el

chn

on og did caconC-6nputndrotoncythan

topologies has been discussed by Singh et al. [3, 4]. Thetraditional two-stage PFC-based LED drivers have manydrawbacks such as high component count, high cost andislcc

www.ietdl.org

9&nefciency, which can be improved by the use ofingle-stage single switch PFC acdc converters. Inow-power applications, single-stage buck and yback PFConverter topologies are most suitable because of lowomponent count and cost. In yback converter topology,

haAwm46The Institution of Engineering and Technology 2014

Downloaded from http://www.elearnica.irthe LED driver. A PWM dimming is the most populartechnique to be used to drive multiple LED lamps foruniversal voltage applications [16]. For medium andhigh-power applications, both single-stage and two-stagealf bridge LLC resonant converter with soft switching aregood candidate for driving LED lamps [1720].transformerless single-stage single-switch acdc converterith improved efciency is discussed for the universal acains in [21]. A novel output voltage regulated acdcsingle-stage PFC converter-based topologies with improvedpower quality. An exhaustive review of PFC converter

much less as compared with the other circuit components of

preferred. Many researchers are working to develop1 Introduction

In the past few years, LED (light emitting diode) lighting hasbecome popular because of many advantages such as highluminous efciency, long lifetime, small size, durability, nomercury contents, ickerless start, robust and so on.Moreover, high brightness LEDs are solid state devices,hence they can withstand impact and vibration whichallows their utility in automotive and aircraft lightings,trafc lightings, railway signals, indoor and outdoorlightings and so on. LEDs are semiconductor devices whichemit visible light from a small square block ofsemiconductor material, thus LED lighting is also known assolid state lighting. The advantages of LEDs over compactuorescent lamps are that they do not emit harmfulultraviolet rays, turn on instantly to full brightness, theirlifespan is not shortened because of frequent use and alsothere is no requirement of high ignition voltage [1, 2].In general-purpose LED lighting, non-isolated and isolated

PFC (power factor corrected) LED drivers are used. From asafety point of view, isolated converter topologies are

because of high voltage stress across active switch owing toringing phenomenon between the leakage inductanceand transition capacitance of the MOSFET, a good snubbercircuit design is required [58]. Moreover, this adds extracost and power loss in the snubber circuit. Thereforebecause of low component count and minimum cost, anoptocouplerless buck PFC converter is preferred in thiswork. The buck converter can be operated in DCM(discontinuous conduction mode), CCM (continuousconduction mode) or critical conduction mode and they arediscussed in detail in [911]. With an efcient design ofPFC buck converter, input power factor can be achievedclose to unity for the universal ac mains. In low powerLED lighting application, it is a tough task to full therequirement as per the international mandatory regulationsIEC-61000-3-2 for class D equipments [12]. The concept ofleakage inductance energy transfer is used to achieve betterconversion efciency in the DCM buckboost converterintegrated with DCM yback converter based topology [7].To increase the overall lifetime of the LED driver circuits,electrolytic capacitorless topologies are reported in theliterature [1315], as the life of the electrolytic capacitor isPublished in IET Power ElectronicsReceived on 19th May 2013Revised on 12th August 2013Accepted on 27th August 2013doi: 10.1049/iet-pel.2013.0391

Buck converter-based powpower light emitting diodeBhim Singh, Ashish ShrivastavaDepartment of Electrical Engineering, Indian Institute of TeE-mail: rewa.ashish@gmail.com

