An Isolated AC-DC LED Electronic Lighting Driver Circuit with Power Factor Correction

Abstract

Light-emitting diodes (LEDs) have gained widespread adoption as solid-state lighting sources due to their compact size, long operational lifetime, high brightness, and mechanical robustness. This paper presents the development and implementation of an isolated AC-DC LED electronic lighting driver circuit that integrates a modified flyback converter with a lossless snubber circuit, along with inherent power factor correction (PFC). The proposed design operates the transformer’s magnetizing inductor in the discontinuous conduction mode (DCM), thereby naturally achieving PFC without the need for complex control circuitry. Furthermore, the circuit is capable of recycling the energy stored in the transformer’s leakage inductance, improving overall efficiency. The input current harmonics are shown to comply with the IEC 61000-3-2 Class C standard. A 72 W (36 V/2 A) prototype has been constructed and tested under a 110 V AC input. Experimental results confirm the effectiveness of the proposed design, achieving a power factor of 0.9816, a total harmonic distortion (THD) of 12.094%, an output voltage ripple factor of 9.7%, and an output current ripple factor of 11.22%. These results validate the performance and practical viability of the proposed LED driver architecture.

1. Introduction

Lighting plays a fundamental role in human life, far exceeding basic visual needs. It influences physical health, enhances environmental aesthetics, supports economic productivity, and ensures safety in various environments. Therefore, the development and optimization of lighting sources remain a key area for further research and technological advancement. Lighting sources are indispensable in modern life, encompassing functional, psychological, economic, and environmental dimensions. Strategic design and implementation of lighting systems not only improve quality of life but also enhance safety, efficiency, and sustainability across various industries. As lighting technology continues to evolve, its social significance will grow increasingly important, underscoring the necessity for interdisciplinary research and innovation in this field. The benefits and impacts of lighting sources in our daily lives are as follows: (1) Human vision and visual comfort: The most immediate and essential function of lighting is to facilitate human vision. Adequate illumination allows for accurate visual perception, which is indispensable for daily activities, occupational tasks, and recreational engagement. Proper lighting reduces visual fatigue, enhances contrast sensitivity, and improves performance in both residential and professional environments. Inadequate or poorly designed lighting can lead to eye strain, decreased productivity, and increased incidence of errors and accidents. (2) Psychological and physiological impacts: Scientific studies have established that lighting conditions significantly affect human circadian rhythms, mood, and cognitive functioning. Exposure to appropriate lighting at specific times of day helps regulate melatonin production and promotes healthy sleep–wake cycles. Natural daylight and high-quality artificial lighting can improve alertness, reduce symptoms of depression, and enhance overall psychological well-being. Therefore, lighting design has become a crucial component in architectural and healthcare applications. (3) Safety and security: Lighting is a key factor in ensuring personal and public safety. In urban infrastructure, streetlights and traffic signals enhance visibility for pedestrians and drivers, thereby reducing the risk of accidents. In industrial and commercial settings, well-illuminated environments prevent workplace injuries and enable the safe operation of machinery. Emergency lighting systems are vital for facilitating evacuation during power outages or hazardous events. (4) Economic and industrial significance: Illumination directly influences economic activity by enabling extended operational hours and improving working conditions. In sectors such as manufacturing, retail, healthcare, and education, appropriate lighting increases efficiency and supports task-specific requirements. Moreover, the lighting industry itself constitutes a significant segment of the global economy, with substantial investments in research, innovation, and sustainable development. (5) Aesthetic and cultural value: Lighting contributes to the aesthetic quality of built environments, shaping perceptions of space, color, and texture. It is an essential element in interior and architectural design, as well as in cultural and artistic expression, such as theater, photography, and public installations. The ability to manipulate light color, intensity, and direction provides designers with a versatile tool for enhancing user experience and ambiance. (6) Environmental considerations: With growing concerns about energy consumption and environmental sustainability, lighting technologies have come under increased scrutiny. Traditional lighting sources often involve significant energy losses and the use of hazardous materials. The shift toward energy-efficient lighting, particularly light-emitting diodes (LEDs), has contributed to reductions in greenhouse gas emissions and resource consumption. Thus, lighting also plays a pivotal role in global sustainability efforts [1,2].

