration of different sources, such as: Rectifiers, PhotovoltaicSystems, Fuel Cells, Batteries, Supercapacitors, and, in some cases, Wind Energy Systems.Fundamentally, MIMO converters are implemented according with two structures: sharinga high voltage or low voltage common DC bus; and sharing one or more transformers; orboth architectures are also possible.

MIMO isolated configurations use a multi-winding transformer to transfer the energyfrom the primary side to the secondary side and to couple the different sources and loads,with several power switches and centralized or distributed control signals. Several con-figurations can be derived from Full-Bridge, Half-Bridge Push–Pull Forward and Flybacktopologies, and other such as those shown in Figure 11 [81,82]. These converters consistof Boost, Half-Bridge, or the called Boost–Dual-Half-Bridge (BDHB) topologies. In theseconverters, the conversion ratio and output voltages depend on the control strategy of thepower switches, operation modes, and the turns ratio between the transformer windings.Normally, the power switches are controlled by phase-shifted PWM operating at 50% dutycycle, in CCM and DCM. Table 7 shows some features of the MIMO isolated converters.


( )

( )

1 3

1 2

2 3

2

1

1

1

o g

o g

o g

DV V CCM

D

DV V CCM

D

V V

−

−

−

=−

+=

−

=

gVgi

1Li

1LV1L

S

3LV3L

3oC2CV

3Li

2C

3D

2Li2L

1D

2LV

1oC1CV

1C

2oC

2D

2oV

3oi

1oi

2oi

1 3R −

1R1 2oV− 1oV

2R

3R

1 2R −

2 3R −

2 3oV− 3oV

1 3oV−

2oV

3oV

1oV

( )

( )

1 3

2

1

1

1

o o g

o g

DV V V CCM

D

V V CCMD

= =−

=−

PWM



In the same way, MIMO DC–DC converters for combining various output loads

and input sources, they have become an interesting alternative in recent years, especially

because they allow the integration of different sources, such as: Rectifiers, Photovoltaic

Systems, Fuel Cells, Batteries, Supercapacitors, and, in some cases, Wind Energy Sys-

tems. Fundamentally, MIMO converters are implemented according with two struc-

tures: sharing a high voltage or low voltage common DC bus; and sharing one or more

transformers; or both architectures are also possible.

MIMO isolated configurations use a multi-winding transformer to transfer the en-

ergy from the primary side to the secondary side and to couple the different sources and

loads, with several power switches and centralized or distributed control signals. Sever-

al configurations can be derived from Full-Bridge, Half-Bridge Push–Pull Forward and

Flyback topologies, and other such as those shown in Figure 11 [81,82]. These converters

consist of Boost, Half-Bridge, or the called Boost–Dual-Half-Bridge (BDHB) topologies.

In these converters, the conversion ratio and output voltages depend on the control

strategy of the power switches, operation modes, and the turns ratio between the trans-

former windings. Normally, the power switches are controlled by phase-shifted PWM

operating at 50% duty cycle, in CCM and DCM. Table 7 shows some features of the

MIMO isolated converters.

1gV

1gi

1

´S

1Li 1L

1LV

1S

2gV

2gi

2

´S

2Li 2L

2LV

2S

gNV

gNi

´

NS

LNi L

LNV

NS

C

C

1N1

´

oS

1oS

1oC

1oC2N

1R

1oI

1oV

´

oNS

oNS

oNC

oNCNN

NR

oNI

oNV

Controller

Controller

Controller

(a)

Figure 11. Cont.


1

´

oS

1oS

1oC

1oC2 1N ,

1R

1oI

1oV

´

oNS

oNS

oNC

oNC2 NN ,

NR

oNI

oNV

Controller

Controller

1gV

1gi

1S´

1Li 1L

1LV

1S

C

C

11N ,

Controller

gNV

gNi

´

NS

LNi NL

LNV

NS

C

C

1 NN ,

Controller

(b)

1gV

1gi

C

C

11,N

gNV

gNi

C

C

1,NN

1oC

1oC2 1N ,

1R

1oI

1oV

´

oNS

oNS

oNC

oNC2 NN ,

NR

oNI

oNV

Controller

1

´

oS

1oS

Controller

1S´

1S

Controller

NS´

NS

Controller

(c)

Figure 11. Cont.


1

´

oS

1oS

1oC

1oC2 1N ,

1R

1oI

1oV

´

oNS

oNS

oNC

oNC2 NN ,

NR

oNI

oNV

Controller

Controller

1gV

1gi

1S´

1Li 1L

1LV

1S

C

C

11N ,

Controller

gNV

gNi

C

C

1,NN

NS´

NS

Controller

(d)

Figure 11. MIMO isolated. (a) Boost parallel converter. (b) Boost ports converter. (c) Half-Bridge

converter. (d) Boost–Half-Bridge converter combination.

Table 7. Comparative summary of MIMO DC–DC Converters Isolated.

Type

Converter

Number

Switches

Number

Components

Voltage

Stress

Transformer

Utility

Floating

Switches

Input/Output

Feature

Boost

parallel High High Medium Good Yes

Continuous input currents


Boost ports High High Medium Good Yes Continuous input currents


Half-Bridge High Medium Medium Good Yes Continuous input currents


Boost–Half

Bridge High High Medium Good Yes

Continuous input currents


2.4. MIMO DC–DC Converters Non-Isolated

In the same sense, for MIMO transformerless configurations, based on high-voltage

or low-voltage common DC bus, two architectures are established: independent and/or

integrated DC–DC converters. MIMO non-isolated integrated uses a single conversion

stage, simplifying architecture and control, and have been proposed as an alternative to

independent architecture connection. These converters are based on single-input single-

output configurations such as: Boost, Buck, Buck–Boost, SEPIC, and Ćuk, as well as

combinations of these configurations, with common ground [83–85] or series connec-

tions [44,86], as shown in Figure 12. Table 8 summarizes some features of the non-

isolated MIMO DC–DC Converters.

Figure 11. MIMO isolated. (a) Boost parallel converter. (b) Boost ports converter. (c) Half-Bridgeconverter. (d) Boost–Half-Bridge converter combination.

Table 7. Comparative summary of MIMO DC–DC Converters Isolated.