Abstract: This study deals with the analysis and implementaticonverter-based power supply design for an LED (light emittingeneral purpose lighting applications, a buck converter is a gooand reduced cost. In low-power lighting, it is a tough task tounder the limits of strict international standards such as IEIn the proposed optocouplerless topology, HPF operation at iin continuous conduction mode. The design, modelling aMATLAB-Simulink and sim-power system toolboxes. A pmultiple LEDs connected in series conguration. The efcierated voltage of 220 V and the THD of ac mains current lessISSN 1755-4535

r supply design for lowamp lighting

ology Delhi, New Delhi-110016, India

f an HPF (high power factor) single-stage, single switch buckode) lamp load of 13 W operated at the universal ac mains. Inndidate for power factor correction with low component counttrol the THDi (total harmonic distortion) of ac mains current1000-3-2 with universal ac mains for class D equipments.ac mains is achieved by operating the buck acdc convertersimulation of the proposed topology are executed usingtype of the power supply for LED lamp is developed forof the proposed LED lamp driver is observed as 83.76% at17.27% for a wide range of voltages of 90270 V.IET Power Electron., 2014, Vol. 7, Iss. 4, pp. 946956doi: 10.1049/iet-pel.2013.0391

converter with less stress on the dc-link capacitor using resetwinding is reported in the literature [22]. An implementationof the buckboost converter to minimise the output voltageripples is discussed in the literature [23].In this paper, PQI (power quality improvement) is

performed using an optocouplerless buck PFC converteroperating in CCM. The proposed buck converter is thesimplest, most cost-effective and efcient switchingconverter for low power LED lighting applications.A proper design of the PFC circuit is required to make itsuitable for the universal ac mains. The proposed LEDdriver exhibits almost unity power factor with totalharmonic distortion (THD) of ac mains current less than17.27% and CF (crest factor) of the order of 1.46 for theuniversal ac mains voltage, which is as per theIEC-61000-3-2 class D requirements [12].

shown in Fig. 1. The circuit is a combination of DBR

average output voltage Vin of DBR is given as

Vin =2

NameMeNameMe2

Vs

p(1)

where Vs is the rms value of the input voltage.The buck converter maintains dc-link voltage at a set

reference value given as

www.ietdl.orgFig. 1 Schematic of the buck converter-based power supply designfor LED lamp3 Analysis and design of the PFC buck LEDdriver

The PFC buck acdc converter topology consists of a DBR, abuck converter and an output ripple lter. The inductor storesenergy during turn on time and delivers power to the loadduring off time of switch M. The detailed analysis anddesign of the single-switch PFC buck converter arepresented for CCM of operation.

3.1 Design of the buck converter

The design of a PFC buck converter is carried out in CCM forimproving the power quality at the universal ac mains. The(diode bridge rectier) followed by a ripple lter and a PFCbuck converter to achieve improved power quality at theuniversal ac mains.The PFC buck converter using the current multiplier

control scheme draws sinusoidal ac current and maintainsnearly unity power factor. This closed-loop control allowsfor achieving constant lamp current at high frequency tomaintain proper illumination. The operating switchingfrequency under steady state is maintained at 66 kHz.2 Proposed buck LED driver

The schematic of the proposed power supply design for theLED consists of a single-switch PFC buck converter asIET Power Electron., 2014, Vol. 7, Iss. 4, pp. 946956doi: 10.1049/iet-pel.2013.0391Vdc = DVin (2)

where D is the duty cycle of the PFC converter which isvarying over a complete cycle of input voltage by the PFCcontroller.A lter is designed for achieving constant output voltage so

that peak voltage ripples are maintained within speciedvalue for a particular switching frequency ( fs). The use of ahigh switching frequency helps in reducing the size of themagnetics and the lters.For operating the PFC buck converter in CCM, minimum

or critical value of buck inductance, Lcrit is determined as

Lcrit =1 Dmax( )

Vdc2fsIo

= 543.3 mH (3)

where Dmax is the maximum duty cycle (0.2828), Vdc is the dcoutput voltage (36 V), Io is the output rated current (0.36 A)and fs is the switching frequency (66 kHz). A value of 700H for CCM is used in the implementation.The output capacitor (Co) should have low ESR (equivalent

series resistance) and sufcient capacitance to store charge forlonger duration to maintain constant dc-link voltage. It shouldalso serve for eliminating the second harmonic componentpresent in dc-link voltage. It is calculated as

Co Io

2vDVco= 199.044 mF (4)

where Io is the output rated current (0.36 A), is the angularfrequency of the ac mains (2f), Vco is the % ripple voltageof the output capacitor (selecting 8% voltage ripple). A valueof 220 F is used in this work.Table 1 shows the selected values of the components of the

proposed LED driver.

