Solid State Lightning Rewiew - Alonso

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6 IEEE INDUSTRIAL ELECTRONICS MAGAZINE DECEMBER 2013 1932-4529/13/$31.00©2013IEEE

A System Review

CHRISTIAN BRAÑAS,FRANCISCO J. AZCONDO,and J. MARCOS ALONSO

This article presents the background on the development of solid-

state lighting technology, which is gaining popularity as a light

source application. This review focuses on the main character-

istics of solid-state lighting devices as well as their supply re-

quirements and the effect of temperature on light-emitting diode

(LED) performance. LED drivers are designed to achieve the best

operation conditions without degrading the longer lifetime thatthis technology achieves in comparison to other popular light sources. Offline

LED drivers include active power factor correction while current control with

low ripple is required to supply the LED units or string arrangements. Methods

to achieve balanced current sharing on paralleled LED str ings and some of the

latest contributions on LED drivers are also explained.

LED Overview The primary goal of this article is to provide a starting point for designers inter-

ested in lighting systems based on LEDs, which are the most recent revolution in

the consumer and industrial lighting application field.

Digital O bject Identifier 10.1109/MIE.2013.2280 038

Date of publication: 12 December 2013

IMAGE LICENSED BY INGRAM PUBLISHING



DECEMBER 2013 IEEE INDUSTRIAL ELECTRONICS MAGAZINE 7

The emission mechanism of LEDs

is electroluminescence. Contrary to

the perception that this technology

is something new, to find the founda-

tion of LEDs based on semiconduc-

tor materials, one should look back

to 1907, when Captain Henry Joseph

Round observed the electrolumines-

cence phenomenon when a currentflowed through a crystal of silicon

carbide [1]. Independently, in 1923,

the Russian radio technician Oleg V.

Lossev made the first attempt to ex-

plain the electroluminescence in p-n

junctions with a scientific approach,

describing the current versus volt-

age characteristic of the new device

[2], [3]. The modern age of LED tech-

nology can be dated to the beginning

of the 1960s, when Robert Hall, Nick

Holonyak, Marshall Nathan, and Rob-ert Rediker reported simultaneously

[4]–[6] the laser emission of gallium

arsenide crystals. LEDs have been

commercially available since then in

red, amber, and green colors. The ap-

plications of LEDs have mainly been

signaling, seven-segment displays,

and remote control.

The next remarkable breakthrough

in LED technology was the develop-

ment of the first feasible blue LED by

Shuji Nakamura at Nichia Corpora-

tion [7]. The blue LED paved the way

for the development of white-light

sources by mixing red, green, and

blue (RGB) LEDs [8]–[10]. As this

method could prove expensive, the

method most widely used to produce

white light based on LED technology

is by adding a phosphor layer to a

blue LED to modify the emission spec-trum. The phosphor emits yellow light

under excitation of the blue light, and

the resulting mixture produces the ap-

pearance of white light [11]. Recently,

phosphor-free white-light LEDs have

been proposed [12], providing a more

efficient light source. In this case, the

white light is produced in a multilayer

monolithic structure where blue and

yellow light are emitted from different

active regions.

Today, white LEDs are still un-der development. Every year, the

lumen per watt (lm/W) efficiency is

increased, while the cost is dimin-

ished. For example, several devices

from the OSRAM OSLON SSL 80 [13]

and Philips Lumileds Luxeon Rebel

ES [14] families are available, achiev-

ing higher energy efficiency than

100 lm/W (Figure 1). Although these

values of efficiency are obtained for

a pulsed regime to avoid the effect

of the self-heating of the die, such

devices are competitive with tradi-

tional light sources. Because of the

nature of the LED spotlight, it is pos-

sible to design a very efficient optic

to bring the light where it is needed

[15], reducing light pollution. On the

other hand, improvements in the

packaging, such as the flip-chip tech-

nology [16] combined with the use ofnew materials such as ceramic sub-

strates increase the thermal capabili-

ty [17] of the device, which increases

reliability [18], lifetime up to 50,000

h, and light efficiency. Together with

the aforementioned advantages, LED

technology also overcomes draw-

backs of traditional discharge lamps

such as hot reignition, acoustic reso-

nance, and warm-up time. LED tech-

nology is environmentally friendly

and free of mercury and infrared andultraviolet radiation.