In recent years, the development of solid-state lighting technologies, particularly light-emitting diode (LED) lamps, has significantly transformed the lighting industry. A comprehensive comparison between traditional lighting sources and LED lighting, with a focus on their respective advantages and disadvantages in terms of energy efficiency, operational characteristics, environmental impact, and economic considerations, is addressed as follows. (1) Energy efficiency: Traditional lighting sources exhibit relatively low luminous efficacy, typically offering approximately 60–100 lm/W efficiency; however, they still fall short when compared to LED technology. In contrast, LED lamps demonstrate superior energy efficiency, often exceeding 100 lm/W and reaching up to 150 lm/W in high-performance applications. This improvement results in significant reductions in electricity consumption and operational costs over time. (2) Lifespan and maintenance: The operational lifespan of traditional lighting sources is limited and may achieve 6000 to 15,000 h of use. LEDs, on the other hand, offer an extended service life, commonly rated at 25,000 to 50,000 h or more. Consequently, the maintenance frequency and associated costs for LED systems are substantially reduced, particularly in large-scale or hard-to-access installations. (3) Thermal characteristics: One of the major drawbacks of traditional lighting is excessive heat generation. Traditional lighting sources convert a significant portion of electrical energy into thermal energy, which not only reduces efficiency but also increases the risk of thermal damage or fire. LED lamps operate at much lower temperatures, making them inherently safer and more energy-efficient. (4) Durability and reliability: Traditional lighting technologies often rely on fragile components such as filaments or glass tubes, which are susceptible to mechanical shock and vibration. LEDs, being solid-state devices, are inherently more robust and resistant to external impacts. This attribute enhances their reliability and makes them suitable for a wide range of indoor and outdoor applications. (5) Environmental and health considerations: Traditional lighting sources, such as fluorescent lamps, contain small amounts of mercury, a hazardous substance that poses environmental and health risks if improperly disposed of. Additionally, the higher energy consumption of traditional lighting contributes to increased greenhouse gas emissions. LEDs are free of toxic materials and, due to their high efficiency, help minimize environmental impact by reducing both energy use and carbon footprint. (6) Light quality and control: In contrast to traditional lighting sources, LEDs provide a wide range of correlated color temperatures (CCTs) and can achieve high color rendering index (CRI) values (>80, and up to 95 for premium products). Moreover, LED systems are compatible with advanced control features, including dimming, color tuning, and smart connectivity, although some models may require compatible dimmer circuits. (7) Economic considerations: While traditional lighting sources generally have a lower initial cost, their short lifespan and high energy consumption result in higher long-term operational expenses. LED lamps involve a higher upfront investment; however, the total cost of ownership is often lower due to savings in energy and maintenance. In summary, while traditional lighting sources offer certain benefits—such as high color fidelity and low initial costs—they are generally surpassed by LED lamps in terms of energy efficiency, longevity, safety, and environmental sustainability. The transition to LED lighting represents a significant advancement in modern illumination technology and supports global initiatives for energy conservation and sustainable development [3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19].

In power electronic systems, snubber circuits are essential for protecting switching devices from voltage spikes and reducing switching losses caused by parasitic inductances. Traditional snubber configurations, such as resistor–capacitor (RC) or resistor–capacitor–diode (RCD) networks, dissipate excess energy as heat, resulting in power loss and reduced efficiency. In contrast, lossless snubber circuits are designed to recover and recycle this energy, thereby enhancing overall system efficiency. A lossless snubber circuit redirects the energy stored in the parasitic elements during switching transitions back to the power source or to a storage component, such as a capacitor or inductor, without significant energy dissipation. These circuits are typically composed of passive components (inductors, capacitors, and diodes) and occasionally include active switches to control the energy recovery process. Advantages and features of the lossless snubber circuit are addressed as follows. (1) High efficiency: Lossless snubbers minimize power dissipation by recovering the switching energy, making them highly suitable for high-efficiency power converters. (2) Improved thermal management: By avoiding resistive dissipation, less heat is generated, which reduces thermal stress on components and simplifies the thermal design. (3) Reduced electromagnetic interference (EMI): Properly designed lossless snubber circuits can smooth voltage and current transitions, thereby reducing high-frequency EMI emissions. (4) Extended switch lifespan: By limiting voltage spikes and reducing turn-off losses, the electrical stress on switching devices is minimized, enhancing their reliability and lifespan. (5) Energy recycling capability: The inherent energy recovery mechanism contributes to power conservation, especially in systems where switching frequency and load dynamics vary significantly. (6) Scalability and adaptability: Lossless snubber designs can be adapted to various converter topologies, including flyback, forward, and resonant converters, offering flexible integration into modern power systems [20,21,22,23,24,25,26,27,28,29].