TypeConverter

NumberSwitches

NumberComponents

VoltageStress

TransformerUtility

FloatingSwitches

Input/OutputFeature

Boostparallel High High Medium Good Yes Continuous input currents


Boost ports High High Medium Good Yes Continuous input currentsContinuous output currents

Half-Bridge High Medium Medium Good Yes Continuous input currentsContinuous output currents

Boost–HalfBridge High High Medium Good Yes Continuous input currents


2.4. MIMO DC–DC Converters Non-Isolated

In the same sense, for MIMO transformerless configurations, based on high-voltage orlow-voltage common DC bus, two architectures are established: independent and/or inte-grated DC–DC converters. MIMO non-isolated integrated uses a single conversion stage,simplifying architecture and control, and have been proposed as an alternative to inde-pendent architecture connection. These converters are based on single-input single-outputconfigurations such as: Boost, Buck, Buck–Boost, SEPIC, and Cuk, as well as combina-tions of these configurations, with common ground [83–85] or series connections [44,86],as shown in Figure 12. Table 8 summarizes some features of the non-isolated MIMODC–DC Converters.


1oC

1oi

1R1oV

1D1gi

L

LVLi

1gV

2oC

2oi

2R2oV

2gi

2gV

NoC

Noi

NRNoV

Ngi

1

´

NS

+1gVND

c

1S

2D

2S2

´D

2

´S

ND

NS

c

cc

cc

´

ND

´

NS

c

Controller

1oC

1oi

1R1oV

1

´D1gi

L

LVLi

1

´S1gV

1S

1D

2oC

2oi

2R2oV

2

´D2gi

2

´S2gV

2S

2D

NoC

Noi

NRNoV

´

NDNgi

´

NS1gV

NS

ND

Controller

(a) (b)

Figure 12. Non-isolated single-inductor MIMO Converters. (a) Series outputs [83–85]. (b) Series

inputs and series outputs [44,86].

Table 8. Comparative summary of MIMO DC–DC Converters Non-Isolated.

Type

Converter

Number

Switches

Number

Components

Voltage

Stress

Floating

Switches

Input/Output

Feature

Series outputs Medium Low High Yes Discontinuous input/

output currents

Series inputs and

series outputs Medium High High Yes

Discontinuous input/

output currents

Compared with independent architecture connection, integrated MIMO DC–DC

converters have the advantage of smaller size, fewer power conversion stages, and lower

cost. On the other hand, both the series inputs and the series inputs and series outputs

connection, with a single inductor, require a complex control system to avoid cross-

regulation problems, and the simultaneous application of different voltages coming

from the input sources, which limits the connection of a large number of sources and

loads.

The current trend in the development of DC–DC converters with multiple outputs

follows general aspects, such as low losses, high-power density, and high efficiency, as

well as the development of new architectures and control strategies. Certainly, simple

structures with a reduced number of components and power switches will be one of the

new trends, especially to reduce the size. However, the incorporation of devices with a

Wide Band Gap (WBG), particularly Gallium Nitride (GaN) and Silicon Carbide (SiC),

will establish future trends, advantages and disadvantages, in the development and ap-

plications of DC–DC converters with multiple outputs.

3. Multiple-Output DC–DC Converters Applications and Solutions

In this section, we present the applications of multiple-output DC–DC converters.

Although it’s impossible to list all type of applications, we try to present a wide variety

that can represent the most important types of applications and solutions that use mul-

tiple-output DC–DC converters. Figure summarizes some DC–DC converters’ applica-

tions, grouped in three major categories: High Power, Medium Power, and Low Power.

Figure 12. Non-isolated single-inductor MIMO Converters. (a) Series outputs [83–85]. (b) Seriesinputs and series outputs [44,86].

Table 8. Comparative summary of MIMO DC–DC Converters Non-Isolated.

TypeConverter

NumberSwitches

NumberComponents

VoltageStress

FloatingSwitches

Input/OutputFeature

Series outputs Medium Low High Yes Discontinuous input/output currents

Series inputs andseries outputs Medium High High Yes Discontinuous input/

output currents

Compared with independent architecture connection, integrated MIMO DC–DC con-verters have the advantage of smaller size, fewer power conversion stages, and lower cost.On the other hand, both the series inputs and the series inputs and series outputs connec-tion, with a single inductor, require a complex control system to avoid cross-regulationproblems, and the simultaneous application of different voltages coming from the inputsources, which limits the connection of a large number of sources and loads.

The current trend in the development of DC–DC converters with multiple outputsfollows general aspects, such as low losses, high-power density, and high efficiency, as wellas the development of new architectures and control strategies. Certainly, simple structureswith a reduced number of components and power switches will be one of the new trends,especially to reduce the size. However, the incorporation of devices with a Wide Band Gap(WBG), particularly Gallium Nitride (GaN) and Silicon Carbide (SiC), will establish futuretrends, advantages and disadvantages, in the development and applications of DC–DCconverters with multiple outputs.

3. Multiple-Output DC–DC Converters Applications and Solutions

In this section, we present the applications of multiple-output DC–DC converters.Although it’s impossible to list all type of applications, we try to present a wide varietythat can represent the most important types of applications and solutions that use multiple-output DC–DC converters. Figure summarizes some DC–DC converters’ applications,grouped in three major categories: High Power, Medium Power, and Low Power. Again,a partition like this will never be straightforward or even definitive, but it represents thetypical mindset when one thinks of general DC–DC converters.

Electronics 2022, 11, 1258 20 of 34

Also, in Figure 13, we can identify areas of applications like: telecommunication,medical, automotive, energy and power, robotic, UAVs, and drones. In the next sections,some of these areas are detailed, giving concrete examples of applications and solutionsused with multiple DC–DC converters.


Again, a partition like this will never be straightforward or even definitive, but it repre-

sents the typical mindset when one thinks of general DC–DC converters.

Also, in Figure 13, we can identify areas of applications like: telecommunication,

medical, automotive, energy and power, robotic, UAVs, and drones. In the next sections,

some of these areas are detailed, giving concrete examples of applications and solutions

used with multiple DC–DC converters.

Figure 13. Multiple-Output DC–DC Converters Applications.