4 Control scheme

As shown in Fig. 1, the current multiplier control strategy isused in order to operate the dcdc converter in CCM. Thiscontrol scheme allows for controlling the input current inphase with the input voltage to achieve nearly unity powerfactor using a PFC buck converter. This control scheme isformed by a PI (proportional integral) current controller,reference current generation and PWM generation,eventually it provides switching pulses to the solid statepower switch (M).

Table 1 Selected component values

buck inductance (L) 700 HPFC controller with integratedMOSFET

LNK406EG

bulk capacitor 220 F, 50 Vultrafast recovery diode (D) US1Mfilter components (Lf, Cf) 2 1 mH, 100 nF (400 V)947& The Institution of Engineering and Technology 2014

x = 1x2 = 1

Co

1RCo

1x2 + L0 vin= Ax+ Bv (12)

y = vdciin

[ ]= 0 1

1 0

( )x1x2

[ ]+ 0

0

[ ]vin (13)

when the switch is open for the (1D)T interval, thendifferent equations can be written as

0 = L diLdt+ vdc = L x1

+x2 (14)

x1 = iL = Codvdcdt

+ vdcR= Co x2

+ x2R

(15)

The above equations can be written in the state-space matrixform during the turn off period as

x = x1

x2

[ ]=

01L

1

Co

1RCo

x1x2[ ]

+ 00

[ ]vin (16)

y = vdciin

[ ]= 0 1

0 0

( )x1x2

[ ]+ 0

0

[ ]vin (17)

www.ietdl.org

4.1 PI current controller

A PI current controller is selected for the outer current loop toachieve good current regulation with zero steady-state error.The dc current, Io is sensed and then compared with the setreference current Io . The output current error Ier(t) is given as

Ier(t) = Io (t) Io(t) (5)

This output current error is fed to a PI controller and the PIcurrent controller output is given as

Ic(t) = KpIer(t)+ KitoIer(t) dt (6)

where Kp and Ki are the proportional and integral gains.

4.2 Reference current generation

The purpose of the current controller is to control current suchthat it follows the shape of rectied line voltage as close aspossible to improve the input power factor. The inputvoltage template, u(t) obtained from the ac mains voltage ismultiplied with the output of the PI current controller andthe resulting signal forms the reference for the input current

Idc(t) = Ic(t)u(t), u(t) = |Vsm|/Vsm (7)

4.3 PWM generation

The current error is the difference between the referencecurrent and the sensed rectied current. This error signal isamplied by a gain Kc and compared with a xedfrequency carrier wave to generate PWM signals required toturn on the power MOSFET of the buck converter

DIdc = Idc(t) Idc(t) (8)If KcDIdc . carrier signal thenM = 1 else M = 0

This PWM signal (M = 1) is applied at the gate terminal of theMOSFET.

5 Design of the controller and its stabilityanalysis

The stability analysis of the CCM buck converter-based LEDdriver is conducted by using a small-signal state-space model.The state-space model of the buck converter is developedconsidering that the active switch, diode, PFC buckinductor and dc-link capacitor are considered ideal. Fig. 2ashows the basic diagram of the buck converter. When theswitch is closed for the DT interval, then differentequations can be written as

vin = LdiLdt+ vdc = L x1

+vdc (9)

iL = Codvdcdt

+ vdcR= Co x2

+ x1R

(10)

iin = iL = x1 and vdc = x2 (11)

The above equations can be written in the state space matrix948& The Institution of Engineering and Technology 2014form during the turn on period as

x[ ] 0 1

L

x[ ] 1[ ]

