A Single-Stage LED Tube Lamp Driver with Power-Factor Corrections and Soft Switching for Energy-Saving Indoor Lighting Applications

Abstract: This paper presents a single-stage alternating current (AC)/direct current (DC) light-emitting diode (LED) tube lamp driver for energy-saving indoor lighting applications; this driver features power-factor corrections and soft switching, and also integrates a dual buck-boost converter with coupled inductors and a half-bridge series resonant converter cascaded with a bridge rectifier into a single-stage power-conversion topology. The features of the presented driver are high efficiency (>91%), satisfying power factor (PF > 0.96), low input-current total-harmonic distortion (THD < 10%), low output voltage ripple factor (<7.5%), low output current ripple factor (<8%), and zero-voltage switching (ZVS) obtained on both power switches. Operational principles are described in detail, and experimental results obtained from an 18 W-rated LED tube lamp for T8/T10 fluorescent lamp replacements with input utility-line voltages ranging from 100 V to 120 V have demonstrated the functionality of the presented driver suitable for indoor lighting applications.


Introduction
Latest developments and applications of solid-state lighting have begun gaining greater attention due to the requirements for efficient energy usage nowadays [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16].With features of energy-savings, lower maintenance costs and long lifetime, light-emitting diode (LED) tube lamps have begun to be favorable alternatives to replace traditional T8/T10-type fluorescent lamps in building-lighting applications [17][18][19].According to the specifications shown in [20,21] with almost the same color temperature and color-rendering index, the LED tube lamp has better lighting efficiency, less power consumption, longer lamp lifetime, and contains no mercury inside the lamp tube, as compared to its T8-type counterparts.Therefore, T8-type LED tube lamps have become increasingly popular lighting sources for indoor lighting applications such as public architecture, offices, classrooms, and so on [17][18][19][20][21]. Figure 1 shows the commercial two-stage driver for supplying a T8-type LED tube lamp; it is composed of an AC-DC (alternating current-direct current) converter (typically a boost converter) with power-factor corrections (PFCs) as the first stage, and a DC-DC converter (typically a buck converter) as the second stage for regulating the voltage/current of the LED tube lamp.Separate controllers for each stage are required, and the circuit efficiency is restricted due to the two-stage power conversion.Some single-stage AC-DC drivers for providing a T8-type LED tube lamp to replace T8/T10-type fluorescent lamps have been presented: reference [18] utilizes a flyback PFC converter, and a buck converter with input-current shaping is presented in reference [19].These single-stage versions are cost-effective in comparison to their two-stage counterpart; however, their power switches do not include the soft-switching function, which results in limited efficiency.
counterpart; however, their power switches do not include the soft-switching function, which results in limited efficiency.In response to these concerns, this paper presents a single-stage LED tube lamp driver suitable for indoor lighting applications with features of power-factor corrections and soft-switching characteristics.Theoretical analyses of operating modes, design equations for key circuit parameters, and experimental results from a prototype driver circuit for supplying an 18 W-rated T8-type LED tube lamp with input voltages ranging from 100 V to 120 V are demonstrated.This paper is organized as follows.Section 2 introduces and analyzes the presented single-stage LED tube lamp driver.Section 3 shows design equations of key components in the presented driver.Section 4 demonstrates experimental results of a prototype circuit for supplying an LED tube lamp.Finally, some conclusions are provided in Section 5.

