A Single-Stage LED Tube Lamp Driver with Input-Current Shaping for Energy-Efficient Indoor Lighting Applications

Abstract

This study proposes a single-stage light-emitting diode (LED) tube lamp driver with input-current shaping for T8/T10-type fluorescent lamp replacements. The proposed AC-DC LED driver integrates a dual-boost converter with coupled inductors and a half-bridge series-resonant converter with a bridge rectifier into a single-stage power conversion topology. This paper presents the operational principles and design considerations for one T8-type 18 W-rated LED tube lamp with line input voltages ranging from 100 V rms to 120 V rms. Experimental results for the prototype driver show that the highest power factor (PF = 0.988), lowest input current total harmonic distortion (THD = 7.22%), and highest circuit efficiency (η = 92.42%) are obtained at an input voltage of 120 V. Hence, the proposed driver is feasible for use in energy-efficient indoor lighting applications.

I. INTRODUCTION

Fluorescent lamps are cost-effective gas-discharge lamps for general indoor lighting applications. As a result of the current issues in environmental protection, carbon reduction and energy savings have become a cause for great concern, and the search for energy-efficient alternatives for lighting applications has intensified at a global scale. The up-to-date development of solid-state lighting technology has gained traction because of the urgent need for efficient energy usage [1]-[5]. Light-emitting diodes (LEDs) are compact electronic devices that allow electricity to flow through them in one direction to produce a small amount of light. Tube lamps and bulbs for household usage include a large number of LEDs; thus, these fixtures produce bright light. LEDs offer numerous attractive features, such as their non-polluting property because of the absence of mercury as a component, high luminous efficacy, long lifetime, and significant energy savings brought about by their low power consumption [6]-[17]. Therefore, LEDs are beginning to replace traditional lighting sources used in households and other indoor lighting applications. As an illustrated example, Table I shows a comparison between a T8-type fluorescent lamp (China Electric FL40D-EX) and a T8-type LED tube lamp (EVERLIGHT FBW/T8/857/U/4ft) [18], [19]. The two lamps share almost the same color temperature and color-rendering index, but the LED tube lamp achieves better lighting efficiency, consumes less power, and offers longer lamp lifetime than its T8-type counterpart. Moreover, the LED tube lamp contains no mercury and does not require high ignition voltage. Therefore, energy-efficient LED tube lamps have become increasingly popular alternatives to fluorescent lamps for use in household and other indoor lighting applications, such as in public infrastructure, offices, classrooms, and parking decks [20]-[25]. Fig. 1 shows a typical two-stage driver for a T8-type LED tube lamp. This driver is composed of an AC–DC converter with power factor corrections (PFC) as the first stage (such as a boost converter) and a DC–DC converter (such as a buck converter) as the second stage for regulating the voltage/current of the LED lamp. The converter in each stage requires a separate control scheme, and the circuit efficiency is restricted because of the two-stage power conversion. A number of single-stage AC–DC drivers for T8-type LED tube lamps, which are used as alternatives to T8/T10 fluorescent lamps, have been introduced, with flyback converters, buck converters, and buck-boost converters serving as the main circuit topology of the drivers in [23], [24], and [25] and all featuring PFC. These single-stage versions offer cost-effectiveness and low component counts in comparison with their two-stage counterparts; however, their power switches do not include a soft-switching function, hence their limited efficiencies.

TABLE ICOMPARISON BETWEEN T8-TYPE FLUORESCENT AND LED TUBE LAMPS

Fig. 1.Typical two-stage driver for a T8-type LED tube lamp.

In response to these concerns, the present study proposes a single-stage AC–DC driver with input-current shaping and enhanced circuit efficiency for use in a T8-type LED tube lamp. Moreover, this study presents the theoretical analysis of the operating modes and the experimental results obtained from the prototype circuit of the proposed driver used to supply an 18 W-rated T8-type LED tube lamp. The paper is organized as follows. Section II describes and analyzes the proposed LED tube lamp driver. Section III presents the design considerations of the proposed LED tube lamp driver. Section IV describes the experimental results obtained from a prototype LED driver for an 18 W-rated T8-type LED tube lamp with input utility line voltages ranging from 100 V to 120 V. Finally, Section V provides relevant conclusions.