Fig. 2 Basic diagram of the buck convertera Schematic of the buck converterb PI controller networkIET Power Electron., 2014, Vol. 7, Iss. 4, pp. 946956doi: 10.1049/iet-pel.2013.0391

The state-space average equilibrium matrices are calculated as

A = DA1 + (1 D)A2 =0

1L

1

Co

1RCo

D[ ](19)

www.ietdl.orgFrom (12) and (13) and (16) and (17), the state equationmatrices are given as

A1 = A2 =0

1L

1

Co

1RCo

, B1 =

1

L0

[ ], B2 =

0

0

[ ]

C1 =0 1

1 0

( ), C2 =

0 1

0 0

( ), E1 = E2 =

0

0

[ ](18)

Fig. 3 Bode plots of the buck convertera Bode plot of the buck converter without compensationb Bode plot of the buck converter with compensation

Fig. 4 Proposed PFC buck converter-based LED driver

IET Power Electron., 2014, Vol. 7, Iss. 4, pp. 946956doi: 10.1049/iet-pel.2013.0391B = DB1 + (1 D)B2 = L0

C = DC1 + (1 D)C2 =0 1

D 0

( )

E = DE1 + (1 D)E2 =0

0

[ ] (20)

The equilibrium state equations are given as

0 = AX + BVY = CX + EV (21)

00

[ ]=

01L

1

Co

1RCo

ILVDC[ ]

+D

L0

[ ]Vin (22)

X = ILVDC

[ ]=

DVinR

DVin

[ ](23)

The equilibrium output equation is given as

Y = 0 1D 0

( )ILVDC

[ ]=

DVinD2VinR

(24)

To construct a small-signal ac model at an operating point, theduty ratio is considered as

d(t) = D+ d(t) = D+ dm sinvt (25)

where D and dm are the constants and dm DThe small-signal ac model can be given by the following

state equations

dx(t)

dt= Ax(t)+ Bv(t)+ A1 A2

( )X + B1 B2

( )V

{ }d(t)

y(t) = Cx(t)+ Ev(t)+ C1 C2( )

X + E1 E2( )

V{ }

d(t)

(26)949& The Institution of Engineering and Technology 2014

R3 =R2Vref

Vdc Vref= 5.35 kV selected as 5 kV( ) (35)

R1 =R3Vref

Vosc Vref= 5.36 kV selected as 5 kV( ) (36)

Fig. 5 Simulated performance of the proposed LED driver in termsof different ac mains voltages

a Simulated performance of the proposed LED driver in terms of ac mains

www.ietdl.org

The small-signal ac state-space equations are given as

diL(t)

dtdvdc(t)

dt

=

01L

1

Co

1RCo

iL(t)vdc(t)[ ]

+D

L0

[ ]vin(t)

+1

L0

[ ]Vind(t) (27)

vdc(t)iin(t)

[ ]= 0 1

D 0

( )iL(t)vdc(t)

[ ]+ 0 0

1 0

( )ILVDC

[ ]d(t) (28)

From (27), after taking the Laplace transform andsimplication, the equation can be written as

vdc(s) =D

LCos2 + (L/R)s+ 1 vin(s)

+ VinLCos

2 + (L/R)s+ 1 d(s)(29)

Gvd(s) =vdc(s)

d(s)

vin(s)=0

= VinLCos

2 + (L/R)s+ 1 (30)

where Gvd(s) is the converter control-to-output transferfunction of the buck converter.The transfer function of the pulse-width modulator is

estimated as

Gdc(s) =d(s)

vdc(s)

= 1Vosc (31)

For the rated ac input voltage of 220 V, the open-loop transferfunction of the buck converter Go(s) is estimated as

Go(s) = Gvd(s)Gdc(s)H(s) = Gvd(s)