Organic LEDs

Electronics based on organic materi-

als started in 1977 when Heeger, Mac

Diarmid, and Shirakawa published a

paper describing a polymeric conduc-

tor [19]. The term organic is associat-

ed with the use of polymers based on

some types of carbon composite. De-

vices such as transistors, diodes, and

even integrated circuits are being im-

plemented in this technology, receiv-

ing time and resource investments

from different companies. The advan-

tages of polymer-based electronics

are mainly the mechanical properties,

such as high flexibility, and the sim-

plicity of the manufacturing process.

(a) (b) (c)

FIGURE 1 – An example of an LED fixture for outdoor application. (a) Lateral view with heatsink detail. (b) Front view showing a four LED matrix arrange-ment. (c) Front view with the LEDs on.

The blue LED paved the way for the development

of white-light sources by mixing red, green,

and blue LEDs.



8 IEEE INDUSTRIAL ELECTRONICS MAGAZINE DECEMBER 2013

In addition, this technology is environ-

mentally friendly.

Electroluminescence is found inorganic materials, as was reported in

the early 1950s [20]. The first organic

LED (OLED) was developed by Tang

and Van Slyke in 1987 [21]. The device

was obtained by vacuum evaporation

of organic small-molecule material

with a metallic cathode on a conduc-

tive substrate. The first OLED based

on polymers was created in 1990 by

Buroughs et al. [22], with a single-

layer device of polyphenylenevinilene

made by using a spin coating process.Presently, OLEDs based on small mol-

ecules and polymers are feasible, with

similar performances for both families

of devices (Figure 2).

Because of the organic nature of

OLEDs, it is possible to achieve uni-

form light emission along a large sur-

face, which is especially suitable for

display applications. OLED technology

allows self-emitting displays, without

the necessity of backlighting [23]. For

lighting applications, the luminous

rendering of the OLEDs is still low,

being about 50 lm/W. The research ef-

fort on OLEDs is focused on increas-

ing the luminous rendering as well as

enlarging the emitting surface and ex-

tending the device life. Typically, the

luminance of OLEDs decreases down

to 50% of its initial value after 15,000 h.

The degradation of the luminance of

OLED devices is caused basically by

two mechanisms: electrode degrada-

tion and the intrinsic decrement of the

electroluminescence efficiency of theemissive area [24].

Recently, devices based on field-

induced polymer electroluminescence

(FIPEL) have been reported [25] as a

potential alternative to OLEDs. FIPEL

devices are formed by a multilayer

structure of polymers and carbon

nanotubes, achieving an enhanced

electroluminescence emission in ac

operation.

Indoor LightingAdvances in domotic, wired, and wire-

less communication systems and the

so-called Internet of Things are avail-

able technologies to optimize the opera-

tion of the lighting system according to

different criteria such as safety, com-

fort, work place specifications, and en-

ergy savings. The fast response of LEDs

under turn-on, turn-off, and dimming

commands makes them superior to pre-

vious lighting technologies for smart

lighting system implementations.

Solid-state lighting is well suited

to some special requirements for

indoor lighting, such as ambience

creation and decorative light. Ambi-

ence creation is not a minor question

as it is related, among other effects,

to the circadian rhythm of human

beings [26]. The benefits of the prop-

er light, according to the time of day,

have been proven in hospitals and

working places. LED lighting also has

other advantages such as the pos-

sible reconfiguration of the lighting

infrastructure for meeting specific

requirements. Recently, the innova-

tive idea of implementing a dedi-

cated dc microgrid in buildings to

supply LED-based lighting systems

has been proposed [27]. This idea di-rectly links modern lighting systems

to renewable energy sources, e.g.,

photovoltaic systems. Sometimes,

economic reasons and installation

times drive a different approach, e.g.,

retrofitting the infrastructure [28].

To make the most of old instal lations,

manufacturers provide LED lamps

designed for direct replacement of

fluorescent or halogen lamps. In such

a case, special attention must be paid

to the thermal management of theLED lamp [29], [30].

OLED technology also fulfils some

of the requirements for indoor light-

ing. White OLEDs provide a more uni-

form light source, avoiding glare and

flicker effects, which increases the

comfort of users. Moreover, the color

rendering of OLEDs is better than that

of fluorescent lamps, and they can

also save energy.

Outdoor LightingOne significant advantage of LED

lamps in comparison to high-intensity

discharge lamps is the absence of

warm-up time as well as acoustic

resonance and hot reignition prob-

lems. This feature overcomes some

safety issues of outdoor lighting

installations and facilitates control.