The Description and Analysis of the Presented LED Tube Lamp Driver
Figure 2 shows the presented driver, which integrates the dual buck-boost converter with coupled inductors (one buck-boost converter includes a diode Db1, a coupled inductor LPFC1, a switch S1, a body diode of the switch S2, and a DC-linked capacitor CDC1; another buck-boost converter includes a diode Db2, a coupled inductor LPFC2, a switch S2, a body diode of the switch S1, and the capacitor CDC2) with the half-bridge series resonant converter cascaded with a bridge rectifier (including two DC-linked capacitors CDC1 and CDC2, two switches S1 and S2, a resonant inductor Lr, a resonant capacitor Cr, a full-bridge rectifier (including diodes D1, D2, D3 and D4), and an output capacitor Co) into a single-stage topology for supplying an LED tube lamp [17].In addition, an LC filter (an inductor Lf and a capacitor Cf) is connected with the input utility-line voltage.In order to analyze the operations of the presented LED tube lamp driver, the following assumptions are made.In response to these concerns, this paper presents a single-stage LED tube lamp driver suitable for indoor lighting applications with features of power-factor corrections and soft-switching characteristics.Theoretical analyses of operating modes, design equations for key circuit parameters, and experimental results from a prototype driver circuit for supplying an 18 W-rated T8-type LED tube lamp with input voltages ranging from 100 V to 120 V are demonstrated.This paper is organized as follows.Section 2 introduces and analyzes the presented single-stage LED tube lamp driver.Section 3 shows design equations of key components in the presented driver.Section 4 demonstrates experimental results of a prototype circuit for supplying an LED tube lamp.Finally, some conclusions are provided in Section 5. counterpart; however, their power switches do not include the soft-switching function, which results in limited efficiency.In response to these concerns, this paper presents a single-stage LED tube lamp driver suitable for indoor lighting applications with features of power-factor corrections and soft-switching characteristics.Theoretical analyses of operating modes, design equations for key circuit parameters, and experimental results from a prototype driver circuit for supplying an 18 W-rated T8-type LED tube lamp with input voltages ranging from 100 V to 120 V are demonstrated.This paper is organized as follows.Section 2 introduces and analyzes the presented single-stage LED tube lamp driver.Section 3 shows design equations of key components in the presented driver.Section 4 demonstrates experimental results of a prototype circuit for supplying an LED tube lamp.Finally, some conclusions are provided in Section 5.