1Vosc

VrefVdc

= 4.4621.6 107s2 + 7.4 106s+ 1

(32)

where Vosc = 2.4 V, Vref = 1.24 V (from IC datasheet) andVdc = 36 V.The phase margin of the open-loop buck converter is only

0.555. Hence, a proper controller design is required toincrease the phase margin by more than 45. Thus, a PIcontroller is selected for the stability of the buck converterin closed-loop control. Fig. 2b shows the schematic of thePI controller network. The transfer function of this networkis calculated as

Gcontroller(s) =1+ sR1C1( )

sR2 C1 + C2( )+ sR1C1C2{ } (33)

For the buck converter values of L = 700 H, Co = 220 F,fs = 66 kHz, Vdc = 36 V and Vovp = 3 V (from the ICdatasheet), BW = 30 Hz, the values of different componentsof the PI controller network are given as

R2 =DVovp20 mA

= 150 kV (34)950& The Institution of Engineering and Technology 2014voltage (Vs), ac mains current (Is), dc current (Idc), buck inductor current(ILbuck), lamp voltage (Vlamp) and lamp current (Ilamp) at 90 Vb Simulated performance of the proposed LED driver in terms of ac mainsvoltage (Vs), ac mains current (Is), dc current (Idc), buck inductor current(ILbuck), lamp voltage (Vlamp) and lamp current (Ilamp) at 220 Vc Simulated performance of the proposed LED driver in terms of ac mainsvoltage (Vs), ac mains current (Is), dc current (Idc), buck inductor current(ILbuck), lamp voltage (Vlamp) and lamp current (Ilamp) at 270 VIET Power Electron., 2014, Vol. 7, Iss. 4, pp. 946956doi: 10.1049/iet-pel.2013.0391

Fig. 6 Simulated performance of the proposed LED driver in terms of ac mains current waveform and its harmonic spectra at ac mainsvoltages of

a 90 Vb 220 Vc 270 V

Table 2 Simulated performance parameters of the proposed LED dri

www.ietdl.orgVs, V Is, mA Vlamp, V Ilamp, mA

90 131.0 34.87 332.1100 123.5 35.68 321.4110 115.9 36.25 326.9120 109.5 36.80 331.6fo =1

2pNameMeNameMeNameMeNameMeNameMeLCo

= 380 Hz (37)

fz = 0.75foHz = 285 Hz (38)

130 102.4 37.02 333.9140 96.39 37.25 336.0150 91.04 37.45 337.9160 86.14 37.61 339.2170 81.35 37.65 339.7180 77.51 37.77 340.7190 73.57 37.78 340.9200 70.11 37.81 341.4210 67.17 37.86 341.7220 64.19 37.85 341.8230 61.57 37.87 341.9240 59.43 37.89 342.1250 57.21 37.91 342.4260 55.22 37.89 342.3270 53.60 37.87 342.3

Fig. 7 Complete prototype circuit diagram of the proposed topology

IET Power Electron., 2014, Vol. 7, Iss. 4, pp. 946956doi: 10.1049/iet-pel.2013.0391ver

PF DPF %THDi CF

0.9969 1 5.18 1.3870.9968 1 4.89 1.3910.9966 1 4.84 1.3950.9964 1 4.82 1.396C1 =1

2pR1fz= 111.74 nF selected as 100 nF( ) (39)

C2 =1

2p R2||R3( )

BW= 1.06 mF selected as 1 mF( ) (40)

0.9955 0.9999 4.98 1.3980.9953 0.9999 4.85 1.3920.9941 0.9999 5.43 1.3960.9933 0.9999 5.62 1.3980.9927 0.9999 5.98 1.3980.9906 0.9999 6.32 1.3970.9893 0.9999 7.15 1.4080.9879 0.9999 7.19 1.3940.9846 0.9999 7.85 1.3900.9834 0.9999 8.56 1.3880.9816 0.9999 8.85 1.3860.9757 0.9999 10.58 1.3780.9740 1 10.48 1.3740.9699 1 11.46 1.3700.9615 1 14.15 1.360