3.1. Converters for More Electric Aircraft

In an airplane, the necessary power generated by an engine is converted into four

types of energy: hydraulic, mechanical, pneumatic, and electrical. In addition to the

power required for pushing, the current trend is to replace mechanical, pneumatic, and

hydraulic systems with an electric alternative [87,88]. This has led to a significant in-

crease in the electrical power of an aircraft, reaching values of the order of megawatts in

some models [89]. As a consequence, the electrical system has increased in complexity

with a large number of electronic converters, electrical machines, switches, protections,

and a variety of loads [90,91]. These systems are similar to a ground-based microgrid,

although there are some differences that make them unique. In this sense, a system with

a high level of reliability and safety is required with the advantage of having more pre-

dictable loads, changing their priority during the flight.

The electrical power system of an airplane is a system of multiple voltage levels,

connected through electronic power converters. The different voltage levels are stand-

ardized [92]:

— DC Voltages: 28 V, 270 V (±135 V) and 540 V (±270 V); and

Multiple Output DC-DC Converters

Se

gm

en

ted

Vo

lum

e o

f A

pp

lic

ati

on

s

High Power

Medium Power

Low Power

Medical

Charging Stations

E-Mobility

FCVs HEVsPHEVsBEVs

Passenger Vehicles Commercial Vehicles

Automotive

Robots, UAVs and DronesEnergy & Power

Telecommunication

Satellite Communication: Small Satellite, Nano Satellite, Mini Satellite

Renewable Energy

HVDC

Railway

More Electric Aircraft

Electric Ships

Aerial Robots Mobile Robots Marine Robots

Industrial Robots

IoT

Towers, Data Centres, Infrastructure and Data Security

Servers, Storage and Networking

(More than 10 kW)

(1 kW – 10 kW)

(1 kW and below)

Industry 4.0 IIoT

Non-Electric Vehicles/Electric Vehicles

Power Supply

Wireless Sensors

TherapeuticDiagnostic

Healthcare Devices

LVDC

Lighting

Figure 13. Multiple-Output DC–DC Converters Applications.

3.1. Converters for More Electric Aircraft

In an airplane, the necessary power generated by an engine is converted into fourtypes of energy: hydraulic, mechanical, pneumatic, and electrical. In addition to thepower required for pushing, the current trend is to replace mechanical, pneumatic, andhydraulic systems with an electric alternative [87,88]. This has led to a significant increasein the electrical power of an aircraft, reaching values of the order of megawatts in somemodels [89]. As a consequence, the electrical system has increased in complexity with alarge number of electronic converters, electrical machines, switches, protections, and avariety of loads [90,91]. These systems are similar to a ground-based microgrid, althoughthere are some differences that make them unique. In this sense, a system with a high levelof reliability and safety is required with the advantage of having more predictable loads,changing their priority during the flight.

Electronics 2022, 11, 1258 21 of 34

The electrical power system of an airplane is a system of multiple voltage levels,connected through electronic power converters. The different voltage levels are standard-ized [92]:

- DC Voltages: 28 V, 270 V (±135 V) and 540 V (±270 V); and- AC Voltages: 230/115 V with fixed frequency of 400 Hz and 230/115 V with variable

frequency (350–800 Hz).

There are different configurations of power systems for this type of application, one ofthem is the one shown in Figure 14. The two generators (coupled to each motor) and theAuxiliary Power Unit (APU) are connected to a three-phase AC 230 V network at variablefrequencies (350–800 Hz). Several AC–DC converters supply the ±270 V DC bus from thisnetwork. High power loads are directly fed from this bus, a low-voltage DC bus (28 V) andan AC network at a frequency of 400 Hz, by means a DC-AC converter.


— AC Voltages: 230/115 V with fixed frequency of 400 Hz and 230/115 V with variable

frequency (350–800 Hz).

There are different configurations of power systems for this type of application, one

of them is the one shown in Figure 14. The two generators (coupled to each motor) and

the Auxiliary Power Unit (APU) are connected to a three-phase AC 230 V network at

variable frequencies (350–800 Hz). Several AC–DC converters supply the ±270 V DC bus

from this network. High power loads are directly fed from this bus, a low-voltage DC

bus (28 V) and an AC network at a frequency of 400 Hz, by means a DC-AC converter.

In theses type of applications, the converters used are numerous and different, but

they all have in common that they are reliable, that they have high efficiency, and in

their designs the weight and size of the converter must be reduced [93,94]. In this sense,

multi-port converters are a solution that meets these design restrictions [95–97].

AC

DC

ESS

DC

AC

AC Three-Phase 230/115 V

G2APUS2G1 S1

350-800 Hz

AC

DC

HVDC

DC±270 V

DC

AC

DC

AC

DC

DC

DC

DC

DC

DC

Loads

S

S

DC

Loads

LVDC

S

DC 28 V


400 Hz

AC

Loads

AC

Loads


350-800 Hz

HVDC

DC±270 V

LVDC

DC 28 V


400 Hz

Figure 14. Electric scheme for a More Electric Aircraft.

3.2. Converters for All Electric Ships

Recently, in ship design, the concept of All Electric Ship (AES) has emerged [98,99].

These types of applications include different loads, electric generators governed by die-

sel engines, energy storage systems, renewable energy sources, and a distribution net-

work that manages the energy of the entire system [100].

Traditionally, systems based on the AC system have been used, however, recently,

there is a trend towards the use of DC distribution systems, due to the advantages that

these present compared to AC distribution systems [101–103].

An example of a ship’s electrical system topology based on a DC distribution is

shown in Figure 15. Generally, the main power source is based on Synchronous Genera-

tors (GS) driven by diesel engines (fuel). The AC-DC converters feed the DC network

that can be monopolar or bipolar [104]. Virtually the entire system is powered from the

DC bus. Through DC–DC converters, the Renewable Energy Sources (RES), Energy

Storage System (ESS), and different loads of the DC type are connected. The Electric

Propulsion (EP) system is connected via a DC–AC converter. This can also have a small

isolated AC network.

Therefore, the electrical system of an AES is made up of a microgrid where the

power converters are a fundamental part of the system [105,106]. An adequate control

allows the system to function properly, with suitable DC bus voltage regulation and bal-

ancing the power flow between sources and loads. In this sense, the use of multiple-

output converters plays an important role since they allow the control of the system

when the DC network is bipolar type or to establish a common power strategy to differ-

ent loads through the converter itself.