The Description and Analysis of the Presented LED Tube Lamp Driver
Figure 2 shows the presented driver, which integrates the dual buck-boost converter with coupled inductors (one buck-boost converter includes a diode Db1, a coupled inductor LPFC1, a switch S1, a body diode of the switch S2, and a DC-linked capacitor CDC1; another buck-boost converter includes a diode Db2, a coupled inductor LPFC2, a switch S2, a body diode of the switch S1, and the capacitor CDC2) with the half-bridge series resonant converter cascaded with a bridge rectifier (including two DC-linked capacitors CDC1 and CDC2, two switches S1 and S2, a resonant inductor Lr, a resonant capacitor Cr, a full-bridge rectifier (including diodes D1, D2, D3 and D4), and an output capacitor Co) into a single-stage topology for supplying an LED tube lamp [17].In addition, an LC filter (an inductor Lf and a capacitor Cf) is connected with the input utility-line voltage.In order to analyze the operations of the presented LED tube lamp driver, the following assumptions are made.In order to analyze the operations of the presented LED tube lamp driver, the following assumptions are made.
(a) Since the switching frequencies of the two switches (S 1 and S 2 ) are much higher than that of the utility-line voltage v AC , the sinusoidal utility-line voltage can be considered as a constant value for each high-frequency switching period.The operating modes and key waveforms of the presented LED tube lamp driver during the positive half-cycle of input utility-line voltage are shown in Figures 3 and 4, respectively, and the analysis of operations for the presented driver are described in detail as follows.
Mode 1 (t 0 ≤ t < t 1 ; in Figure 3a): The drain-source voltage v DS1 of S 1 is decreased to zero at time t 0 ; thus, the body diode of switch S 1 is forward-biased.The resonant capacitor C r provides energy to resonant inductor L r , capacitors C DC1 , C DC2 , C o and the LED tube lamp through S 1 's body diode, D 2 , and D 3 .When power switch S 1 turns on with zero-voltage switching (ZVS) at t 1 , this mode ends.
Mode 2 (t 1 ≤ t < t 2 ; in Figure 3b): This mode begins when switch S 1 achieves ZVS turn-on at t 1 .The input voltage v AC provides energy to coupled inductor L PFC1 through diode D b1 and switch S 1 .The inductor current i LPFC1 linearly increases from zero, and can be expressed as where v AC-rms is the root-mean-square (rms) value of the input utility-line voltage, and f AC is the utility-line frequency.The resonant capacitor C r still provides energy to inductor L r , capacitors C DC1 , C DC2 , C o and the LED tube lamp through S 1 , D 2 , and D 3 .This mode finishes when the resonant inductor current i Lr is zero at t 2 .
Mode 3 (t 2 ≤ t < t 3 ; in Figure 3c): The input voltage v AC still provides energy to the coupled inductor L PFC1 through diode D b1 and switch S 1 .The DC-bus capacitors C DC1 and C DC2 supply energy to resonant inductor L r , capacitors C r and C o , and the LED tube lamp through switch S 1 , D 1 , and D 4 .This mode ends when inductor current i LPFC1 reaches its peak value at t 3 , which is denoted as i LPFC1-pk (t), and can be expressed as where D and T S are the duty cycle and period, respectively, of the power switch.Mode 4 (t 3 ≤ t < t 4 ; in Figure 3d): This mode begins when S 1 turns off at t 3 .The utility-line voltage v AC and the coupled inductor L PFC1 supply energy to the drain-source capacitor of S 1 through diode D b1 .
The DC-bus capacitors C DC1 and C DC2 , the drain-source capacitor of S 2 and resonant inductor L r provide energy to capacitors C r and C o and the LED tube lamp through diodes D 1 and D 4 .When the drain-source voltage v DS2 of S 2 is decreased to zero at t 4 , this mode ends.
Mode 5 (t 4 ≤ t < t 5 ; in Figure 3e): This mode begins when the body diode of switch S 2 is forward-biased at t 4 .The coupled inductor L PFC1 provides energy to C DC1 through diode D b3 .The inductor current i LPFC1 linearly decreases, and can be given by where V DC /2 is the voltage of the DC-linked capacitor C DC1 .
Inductor L r provides energy to capacitors C r and C o and the LED tube lamp through S 2 's body diodes, D 1 and D 4 .When power switch S 2 is turned on with ZVS at t 5 , this mode ends.
Mode 6 (t 5 ≤ t < t 6 ; in Figure 3f): This mode begins when switch S 2 achieves ZVS turn-on at t 5 .Inductor L r continues providing energy to capacitors C r and C o and the LED tube lamp through S 2 , D 1 and D 4 .The mode ends when the resonant inductor current i Lr decreases to zero at t 6 .
Mode 7 (t 6 ≤ t < t 7 ; in Figure 3g): This mode begins when current i Lr decreases to zero at t 6 .Capacitor C r provides energy to inductor L r , capacitor C o and the LED tube lamp through S 2 and diodes D 2 and D 3 .The mode ends when switch S 2 turns off at t 7 .
Mode 8 (t 7 ≤ t < t 8 ; in Figure 3h): In this mode, capacitor C r and the drain-source capacitor of switch S 1 provide energy to inductor L r , the drain-source capacitor of S 2 , capacitors C DC1 , C DC2 , C o , and the LED tube lamp through diodes D 2 and D 3 .When the drain-source voltage v DS1 of S 1 is decreased to zero at t 7 , this mode ends.Then, Mode 1 begins for the next high-frequency switching period.Figure 5 shows the circuit diagram for controlling the single-stage LED tube lamp driver.Referring to Figure 5 and utilizing a constant voltage/current controller (IC1 SEA05) for regulating the LED tube lamp's output voltage and current, the output voltage V o can be sensed through resistors R vs1 , VR 1 and R vs2 , and the output current can be sensed through resistor R 3 .The sensed output signal from pin 5 of the IC1 feeds into the high-voltage resonant controller (IC3 ST L6599) through a photo-coupler (IC2 PC817).Two gate-driving signals v GS1 and v GS2 are generated from pin 15 and pin 11, respectively, of the IC3, to carry out regulating the LED tube lamp's output voltage and current.In addition, an AC-DC switching power module with dual output voltages is utilized for providing the 15 V power supply voltages of IC1 and IC3 in the control circuit.

Design of Coupled Inductors LPFC1 and LPFC2
The design equation of the coupled inductor LPFC1 (LPFC2) is expressed as [22] 2 2 where η is the estimated circuit efficiency, Plamp is the rated power of the LED tube lamp, and fS is the switching frequency.With a η of 0.9, a vAC-rms of 110 V and a Plamp of 18 W, an fS of 55 kHz and a D of 0.5, the coupled inductors LPFC1 and LPFC2 are given by: 0.9 110 0.5 1.34mH 2 18 55000

Design of Series Resonant Tank Lr and Cr
Figure 6 depicts the equivalent circuit during the design of the series resonant tank; Ro is the equivalent resistance of the T8-type LED tube lamp, and can be represented by Ro = Vo/Io.By using the fundamental approximation theory, the fundamental components of the switch voltage vDS2 can be expressed by [23,24] 2 2 sin 2π π Figure 5.The utilized control circuit for the presented LED tube lamp driver.