951& The Institution of Engineering and Technology 2014

Using the above calculated values of different components ofthe PI controller network, the transfer function can be given as

Gcontroller(s) =1+ 5 104s

7.5 105s2 + 0.165 s (41)

Without compensating network, the open-loop phase marginof the system has been obtained as 0.555 as shown inFig. 3a. Now from the Bode plot shown in Fig. 3b, thephase margin of the buck converter with a PI controller hasreached 90.1, which ensures the stable operation of thebuck converter in closed-loop control.

6 Results and discussion

To validate the design of the proposed power supply for theLED lamp, a prototype has been developed and tested forthe universal ac voltage applications. Fig. 4 shows thephotograph of the developed single-stage single-switchbuck converter-based LED driver.

6.1 Simulation results

current and CF of the simulated PFC buck converter-basedLED driver with improved power quality at the universal acmains.

6.2 Experimental results

The developed prototype of a CCM operated PFC buckconverter-based LED driver is meeting strict power qualityrequirements as per the mandatory international standard ofIEC 61000-3-2 (Class D) at universal ac mains. Thecomplete prototype of the proposed topology is shown inFig. 7, which conrms the low component count and cost.The buck converter-based proposed circuit (Fig. 7) iscomposed of LNK406EG (power switch + controller), D3(free-wheeling diode), L (buck inductor) and C0 (outputcapacitor). Diode D2 is used to prevent negative voltageappearing across the drain-source of LNK406EG especiallynear the zero-crossing of the input voltage. Diode D1 andcapacitor C1 detect the peak ac mains voltage. The voltageacross C1 along with R1, R2 and R3 sets input current fedinto the V pin. This current is used to control the lineunder-voltage (UV), over-voltage (OV) and feed-forward

LED

13.63 83.61 0.974 14.31 1.445

www.ietdl.orgThe analysis, design and simulation of the proposed LEDdriver are conducted to achieve improved power qualitysuch as low crest factor, high power factor (HPF) and lowTHD of the ac mains current. With the use of the CCMcontrol scheme and proper buck converter design, the lampvoltage is maintained almost constant at 36 V, thus, thelamp current remains nearly constant for a universal acmains. This is conrmed by observing the waveformsshown in Figs. 5ac of the input ac mains voltage (Vs),input ac mains current (Is), dc current (Idc), buck inductorcurrent (ILbuck), lamp voltage (Vlamp) and lamp current(Ilamp) at ac mains voltages of 90, 220 and 270 V,respectively.The input ac mains current waveforms along with their

harmonic spectra and THD are shown in Fig. 6 at the acmains voltages of 90, 220 and 270 V, which ensures thelow THD of the ac mains current of the simulated proposedLED driver for the universal ac mains.Table 2 shows the variations of the PF (power factor), the

DPF (displacement power factor), % THD of the ac mains

Table 3 Experimental performance parameters of the proposed

Vs, V Is, mA Vlamp, V Ilamp, mA Pin, W

90 136.15 36.789 279.9 12.14100 131.17 36.797 300.5 13.05110 124.95 36.784 315.7 13.70120 117.39 36.891 323.2 14.06130 109.07 36.761 326.2 14.15140 105.71 36.773 339.9 14.75150 103.40 37.244 352.4 15.45160 97.40 37.079 355.0 15.48170 92.87 37.092 358.0 15.65180 88.94 37.146 361.5 15.84190 85.42 37.120 365.4 16.04200 82.02 37.158 367.6 16.18210 78.76 37.147 369.0 16.28220 75.76 37.220 368.6 16.38230 73.01 37.292 369.9 16.45240 69.68 37.192 366.4 16.30250 66.81 37.146 363.3 16.21260 64.31 37.130 360.9 16.14270 62.01 37.201 357.2 16.06952& The Institution of Engineering and Technology 201413.50 83.28 0.970 15.46 1.44813.40 83.02 0.965 16.34 1.45213.29 82.75 0.959 17.27 1.462current which in conjunction with the FEEDBACK (FB)pin current provides constant current to the LED load.The FEEDBACK pin current is provided by the voltage to