To address the need for efficient power conversion and improved input current quality, this paper proposes and implements a novel LED electronic lighting driver circuit featuring input current shaping capability. The proposed topology integrates a lossless snubber circuit with a flyback converter to realize an isolated, single-switch power conversion architecture, herein referred to as a modified flyback converter. Furthermore, the transformer’s magnetizing inductor within the proposed driver is designed to operate in discontinuous conduction mode (DCM), thereby inherently achieving power factor correction (PFC) without the need for additional circuitry. The original concept of the proposed circuit is described in [30], and this paper is an expanded version of [30] with improvements in content for applications with higher LED output power. The remainder of this paper is structured as follows. Section 2 provides a detailed description and analysis of the operational modes of the proposed isolated AC-DC LED electronic lighting driver circuit incorporating power factor correction. Section 3 discusses the key design considerations associated with the proposed driver architecture. In Section 4, experimental results obtained from a fabricated prototype are presented to validate the circuit’s performance. Finally, Section 5 concludes the paper with a summary of the findings.

2. Descriptions and Analysis of the Isolated AC-DC LED Electronic Lighting Driver Circuit with Power Factor Correction

Figure 1 shows the proposed AC-DC LED electronic lighting driver circuit with power factor correction, which consists of a lossless snubber circuit and a modified flyback converter as the main circuit, and the entire isolated AC-DC LED electronic lighting driver circuit topology includes a filter inductor L_f, a filter capacitor C_f, a full-wave rectifier (including four diodes D₁, D₂, D₃, and D₄), a power switch S₁, an inductor L_B, three diodes D₅, D₆ and D₇, a DC-linked capacitor C_DC, a transformer T₁ with a turn n_p in the primary-side and a turn n_s in the secondary-side, an output capacitor C_o and the LEDs.

Figure 2 shows the equivalent circuit of the isolated AC-DC LED electronic lighting driver circuit with power factor correction, obtained while analyzing the operational modes. In order to analyze the circuit operation of the proposed isolated AC-DC LED electronic lighting driver circuit with power factor correction, the following assumptions were made.

(a)

The input AC voltage source v_AC is connected to the filter inductor L_f and filter capacitor C_f and rectified by a full-bridge rectifier, and then the voltage presented on the input capacitor C_in is denoted as v_REC(t).

(b)

The magnetizing inductor L_m of the transformer T₁ is designed to operate in discontinuous conduction mode (DCM), and L_lk is the leakage inductance of the transformer T_1, respectively. In addition, the values of leakage inductors L_lk are much smaller than the magnetizing inductor L_m; therefore, the voltage drops of the leakage inductor L_lk can be neglected.

(c)

The intrinsic diode and the turn-on resistor of the power switch S₁ are neglected.

(d)

Neglect the on-state voltage drops and equivalent resistance of diodes D₅ and D₆ and output diode D₇.

(e)

The rest of the circuit elements are considered ideal.

Figure 3, Figure 4, Figure 5, Figure 6, Figure 7 and Figure 8 illustrate the operating modes and theoretic waveforms of the isolated AC-DC LED electronic lighting driver circuit with power factor correction, respectively, and each operation mode is analyzed and introduced in detail below.

Operation Mode 1 (t₀ ≤ t < t₁): Figure 3 represents the operation mode 1 of the isolated AC-DC LED electronic lighting driver circuit with power factor correction. At time t₀, the power switch S₁ is driven on and starts to enter operation mode 1. The full-wave rectified voltage v_REC(t) is supplied to the magnetizing inductor L_m and the leakage inductor L_lk via the power switch S₁; the magnetizing inductor current i_Lm and the leakage inductor current i_Llk show a linear rise; the DC-linked capacitor C_DC is supplied to the inductor L_B via the power switch S₁ and the diode D₅; and the inductor current i_LB shows a linear rise, and the output capacitor C_o provides energy to the LEDs. At time t₁, the inductor currents i_Lm and i_LB will reach their maximum values, and operation mode 1 ends when the power switch S₁ cuts off at time t₁.