Figure 14. Electric scheme for a More Electric Aircraft.

In theses type of applications, the converters used are numerous and different, but theyall have in common that they are reliable, that they have high efficiency, and in their designsthe weight and size of the converter must be reduced [93,94]. In this sense, multi-portconverters are a solution that meets these design restrictions [95–97].

3.2. Converters for All Electric Ships

Recently, in ship design, the concept of All Electric Ship (AES) has emerged [98,99].These types of applications include different loads, electric generators governed by dieselengines, energy storage systems, renewable energy sources, and a distribution networkthat manages the energy of the entire system [100].

Traditionally, systems based on the AC system have been used, however, recently,there is a trend towards the use of DC distribution systems, due to the advantages thatthese present compared to AC distribution systems [101–103].

An example of a ship’s electrical system topology based on a DC distribution is shownin Figure 15. Generally, the main power source is based on Synchronous Generators (GS)driven by diesel engines (fuel). The AC-DC converters feed the DC network that canbe monopolar or bipolar [104]. Virtually the entire system is powered from the DC bus.Through DC–DC converters, the Renewable Energy Sources (RES), Energy Storage System(ESS), and different loads of the DC type are connected. The Electric Propulsion (EP) systemis connected via a DC–AC converter. This can also have a small isolated AC network.


DC Bus

AC

DC

GFuel

AC

DC

GFuel

ESS

DC

DC

RES

DC

DC

AC

Microgrid

DC

AC

EP

DC

AC

RES

DC

DC

Loads

Figure 15. Electric scheme for all Electric Ships.

3.3. Converters for Electric/Hybrid Vehicles

The number of electric/hybrid vehicles is increasing considerably every year. In this

type of application, power electronics plays a fundamental role, both from the point of

view of efficiency and having lighter and smaller systems [107,108].

An important evolution has been the development of new semiconductor devices

that have made it possible to increase power, switching frequencies, and performance, at

the same time with reduced losses, weight, and cost [109,110].

Modern vehicles often have similar power schemes. Figure 16 represents a simpli-

fied diagram of an electric vehicle. The main source of energy is the battery, which is

usually of relatively high voltage. This feeds the traction motor of the vehicle through a

DC–DC converter and the traction control converter [111,112]. These converters are usu-

ally bidirectional to return energy in the event of vehicle braking [113,114]. In some cas-

es, there are several sources of energy storage (Li-Ion batteries, fuel cells, etc.) so the DC

converter is usually of the type of multiple input and single output [115,116].

A DC–DC converter makes it possible to supply vehicle auxiliary elements, such as

pumps, heaters, cooling system, lighting, etc., at lower voltages [117]. In addition, a low-

voltage auxiliary battery is usually included to power the entire control and safety sys-

tem of the vehicle.

In the case of electric or plug-in hybrid vehicles, the design of electronic systems for

charging batteries is of special interest. This has probably been one of the main reasons

why the electric vehicle has not been widely used in many countries. This has given rise

to research in two lines: the development of efficient and fast charging systems and the

development of network infrastructures that integrate the generation, transmission, dis-

tribution, and charging of vehicles [118]. In this sense, the possibility of designing smart

battery charging systems that are bi-directional is being studied, so that they not only act

as loads connected to the grid but at some point they can inject energy into the grid and,

thus, can contribute to the stability of the electrical system [119,120], such as Grid to Ve-

hicle (G2V) and Home to Vehicle (H2V), as well as Vehicle to Vehicle (V2V), Vehicle to

Home (V2H), Vehicle to Building (V2B), Vehicle to Grid (V2G), and Vehicle to Every-

thing (V2X) concepts.

Figure 15. Electric scheme for all Electric Ships.

Therefore, the electrical system of an AES is made up of a microgrid where the powerconverters are a fundamental part of the system [105,106]. An adequate control allows thesystem to function properly, with suitable DC bus voltage regulation and balancing thepower flow between sources and loads. In this sense, the use of multiple-output convertersplays an important role since they allow the control of the system when the DC networkis bipolar type or to establish a common power strategy to different loads through theconverter itself.

3.3. Converters for Electric/Hybrid Vehicles

The number of electric/hybrid vehicles is increasing considerably every year. In thistype of application, power electronics plays a fundamental role, both from the point ofview of efficiency and having lighter and smaller systems [107,108].

An important evolution has been the development of new semiconductor devices thathave made it possible to increase power, switching frequencies, and performance, at thesame time with reduced losses, weight, and cost [109,110].

Modern vehicles often have similar power schemes. Figure 16 represents a simplifieddiagram of an electric vehicle. The main source of energy is the battery, which is usuallyof relatively high voltage. This feeds the traction motor of the vehicle through a DC–DC converter and the traction control converter [111,112]. These converters are usuallybidirectional to return energy in the event of vehicle braking [113,114]. In some cases, thereare several sources of energy storage (Li-Ion batteries, fuel cells, etc.) so the DC converter isusually of the type of multiple input and single output [115,116].

A DC–DC converter makes it possible to supply vehicle auxiliary elements, suchas pumps, heaters, cooling system, lighting, etc., at lower voltages [117]. In addition, alow-voltage auxiliary battery is usually included to power the entire control and safetysystem of the vehicle.

In the case of electric or plug-in hybrid vehicles, the design of electronic systems forcharging batteries is of special interest. This has probably been one of the main reasonswhy the electric vehicle has not been widely used in many countries. This has givenrise to research in two lines: the development of efficient and fast charging systems andthe development of network infrastructures that integrate the generation, transmission,distribution, and charging of vehicles [118]. In this sense, the possibility of designing smartbattery charging systems that are bi-directional is being studied, so that they not only

Electronics 2022, 11, 1258 23 of 34

act as loads connected to the grid but at some point they can inject energy into the gridand, thus, can contribute to the stability of the electrical system [119,120], such as Grid toVehicle (G2V) and Home to Vehicle (H2V), as well as Vehicle to Vehicle (V2V), Vehicle toHome (V2H), Vehicle to Building (V2B), Vehicle to Grid (V2G), and Vehicle to Everything(V2X) concepts.


Figure 16. Scheme of an electric vehicle.