The most significant energy savings

can be achieved by using sensors

that detect the presence of pedestri-

ans or vehicles on the street to adjust

the light to a safe level. Additionally,

LED technology allows the design of

very efficient optics for the lamp to

focus the light where it is required. In

this way, the highway is uniformly il-

luminated, offering better comfort for

drivers, while using less energy and

reducing light pollution. Finally, the

installation of LED luminaries in open

spaces makes heat dissipation easier,

approaching the maximum renderingof the lamp in terms of lm/W.

(a) (b)

FIGURE 2 – OLEDs can emit light uniformly, even over a large surface area. (a) A flexible amberOLED and (b) a flexible white OLED. (Photos courtesy of OSRAM SYLVANIA.)

LED technology is environmentally friendly and free

of mercury and infrared and ultraviolet radiation.




Thermal IssuesOne of the most important aspects when

designing an LED-based lighting system

is its thermal design [31]. As in any other

semiconductor-based device, an LED’s

electrical characteristics are strongly

dependent on its operating temperature.

Furthermore, temperature also strongly

affects the LED photometric character-istics. An increase in LED temperature

produces a decrease in LED operating

voltage, and it also modifies the equiva-

lent series resistance [32]. If the LED cur-

rent is regulated, that is, kept constant,

an increase in temperature will generate

a decrease in the LED light output. Ad-

ditionally, an increase in LED junction

temperature also produces a decrease

in light output due to a higher level of

nonradiating recombination inside the

crystal lattice. Therefore, an increasein temperature can lead to a substantial

light output decrease.

Junction temperature also affects the

maximum current that an LED can han-

dle for a given total thermal resistance

of the heat transfer path (junction to

environment). For example, for a given

total thermal resistance of 70 °C/W, an

LED can manage 350 mA up to 50 °C

ambient temperature but only 200 mA

for an ambient temperature of 75 °C.

The manufacturers usually provide

current derating curves, which give

the maximum allowable current

through the LED for a given ambient

temperature and thermal resistance.

The junction temperature also

modifies the color of the light emitted

by a monochromatic LED because of

changes in its spectrum peak wave-

length. In white LEDs, the junction tem-perature produces variations in the

light color temperature that can lead to

low color rendition.

Because of their low operation

temperature, LEDs can barely transfer

heat by infrared emission, and there-

fore, most of the heat is transferred

from the junction to the case by heat

conduction mechanisms. The typical

dynamic model to study the tempera-

ture distribution in an LED fixture is

illustrated in Figure 3.Thermal impedance given by a par-

allel thermal capacitance ( )C xy and a

series thermal resistance ( ) R xy exists

between any two materials that make

up the fixture, from the LED junction

to the surrounding environment. The

thermal resistances and capacitances

of a given fixture are usually obtained

experimentally in a laboratory test.

Once obtained, the model can suc-

cessfully be used to predict the LED

junction temperature under various

operating modes, including analog

and pulsewidth modulation (PWM)

dimming. The electrical, photometri-

cal, and thermal characteristics are

dependent on each other. Interesting

studies on this topic can be found in

[33] and [34]. It should be noted that

the model presented in Figure 3 must

only be used as a first approximationto solve the LED thermal design prob-

lem. There are some effects that are not

considered in this model, for example,

heat radiation, phosphor conversion

losses, and three-dimesional effects. To

accurately predict the LED junction

temperature, precise finite element

analysis is employed [35]. Thermal

modeling is usually combined with

mechanical modeling, which takes

into account the mechanical stress in

the materials due to the effect of dif-ferent thermal expansion coefficients.

Driver ArchitectureThe static and dynamic character-

istics of an LED matrix impose the

specifications of the drivers. In an

initial approach, LED light sources

lead to a simplification of the power

supply compared with the electronic

ballast counterparts required to sup-

ply discharge lamps. Ballast circuits

have a double function: to stabilize

the discharge arc, whose small-

signal impedance is negative, and to fix

the operation point at the required

current/power level with limited rip-

ple. Only the second function remains

as a general objective for LED drivers.