Operational Mode 2 (t₁ ≤ t < t₂): Figure 4 represents the operation mode 2 of the isolated AC-DC LED electronic lighting driver circuit with power factor correction. At time t₁, the power switch S₁ cuts off and the diodes D₅ and D₆ are biased in the forward direction. The inductor L_B sends energy back to the full-wave rectified voltage v_REC(t) via diodes D₅ and D₆, and the inductor current i_LB decreases linearly. The magnetizing inductor L_m and the leakage inductor L_lk are supplied with energy via diode D₆ to the DC-linked capacitor C_DC, and the magnetizing inductor current i_Lm and the leakage inductor current i_Llk decrease linearly. In addition, the output diode D₇ on the secondary side of the transformer is forward biased, so the magnetizing inductor L_m provides energy to the LEDs through the diode D₇, and operation mode 2 ends when the inductor L_B finishes releasing energy at time t₂.

Operational Mode 3 (t₂ ≤ t < t₃): Figure 5 represents operation mode 3 of the isolated AC-DC LED electronic lighting driver circuit with power factor correction. In this mode, the magnetizing inductor L_m and the leakage inductor L_lk continue to provide energy to the DC-linked capacitor C_DC via diode D₆ and continue to provide energy to the LEDs via diode D₇, and the magnetizing inductor current i_Lm and the leakage inductor current i_Llk continue to decrease linearly. When the leakage inductor L_lk finishes releasing energy at time t₃, operation mode 3 ends.

Operational Mode 4 (t₃ ≤ t < t₄): Figure 6 represents the operation mode 4 of the isolated AC-DC LED electronic lighting driver circuit with power factor correction. In this mode, the magnetizing inductor L_m continues to provide energy to the LEDs via diode D₇, and the magnetizing inductor current i_Lm continues to decrease linearly. When the magnetizing inductor L_m finishes releasing energy at time t₄, operation mode 4 ends.

Operational Mode 5 (t₄ ≤ t < t₅): Figure 7 represents operation mode 5 of the isolated AC-DC LED electronic lighting driver circuit with power factor correction. In this mode, energy is supplied to the LEDs by the output capacitor C_o. When the power switch S₁ is turned on again at time t₅, operation mode 5 ends and the circuit reverts back to operation mode 1.

3. Design Equations and Considerations of Key Components in the Proposed AC-DC LED Electronic Lighting Driver Circuit

3.1. Design Formula of the Magnetizing Inductor L_M

The utility-line voltage v_AC(t) can be expressed by

$$v_{AC}(t)=\sqrt{2}{v}_{AC-rms}\sin (2\pi f_{AC}t)$$

(1)

where v_AC-rms and f_AC are the rms value and the frequency of the utility-line voltage.

The voltage occurred on the input capacitor C_in, which is denoted as v_REC(t), can be given by

$$v_{REC}(t)=\sqrt{2}{v}_{AC-rms}\left|\sin (2\pi f_{AC}t)\right|$$

(2)

The peak value of the magnetizing inductor current i_LM in the transformer T₁, which is denoted as i_LM,peak(t), can be represented by

$$i_{LM,peak}(t)={\displaystyle \frac{\sqrt{2}{v}_{AC-rms}\left|\sin (2\pi f_{AC}t)\right|Duty{T}_S}{L_M}}$$

(3)

where Duty is the duty cycle of the power switch.

The input utility-line current i_AC is equal to the average level of i_LM,peak(t) during one switching period and can be expressed as

$$i_{AC}(t)={\displaystyle \frac{1}{T_{AC}}}{\displaystyle \underset{0}{\overset{T_{AC}}{\int }}{i}_{LM,peak}(t)dt}={\displaystyle \frac{\sqrt{2}{v}_{AC-rms}Dut{y}^2{T}_S}{2L_M}}\sin (2\pi f_{AC}t)$$

(4)

where T_AC is the utility-line period.