Design Equations of Key
where η is the estimated circuit efficiency, P lamp is the rated power of the LED tube lamp, and f S is the switching frequency.With a η of 0.9, a v AC-rms of 110 V and a P lamp of 18 W, an f S of 55 kHz and a D of 0.5, the coupled inductors L PFC1 and L PFC2 are given by:

Design of Series Resonant Tank L r and C r
Figure 6 depicts the equivalent circuit during the design of the series resonant tank; R o is the equivalent resistance of the T8-type LED tube lamp, and can be represented by R o = V o /I o .By using the fundamental approximation theory, the fundamental components of the switch voltage v DS2 can be expressed by [23,24]  Referring to Figure 6, the equivalent load resistance Req can be expressed as [24] 2 2 With a Vo of 60 V and an Io of 0.3 A, the equivalent load resistance Req is given by Referring to Figure 6, the series resonant tank is composed of a resonant inductor Lr in series connection with a resonant capacitor Cr; and the resonant frequency fo can be expressed by The loaded quality factor QL is expressed by In order to obtain ZVS for the two active switches, the switching frequency fS is designed to be larger than the resonant frequency fo so that the resonant tank resembles an inductive network [24].
Therefore, the relationship between switching frequency fS and resonant frequency fo is selected as Combining ( 7) and ( 8) with ( 9), the resonant capacitor Cr is given by By selecting an fS of 55 kHz and a QL of 0.9, the resonant capacitor Cr is computed as 2 79.3nF π 55 162.1 0.9 In addition, Cr is selected to be 82 nF.Combining ( 7) with ( 9), the resonant inductor Lr is given by Referring to Figure 6, the equivalent load resistance R eq can be expressed as [24] With a V o of 60 V and an I o of 0.3 A, the equivalent load resistance R eq is given by Referring to Figure 6, the series resonant tank is composed of a resonant inductor L r in series connection with a resonant capacitor C r ; and the resonant frequency f o can be expressed by The loaded quality factor Q L is expressed by In order to obtain ZVS for the two active switches, the switching frequency f S is designed to be larger than the resonant frequency f o so that the resonant tank resembles an inductive network [24].
Therefore, the relationship between switching frequency f S and resonant frequency f o is selected as Combining ( 7) and ( 8) with ( 9), the resonant capacitor C r is given by By selecting an f S of 55 kHz and a Q L of 0.9, the resonant capacitor C r is computed as In addition, C r is selected to be 82 nF.Combining ( 7) with ( 9), the resonant inductor L r is given by Appl.Sci.2017, 7, 115 9 of 14 With an f S of 55 kHz and a C r of 82 nF, the resonant inductor L r is computed as

Experimental Results
A prototype driver has been built and tested for supplying an 18 W-rated T8-type LED tube lamp (EVERLIGHT FBW/T8/857/U/4ft, ELECTRONICS Co., Ltd., New Taipei City, Taiwan), whose rated voltage and current are 60 V and 0.3 A, respectively.The components utilized in the LED tube lamp driver are shown in Table 1.8, and the series resonant tank resembles an inductive load.The measured DC-bus voltage is shown in Figure 9, and the average value of V DC is approximately 318 V. Figure 10a,b presents the measured voltages v DS1 and v DS2 and currents i DS1 and i DS2 of the power switches S 1 and S 2 , respectively.ZVS is obviously achieved on the power switches; thus, the circuit efficiency is increased.

Experimental Results
A prototype driver has been built and tested for supplying an 18 W-rated T8-type LED tube lamp (EVERLIGHT FBW/T8/857/U/4ft, ELECTRONICS Co., Ltd., New Taipei City, Taiwan), whose rated voltage and current are 60 V and 0.3 A, respectively.The components utilized in the LED tube lamp driver are shown in Table 1.8, and the series resonant tank resembles an inductive load.The measured DC-bus voltage is shown in Figure 9, and the average value of VDC is approximately 318 V. Figure 10a,b presents the measured voltages vDS1 and vDS2 and currents iDS1 and iDS2 of the power switches S1 and S2, respectively.ZVS is obviously achieved on the power switches; thus, the circuit efficiency is increased.