 

II. DESCRIPTION AND ANALYSIS OF THE PROPOSED LED TUBE LAMP DRIVER

Fig. 2 shows the proposed LED tube lamp driver, which combines a dual-boost converter with coupled inductors. Specifically, one boost converter contains a diode Db1, a coupled inductor LPFC1, a switch S1, the body diode of switch S2, and a DC-linked capacitor CDC; the other boost converter includes a diode Db2, a coupled inductor LPFC2, a switch S2, the body diode of switch S1, and a capacitor CDC. The figure also shows a half-bridge series-resonant converter with a bridge rectifier; it includes a DC-linked capacitor CDC, two switches S1 and S2, a resonant inductor Lr, a resonant capacitor Cr, a full-bridge rectifier D1–D4, and an output capacitor Co. These components are combined into a single-stage topology for a T8-type LED tube lamp. In addition, an LC filter (inductor Lf and capacitor Cf) is connected to the input utility line voltage [26].

Fig. 2.Proposed single-stage driver for a LED tube lamp.

To analyze the operations of the proposed driver for an LED lamp, the following assumptions are made.

The operating modes and theoretical waveforms of the proposed LED tube lamp driver operated during the positive half cycle of the input utility line voltage are shown in Figs. 3 and 4, respectively. The operations are analyzed in detail in the following sections.

Fig. 3.Operation modes of the proposed driver during the positive half cycle of input voltage vAC.

Fig. 4.Theoretical waveforms during the positive half cycle of input voltage vAC.

Mode 1 (t0 ≤ t < t1; in Fig. 3(a)): This mode begins when the voltage vDS1 of S1 decreases to zero. Thereafter, the body diode of switch S1 is forward-biased at time t0. The resonant capacitor Cr provides energy to the resonant inductor Lr, capacitors CDC and Co, and LED tube lamp through the body diodes D2 and D3 of S1. This mode ends when S1 shifts to the on state with zero-voltage switching (ZVS) at time t1.

Mode 2 (t1 ≤ t < t2; in Fig. 3(b)): This mode begins when S1 achieves ZVS turn-on at t1. The input voltage vAC provides energy to the coupled inductor LPFC1 through the diode Db1 and switch S1. The inductor current iLPFC1 linearly increases from zero and can be expressed as

where vAC-rms is the root-mean-square (rms) value of the input utility line voltage and fAC is the utility line frequency.

The resonant capacitor Cr still provides energy to the resonant inductor Lr, capacitors CDC and Co, and LED tube lamp through the switch S1 and diodes D2 and D3. This mode finishes when the current iLr decreases to zero at t2.

Mode 3 (t2 ≤ t < t3; in Fig. 3(c)): The voltage vAC still provides energy to the coupled inductor LPFC1 through the diode Db1 and switch S1. The DC bus capacitor CDC supplies energy to the inductor Lr, capacitors Cr and Co, and LED tube lamp through the switch S1 and diodes D1 and D4. At t3, the switch S1 shifts to the off state, and the inductor current reaches its peak value; this condition is defined as iLPFC1-pk(t), which is given by

where D and TS are the duty cycle and switching period of the power switch, respectively.

Mode 4 (t3 ≤ t < t4; in Fig. 3(d)): This mode starts when the power switch S1 is in the off state at t3. The utility line voltage vAC and coupled inductor LPFC1 supply energy to the drain-source capacitor of S1 through the diode Db1. The inductor current iLPFC1 linearly decreases from the peak level and can be given by

where VDC is the voltage of the DC-bus capacitor CDC.

The drain-source capacitor of S2 provides energy to the inductor Lr, capacitors Cr and Co, and LED tube lamp through the diodes D1 and D4. This mode ends when the drain-source voltage vDS2 of S2 decreases to zero at t4.

Mode 5 (t4 ≤ t < t5; in Fig. 3(e)): This mode starts when the voltage vDS2 of S2 decreases to zero and the body diode of switch S2 is forward-biased at time t4. The utility line voltage vAC and coupled inductor LPFC1 provide energy to CDC through the diode Db1 and body diode of switch S2. The inductor Lr provides energy to the capacitors Cr and Co and LED tube lamp through the diodes D1 and D4. At t5, the inductor current iLr decreases to zero, and the mode ends.

Mode 6 (t5 ≤ t < t6; in Fig. 3(f)): This mode begins when the switch S2 achieves ZVS turn-on at t5. The resonant inductor Lr provides energy to the capacitors Cr and Co and LED tube lamp through S2 and the diodes D1 and D4. At t6, the inductor current iLr decreases to zero, and the mode ends.

Mode 7 (t6 ≤ t < t7; in Fig. 3(g)): During this mode, the capacitor Cr provides energy to the inductor Lr, capacitor Co, and LED tube lamp through S2 and the diodes D2 and D3. The mode ends when the switch S2 shifts to the off state at t7.