The average input power of the utility line, P_IN, is determined by multiplying the instantaneous utility line voltage, v_AC(t), by the instantaneous line current, i_AC(t), and subsequently averaging the product over one complete cycle, as expressed by the following equation.

$$P_{IN}={\displaystyle \frac{1}{T_{AC}}}{\displaystyle \underset{0}{\overset{T_{AC}}{\int }}{v}_{AC}(t)i_{AC}(t)dt}={\displaystyle \frac{{v_{AC-rms}}^{2}Dut{y}^2{T}_S}{2L_M}}$$

(5)

The rated output power of the LEDs, P_O, is related to the input power through the estimated efficiency of the driver circuit, η, according to the following relationship.

$$P_O=\eta P_{IN}={\displaystyle \frac{\eta {v_{AC-rms}}^{2}Dut{y}^2{T}_S}{2L_M}}$$

(6)

By rearranging this Expression (6), the design formula for the magnetizing inductance, L_M, can be derived as follows:

$$L_M={\displaystyle \frac{\eta {v_{AC-rms}}^{2}Dut{y}^2{T}_S}{2P_O}}$$

(7)

With a v_AC-rms of 110 V, a P_O of 72 W, an η of 0.8, a Duty of 0.25 and a switching period T_S of 1/(40 kHz), the inductances of the magnetizing inductor L_M are calculated as

$$L_M={\displaystyle \frac{\eta {v_{AC-rms}}^{2}Dut{y}^2{T}_S}{2P_O}}={\displaystyle \frac{0.8\cdot {110}^2\cdot {0.25}^2}{2\cdot 72\cdot \mathrm{40,000}}}=105.03 \mu H$$

In order to operate the magnetizing inductor current in discontinuous continuous mode, the magnetizing inductor L_M is selected to be 79 μH when the prototype driver circuit was realized.

3.2. Design Consideration of the Turns Ratio n in the Transformer T₁

Based on the volt-second balance theorem, the voltage across the magnetizing inductor L_M during the switch’s turn-on time is equal to the voltage across L_M during the switch’s turn-off time. This relationship can be expressed using the following formula:

$$v_{REC-\max }\cdot Duty\cdot T_S={\displaystyle \frac{n_p}{n_s}}\cdot V_O\cdot \left(1-Duty\right)\cdot T_S$$

(8)

where v_REC-max is the maximum value of the voltage v_REC(t); T_S is the switching period.

By organizing Equation (8), the turns ratio n in the transformer T₁ can be expressed by

$$n={\displaystyle \frac{n_p}{n_s}}={\displaystyle \frac{v_{REC-\max }}{V_O}}\cdot {\displaystyle \frac{Duty}{1-Duty}}$$

(9)

In accordance with Equation (9), Figure 9 demonstrates the correlation between the turns ratio n and the duty cycle Duty for various output voltage V_O. In addition, with an output voltage V_O of 36 V, a v_REC-max of 155 V, and a duty cycle Duty of 0.25, the turns ratio n is selected as 1.4 when implementing the prototype of the LED electronic lighting driver circuit.

3.3. Design Guideline of the LC Non-Dissipative Snubber Circuit

The main function of the LC non-dissipative snubber circuit is to absorb and recover the energy of high voltage spikes caused by the leakage inductance of the transformer, reducing the voltage stress on the power switching elements. When designing the capacitance C_DC of a non-dissipative snubber, it is necessary to consider that it is sufficient to temporarily absorb the energy of the leakage inductance L_lk, so as not to oversurge the spike voltage of the power switch. The energy of the capacitance C_DC can be calculated by the energy conservation theorem as follows:

$$E_{CDC}={\displaystyle \frac{L_{lk}\cdot {I_{peak}}^2}{2}}$$

(10)

where I_peak is the peak value of the switch current.

The energy in the above equation will be temporarily stored in the capacitor C_DC, so the magnitude of the voltage change ΔV_DC on the capacitor C_DC can be expressed as follows.

$$\Delta V_{DC}={\displaystyle \frac{E_{CDC}}{\frac{1}{2}{C}_{DC}\cdot {V_{DC}}^2}}={\displaystyle \frac{L_{lk}\cdot {I_{peak}}^2}{C_{DC}\cdot {V_{DC}}^2}}$$

(11)

Rearranging Equation (11), the equation for calculating the capacitance C_DC can be expressed as follows.

$$C_{DC}\ge {\displaystyle \frac{L_{lk}\cdot {I_{peak}}^2}{{V_{DC}}^2\cdot \left(\frac{\Delta V_{DC}}{V_{DC}}\right)}}$$

(12)

