A Single-Stage Electronic Lighting Driver Circuit Utilizing SiC Schottky Diodes for Supplying a Deep Ultraviolet LED Disinfection and Sterilization Lamp

Abstract

Recently, a new type of lighting source, deep ultraviolet light-emitting diode (LED), has appeared in the markets of space purification and surface sterilization. In this paper, a new type of electronic lighting driver for supplying a deep-ultraviolet LED sterilization lamp is proposed and developed. The main circuit combines a buck converter and a flyback converter into a single-stage single-switch buck-flyback AC-DC power converter with power factor correction. In addition, the proposed electronic lighting driver leverages a wide bandgap SiC Schottky diode as the output diode to lower the power diode losses and recycles the energy stored in the leakage inductance of the transformer in order to improve the circuit efficiency. The magnetizing inductor inside the presented AC-DC power converter is designed to operate in discontinuous conduction mode (DCM), which naturally enables power factor correction (PFC). A single-stage prototype driver with a power rating of 3.6 W (90 V/40 mA) was developed and implemented for providing a deep ultraviolet LED disinfection and sterilization lamp. Experimental results show that the measured power factor (PF) is greater than 0.9 and the measured total harmonic distortion (THD) of the input current is less than 18% at an input utility voltage of 110 V. Furthermore, the measured output voltage ripple factor is less than 1% and the output current ripple factor is less than 4%. In addition, the proposed single-stage electronic lighting driver for supplying a deep ultraviolet LED disinfection and sterilization lamp achieves high circuit efficiency (greater than 90%), low circuit component count, and low circuit cost.

1. Introduction

Microorganisms such as bacteria, viruses, cysts and molds use germination or spore production to reproduce. When microorganisms are irradiated or exposed to disinfecting and sterilizing lamps, the light penetrates through the cell walls and destroys their DNA, changing their DNA so they become harmless and incapable of reproducing, or even die, thus achieving the effect of disinfecting and sterilizing. Sterilization and disinfection lamps are used in a wide range of applications in a variety of sectors, including healthcare facilities, the food and beverage industry, public spaces and transportation, commercial and office buildings, residential buildings, hospitality, educational institutions, retail and grocery stores, water treatment and agriculture. These diverse applications highlight the versatility and effectiveness of disinfecting and sterilizing lamps in promoting health and safety in different environments [1,2,3,4]. The traditional light source for sterilization and disinfection is the ultraviolet (UV) mercury lamp, which has the advantages of low price and high luminous power and is commonly used in large places such as hospitals, factories, restaurants and schools. However, the disadvantages of UV mercury lamps are long warm-up time, short lamp life, and that the mercury content in the lamps does not meet environmental requirements. UV light is invisible to the human eye and has a wavelength of 100 to 400 nanometers. Depending on the wavelength, UV can be subdivided into three types: long-wave UV-A (wavelengths of 320–400 nm), medium-wave UV-B (wavelengths of 280–320 nm) and short-wave UV-C (wavelengths of 100–280 nm). Short-wave UV-C, which can also be referred to as deep ultraviolet, has disinfecting and germicidal properties. The use of short-wave ultraviolet UV-C or deep ultraviolet light destroys the DNA or RNA molecular structure of microbial cells, thereby preventing cell growth or regeneration, and ultimately achieving the effect of disinfection and sterilization. Deep UV LEDs are characterized by environmental protection and energy saving, long life, no warm-up time, no mercury, and miniaturization of light source. Traditional UV mercury lamps have been gradually replaced by deep UV LEDs, which have become a new light source for space purification and surface sterilization markets such as homes, schools, hospitals, office buildings, supermarkets or department stores. In addition, deep ultraviolet disinfection and sterilization lamps can easily kill bacteria, but due to the low penetrating power of deep ultraviolet disinfection and sterilization lamps, they can be affected by dust particles; if the cells damaged by deep ultraviolet disinfection and sterilization lamps are not completely destroyed, the cells are still able to be repaired and revitalized. Therefore, it is important to provide the appropriate distance and sufficient irradiation time and intensity of the deep ultraviolet disinfection and sterilization lamp to the disinfected objects in order to achieve a good sterilization effect [5,6,7,8].