Mode 8 (t7 ≤ t

Fig. 5 shows the circuit diagram for controlling the single-stage LED tube lamp driver. Utilizing a constant voltage/current controller (IC1 SEA05) to regulate the output voltage and current of the LED lamp, we determine the output lamp voltage Vo through the resistors Rvs1, VR1, and Rvs2, as well as the output lamp current through the resistor R1. The sensed output signal from pin 5 of the IC1 is fed into the high-voltage resonant controller (IC3 ST L6599) through a photo-coupler (IC2 PC817). Two gate-driving signals vGS1 and vGS2 are generated from pins 15 and 11 of the IC3, respectively, to regulate the output voltage and current of the LED tube lamp.

Fig. 5.Control circuit for the proposed LED tube lamp driver.

 

III. DESIGN CONSIDERATIONS FOR KEY COMPONENTS OF THE PROPOSED LED DRIVER

A. Design of Coupled Inductors LPFC1 and LPFC2

The design equation for the coupled inductor LPFC1 (LPFC2) is expressed as [26]

where η is the estimated circuit efficiency, Plamp is the rated power of the LED lamp, and fS is the switching frequency.

Fig. 6 shows the coupled inductors LPFC1 and LPFC2 versus the duty cycle D under different switching frequencies. With η of 0.9, vAC-rms of 110 V and Plamp of 18 W, fS of 50 kHz, and D of 0.5, the coupled inductors LPFC1 and LPFC2 are designed to be 1.5 mH.

Fig. 6.Coupled inductors LPFC1 and LPFC2 versus duty cycle D under different switching frequencies fS.

B. Design of Series Resonant Tank (Lr and Cr)

Fig. 7 depicts the equivalent circuit for designing the series resonant tank; Ro is the equivalent resistance of the T8-type LED tube lamp and can be written as Ro = Vo/Io. As shown in Fig. 7, the series resonant tank is composed of a resonant inductor Lr in a series connection with a resonant capacitor Cr. The resonant frequency fo can be expressed as

Fig. 7.Equivalent circuit for designing the series resonant tank.

The design considerations for the series resonant tank Lr and Cr are shown in the following.

(a) The estimated efficiency ηR of the bridge rectifier component is expressed as [27]

where VF and RF are the forward voltage drop and equivalent resistor of the diodes, respectively, and rC is the equivalent resistor of capacitor Co.

With rC of 50 mΩ, Ro of 200 Ω, VF of 1.5 V, and RF of 0.15 Ω (according to the datasheet of the utilized diode), the estimated efficiency ηR is given by

(b) The input resistor Ri of the bridge rectifier is expressed as

(c) The voltage gain MVR of the bridge rectifier is expressed as

(d) The total voltage gain MV of the half-bridge series resonant converter with a bridge rectifier is expressed as

(e) The voltage gain MVr of the series resonant component is expressed as

where MVS is the voltage gain of the half-bridge converter. With MVS of 0.45 (=√2/π), the voltage gain MVr is given as

(f) The loaded quality factor QL is expressed as [27]

where ηI is the estimated efficiency of the half-bridge series resonant converter with a bridge rectifier.

To obtain the 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 [27].

Therefore, the relationship between switching frequency fS and resonant frequency f0 is assumed as

With ηI of 0.99 and fs of 50 kHz, the quality factor QL is given as

(g) The input resistor R of the half-bridge series resonant converter with a bridge rectifier is expressed as

(h) The resonant capacitor Cr is expressed as and computed with

In addition, Cr is set to 82 nF.

(i) The resonant inductor Lr is expressed as and computed with

In addition, Lr is set to 2 mH.

 

IV. EXPERIMENTAL RESULTS FOR A PROTOTYPE DRIVER

A prototype driver was built and tested for an 18 W-rated T8-type LED tube lamp (EVERLIGHT FBW/T8/857/U/4ft), the rated voltage and current of which are 60 V and 0.3 A, respectively. The components utilized in the LED tube lamp driver are shown in Table II.

TABLE IIKEY COMPONENTS USED IN THE PROPOSED LED TUBE LAMP DRIVER

Fig. 8 shows the measured inductor currents iLPFC1 and iLPFC2. The measured switch voltage vDS2 and inductor current iLr are depicted in Fig. 9. The series resonant tank resembles an inductive load. Figs. 10 and 11 present the measured voltages (vDS1 and vDS2) and currents (iDS1 and iDS2) of the two power switches S1 and S2, respectively. ZVS is obviously achieved for these power switches, consequently boosting the circuit efficiency.