current converter network formed by resistances R5R8, PNPtransistor Q, capacitor C5 and diode D4. Resistor R5 sets thefeedback current (IFB) for a given output voltage. Changesin the output voltage are seen by the voltage acrossresistance R7 which serves as the reference for the currentsource formed by R5, R7 and Q. Zener diode D5 protectsthe output circuitry during an open load condition. If theload is open for an extended period then the unit will gointo the auto-restart condition.Test results of the developed prototype of the PFC buck

converter-based LED driver are demonstrated and theresults are given in Table 3 for varying voltages of the acmains. Figs. 8ac show the input ac mains voltage (Vs) andcurrent (Is) waveforms at 90, 220 and 270 V, which conrmthe operation of the proposed circuit at almost unity powerfactor. It has been observed that controlling the powerfactor for high ac mains voltage is difcult, since the inputcurrent magnitude decreases substantially. The task

driver

Po, W % PF %THDi CF

10.30 84.84 0.989 14.34 1.42211.06 84.75 0.992 11.79 1.42611.61 84.74 0.994 9.81 1.42811.92 84.77 0.995 8.73 1.42111.99 84.73 0.996 8.18 1.41512.50 84.74 0.994 8.42 1.41913.13 84.98 0.995 8.10 1.42213.16 85.01 0.993 9.56 1.42513.28 84.85 0.991 9.91 1.43013.43 84.78 0.990 10.56 1.43213.56 84.53 0.988 11.13 1.43513.66 84.42 0.986 11.70 1.44113.71 84.21 0.984 12.11 1.44213.72 83.76 0.982 12.74 1.44213.79 83.82 0.979 13.34 1.446IET Power Electron., 2014, Vol. 7, Iss. 4, pp. 946956doi: 10.1049/iet-pel.2013.0391

www.ietdl.orgbecomes more troublesome when the circuit is designed forlow-power lighting applications (< 25 W), but in thedeveloped prototype of the LED lamp driver, input powerfactor has been obtained in the range of 0.9590.996 and%

Fig. 8 Experimental results of the PFC buck LED driver in terms of dia Experimental results of the PFC buck LED driver in terms of ac mains voltage (Vs)b Experimental results of the PFC buck LED driver in terms of ac mains voltage (Vs)c Experimental results of the PFC buck LED driver in terms of ac mains voltage (Vs) a

IET Power Electron., 2014, Vol. 7, Iss. 4, pp. 946956doi: 10.1049/iet-pel.2013.0391THD of the ac mains current is less than 17.27% for theuniversal ac mains. The evaluation of the test results ofreduced cost, low component count and optocouplerlessproposed single-stage prototype are considered as good PQI

fferent ac mains voltages

and ac mains current (Is) at 90 V (Scale: 100 V/div, 200 mA/div and 10 ms/div)and ac mains current (Is) at 220 V (Scale: 200 V/div, 50 mA/div and 10 ms/div)nd ac mains current (Is) at 270 V (Scale: 100 V/div, 50 mA/div and 10 ms/div)