Figure 1 shows the two-stage circuit topology of an existing electronic lighting driver for supplying deep ultraviolet LED sterilization and disinfection lamps. The first stage is an AC-DC power converter with power factor correction (PFC), and the second stage is a DC-DC converter and delivers the required DC power to the deep-UV LED sterilization lamp [8]. Two-stage electronic lighting driver circuits that can be applied to deep ultraviolet light-emitting diode (LED) sterilization lamps require separate controllers for both the front and rear stages, making the circuits more complex and requiring a larger number of circuit components. In order to reduce the number of power switches and circuit components and to improve the overall efficiency of the conventional two-stage version of the circuit, the literature [9,10,11,12,13,14,15,16,17,18,19,20] has developed a number of single-stage, single-switch LED driver circuits that integrate an AC-DC power converter and a DC-DC power converter suitable for powering deep ultraviolet LED sterilization and disinfection lamps.

As the environmental issues derived from global warming and carbon emissions have become more and more serious in recent years, human beings have taken energy saving, carbon reduction, and love for the earth as the common primary development direction. Thus, fossil fuels must be gradually reduced and rapidly introduced into green energy and power saving applications, and, therefore, high energy efficiency and low energy consumption are also gradually adopted as the goal in daily life products. In the Paris Agreement of the United Nations Conference on Climate Change, it is declared that the global warming rate must be kept within 2 °C. Based on the current economic development trend, even if the warming is kept within 2 °C in 2050, CO₂ emissions will still increase by 21%, and up to 50% more electricity will have to be generated to cope with and provide for various human activities. Therefore, it is increasingly important to significantly upgrade and improve existing energy sources. The largest raw material for semiconductors is the production of first-generation silicon (Si) wafers. However, the physical properties of this material have reached their limits in existing Si-based products and it is no longer possible to increase power, reduce heat loss and increase speed. As a result, there is a need to evolve to other materials that can better utilize the efficiency of electron transfer and low energy consumption, and it is in this context that the third-generation wide-bandgap semiconductors that are currently hotly debated in the marketplace, namely, silicon carbide (SiC) and gallium nitride (GaN), which are characterized by high energy efficiency and low energy consumption, have come into being. In addition, power devices made of wide-gap semiconductor materials can operate at higher voltages, generate more power, and have lower energy losses, while being significantly smaller than power devices made of silicon semiconductor materials. Silicon carbide (SiC) is a compound semiconductor material consisting of silicon (Si) and carbon (C). SiC has a lower resistance of the drift layer than Si, does not require conduction modulation, has an energy gap about 3-times wider than that of Si, and has an insulation breaking field strength about 10-times higher than that of Si. Compared to the high-voltage Si-PN diodes and high-speed Si-Fast Recovery diodes, SiC Schottky diodes made of wide-gap semiconductor materials have excellent high-speed and high-voltage characteristics. Since the reverse recovery time of SiC Schottky diodes is extremely short, the energy lost during reverse recovery can be greatly reduced, which is suitable for applications with high switching frequency, and is conducive to the miniaturization of the overall circuit as well as the improvement of power density [21,22]. Supplementary notes on the long-term reliability and potential degradation of silicon carbide Schottky diodes under thermal and electrical stresses are given below. According to the literature [21], silicon carbide Schottky diodes do not have minority carrier injection and their recovery time does not increase with temperature compared to conventional silicon diodes. In addition, SiC Schottky diodes are majority carrier devices and therefore the reverse current is smaller and temperature independent. In addition, compared to silicon diodes, SiC Schottky diodes have the advantage of faster recovery, which reduces switching losses and noise, and lower forward voltage, which reduces conduction losses. Furthermore, the literature [22] mentions the long-term reliability of SiC Schottky diodes with respect to dV/dt failure and dI/dt failure. Furthermore, in silicon diodes, if dI/dt is large, a pattern of increased recovery current (Irr) occurs, which can damage the device through current concentration. In contrast, since the recovery current in SiC Schottky diodes is very small, it can be assumed that such a pattern is unlikely to occur.

To address the above issues, a novel electronic lighting driver for providing a deep ultraviolet LED disinfection and sterilization lamp is proposed and developed in this paper, which is an extension and further improvement of the literature [20]. The main circuit combines a buck converter and a flyback converter into a single-stage single-switch buck-flyback AC-DC power converter with input-current shaping. In addition, the proposed driver recycles the energy stored in the leakage inductance of the transformer and exploits a wide bandgap silicon carbide Schottky diode as the output diode to enhance the circuit efficiency.