The current mode control is gener-

ally adopted because the current is

the electrical variable with closest

relationship to the emitted light and

the power dissipated in the LED, due

to the rigid current versus voltage

J u n c t i o

n

C a s

e

I s o l a t i n g T a p

e

H e a t s i n

k

A m b i e n

t

T J T C R CI R IHT I T H

R HAR JC

C JC C CI C IH C HA T A

Ambient

TemperatureLEDPowerP D

FIGURE 3 – A simplified thermal model of an LED fixture: different complex mechanisms that

result in heat sources, such as conduction losses in LEDs, driver operation, and phosphor conversion, are not detailed.

V dc +

– –

I o

R s

+

V dc/dc

f B

FIGURE 4 – Current control is achieved viathe voltage sensed in the shunt resistor R s.

White OLEDs provide a more uniform light source,

avoiding glare and flicker effects, which increases

the comfort of users.




characteristic of the diode. Moreover,

the need to limit the current ripple de-

rives from the fast lux versus current

response of the LED.

Low-power applications such as

flashlights or bicycle lights require few

LEDs arranged in a single string thatcan be driven by a dc-to-dc converter

controlled in current mode. Commer-

cial controllers designed to control dc-

to-dc converters in voltage mode can

be adapted for driving LEDs [36], [37]

(see Figure 4), paying special attention

to reducing the feedback voltage so

that excessive power dissipation in the

current sensor ( Rs ) can be avoided.

Drivers to supply higher-power

indoor and outdoor illumination-

oriented applications face different

challenges, not just current control, to

optimize the use of LEDs. For lightingsystems connected to the utility, stan-

dards such as International Electro-

technical Commission (IEC)-61000-3-2

and Energy Star must be taken into

account. As is illustrated in Figure 5,

offline power supplies include power

factor correction as a single stage [38],

[39], integrated [40]–[43], or with a

two-stage arrangement where the first

stage supplies a front-end dc voltage

for a second stage that controls the

LED array current.

One important aspect to consider

when designing LED drivers is reli-

ability. This is because LEDs have ex-

tremely long lifetimes that can reach

105 hours under some circumstances.

When developing offline drivers,

large capacitances are required to

smooth the changing low-frequency

line voltage. They are needed because

designers like to have an LED cur-

rent with low line-frequency ripple so

that the emitted light is high quality

and able to be used in any applica-

tion. Electrolytic capacitors are usu-

ally employed because of their highcapacitance/(volume * cost) figure of

merit, but they can barely reach

10,000 h lifetime under strict tem-

perature conditions. In this aspect,

integrated converters can help to attain

low LED current ripple while maintain-

ing low filter capacitances with a lim-

ited cost and volume. Figure 6 shows

the block diagram of an integrated LED

driver, which includes a power factor

correction to provide low-current har-

monic injection into the mains, and

a dc–dc converter to supply the LED

lamp with low ripple current [37].

An example of an integrated con-

verter is illustrated in Figure 7, where

two buck-boost converters have been

merged by sharing their controlled

switches. In this way, a single switch

converter is obtained, thus simplify-

ing the control circuitry and reducing

cost [40], [41]. Using this converter, a

70-W LED driver with a 12-µF bulk ca-

pacitor and a 3-µF output capacitor

with 86% efficiency has been demon-

strated [41]. Electrolytic capacitors

were avoided so that the converter

lifetime matches that of the LED lamp.

The requirements of Energy Star and

IEC-61000-3-2 are also fulfilled. In

addition, the converter admits am-

plitude (AM) and PWM dimming to

control LED lamp luminosity.

Another area of research on the

use of integrated converters for LEDdrivers is presented in [42]. There, a

V ac

I o

R s

+

–

V ac/dc

f B

I o

R s

+

–

V dc/dc

f B

V ac

ac/dcC B

(a) (b)

FIGURE 5 – (a) Single- and (b) two-stage architectures used for LED drivers.

i g

v g

C B

i o Lamp

+

–

v o

+

–

IntegratedPFC/dc–dc

Stage

FIGURE 6 – A high power factor integratedLED driver can be used to maintain lowripple current.

D 1 D 2 D 3LED Lamp

LineL1

L2 C 2

+

+C 1

M

FIGURE 7 – An integrated double buck-boost converter simplifies control circuitry andreduces costs.




buck-boost converter integrated with

a buck converter is used to supply two

low-voltage LED arrays used in high-

pressure lamp retrofit applications.

A general study on the use of integrat-

ed converters for high-reliability LED

drivers can be found in [43]. The in-

tegration of resonant converters and

high power factor correction stagesas offline LED drivers is also possible.