With a V_DC of 100 V, a ΔV_DC of 1 V, a L_lk of 4 μH, and a I_peak of 10 A, the minimum value of the capacitance C_DC is calculated as

$$C_{DC}\ge {\displaystyle \frac{L_{lk}\cdot {I_{peak}}^2}{{V_{DC}}^2\cdot \left(\frac{\Delta V_{DC}}{V_{DC}}\right)}}={\displaystyle \frac{4\mu \cdot {10}^2}{{100}^2\cdot \left(0.01\right)}}=4 \mu F$$

In addition, the capacitor C_DC was selected to be 47 μF when the prototype of the LED electronic lighting driver circuit was realized. As indicated by Equation (12), the voltage ripple across the capacitor C_DC is inversely related to their capacitance. A capacitance value exceeding the calculated minimum is deliberately selected to further suppress voltage ripple. Moreover, capacitors with slightly larger capacitance values typically exhibit negligible differences in physical size when their voltage ratings are identical, making such a design choice both electrically and mechanically practical.

When designing the inductance L_B of a non-dissipative snubber, it is important to consider that the energy stored in the capacitor C_DC can be transferred back to the main circuit or to the power supply. Therefore, the inductance L_B should be designed so that it is in approximate resonance with the capacitor C_DC so that the energy can be transferred back and forth. The formula for the resonant frequency f_r can be expressed as:

$$f_r={\displaystyle \frac{1}{2\pi \sqrt{L_B{C}_{DC}}}}$$

(13)

Usually, the design objective is to make the resonant frequency, f_r, is different from the switching frequency, so that the energy transfer procedure of the non-dissipative snubber will not interfere with the switching frequency of the main circuit. The design equation of inductive L_B is as follows:

$$L_B={\displaystyle \frac{1}{{\left(2\pi f_r\right)}^2{C}_{DC}}}$$

(14)

With a resonant frequency f_r of 2 kHz and a C_DC of 47 μF, the turns ratio n is calculated as

$$L_B={\displaystyle \frac{1}{{\left(2\pi f_r\right)}^2{C}_{DC}}}={\displaystyle \frac{1}{{\left(2\pi \cdot 2000\right)}^2\cdot 47\mu }}=134.74\mu H$$

To enable power factor correction (PFC) in the driver circuit, the inductor L_B was designed to operate in discontinuous conduction mode (DCM). For the implementation of the prototype LED electronic lighting driver circuit, L_B was selected with a value of 115 μH. This design choice ensures proper PFC operation while maintaining the desired performance characteristics of the driver.

4. Experimental Results Obtained from the Implemented Prototype of the Isolated AC-DC LED Electronic Lighting Driver Circuit

A prototype isolated AC-DC LED electronic lighting driver circuit applied to an AC input voltage of 110 V root-mean-square (rms) value has been successfully implemented and tested for powering a 72 W-rated LEDs with an output rated voltage of 36 V and an output rated current of 2 A.

Table 1. Specifications of the proposed isolated AC-DC LED electronic lighting driver circuit with power factor correction.

Parameter	Value
AC Input Voltage Source vAC	110 V
Rated Output Voltage VO	36 V
Rated Output Current IO	2 A
Rated Output Power PO	72 W

and

Table 2. Key components used in the proposed isolated AC-DC LED electronic lighting driver circuit with power factor correction.

Component	Value
Filter Inductor LF	3 mH
Filter Capacitor CF	2 μF
Full-Wave Rectifier (D1, D2, D3, D4)	KBPC1006
Input Capacitor Cin	220 nF/400 V
Power Switches S1	STP20NM60
Inductor LB	115 μH
DC-linked Capacitor CDC	47 μF/250 V
Diodes D5, D6, D7	MUR460
Transformer T1
Magnetized Inductor LM	79 μH
Leakage Inductor Llk	4 μH
Turns Ratio nP:nS	10:7
Output Capacitor Co	100 μF/250 V
PWM Control IC	TL494

show the specifications and the key components used in the proposed isolated AC-DC LED electronic lighting driver circuit with power factor correction, respectively. Considering the variability of LED parameters in practical applications, a prototype of the proposed LED electronic lighting driver circuit was designed, implemented, and experimentally evaluated. The circuit employs a PWM control IC (TL494) to regulate both the voltage and current of the LED load, thereby ensuring operation at their respective nominal values.