This paper is organized and introduced as follows. Section 2 describes and analyzes the mode of operation of a single-stage electronic lighting driver circuit utilizing a SiC Schottky diode to supply a deep ultraviolet LED disinfection and sterilization lamp, and provides design guidelines for some circuit parameters. Section 3 shows the experimental results of a prototype electronic lighting driver circuit utilizing a SiC Schottky diode to supply a deep ultraviolet LED sterilization and disinfection lamp. Finally, some conclusions are given in Section 4.

2. Descriptions and Analysis of Operational Modes in the Proposed Single-Stage Electronic Lighting Driver Circuit Utilizing SiC Schottky Diodes for Supplying a Deep Ultraviolet LED Disinfection and Sterilization Lamp

The electronic lighting driver with PFC for powering a deep ultraviolet LED disinfection and sterilization lamp developed in this paper is shown in Figure 2, which integrates a buck converter and a flyback converter into a single-stage AC-DC power conversion and includes a filter inductor L_F, a filter capacitor C_F, a full-bridge rectifier (including D₁, D₂, D₃ and D₄), a power switch S_B, two diodes D_B and D_F, a transformer T_R with a magnetizing inductor L_M and a leakage inductor L_lk, two output capacitors C_O1 and C_O2, and the deep ultraviolet LED disinfection and sterilization lamp. By designing the magnetizing inductor L_M in the proposed electronic lighting driver circuit to operate in discontinuous conduction mode (DCM), PFC can be realized naturally. In addition, the stored energy in the leakage inductance L_lk of the transformer T_R in the proposed electronic lighting driver circuit can be recovered and the circuit efficiency can be enhanced by exploiting a wide-bandgap SiC Schottky diode as an output diode.

Figure 3 is the equivalent diagram of the single-stage electronic lighting driver circuit utilizing SiC Schottky diodes for supplying a deep ultraviolet LED disinfection and sterilization lamp developed in this paper with the power factor correction function. Theoretical waveforms of the proposed single-stage electronic lighting driver utilizing SiC Schottky didoes for supplying a deep ultraviolet LED disinfection and sterilization lamp are shown in Figure 4. When analyzing the proposed single-stage electronic lighting driver circuit for the deep ultraviolet LED disinfection and sterilization lamp, assumptions are made during descriptions and explanations of the operation mode in the presented driver circuit and are shown as follows:

(a)

The equivalent voltage source of the input utility-line voltage after passing through the full-wave rectifier circuit is denoted by V_REC. Since the switching frequency f_s is much larger than the line frequency f_AC, the rectified voltage V_REC can be regarded as a constant value during one switching cycle in the circuit mode analysis.

(b)

The leakage inductance L_lk of the transformer T_R is considered.

(c)

The magnetizing inductor L_M of the transformer T_R is designed to operate in discontinuous conduction mode (DCM).

(d)

Neglecting the conduction voltage drops and their equivalent resistances of all diodes.

(e)

The remaining circuit components are considered as ideal components.

Operation Mode 1 (t₀ ≤ t < t₁): Figure 5 shows the equivalent circuit of the proposed single-stage electronic lighting driver circuit for supplying a deep ultraviolet LED disinfection and sterilization lamp during Mode 1. The power switch S_B is driven on, and the equivalent voltage source V_REC is connected to both ends of the diode D_B, making the diode D_B a reverse biased non-conducting state. The equivalent voltage source V_REC provides energy to the output capacitor C_O2 and the magnetizing inductor L_M of the transformer T_R as well as the leakage inductor through the switch S_B, which results in a linear increase in the current of the magnetizing inductor L_M, and the voltage polarity on both sides of the magnetization inductor L_M and the leakage inductor L_lk is positive left and negative right. The output capacitors C_O1 and C_O2 provide energy to the deep ultraviolet LED disinfection and sterilization lamp. When the switch S_B turns off, the current of the magnetizing inductor L_M reaches its maximum value and the mode ends.