Experimental Results
A prototype driver has been built and tested for supplying an 18 W-rated T8-type LED tube lamp (EVERLIGHT FBW/T8/857/U/4ft, ELECTRONICS Co., Ltd., New Taipei City, Taiwan), whose rated voltage and current are 60 V and 0.3 A, respectively.The components utilized in the LED tube lamp driver are shown in Table 1.8, and the series resonant tank resembles an inductive load.The measured DC-bus voltage is shown in Figure 9, and the average value of VDC is approximately 318 V. Figure 10a,b presents the measured voltages vDS1 and vDS2 and currents iDS1 and iDS2 of the power switches S1 and S2, respectively.ZVS is obviously achieved on the power switches; thus, the circuit efficiency is increased.2 presents the measured output voltage and current of the presented LED tube lamp driver under different input voltages.Figure 12 shows the calculated voltage and current ripple factors of the presented LED tube lamp driver under different input utility-line voltages.In addition, the output voltage (current) ripple factor is obtained by the peak-to-peak (pk-pk) level divided by the average value of output voltage (current).According to Figure 12, the highest and lowest measured output-voltage ripple factors are 7.2% and 6.26%; these occurred at a utility-line rms voltage of 120 V and 100 V, respectively.Moreover, the highest and lowest measured output-current ripple factors are 7.45% and 6.74%; these occurred at a utility-line rms voltage of 100 V and 120 V, respectively.2 presents the measured output voltage and current of the presented LED tube lamp driver under different input voltages.Figure 12 shows the calculated voltage and current ripple factors of the presented LED tube lamp driver under different input utility-line voltages.In addition, the output voltage (current) ripple factor is obtained by the peak-to-peak (pk-pk) level divided by the average value of output voltage (current).According to Figure 12, the highest and lowest measured output-voltage ripple factors are 7.2% and 6.26%; these occurred at a utility-line rms voltage of 120 V and 100 V, respectively.Moreover, the highest and lowest measured output-current ripple factors are 7.45% and 6.74%; these occurred at a utility-line rms voltage of 100 V and 120 V, respectively.2 presents the measured output voltage and current of the presented LED tube lamp driver under different input voltages.Figure 12 shows the calculated voltage and current ripple factors of the presented LED tube lamp driver under different input utility-line voltages.In addition, the output voltage (current) ripple factor is obtained by the peak-to-peak (pk-pk) level divided by the average value of output voltage (current).According to Figure 12, the highest and lowest measured output-voltage ripple factors are 7.2% and 6.26%; these occurred at a utility-line rms voltage of 120 V and 100 V, respectively.Moreover, the highest and lowest measured output-current ripple factors are 7.45% and 6.74%; these occurred at a utility-line rms voltage of 100 V and 120 V, respectively.2 presents the measured output voltage and current of the presented LED tube lamp driver under different input voltages.Figure 12 shows the calculated voltage and current ripple factors of the presented LED tube lamp driver under different input utility-line voltages.In addition, the output voltage (current) ripple factor is obtained by the peak-to-peak (pk-pk) level divided by the average value of output voltage (current).According to Figure 12, the highest and lowest measured output-voltage ripple factors are 7.2% and 6.26%; these occurred at a utility-line rms voltage of 120 V and 100 V, respectively.Moreover, the highest and lowest measured output-current ripple factors are 7.45% and 6.74%; these occurred at a utility-line rms voltage of 100 V and 120 V, respectively.The measured input utility-line voltage and current are shown in Figure 13, and the input current is in phase with the input voltage.Figure 14 presents the measured input-current harmonics compared with the International Electrotechnical Commission (IEC) 61000-3-2 Class C standards under input utility-line voltages ranging from 100 V to 120 V; all measured current harmonics meet the requirements.Figure 15 shows the measured power factor (PF) and current THD at input utility-line voltages ranging from 100 V to 120 V.At a utility-line rms voltage of 110 V, the measured PF and current THD are 0.96 and 9.3%, respectively.The maximum PF is 0.97 occurred at a utility-line rms voltage of 120 V, and the minimum current THD is 6.9% occurred at a utility-line rms voltage of 100 V.The measured input utility-line voltage and current are shown in Figure 13, and the input current is in phase with the input voltage.Figure 14 presents the measured input-current harmonics compared with the International Electrotechnical Commission (IEC) 61000-3-2 Class C standards under input utility-line voltages ranging from 100 V to 120 V; all measured current harmonics meet the requirements.Figure 15 shows the measured power factor (PF) and current THD at input utility-line voltages ranging from 100 V to 120 V.At a utility-line rms voltage of 110 V, the measured PF and current THD are 0.96 and 9.3%, respectively.The maximum PF is 0.97 occurred at a utility-line rms voltage of 120 V, and the minimum current THD is 6.9% occurred at a utility-line rms voltage of 100 V.    