Resonant converters can help to in-

crease the driver efficiency owing to

their inherently low switching losses.

Some converters have been investigated

in recent literature [44]–[46].

Dimming ControlThe modification of the LED current

reference, i.e., amplitude modulation

Line

Integrated

High PowerFactor

LED Driver

LED Lamp

PWM

DimmingSwitch

CurrentSense

ActualLED MeanCurrent

LED MeanCurrent Error

LED MeanCurrent Reference

Low-PassFilter

PWMDimming Switch

DimmingLevel

PWMDimming

Generator

LED Peak

Current Reference

ErrorAmplifier

DimmingDuty Cycle

+ –

∑

FIGURE 8 – A high-frequency PWM dimming circuit ensures constant LED peak current andregulated LED mean current.

2

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Ch2 Frequency500.8 Hz

Ch2 500 mAΩ Ch2400 µs

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P 1.24 AA

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2

Ch2 Average1.347 A



0.00000 s 19 January 201211:04:11

P 1.24 AA

T

2

Ch2 Average766.6 mA



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P 990 mAA

T

2

Ch2 Average888 mA



0.00000 s 19 January 201212:09:59

P 1.24 AA

T

(a) (b)

(c) (d)

FIGURE 9 – Current prof iles at 500 Hz for dimming implementation of LED lamps: (a) PWM, (b) bilevel, (c) negative sawtooth, and (d) low-resolution sine.




(AM) of the LED current, to perform

dimming control modifies the LED

color rendering; while a low-speedPWM generates undesired flickering

effects and, possibly, utility ac cur-

rent distortion. On the other hand, the

high-speed performance is not com-

patible with the low-frequency band-

width required for the control of the

power factor correction (PFC) stage

output voltage where it is necessary

to keep the input current shape pro-

portional to the utility voltage.

Integrated converters are particu-

larly suitable to incorporate high-frequency PWM dimming capability.

A special control circuitry can be in-

corporated into the driver so that the

LED peak current is kept constant ateach dimming level [47], [48]. Pro-

vided that a greater PWM dimming

frequency is chosen than the con-

verter cut-off frequency, which usu-

ally means a few kilohertz, dimming

can be performed without distorting

the line current so that harmonic in-

jection related standards can be sat-

isfied. Figure 8 illustrates the block

diagram of this circuit.

Basically, the LED mean current

reference is indirectly obtained bymultiplying the dimming level by the

desired LED peak current. The cur-

rent reference is then compared to

the actual LED mean current and the

difference is applied to an error ampli-

fier. The converter operates by regu-

lating the average LED current, even

in PWM mode, while maintaining the

LED peak current at the desired value

so that constant color coordinatesare assured.

A combination of amplitude and

PWM is also proposed to create different

current profiles [49], [50], while prevent-

ing flicker effects. The experimental LED

current waveforms illustrating this case

are shown in Figure 9.

In many situations, LED lamps are

used to replace incandescent lamps

in applications where dimming is at-

tained using inexpensive TRIAC-based

dimmers. In these applications, LEDdrivers must be designed so that the

LED power can be adjusted depend-

ing on the TRIAC firing angle. A very

typical solution used for this purpose

is based on the flyback converter op-

erating in discontinuous conduction

mode (DCM) or in the boundary be-

tween continuous conduction mode

and DCM. In this manner, automatic

power factor correction is achieved,

and some kind of control algorithm

can be used to detect the TRIAC firing

angle and control the LED power [51].

Current SharingThe distribution of LEDs in a set of dif-

ferent strings to form an array requires

action to be taken to balance the cur-

rent distribution among the strings

when the paralleled strings are not

matched to avoid uneven current shar-

ing. As has been studied for the par-

allel connection of junction devices,

sufficiently large series impedance in

each LED string (Figure 10) makes the

dispersion of the current negligible.

This solution, however, decreases the

efficiency of the whole lamp.

On the other hand, active cur-

rent control in each string, as shown

in Figure 11 [52], not only assures

adequate current distribution but

also solves the problem of using LED

strings with different i versus v charac-

teristics, as is the case of LED stringsemitting light of different colors so

ac/dc

or

dc/dc

V o

V ref +

–

R

I o = V ref / R Current

Control

Unit

V o I o

I o 1 I o 2 I oN

FIGURE 10 – The current of LED strings is adjusted by independent current sources.

dc/dcV o 1

V o

dc/dc

V dc

+

–

I oN

I o 2

I o 1

dc/dc

V oN

FIGURE 11 – Independent active control of each LED string allows LEDs of different colors tobe used together to create a variety of lighting effects.