Operational Mode 2 (t₁ ≤ t < t₂): Figure 6 shows the equivalent circuit of the proposed single-stage electronic lighting driver circuit for supplying a deep ultraviolet LED disinfection and sterilization lamp during Mode 2. When the power switch S_B turns off, the voltage polarity of the magnetizing inductor L_M and the leakage inductor L_lk is changed to right positive and left negative according to the Lenz’s law, which turns the diode D_B to be the on state of forward bias. The current of the magnetizing inductor L_M flows into the position where the primary-side winding N_P of the transformer T_R does not have a dot end, and the voltage polarity of the two ends of the winding N_P is right-positive and left-negative. Therefore, the polarity of the voltage reflected to both ends of the secondary-side winding N_S is positive left and negative right, which makes the diode D_F work in the forward-biased conduction state. At this time, the magnetizing inductor L_M and the leakage inductor L_lk are in the state of releasing energy, causing the current of the magnetizing inductor L_M to decrease linearly. Since the diode D_B is in the forward-biased conduction state, the energy of the magnetizing inductor L_M and the leakage inductor L_lk is supplied to the output capacitor C_O2 through the diode D_B, and the current of the magnetizing inductor L_M shows a linear decrease. Due to the forward-biased conduction of the diode D_F, the energy of the magnetizing inductor L_M is supplied through the transformer T_R and the diode D_F to the output capacitance C_O1 and C_O2 as well as to the deep ultraviolet LED disinfection and sterilization lamp. In addition, the output capacitors C_O1 and C_O2 continue to provide energy to the deep ultraviolet LED disinfection and sterilization lamp. The mode ends when the leakage inductor L_lk finishes releasing energy and the current I_Llk of the leakage inductor L_lk drops linearly to zero.

Operational Mode 3 (t₂ ≤ t < t₃): Figure 7 shows the equivalent circuit of the proposed single-stage electronic lighting driver circuit for supplying a deep ultraviolet LED disinfection and sterilization lamp during Mode 3. The energy of the magnetizing inductor L_M is continuously supplied through the transformer T_R and the diode D_F to the output capacitors C_O1 and C_O2 and to the deep ultraviolet LED disinfection and sterilization lamp. In addition, the output capacitors C_O1 and C_O2 continue to provide energy to the deep ultraviolet LED disinfection and sterilization lamp. This mode ends when the magnetizing inductor L_M has finished releasing energy and the magnetizing inductor current I_LM drops linearly to zero.

Operational Mode 4 (t₃ ≤ t < t₄): Figure 8 shows the equivalent circuit of the proposed single-stage electronic lighting driver circuit for supplying a deep ultraviolet LED disinfection and sterilization lamp during Mode 4. The output capacitors C_O1 and C_O2 continuously provide energy to the deep ultraviolet LED disinfection and sterilization lamp. When the power switch S_B is turned on again, this mode ends and the circuit reverts to the first mode of operation.

2.1. Design Guideline of the Magnetizing Inductor L_M in the Transformer T_R

In order to show the design guideline of the magnetizing inductor L_M in the transformer T_R, Figure 9 illustrates theoretical waveforms of the magnetizing inductor current i_LM(t), the peak level of i_LM-pk(t) and the input utility-line current i_AC(t) in the positive half-cycle of the utility-line voltage v_AC(t).

Referring to Figure 9, the positive half-cycle of the instantaneous utility-line voltage v_AC(t) can be expressed by

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

(1)

The peak level of the magnetizing inductor current i_LM, denoted as i_LM,peak, can be represented by

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

(2)

By filtering the high-frequency components of the peak level of the magnetizing inductor current i_LM,peak(t), 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

$$i_{AC}(t)={\displaystyle \frac{1}{T_{AC}}}{\displaystyle \underset{0}{\overset{T_{AC}}{\int }}{i}_{LM,peak}(t)dt}={\displaystyle \frac{\sqrt{2}{v}_{AC-rms}Dut{y}^2{T}_S}{4L_M}}\sin (2\pi f_{AC}t)$$

(3)

where T_AC is the utility-line period.

The average value of the input utility line power P_IN is obtained by multiplying the instantaneous value of the utility line voltage v_AC(t) by the instantaneous value of the utility line current i_AC(t), and then averaging it over a period of one cycle, which is calculated as follows

$$P_{IN}={\displaystyle \frac{1}{T_{AC}}}{\displaystyle \underset{0}{\overset{T_{AC}}{\int }}{v}_{AC}(t)i_{AC}(t)dt}={\displaystyle \frac{v_{AC-rms}{}^{2}Dut{y}^2{T}_S}{4L_M}}$$

(4)