3.4. Converters for DC Microgrids

For almost a century, an electrical system model based on AC system has been fol-

lowed. In this model, the energy is generated in large power plants and is transported

through transmission networks to the places of consumption, which are usually far from

the production centers. The advantage of AC is that it is easy to modify the voltage lev-

els, which is necessary to reduce losses in energy transport.

With the proliferation of renewable energies, the electrical system has changed to-

wards a system in which small power generators are incorporated, located close to con-

sumers. This new model has been called a distributed generation system. Recently, a

system has been proposed in which consumers have a net balance of zero energy. For

this, electrical microgrids are proposed [121–123], where together with the loads and

generators, energy storage systems are added to make the system self-sufficient and

manageable. In many cases, the storage system is replaced by the public electricity grid

so that energy is injected into it if it exceeds the microgrid and is absorbed from the grid

if necessary.

Microgrids can be of the AC or DC type [124,125]. In this case, the debate between

these two systems has been raised again, since most of the generation systems with re-

newable energies work in DC and on the other hand, currently, most of the loads work

in DC form [126]. In addition, DC networks have the following advantages from a tech-

nical point of view:

• DC networks are more efficient, they have less loss in the transmission of energy,

because the effective resistance, for equal section, is lower;

• Fewer conductors are required for distribution;

• They are more stable than AC networks;

• There are no line reactances, which results in lower voltage drops;

• The frequency is zero, thus eliminating the need for a synchronization system when

connecting a generation system to the grid;

• There is no transient stability problem as in AC networks; and

• No electromagnetic interference is generated.

However, from an implementation point of view, it has two clear drawbacks

[127,128]:

• Currently there are no infrastructures for this type of networks; and

• The protection of DC systems is usually more complex due to the constant value of

the voltage.

Figure 16. Scheme of an electric vehicle.

3.4. Converters for DC Microgrids

For almost a century, an electrical system model based on AC system has been fol-lowed. In this model, the energy is generated in large power plants and is transportedthrough transmission networks to the places of consumption, which are usually far fromthe production centers. The advantage of AC is that it is easy to modify the voltage levels,which is necessary to reduce losses in energy transport.

With the proliferation of renewable energies, the electrical system has changed towardsa system in which small power generators are incorporated, located close to consumers.This new model has been called a distributed generation system. Recently, a system hasbeen proposed in which consumers have a net balance of zero energy. For this, electricalmicrogrids are proposed [121–123], where together with the loads and generators, energystorage systems are added to make the system self-sufficient and manageable. In manycases, the storage system is replaced by the public electricity grid so that energy is injectedinto it if it exceeds the microgrid and is absorbed from the grid if necessary.

Microgrids can be of the AC or DC type [124,125]. In this case, the debate between thesetwo systems has been raised again, since most of the generation systems with renewableenergies work in DC and on the other hand, currently, most of the loads work in DCform [126]. In addition, DC networks have the following advantages from a technical pointof view:

• DC networks are more efficient, they have less loss in the transmission of energy,because the effective resistance, for equal section, is lower;

• Fewer conductors are required for distribution;• They are more stable than AC networks;• There are no line reactances, which results in lower voltage drops;• The frequency is zero, thus eliminating the need for a synchronization system when

connecting a generation system to the grid;• There is no transient stability problem as in AC networks; and• No electromagnetic interference is generated.

However, from an implementation point of view, it has two clear drawbacks [127,128]:

• Currently there are no infrastructures for this type of networks; and

Electronics 2022, 11, 1258 24 of 34

• The protection of DC systems is usually more complex due to the constant value ofthe voltage.

It can be concluded that DC networks can be an alternative to AC networks whenthere are distributed generation systems and high quality and efficiency are sought inthe system.

There are three different topologies for DC networks: homopolar, bipolar, and monopo-lar [69]. Among these topologies, the most versatile is the bipolar DC network, despitepresenting greater complexity. In a bipolar DC network, there are three conductors “+”,“−”, and “0”, Figure 17. The loads can be connected to two voltage levels. This is interestingin the case of loads with high consumption that, if connected to the highest voltage, reducethe absorbed current by half. On the other hand, part of the network could continue tofunction when a failure occurs in the other part. It is also interesting to note that the currentthrough the “0” conductor is much smaller than through the other conductors, so thesystem could be designed for a smaller section of this conductor.


It can be concluded that DC networks can be an alternative to AC networks when

there are distributed generation systems and high quality and efficiency are sought in

the system.

There are three different topologies for DC networks: homopolar, bipolar, and

monopolar [69]. Among these topologies, the most versatile is the bipolar DC network,

despite presenting greater complexity. In a bipolar DC network, there are three conduc-

tors “+”, “−”, and “0”, Figure 17. The loads can be connected to two voltage levels. This

is interesting in the case of loads with high consumption that, if connected to the highest

voltage, reduce the absorbed current by half. On the other hand, part of the network

could continue to function when a failure occurs in the other part. It is also interesting to

note that the current through the “0” conductor is much smaller than through the other

conductors, so the system could be designed for a smaller section of this conductor.

For the connection of distributed generation systems to a bipolar network, reliable

and efficient DC–DC converters with a bipolar input and output are required. The con-

verter will make it possible to adapt the output voltage of the source and control the

power flow between the source and the microgrid. Its design and control play a funda-

mental role for the proper functioning of the microgrid. There are many topologies pro-

posed in the literature, both in their non-isolated and isolated versions, unidirectional or

bidirectional, for applications in DC microgrids [129–131]. There are also many control

strategies proposed, so as to ensure adequate power quality or the balance of system

voltages [76,132].

Bipolar

DC

ConsumerDC

DC

+0

-

DC

DC

DC

DC

Storage

Energy

DC

DC

Small

Consumer

AC

Microgrid

AC

DC

Win

Energy

Figure 17. Bipolar DC microgrid.

3.5. Converters for LED Ilumination Systems

LED (Light Emitting Diode) lighting has become the main source of artificial light

today. It is expected to be the primary source for decades to come due to its long service

life, high luminous efficacy, and flexibility in color mixing. Above all this is the great en-

ergy savings compared to traditional light sources that together with the reduction in

the cost of LEDs have made them widely used in the lighting of streets, buildings,

homes, monuments, traffic signs, screens, etc. [133].