Figure 10 illustrates the experimentally measured gate-driving signal V_GS of the power switch. The switching frequency and duty cycle were set to 40 kHz and 0.25, respectively. Figure 11 presents the corresponding measured waveforms of the switch voltage V_DS and switch current I_DS. As illustrated in Figure 11, a substantial voltage is observed across (V_DS) during the conduction period of the MOSFET. The MOSFET employed in the prototype driver circuit (STP20NM60), which is commonly available in our laboratory, exhibits a channel resistance (R_DSon) of 0.29 Ω. Consequently, considerable conduction losses occur in the device, leading to a reduction in overall circuit efficiency. To enhance conversion efficiency, future work may consider replacing the existing MOSFET with one possessing a lower (R_DSon), thereby mitigating conduction losses and improving the performance of the LED driver circuit. Figure 12 depicts the measured currents of the magnetizing inductor (i_Lm) and the secondary inductor (i_LB), both operating in discontinuous conduction mode (DCM). In addition, both inductor currents exhibit an extended interval of discontinuity. This behavior arises because the experimental waveforms illustrated in Figure 12 were obtained at an operating point significantly distant from the peak value of the input voltage (i.e., at 90 degrees). Figure 13 illustrates the measured output voltage V_O and output current I_O, with corresponding average values of 36.2 V and 2.0909 A. The peak-to-peak variations in the output voltage and current are observed to be 3.5114 V and 0.2346 A, respectively. Based on these measurements, the ripple factors—defined as the ratio of the peak-to-peak value to the average value—are calculated to be 9.7% for the output voltage and 11.22% for the output current.

Figure 14 presents the input utility-line voltage (v_AC) and input current (i_AC). It can be observed that the input current waveform closely follows the voltage waveform, thereby demonstrating the power factor correction (PFC) capability of the proposed isolated LED electronic lighting driver circuit.

Table 3. Measured harmonic components of the input current in the proposed isolated AC-DC LED electronic lighting driver circuit with power factor correction compared with the IEC 61000-3-2 class C standard values.

Order of Harmonic	IEC61000-3-2 Class C Standard Value	Measured Value
2nd	2	0.8469
3rd	27	10.541
5th	10	5.6463
7th	7	1.5166
9th	5	0.4146
11th	3	1.0449
13th	3	0.2885
15th	3	0.5506
17th	3	0.1599
19th	3	0.2186
21th	3	0.3318
23th	3	0.1474
25th	3	0.148
27th	3	0.3089
29th	3	0.2176
31th	3	0.1173
33th	3	0.2272
35th	3	0.1599
37th	3	0.0954
39th	3	0.1418

summarizes the harmonic components of the input current, obtained from measurements conducted with a power analyzer under a 110 V AC input condition. These measured values are compared with the IEC 61000-3-2 Class C standard limits [31]. The proposed driver circuit achieves a power factor of 0.9816 and a total harmonic distortion (THD) of 12.094%. Additionally, the overall conversion efficiency of the prototype LED driver was measured to be 82.3%.

Figure 15 shows a photograph of the clear top-view schematic of the prototype AC-DC electronic lighting driver circuit. Figure 16 presents a photograph of the prototype AC-DC electronic lighting driver circuit with power factor correction used to power LEDs applied to an AC input voltage source with a value of 110 V rms. In addition, the input AC current harmonics, power factor, and total harmonic distortion of the prototype electronic lighting driver circuit were tested and measured at input voltages ranging from 100 V to 120 V. Figure 17 presents the measured values of input AC current harmonics at each input AC voltage and their comparison with the IEC 61000-3-2 Class C standard. Figure 18 shows the power factor and total harmonic distortion of current measured for the prototype electronic lighting driver circuit at different input AC voltages.

Figure 19 illustrates the detailed power loss distribution of the prototype isolated LED electronic driver circuit incorporating power factor correction, thereby serving as empirical support for the efficiency metrics presented in this study. As shown, the individual contributions to the overall power loss by critical circuit components are quantified as follows: the power switch S₁ accounts for 12% of the total losses, diode D₅ contributes 6%, while diodes D₆ and D₇ are responsible for 5% and 17%, respectively. The remaining 60% of the total power loss is attributed to various other circuit elements and parasitic phenomena. This comprehensive breakdown offers valuable insight into the primary sources of inefficiency within the driver architecture and identifies key areas where future design improvements may be directed to enhance overall performance.