953& The Institution of Engineering and Technology 2014

at the ac mains for high brightness LED load with universalvoltage applications, which is comparable with the resultsachieved in the literature [611, 14].The experimental results shown in Table 3 have good

improvement in the power quality parameters and theefciency of the proposed topology for the universal acmains. The performance of the CCM operated PFC buck

converter-based LED driver in terms of input PF, inputpower (Pin), input current (Is), output power (Po), outputvoltage (Vdc) and output current (Io) have been shown inFigs. 9ac for 90, 220 and 270 V, respectively. The %current THD varies from 8.10 to 17.27% with the universalinput ac voltages and it is well within the norms of the IEC61000-3-2:2005 mandatory requirement in terms of power

driv

of d

of d

of d

www.ietdl.orgFig. 9 Experimental results of the PFC buck converter-based LEDa Experimental results of the PFC buck converter-based LED driver in termsspectrum at 90 Vb Experimental results of the PFC buck converter-based LED driver in termsspectrum at 220 Vc Experimental results of the PFC buck converter-based LED driver in termsspectrum at 270 V954& The Institution of Engineering and Technology 2014er in terms of different parameters

ifferent parameters shown in multimeter reading and total current harmonics

ifferent parameters shown in multimeter reading and total current harmonics

ifferent parameters shown in multimeter reading and total current harmonicsIET Power Electron., 2014, Vol. 7, Iss. 4, pp. 946956doi: 10.1049/iet-pel.2013.0391

www.ietdl.orgfactor correction and harmonic contents for class Dequipments [12].To conrm the CCM operation of the developed prototype,

the buck inductor current waveforms have been shown inFigs. 10ac for 90, 220 and 270 V, respectively. The LEDlamp voltage and current waveforms are also shown inFigs. 11ac at 90, 220 and 270 V, respectively, whichensure approximately constant voltage constant currentoperation.

7 Conclusion

A low component count, cost effective and anoptocouplerless, PFC buck converter have been proposedwith low crest factor and HPF for a 13 W LED lamp loadat the universal input ac mains. In the proposed LED driver,

Fig. 10 Experimental results of the PFC buck converter-basedLED driver in terms of buck inductor current

a Experimental results of the PFC buck converter-based LED driver in termsof buck inductor current at 90 V (Scale: 174 mA/div and 5 ms/div)b Experimental results of the PFC buck converter-based LED driver in termsof buck inductor current at 220 V (Scale: 174 mA/div and 5 ms/div)c Experimental results of the PFC buck converter-based LED driver in termsof buck inductor current at 270 V (Scale: 174 mA/div and 5 ms/div)

IET Power Electron., 2014, Vol. 7, Iss. 4, pp. 946956doi: 10.1049/iet-pel.2013.0391the overall measured efciency is 83.76% at rated input acmains of 220 V. The CCM operated buck converter hasshown good power quality improvement in low powerapplications ( < 25 W) giving 12.74% THD and input PF of0.982 at rated voltage of 220 V. The current harmonics ofthe proposed LED driver has been found well within thelimits of the IEC 61000-3-2 Class-D equipments and alsothe crest factor is well below the limit of 1.7. Thedeveloped prototype has been operated with constant lampvoltage to achieve ac mains current THD between 8.1 and17.27% for the universal ac mains of 90270 V.

8 References

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Fig. 11 Experimental results of the PFC buck converter-basedLED driver in terms of lamp voltage and lamp current

a Experimental results of the PFC buck converter-based LED driver in termsof lamp voltage and lamp current at 90 V (Scale: 7.2 V/div, 340 mA/div andtime: 10 ms/div)b Experimental results of the PFC buck converter-based LED driver in termsof lamp voltage and lamp current at 220 V (Scale: 7.2 V/div, 340 mA/div andtime: 10 ms/div)c Experimental results of the PFC buck converter-based LED driver in termsof lamp voltage and lamp current at 270 V (Scale: 7.2 V/div, 340 mA/div andtime: 10 ms/div)

955& The Institution of Engineering and Technology 2014

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Rated lamp power: 13 W, rated lamp current: 360 mA, ratedlamp voltage: 36 V, switching frequency ( fs): 66 kHz, buckinductor (L): 700 H, dc-link capacitor (Co): 220 F.Power Electron., 2012, 27, (11), pp. 45304539IET Power Electron., 2014, Vol. 7, Iss. 4, pp. 946956doi: 10.1049/iet-pel.2013.0391