In LED lighting, the driver circuit plays a fundamental role, mainly in the efficiency

of the system [134,135]. The driver circuit basically consists of a DC–DC converter and a

Power Factor Correction (PFC) circuit. A current loop is included in the converter in or-

der to obtain a constant current control. The function of the PFC circuit is to eliminate

possible current harmonics and to correct the power factor, which turns out to be an in-

dispensable component in this type of system. Both circuits can be implemented in a

single stage, in two stages or in integrated stages. The single stage LED driver is a DC–

Figure 17. Bipolar DC microgrid.

For the connection of distributed generation systems to a bipolar network, reliable andefficient DC–DC converters with a bipolar input and output are required. The converterwill make it possible to adapt the output voltage of the source and control the power flowbetween the source and the microgrid. Its design and control play a fundamental role forthe proper functioning of the microgrid. There are many topologies proposed in the litera-ture, both in their non-isolated and isolated versions, unidirectional or bidirectional, forapplications in DC microgrids [129–131]. There are also many control strategies proposed,so as to ensure adequate power quality or the balance of system voltages [76,132].

3.5. Converters for LED Ilumination Systems

LED (Light Emitting Diode) lighting has become the main source of artificial lighttoday. It is expected to be the primary source for decades to come due to its long servicelife, high luminous efficacy, and flexibility in color mixing. Above all this is the great energysavings compared to traditional light sources that together with the reduction in the cost ofLEDs have made them widely used in the lighting of streets, buildings, homes, monuments,traffic signs, screens, etc. [133].

In LED lighting, the driver circuit plays a fundamental role, mainly in the efficiencyof the system [134,135]. The driver circuit basically consists of a DC–DC converter and aPower Factor Correction (PFC) circuit. A current loop is included in the converter in order

Electronics 2022, 11, 1258 25 of 34

to obtain a constant current control. The function of the PFC circuit is to eliminate possiblecurrent harmonics and to correct the power factor, which turns out to be an indispensablecomponent in this type of system. Both circuits can be implemented in a single stage, intwo stages or in integrated stages. The single stage LED driver is a DC–DC converter withconstant current output that includes the power factor correction function [136–138]. Thetwo-stage LED driver consists of a PFC circuit plus a separate DC–DC converter [139,140].As an example, Figure 18 presents a block diagram of a LED illumination system. In theintegrated stage topology, the PFC circuit and the DC–DC converter can be simplified in asingle stage, sharing the active power switches and the control circuits [141,142].


DC converter with constant current output that includes the power factor correction

function [136–138]. The two-stage LED driver consists of a PFC circuit plus a separate

DC–DC converter [139,140]. As an example, Figure 18 presents a block diagram of a LED

illumination system. In the integrated stage topology, the PFC circuit and the DC–DC

converter can be simplified in a single stage, sharing the active power switches and the

control circuits [141,142].

Multichannel LEDs are used to ensure a high intensity of illumination. In this way,

high tensions of structures connected in series are avoided. This consists of several

branches each made up of several LEDs connected in series (LED Matrix). In each

branch the intensity is controlled from a DC–DC converter. There are several converter

topologies that have been proposed, both in isolated and non-isolated versions, in order

to obtain the maximum efficiency of the system [143–145]. In this situation it is where

the DC–DC converters with multiple outputs can have a special relevance, which allows

the power supply of each chain of LEDs and their control [146,147].

LED Matrix

Controller

LED Matrix

AC

LED Matrix

Driver

Figure 18. Block Diagram of LED illumination systems.

3.6. Multiple-Output DC–DC Converters for Satellite and Aerospace Applications

In aerospace and satellite applications, because it is an inhospitable and remote en-

vironment, power supplies should meet some important requirements, like size, weight,

impossible/costly online repairs, severe radiation, a wide range of temperatures they

have to withstand, and being a self-sustainable energy system, as the satellite should

generate, distribute, and convert power to different levels in order to provide power to

all the different blocks in the system, and they must have several different power-supply

output voltage levels. Therefore, very often DC–DC converters with multiple outputs

are used in this type of application.

Satellites are usually equipped with solar panels and rechargeable battery cells as

their energy source and storage. Both are complementary to each other during two al-

ternate phases. First, when a satellite faces the sun, photovoltaics in solar panels convert

sunlight into electrical energy; the generated power is supplied to the satellite’s sub-

systems, and, then, the remaining power is stored in battery cells. On the other hand,

during the eclipse phase (or the sun phase with a peak power demand), the stored ener-

gy in battery cells is used to operate the satellite sub-systems [148]. Moreover, power

management is critical because power demands must never exceed the generated power.

Regarding the energy usage in satellites, each sub-system’s power consumption is,

typically, a periodic consumption task, repeatedly in a specified amount of time. As

satellites are indispensable for navigation, weather forecast, broadcast, and many other

applications, several switching and linear regulators are used, according to the sub-

Figure 18. Block Diagram of LED illumination systems.

Multichannel LEDs are used to ensure a high intensity of illumination. In this way,high tensions of structures connected in series are avoided. This consists of several brancheseach made up of several LEDs connected in series (LED Matrix). In each branch the intensityis controlled from a DC–DC converter. There are several converter topologies that havebeen proposed, both in isolated and non-isolated versions, in order to obtain the maximumefficiency of the system [143–145]. In this situation it is where the DC–DC converters withmultiple outputs can have a special relevance, which allows the power supply of each chainof LEDs and their control [146,147].

3.6. Multiple-Output DC–DC Converters for Satellite and Aerospace Applications

In aerospace and satellite applications, because it is an inhospitable and remote en-vironment, power supplies should meet some important requirements, like size, weight,impossible/costly online repairs, severe radiation, a wide range of temperatures they haveto withstand, and being a self-sustainable energy system, as the satellite should generate,distribute, and convert power to different levels in order to provide power to all the dif-ferent blocks in the system, and they must have several different power-supply outputvoltage levels. Therefore, very often DC–DC converters with multiple outputs are used inthis type of application.