Table 4. Comparisons between the existing AC-DC LED electronic lighting driver circuits in [32,33] and the proposed one.

Item	Existing AC-DC LED Electronic Lighting Driver Circuit in Reference [32]	Existing AC-DC LED Electronic Lighting Driver Circuit in Reference [33]	Proposed AC-DC LED Electronic Lighting Driver Circuit
Circuit Topology	Integration of a modified stacked dual boost converter and a half-bridge LLC resonant converter	Inversed buck-boost converter with a lossless snubber	Modified flyback converter with a lossless snubber
Input AC Voltage	110 V	110 V	110 V
Output Rated Power	100 W (36 V/2.77 A)	18 W (60 V/0.3 A)	72 W (36 V/2 A)
Number of Required Switches	2	1	1
Number of Required Capacitors	6	4	4
Number of Required Magnetic Elements	4	3	3
Number of Required Diodes	6	7	7
Measured Circuit Efficiency	>89%	>82%	>82%
Measured Power Factor	0.9879	0.9737	0.9816
Measured Current THD	5.7951%	18.422%	12.094%

provides a comparative analysis of the proposed AC-DC LED driver circuit against two previously reported designs. The first reference [32] describes a 100 W (36 V/2.77 A) driver comprising a modified stacked dual-boost converter integrated with a half-bridge LLC resonant converter, operating from a 110 V AC input. The second design [33] employs an inverted buck-boost converter with a lossless snubber, delivering 18 W (60 V/0.3 A) from the same input voltage. In contrast, the proposed driver circuit utilizes a modified flyback converter integrated with a lossless snubber to achieve an output power of 72 W (36 V/2 A).

Compared to the topology in [32], the proposed design reduces component count by eliminating one power switch, two power diodes, and one magnetic component, thereby offering a more compact and potentially cost-effective solution. However, the circuit in [32] demonstrates superior efficiency due to the implementation of soft-switching techniques and exhibits lower total harmonic distortion (THD) in the input current, as well as better current quality.

In comparison with the design in [33], the proposed circuit requires an equivalent number of components, while achieving a measured efficiency above 82%, similar to both referenced designs. Notably, the proposed driver achieves a higher power factor than the topology in [33], along with a reduced input current THD, signifying enhanced power quality performance.

5. Conclusions

This study presents the design and implementation of an isolated AC-DC LED electronic lighting driver circuit with integrated power factor correction, intended for operation from an AC input voltage source. The proposed topology is based on a modified flyback converter combined with a lossless snubber circuit, which effectively recovers the leakage inductance energy, thereby improving overall efficiency. A 72 W-rated prototype was developed to drive LED loads with an output voltage of 36 V and output current of 2 A under a 110 V AC input condition. Experimental validation confirms that the proposed driver achieves a high-power factor exceeding 0.98 and a low total harmonic distortion (THD) of the input current below 13%. Moreover, all measured input current harmonics comply with the IEC 61000-3-2 Class C standard, demonstrating the suitability of the proposed design for practical and regulatory-compliant LED lighting applications.

In summary, the implemented prototype driver circuit, which integrates a modified flyback converter with a lossless snubber and inherent PFC capability, achieves an overall efficiency of 82.3%. While this efficiency is somewhat lower than that reported for state-of-the-art LED driver technologies—particularly those employing soft-switching strategies—the proposed design nonetheless demonstrates significant advantages. By minimizing the component count, the circuit attains a more compact structure and offers the potential for reduced manufacturing costs. These characteristics highlight the practical relevance of the proposed approach and suggest its suitability for applications where cost-effectiveness and compactness are prioritized over maximum efficiency. Future work will focus on further enhancing the efficiency of the design while preserving its structural simplicity and economic feasibility.

Additionally, the implementation of dimming functionality in the proposed isolated AC-DC LED electronic driver circuit represents another potential direction for future work. This functionality can be achieved by incorporating an additional power switch in series with the LED load. By employing pulse-width modulation (PWM) control, the dimming operation is facilitated through the adjustment of the duty cycle of the supplementary switch. This approach enables modulation of the average current supplied to the LEDs, thereby achieving effective and precise brightness control.