Figure 16 shows the measured efficiency of the presented LED tube lamp driver under input utility-line voltages from 100 V to 120 V.The highest and lowest measured efficiency levels are 94.16% and 91.24%; these occurred at utility-line rms voltages of 100 V and 120 V, respectively.In addition, the efficiency which drops with increased utility-line voltages is related to the voltage gain of the LC series-resonant tank.For providing rated output power (voltage/current), the voltage gain of the LC series-resonant tank will decrease when the utility-line voltages increase, resulting in increasing the switching frequency of the power switches.Thus, the switching losses of power switches and conduction losses of power diodes will increase resulting in lowering the circuit efficiency.The comparisons between the existing T8-Type LED tube lamp drivers and the proposed one are shown in Table 3.A flyback-type AC-DC converter as an LED tube lamp driver is presented in [18], and a buck-type AC-DC converter as an LED tube lamp driver is presented in [19].In addition, these existing LED tube lamp drivers ( [18,19]) operate with universal input voltages while the proposed version operates with American utility-line voltages.Although the circuit components counts in the proposed driver are higher than these existing ones, this table illustrates that the proposed single-stage LED tube lamp driver has smaller input current THD and achieves soft-switching on the power switches to increase circuit efficiency over the two existing versions.Figure 16 shows the measured efficiency of the presented LED tube lamp driver under input utility-line voltages from 100 V to 120 V.The highest and lowest measured efficiency levels are 94.16% and 91.24%; these occurred at utility-line rms voltages of 100 V and 120 V, respectively.In addition, the efficiency which drops with increased utility-line voltages is related to the voltage gain of the LC series-resonant tank.For providing rated output power (voltage/current), the voltage gain of the LC series-resonant tank will decrease when the utility-line voltages increase, resulting in increasing the switching frequency of the power switches.Thus, the switching losses of power switches and conduction losses of power diodes will increase resulting in lowering the circuit efficiency.Figure 16 shows the measured efficiency of the presented LED tube lamp driver under input utility-line voltages from 100 V to 120 V.The highest and lowest measured efficiency levels are 94.16% and 91.24%; these occurred at utility-line rms voltages of 100 V and 120 V, respectively.In addition, the efficiency which drops with increased utility-line voltages is related to the voltage gain of the LC series-resonant tank.For providing rated output power (voltage/current), the voltage gain of the LC series-resonant tank will decrease when the utility-line voltages increase, resulting in increasing the switching frequency of the power switches.Thus, the switching losses of power switches and conduction losses of power diodes will increase resulting in lowering the circuit efficiency.The comparisons between the existing T8-Type LED tube lamp drivers and the proposed one are shown in Table 3.A flyback-type AC-DC converter as an LED tube lamp driver is presented in [18], and a buck-type AC-DC converter as an LED tube lamp driver is presented in [19].In addition, these existing LED tube lamp drivers ( [18,19]) operate with universal input voltages while the proposed version operates with American utility-line voltages.Although the circuit components counts in the proposed driver are higher than these existing ones, this table illustrates that the proposed single-stage LED tube lamp driver has smaller input current THD and achieves The comparisons between the existing T8-Type LED tube lamp drivers and the proposed one are shown in Table 3.A flyback-type AC-DC converter as an LED tube lamp driver is presented in [18], and a buck-type AC-DC converter as an LED tube lamp driver is presented in [19].In addition, these existing LED tube lamp drivers ( [18,19]) operate with universal input voltages while the proposed version operates with American utility-line voltages.Although the circuit components counts in the proposed driver are higher than these existing ones, this table illustrates that the proposed single-stage LED tube lamp driver has smaller input current THD and achieves soft-switching on the power switches to increase circuit efficiency over the two existing versions.Measured Maximum Power Factor 0.99 @ 110 V 0.96 @ 110 V 0.97 @ 120 V Measured Minimum Input Current THD (total-harmonic distortion) 9% @ 180 V 21.54% @ 110 V 6.86% @ 100 V Measured Maximum Efficiency 87.8% @ 180 V 88.56% @ 180 V 94.16% @ 100 V