Satellites are usually equipped with solar panels and rechargeable battery cells as theirenergy source and storage. Both are complementary to each other during two alternatephases. First, when a satellite faces the sun, photovoltaics in solar panels convert sunlightinto electrical energy; the generated power is supplied to the satellite’s sub-systems, and,then, the remaining power is stored in battery cells. On the other hand, during the eclipsephase (or the sun phase with a peak power demand), the stored energy in battery cells is

Electronics 2022, 11, 1258 26 of 34

used to operate the satellite sub-systems [148]. Moreover, power management is criticalbecause power demands must never exceed the generated power.

Regarding the energy usage in satellites, each sub-system’s power consumption is,typically, a periodic consumption task, repeatedly in a specified amount of time. Assatellites are indispensable for navigation, weather forecast, broadcast, and many otherapplications, several switching and linear regulators are used, according to the sub-systemto which they provide power. Figure 19 represents a typical block diagram of an ElectricPower Supply subsystem of a satellite, in this case the CUBEsat [149]. As it can be seen, theElectric Power Supply subsystem contains solar panels, Boost converter with MaximumPower Point Tracker (MPPT), switching and linear regulators, over voltage protection anddifferent load switches on the input of each subsystem. Boost converter steps up the solarpanel voltage (4.4 V) to Power Distribution Bus (PDB) voltage level (14 ± 2 V). MPPToperates solar cells at maximum power point. Over voltage protection circuit keeps thePDB voltage within the operation limits. Switching and linear regulators step down thePDB voltage to different voltage levels required for all the subsystem components. Loadswitches supply and cutoff power from the subsystems through enable signal from anon-board processor.


system to which they provide power. Figure 19 represents a typical block diagram of an

Electric Power Supply subsystem of a satellite, in this case the CUBEsat [149]. As it can

be seen, the Electric Power Supply subsystem contains solar panels, Boost converter

with Maximum Power Point Tracker (MPPT), switching and linear regulators, over

voltage protection and different load switches on the input of each subsystem. Boost

converter steps up the solar panel voltage (4.4 V) to Power Distribution Bus (PDB)

voltage level (14 2 V). MPPT operates solar cells at maximum power point. Over

voltage protection circuit keeps the PDB voltage within the operation limits. Switching

and linear regulators step down the PDB voltage to different voltage levels required for

all the subsystem components. Load switches supply and cutoff power from the

subsystems through enable signal from an on-board processor.

CubeSat

Subsystems

External

Batteries

Over Voltage

Proteccion

Linear

Regulator

1

Linear

Regulator

2

Switching

Regulator

Switching

Regulator

Ref_3 V

3.3 V

3.3 V

5 V

Step-Up

Converter

(MPPT)

Load Switch

1

2

4

3

Load Switch

Load Switch

Load Switch

2

1

PDB4.4 V

Sola

r P

anel

Figure 19. Block diagram of Electric Power Supply subsystem of a satellite (CUBEsat).

3.7. Multiple-Output DC–DC Converters in Computer Applications

Computer systems are probably the most important and widely used systems now-

adays. Like any other electronic systems, computer systems need a Power Supply Unit

(PSU) to convert an input voltage into one or several power supply voltages appropriate

for its circuits. Systems like data centers, modems and communication networks, or even

desktop computers, include some of the major applications and give support to the in-

ter-net, provide data storage, support websites and databases, and support virtually al-

most every corporation and institution.

A computer system power-supply unit is a good example of application of

multiple-output DC–DC converters, as every computer system needs to supply energy

to different modules and, typically, several DC output values are needed. The most

common type of today’s PSU for computer systems is the Switch Mode Power Supply

(SMPS). Regarding this type of PSU, there is a wide variety of topologies used by PSU

manufacturers. However, all topologies use the same basic concepts [150]. For example,

considering the application of DC–DC converters for a common desktop computer,

Figure 20 presents a typical block diagram of a PSU. Usually, it consists of a front-end

Power Factor Correction (PFC) stage and an isolated DC–DC stage [151]. The output

blocks, as it can be seen, present multiple-output converters where three output DC

voltages are available: 3 V, 5 V, and 12 V.

Figure 19. Block diagram of Electric Power Supply subsystem of a satellite (CUBEsat).

3.7. Multiple-Output DC–DC Converters in Computer Applications

Computer systems are probably the most important and widely used systems nowa-days. Like any other electronic systems, computer systems need a Power Supply Unit (PSU)to convert an input voltage into one or several power supply voltages appropriate for itscircuits. Systems like data centers, modems and communication networks, or even desk-top computers, include some of the major applications and give support to the inter-net,provide data storage, support websites and databases, and support virtually almost everycorporation and institution.

A computer system power-supply unit is a good example of application of multiple-output DC–DC converters, as every computer system needs to supply energy to differentmodules and, typically, several DC output values are needed. The most common type oftoday’s PSU for computer systems is the Switch Mode Power Supply (SMPS). Regardingthis type of PSU, there is a wide variety of topologies used by PSU manufacturers. However,all topologies use the same basic concepts [150]. For example, considering the applicationof DC–DC converters for a common desktop computer, Figure 20 presents a typical blockdiagram of a PSU. Usually, it consists of a front-end Power Factor Correction (PFC) stageand an isolated DC–DC stage [151]. The output blocks, as it can be seen, present multiple-output converters where three output DC voltages are available: 3 V, 5 V, and 12 V.


AC 85-265 V

Linear

Regulator

12 V

Power Factor

Correction

Rectifier and

EMI Filter

Voltage and

Current Sense Controller

LLC

Converter

Controller

Step-Up

Converter

Half-Bridge

Converter

AC

DC

Linear

Regulator

Synchronous

Rectifier

Controller

Half-Bridge

Rectifier

Step-Down

Converter

Two Outputs

Converter1ª Power

2ª PowerAuxiliar Power Supply

Multi-Output

Converter5 V Standby

5 V

3 V

Figure 20. Desktop computer power-supply unit.

3.8. Multiple-Output DC–DC Converters in Systems-on-a-Chip (SoC)

The increase complexity of today’s Systems-on-a-Chip (SoC) imposes the need to

integrate in a single chip all the major features that in the past were only available in

computer systems, which includes a power-management unit and, most likely, DC–DC

converters. In fact, a SoC is an electronic circuit that can integrate all the necessary com-

ponents present in a computer and other electronic systems, like a GPU (graphics-

processor unit), memory, power management circuits, CPU (central processing unit), a

USB controller, wireless radios (2G/3G/4G LTE, GPS, WiFi, FM radio, and Bluetooth)

and many more, but all integrated in a single chip. Being a very complex circuit, an SoC

needs a dedicated power-management unit that can be similar to typical computer sys-

tems, but although all integrated in silicon.