The rated output power P_O of the deep ultraviolet LED disinfection and sterilization lamp is related to the estimated efficiency of the driver circuit η multiplied by the input power P_IN, which is expressed as follows

$$P_O=\eta P_{IN}={\displaystyle \frac{\eta v_{AC-rms}{}^{2}Dut{y}^2{T}_S}{4L_M}}$$

(5)

Rearranging (5), the design formula for the inductance of the magnetizing inductor L_M is given by

$$L_M={\displaystyle \frac{\eta v_{AC-rms}{}^{2}Dut{y}^2{T}_S}{4P_O}}$$

(6)

2.2. Design Guideline of the Output Capacitors C_O1 and C_O2

The design consideration of the output capacitors, C_O1 and C_O2, depends on the DC output voltage, the allowable overvoltage, the output power and the desired voltage ripple. The voltage ripple, ∆V_O, is half the peak-to-peak value of the output voltage at twice the mains frequency, and is a function of the capacitance C_O and the peak capacitor current (which is equal to the output current I_O) and can be expressed in the following equation [23].

$$\Delta V_O=I_O\sqrt{{\left({\displaystyle \frac{1}{2\pi \times 2f_{AC}\times C_O}}\right)}^2+R_{ESR}{}^2}$$

(7)

Neglecting the equivalent series resistance, which is denoted as R_ESR, of the output capacitor, the capacitance C_O of the output capacitor can be expressed as

$$C_O\ge {\displaystyle \frac{I_O}{4\pi f_{AC}\times \Delta V_O}}={\displaystyle \frac{P_O}{4\pi f_{AC}\times V_O\times \Delta V_O}}$$

(8)

In addition, the voltage ripple ∆V_O is typically selected from 1% to 5% of the output voltage.

3. Experimental Results of the Proposed Electronic Lighting Driver Circuit Utilizing SiC Schottky Didoes for Supplying a Deep Ultraviolet LED Disinfection and Sterilization Lamp

Figure 10 shows a photograph of the deep ultraviolet LED disinfection and sterilization module used in this paper with specifications that include a wavelength of 275 nm and a point angle of 120 degrees. Moreover, the manufacturer has connected a constant current control IC in series and a Schottky diode in parallel for reverse polarity protection on the aluminum substrate in each deep ultraviolet LED disinfection and sterilization module. The specification of the deep ultraviolet LED disinfection and sterilization lamp used in this paper consists of ten deep ultraviolet LED disinfection and sterilization modules connected in series with a rated voltage of 90 volts, a rated current of 40 milliamps, and a rated power of 3.6 watts.

Table 1. Comparisons between the deep ultraviolet LED disinfection and sterilization module in [24] and the one utilized in this paper.

Item	The Deep Ultraviolet LED Disinfection and Sterilization Module in [24]	The Deep Ultraviolet LED Disinfection and Sterilization Module Utilized in this Paper
Typical value of the peak wavelength	255 nm	275 nm
Typical value of the optical output power	3.5 mW	4 mW
viewing angle	125 degree	120 degree
Spectrum half width	11 nm	12 nm

shows a comparison between the deep ultraviolet LED disinfection and sterilization module in [24] and the module used in this paper. As can be seen from Table 1, the deep ultraviolet LED disinfection and sterilization module used in this paper has a larger peak wavelength, a slightly narrower viewing angle, and a slightly larger optical output power and spectral half-width than the module in [24].

Table 2. Specifications of the proposed electronic lighting driver circuit utilizing SiC Schottky didoes for supplying a deep ultraviolet LED disinfection and sterilization lamp.

Parameter	Value
Input AC voltage vAC	110 V
Rated output power PO	3.6 W
Rated output voltage VO	90 V
Rated output current IO	40 mA

shows the electrical parameters of the single-stage electronic lighting prototype driver circuit for the deep ultraviolet LED disinfection and sterilization lamp developed in this paper. The RMS AC input voltage was 110 volts, and the specifications of the deep ultra LED disinfection and sterilization lamp were used as the output parameters, including: output power of 3.6 watts, output voltage of 90 volts, and output current of 40 milliamps. Moreover, safety concerns and ensuring compliance with regulatory standards for UV exposure and electrical safety include: Do not look directly at the UV light source when using a deep ultraviolet disinfection and sterilization lamp as deep UV radiation may cause skin erythema, conjunctival irritation and fatigue. In addition, do not overuse deep UV disinfection and sterilization lamps as prolonged use or contact with UV lamps or direct exposure to UV radiation may cause skin and eye damage.