Conclusions
This paper has presented and implemented a single-stage driver suitable for energy-saving indoor lighting applications, which integrates a dual buck-boost converter with coupled inductors and a half-bridge series resonant converter cascaded with a bridge rectifier, for supplying an LED tube lamp for T8/T10 fluorescent lamp replacements with power-factor corrections and soft switching.A prototype circuit has been successfully built and tested for supplying an 18 W-rated LED tube lamp with utility-line voltages ranging from 100 V to 120 V.The experimental results have demonstrated high efficiency (>91%), satisfying power-factor (>0.96), low current THD (<10%), and soft-switching of power switches in the presented LED tube lamp driver.

Figure 1 .
Figure 1.The commercial two-stage driver for supplying a T8-Type LED (light-emitting diode) tube lamp.

Figure 2 .
Figure 2. The presented single-stage driver for supplying a T8-type LED tube lamp.

Figure 1 .
Figure 1.The commercial two-stage driver for supplying a T8-Type LED (light-emitting diode) tube lamp.

Figure 2
Figure 2 shows the presented driver, which integrates the dual buck-boost converter with coupled inductors (one buck-boost converter includes a diode D b1 , a coupled inductor L PFC1 , a switch S 1 , a body diode of the switch S 2 , and a DC-linked capacitor C DC1 ; another buck-boost converter includes a diode D b2 , a coupled inductor L PFC2 , a switch S 2 , a body diode of the switch S 1 , and the capacitor C DC2 ) with the half-bridge series resonant converter cascaded with a bridge rectifier (including two DC-linked capacitors C DC1 and C DC2 , two switches S 1 and S 2 , a resonant inductor L r , a resonant capacitor C r , a full-bridge rectifier (including diodes D 1 , D 2 , D 3 and D 4 ), and an output capacitor C o ) into a single-stage topology for supplying an LED tube lamp [17].In addition, an LC filter (an inductor L f and a capacitor C f ) is connected with the input utility-line voltage.

Figure 1 .
Figure 1.The commercial two-stage driver for supplying a T8-Type LED (light-emitting diode) tube lamp.

Figure 2 .
Figure 2. The presented single-stage driver for supplying a T8-type LED tube lamp.

Figure 2 .
Figure 2. The presented single-stage driver for supplying a T8-type LED tube lamp.
(b) Power switches are complementarily operated, and their intrinsic diodes and inherent drain-source capacitors are considered.(c) The conducting voltage drops of all diodes (including D b1 , D b2 , D b3 , D b4 , D 1 , D 2 , D 3 and D 4 ) are neglected.(d) Two coupled inductors (L PFC1 and L PFC2 ) are designed to be operated in discontinuous-conduction mode (DCM) for naturally achieving power-factor correction (PFC).

Figure 4 .
Figure 4. Key waveforms of the presented LED tube lamp driver during the positive half-cycle of the input utility-line voltage.

Figure 5
Figure 5 shows the circuit diagram for controlling the single-stage LED tube lamp driver.Referring to Figure 5 and utilizing a constant voltage/current controller (IC1 SEA05) for regulating the LED tube lamp's output voltage and current, the output voltage Vo can be sensed through

Figure 5
Figure 5 shows the circuit diagram for controlling the single-stage LED tube lamp driver.Referring to Figure 5 and utilizing a constant voltage/current controller (IC1 SEA05) for regulating the LED tube lamp's output voltage and current, the output voltage Vo can be sensed through

Figure 4 .
Figure 4. Key waveforms of the presented LED tube lamp driver during the positive half-cycle of the input utility-line voltage.

Figure 5 .
Figure 5.The utilized control circuit for the presented LED tube lamp driver.

Components in the Presented LED Tube Lamp Driver 3 . 1 .
Design of Coupled Inductors L PFC1 and L PFC2The design equation of the coupled inductor L PFC1 (L PFC2 ) is expressed as[22]

Figure 6 .
Figure 6.Equivalent circuit during the design of the series resonant tank.

Figure 6 .
Figure 6.Equivalent circuit during the design of the series resonant tank.

Figure 11
Figure 11 shows the measured output voltage and current waveforms, and the average values of Vo and Io are 60 V and 0.3 A, respectively.Table2presents the measured output voltage and current of the presented LED tube lamp driver under different input voltages.Figure12shows the calculated voltage and current ripple factors of the presented LED tube lamp driver under different input utility-line voltages.In addition, the output voltage (current) ripple factor is obtained by the peak-to-peak (pk-pk) level divided by the average value of output voltage (current).According to Figure12, the highest and lowest measured output-voltage ripple factors are 7.2% and 6.26%; these occurred at a utility-line rms voltage of 120 V and 100 V, respectively.Moreover, the highest and lowest measured output-current ripple factors are 7.45% and 6.74%; these occurred at a utility-line rms voltage of 100 V and 120 V, respectively.