The static and dynamic characteristics of an LED

matrix impose the specifications of the drivers.




that a variety of light ambiences can

be created.

Nondissipative current balance is

achieved using the coupling of single

or multiple secondary side windings in

a transformer core [53], which is also

used for isolation purposes and to set a

convenient voltage level. Moreover, the

current balance is achieved with thehelp of coupled inductors [54]. In this

case, the current balance is achieved

in ac, so a later rectification and use of

a large capacitor filter are required.

ConclusionsRecent advances in LED and OLED

lamps cover most light source appli-

cations, such as signaling, illumina-

tion, decoration, and ambience, with

improvements in energy efficiency and

light control flexibility.The steep di /dv characteristic

of LED lamps and the effect of tem-

perature on the i – v curve and on

the deviation of the light emission

spectrum require a tightly regulated

current and limitation of the current

ripple to prevent flickering.

The dc bus and output capacitanc-

es are minimized in high-performance

LED drivers to avoid using short life-

time electrolytic capacitors. The PWM

is usually preferred to implement

dimming because the modulation of

the LED current amplitude may affect

color rendering, while combination of

amplitude and PWM paves the way

to carrying out a more flexible dim-

ing and color temperature adjustment

with better EMC.

The integration of the power fac-

tor correction and LED driver stages

results in a robust and cost-effective

solution. Recent contributions on in-

tegrated stages present novel high-

frequency PWM with fast dynamic

response to preserve the light chro-

maticity and power factor in dimming

operation.

AcknowledgmentThe authors would like to thank Jo

Olsen and Eliecer Muñoz from OSRAM

SYLVANIA for their help in obtain-

ing the OLED pictures that appear in

this article. This work was supportedin part by the Spanish Ministry of

Science (TEC—FEDER 2011-23612 andDPI2010-15889).

BiographiesChristian Brañas (branasc@unican.

es) received his Ph.D. degree in elec-

tronics engineering in 2001 from the

University of Cantabria, Santander,

Spain. In 1995, he joined the Micro-

electronic Engineering Group at the

University of Cantabria, where he

is currently an associate professor.

Since 1997, he has been involved inseveral research projects in the field

of power electronics for lighting ap-

plications. He is a coauthor of 15 in-

ternational journal publications and

more than 50 international conference

papers in this field. He also holds a

Spanish patent. He is a Member of the

IEEE and a member of the IEEE Indus-

trial Electronics Society.

Francisco J. Azcondo (azcondof@

unican.es) received his E.E. degree

from the Universidad Politécnica de

Madrid, Spain, in 1989 and the Ph.D.

degree from the University of Cantabria,

Spain, in 1993. He is currently a pro-

fessor in the TEISA Department at

ETS II y T, University of Cantabria,

Spain. Since 1997, he has been co-

ordinating research projects in the

field of lighting applications. He is a

coauthor of 35 international journal

publications, 16 of them in this field,

along with more than 50 international

conference papers. He was a guest

coeditor of the special section on

modern ballast technology and light-

ing applications of IEEE Transactions

on Industry Electronics in 2012 and

coorganizer of special sessions fo-

cused on lighting at IEEE-IECON. He

is a Senior Member of the IEEE and a

member of the IEEE Industrial Elec-

tronics Society.

J. Marcos Alonso (marcos@uniovi.

es) received his M.Sc. degree and Ph.D.degree, both in electrical engineering,

from the University of Oviedo, Spain,in 1990 and 1994, respectively. Since

2007, he has been a full professor with

the Electrical Engineering Department

of the University of Oviedo. In the field

of power electronics for lighting appli-

cations, he has participated in more

than 20 research projects, has been

supervisor of eight Ph.D. theses, and

holds seven Spanish patents. Since

2002, he has served as an associate ed-

itor of IEEE Transactions on Power Elec-

tronics. He has been a co-guest editorof two special issues in lighting appli-

cations published in IEEE Transactions

on Power Electronics (2007) and IEEE

Transactions on Industrial Electronics

(2012). He also serves as secretary of

the IEEE Industry Applications Society

Industrial Lighting and Display Com-

mittee. He is a Senior Member of the

IEEE and a member of the IEEE Indus-

trial Electronics Society.

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