Several publications present PMU for SoC applications that have similar

architectures to PSU in computer systems (e.g., [152]). Figure 21 presents a typical block

diagram of a SoC and we can see the need of several linear regulators to supply different

building blocks with different power-supply voltage levels.

Step-Down

ConverterPower

Supply

Linear

Regulator

Linear

Regulator

RF

Module

Digital

Module

3.3 VStep-Down

Converter

Linear

Regulator

Linear

Regulator

Reference

Module

Analog

Module

1.8 V

1.2 V Linear

RegulatorDigital

Module

Step-Down

Converter

Linear

Regulator

Wake-up

Module

Power

Management IC

System-on-Chip

5 V



The increase complexity of today’s Systems-on-a-Chip (SoC) imposes the need to inte-grate in a single chip all the major features that in the past were only available in computersystems, which includes a power-management unit and, most likely, DC–DC converters. Infact, a SoC is an electronic circuit that can integrate all the necessary components present ina computer and other electronic systems, like a GPU (graphics-processor unit), memory,power management circuits, CPU (central processing unit), a USB controller, wireless radios(2G/3G/4G LTE, GPS, WiFi, FM radio, and Bluetooth) and many more, but all integrated ina single chip. Being a very complex circuit, an SoC needs a dedicated power-managementunit that can be similar to typical computer systems, but although all integrated in silicon.

Several publications present PMU for SoC applications that have similar architecturesto PSU in computer systems (e.g., [152]). Figure 21 presents a typical block diagram of aSoC and we can see the need of several linear regulators to supply different building blockswith different power-supply voltage levels.


AC 85-265 V

Linear

Regulator

12 V

Power Factor

Correction

Rectifier and

EMI Filter

Voltage and

Current Sense Controller

LLC

Converter

Controller

Step-Up

Converter

Half-Bridge

Converter

AC

DC

Linear

Regulator

Synchronous

Rectifier

Controller

Half-Bridge

Rectifier

Step-Down

Converter

Two Outputs

Converter1ª Power

2ª PowerAuxiliar Power Supply

Multi-Output

Converter5 V Standby

5 V

3 V



The increase complexity of today’s Systems-on-a-Chip (SoC) imposes the need to

integrate in a single chip all the major features that in the past were only available in

computer systems, which includes a power-management unit and, most likely, DC–DC

converters. In fact, a SoC is an electronic circuit that can integrate all the necessary com-

ponents present in a computer and other electronic systems, like a GPU (graphics-

processor unit), memory, power management circuits, CPU (central processing unit), a

USB controller, wireless radios (2G/3G/4G LTE, GPS, WiFi, FM radio, and Bluetooth)

and many more, but all integrated in a single chip. Being a very complex circuit, an SoC

needs a dedicated power-management unit that can be similar to typical computer sys-

tems, but although all integrated in silicon.

Several publications present PMU for SoC applications that have similar

architectures to PSU in computer systems (e.g., [152]). Figure 21 presents a typical block

diagram of a SoC and we can see the need of several linear regulators to supply different

building blocks with different power-supply voltage levels.

Step-Down

ConverterPower

Supply

Linear

Regulator

Linear

Regulator

RF

Module

Digital

Module

3.3 VStep-Down

Converter

Linear

Regulator

Linear

Regulator

Reference

Module

Analog

Module

1.8 V

1.2 V Linear

RegulatorDigital

Module

Step-Down

Converter

Linear

Regulator

Wake-up

Module

Power

Management IC

System-on-Chip

5 V

Figure 21. Block diagram showing general architecture of power supply in a SoC (System-on-a-Chip).

Electronics 2022, 11, 1258 28 of 34

However, to facilitate the integration of all blocks, other type of DC–DC convert-ers are used, like Switched-Capacitor (SC) based DC–DC converters, because they allowmonolithic substrate integration due to the reduction of silicon surface required and size,and contribute towards reduced electromagnetic effects and power losses. As an exam-ple, in [153], Multiple-Output Switched-Capacitor DC–DC Combination Converters arepresented, for use in SoC focusing IoT applications.

Moreover, the need to reduce power consumption in today’s chips brings the use ofaggressive power-reduction techniques, and multi-domain power supplies are increasinglybeing used to accomplish power reduction [154]. To achieve ultra-low-power consumptionlevels, especially in new SoC for IoT, Dynamic Voltage and Frequency Scaling (DVFS)techniques should be used, to work at different power-supply voltage (VDD) and clockfrequency levels (as explained in [155]). These new low-power techniques demand newDC–DC converters, with adjustable output-voltage values, or with multiple simultane-ous output values available. Therefore, SoC applications are a good example to showthat DC–DC converters with multiple outputs have still a long way ahead for researchand development.

4. Conclusions

In this paper, we present an overview of the most important topics related to multiple-output DC–DC converters based on their main topologies and configurations, applications,solutions, and trends. Our goal is to highlight a wide variety of configurations and topolo-gies of multiple-output DC–DC converters. We show more than 30 topologies, isolated andnon-isolated, single and multiple switched, based on soft- and hard-switching techniques,which are used in many different applications and solutions. However, the current trendin the development of multiple-output DC–DC converters follows general aspects, suchas high-power density, high efficiency, and low losses, as well as the development of newarchitectures and control strategies. Certainly, simple structures with a reduced number ofcomponents and power switches are one of the new trends, especially to reduce the size.

Also, several applications of multiple-output DC–DC converters were presented in thispaper. A wide variety of examples were presented, to characterize the most important typesof applications and solutions that use these converters, showing High Power, MediumPower, and Low Power application examples.

Author Contributions: S.P.L., E.D., J.S. and C.D.-M. have written the original draft and have reviewedand edited the paper, the conceptualization, the methodology, and the analysis of the state of the art.All authors have read and agreed to the published version of the manuscript.

Funding: This research received no external funding.

Conflicts of Interest: The authors declare no conflict of interest.

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Multiple-Output DC–DC Converters: Applications and Solutions

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