Fig. 8.Measured inductor currents iLPFC1 (1 A/div) and iLPFC2 (1 A/div); time scale: 5 ms/div.

Fig. 9.Measured voltage vDS2 (200 V/div) and inductor current iLr (0.5 A/div); time scale: 5 μs/div.

Fig. 10.Measured voltage vDS1 (200 V/div) and current iDS1 (0.5 A/div); time scale: 5 μs/div.

Fig. 11.Measured voltage vDS2 (200 V/div) and current iDS2 (0.5 A/div); time scale: 5 μs/div.

Fig. 12 shows the measured output voltage and current waveforms; the average values of Vo and Io are 60 V and 0.3 A, respectively. Table III presents the measured output voltage and current of the proposed LED tube lamp driver under different input voltages. In addition, the output voltage (current) ripple is obtained with the peak-to-peak (pk-pk) level divided by the average value of the output voltage (current). According to this table, the highest and lowest measured output voltage ripples are 7.29% and 5.93%, respectively; these ripples occurred at utility line rms voltages of 100 and 120 V, respectively. Moreover, the highest and lowest measured output current ripples are 9.5% and 8.48%, respectively; these ripples occurred at utility line rms voltages of 120 and 105 V, respectively. The measured input utility line voltage and current are shown in Fig. 13. Fig. 14 presents the measured current harmonics compared with the IEC 61000-3-2 Class C standards under input utility line voltages ranging from 100 V to 120 V. All the measured current harmonics meet the requirements. Fig. 15 shows the measured power factor (PF) and current total harmonic distortion (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 0.976 and 7.39%, respectively. Fig. 16 shows the measured efficiency of the proposed LED tube lamp driver under input utility line voltages from 100 V to 120 V. The highest and lowest measured efficiency levels are 92.42% and 90.98% at utility line rms voltages of 120 and 100 V, respectively.

Fig. 12.Measured output voltage Vo (20 V/div) and current Io (0.5 A/div); time scale: 2 ms/div.

TABLE IIIMEASURED OUTPUT VOLTAGE AND CURRENT OF THE PRESENTED LED TUBE LAMP DRIVER UNDER DIFFERENT INPUT VOLTAGES

Fig. 13.Measured input utility line voltage vAC (50 V/div) and current iAC (0.5 A/div); time scale: 5 ms/div.

Fig. 14.Measured input current harmonics compared with the IEC 61000-3-2 Class C standards.

Fig. 15.Measured PF and current THD of the proposed LED driver under different input utility line voltages.

Fig. 16.Measured efficiency under different input utility line voltages.

Table IV shows a comparison of the performance (including maximum PF, minimum current THD, and maximum efficiency) of the proposed driver and various LED tube lamp drivers. The first driver [23] features a flyback converter circuit topology, the second driver [24] features a buck converter circuit topology, and the third driver [25] features a buck-boost converter circuit topology. Two of the AC–DC LED drivers ([23] and [24]) operate with universal input voltages, whereas the other driver [25] and the proposed version operate with American utility line voltages. Table IV shows that the proposed single-stage LED tube lamp driver achieves ZVS on the power switches to enhance circuit efficiency in contrast to the three single-stage drivers.

TABLE IVCOMPARISON OF EXISTING SINGLE-STAGE T8-TYPE LED TUBE LAMP DRIVERS AND THE PROPOSED DRIVER

Fig. 17 shows a picture of the designed prototype of the proposed LED tube lamp driver. Fig. 18 presents the loss breakdown chart of the proposed LED tube lamp driver. The percentages of the conduction losses of the power switches (S1, S2), power diodes (Db1, Db2), and power diodes (D1, D2, D3, D4), as well as the other losses are 14.41%, 15.29%, 60.9%, and 9.4%, respectively. The dominant losses in the proposed driver with a soft-switching feature comprise the conduction losses of the power devices (including the power switches and power diodes), the percentages of which reach 90.6% of the total losses.

Fig. 17.Designed prototype of the proposed LED tube lamp driver.

Fig. 18.Loss breakdown chart of the proposed LED tube lamp driver.

 

V. CONCLUSIONS

This study proposed a single-stage LED tube lamp driver with PFC. This driver integrates a dual-boost converter with coupled inductors and a half-bridge series resonant converter with a bridge rectifier for energy-efficient indoor lighting applications. A prototype circuit was successfully built for an 18 W-rated T8-type LED tube lamp with utility line voltages ranging from 100 V to 120 V. The experimental results revealed high PF (>0.97), low THD (<8%), and high efficiency (>90%), which verify the functionality of the proposed LED driver.