Figure 11
Figure 11 shows the measured output voltage and current waveforms, and the average values of Vo and Io are 60 V and 0.3 A, respectively.Table2presents the measured output voltage and current of the presented LED tube lamp driver under different input voltages.Figure12shows the calculated voltage and current ripple factors of the presented LED tube lamp driver under different input utility-line voltages.In addition, the output voltage (current) ripple factor is obtained by the peak-to-peak (pk-pk) level divided by the average value of output voltage (current).According to Figure12, the highest and lowest measured output-voltage ripple factors are 7.2% and 6.26%; these occurred at a utility-line rms voltage of 120 V and 100 V, respectively.Moreover, the highest and lowest measured output-current ripple factors are 7.45% and 6.74%; these occurred at a utility-line rms voltage of 100 V and 120 V, respectively.

Figure 11
Figure 11 shows the measured output voltage and current waveforms, and the average values of V o and I o are 60 V and 0.3 A, respectively.Table2presents the measured output voltage and current of the presented LED tube lamp driver under different input voltages.Figure12shows the calculated voltage and current ripple factors of the presented LED tube lamp driver under different input utility-line voltages.In addition, the output voltage (current) ripple factor is obtained by the peak-to-peak (pk-pk) level divided by the average value of output voltage (current).According to Figure12, the highest and lowest measured output-voltage ripple factors are 7.2% and 6.26%; these occurred at a utility-line rms voltage of 120 V and 100 V, respectively.Moreover, the highest and lowest measured output-current ripple factors are 7.45% and 6.74%; these occurred at a utility-line rms voltage of 100 V and 120 V, respectively.

Figure 11
Figure11shows the measured output voltage and current waveforms, and the average values of Vo and Io are 60 V and 0.3 A, respectively.Table2presents the measured output voltage and current of the presented LED tube lamp driver under different input voltages.Figure12shows the calculated voltage and current ripple factors of the presented LED tube lamp driver under different input utility-line voltages.In addition, the output voltage (current) ripple factor is obtained by the peak-to-peak (pk-pk) level divided by the average value of output voltage (current).According to Figure12, the highest and lowest measured output-voltage ripple factors are 7.2% and 6.26%; these occurred at a utility-line rms voltage of 120 V and 100 V, respectively.Moreover, the highest and lowest measured output-current ripple factors are 7.45% and 6.74%; these occurred at a utility-line rms voltage of 100 V and 120 V, respectively.

Figure 12 .
Figure 12.Calculated voltage and current ripple factors of the presented LED tube lamp driver under different input utility-line voltages.

Figure 12 .
Figure 12.Calculated voltage and current ripple factors of the presented LED tube lamp driver under different input utility-line voltages.

Figure 16 .
Figure 16.Measured efficiency of the presented LED tube lamp driver under different input utility-line voltages.

Figure 15 .
Figure 15.Measured power factor and current total-harmonic distortion (THD) of the presented LED tube lamp driver under different input utility-line voltages.

14 Figure 15 .
Figure 15.Measured power factor and current total-harmonic distortion (THD) of the presented LED tube lamp driver under different input utility-line voltages.

Figure 16 .
Figure 16.Measured efficiency of the presented LED tube lamp driver under different input utility-line voltages.

Figure 16 .
Figure 16.Measured efficiency of the presented LED tube lamp driver under different input utility-line voltages.

Table 1 .
Key components used in the presented led tube lamp driver.
Figure 7 presents the measured inductor current i LPFC1 .The measured switch voltage v DS2 and inductor current i Lr are shown in Figure With an fS of 55 kHz and a Cr of 82 nF, the resonant inductor Lr is computed as

Table 1 .
Key components used in the presented led tube lamp driver.
Figure 7 presents the measured inductor current iLPFC1.The measured switch voltage vDS2 and inductor current iLr are shown in Figure With an fS of 55 kHz and a Cr of 82 nF, the resonant inductor Lr is computed as

Table 1 .
Key components used in the presented led tube lamp driver.
Figure 7 presents the measured inductor current iLPFC1.The measured switch voltage vDS2 and inductor current iLr are shown in Figure

Table 2 .
Measured output voltage and current of the presented led tube lamp driver under different input voltages.

Table 2 .
Measured output voltage and current of the presented led tube lamp driver under different input voltages.

Table 3 .
Comparisons between the existing t8-type led tube lamp drivers and the proposed one.