3.1. Calculating the Magnetizing Inductor L_M in the Transformer T_R

Referring to (6) with a η of 0.8, a Duty of 0.25, a P_O of 3.6 W, a switching frequency f_S of 50 kHz (which is the reciprocal of the switching period T_S), and a v_AC-rms of 110 V, the inductance of the magnetizing inductor L_M is calculated by

$$L_M={\displaystyle \frac{\eta v_{AC-rms}{}^{2}Dut{y}^2{T}_S}{4P_O}}={\displaystyle \frac{0.8\times {110}^2\times {0.25}^2\times \left(\frac{1}{50,000}\right)}{4\times 3.6}}=834 \mu H$$

(9)

In order to operate the magnetizing inductor current in a discontinuous conduction mode so as to allow the driver circuit to have an input current shaping function and to improve the power factor, the magnetizing inductor L_M is selected as 800 μH for the prototype driver circuit.

3.2. Calculating of the Output Capacitors C_O1 and C_O2

Substituting the circuit parameters into Equation (8), with a P_O of 3.6 W, an f_AC of 60 Hz, a V_O of 90 V, a ΔV_O of 2.7 V (which is 3% of the output voltage V_O), the capacitance C_O can be obtained by:

$$C_O\ge {\displaystyle \frac{P_O}{4\pi f_{AC}\times V_O\times \Delta V_O}}={\displaystyle \frac{3.6}{4\pi \times 60\times 90\times 2.7}}=196.49 \mu F$$

(10)

In implementing the prototype circuit, the capacitance values of the output capacitors C_O1 and C_O2 were selected to be 220 μF and the withstand voltage to be 250 V.

Table 3. Key components used in the proposed electronic lighting driver circuit utilizing SiC Schottky didoes for supplying a deep ultraviolet LED disinfection and sterilization lamp.

Component	Value
Filter inductor Lf	1 mH
Filter capacitor Cf	220 nF
Diodes D1, D2, D3, D4	MUR460
Power switch SB	IRF730
Magnetizing inductor LM	800 μH
Leakage inductor Llk	12 μH
Diodes DB, DF	VS-3C04ET07T-M3
Output capacitor CO1, CO2	220 μF/200 V

shows the component specifications of the single-stage electronic lighting prototype driver circuit for the deep ultraviolet LED disinfection and sterilization lamp developed in this paper. In addition, majority carrier diodes with Schottky technology on silicon carbide wide bandgap material have higher performance and are used as output diodes D_B and D_F. By varying the number of series-connected deep ultraviolet disinfection and sterilization modules used, a scalable design of the proposed electronic lighting driver circuits can be achieved to accommodate higher power applications and varying load conditions. As a result, the output power P_O and output voltage V_O can be varied while the output current I_O remains constant and can be used in a variety of practical application scenarios. Key circuit parameters of the proposed drive circuit, such as the magnetizing inductor and output capacitor, can then be redesigned.

Figure 11 shows the measured waveform of the magnetizing inductor current i_LM. Figure 12 shows the measured unfolded waveform of the magnetizing inductor current i_LM. From Figure 12, it can be seen that the magnetizing inductor current i_LM operates in the discontinuous conduction mode. Figure 13 shows the measured waveforms of output voltage V_O and output current I_O, and the average values of output voltage and current were 91.35 volts and 38.57 milliamps, respectively. Figure 14 shows the ripple waveforms of output voltage V_O and output current I_O.

Table 4. Measurement of output voltage ripple factor and output current ripple factor of electronic lighting prototype driver circuit utilizing SiC Schottky didoes for a deep ultraviolet LED disinfection and sterilization lamp.

Parameters	Values
Peak-to-peak value of the output voltage	143.8 mV
Mean value of the output voltage	91.35 V
Ripple factor of the output voltage	0.16%
Peak-to-peak value of the output current	1.1658 mA
Mean value of the output current	38.57 mA
Ripple factor of the output current	3.02%

shows the output voltage ripple factor and output current ripple factor of the prototype electronic lighting driver circuit for a deep ultraviolet LED disinfection and sterilization lamp at 110 volts RMS AC input voltage. As can be seen in Table 4, dividing the peak-to-peak output voltage of 143.8 millivolts by the average value of 91.35 volts yields a voltage ripple factor of 0.16%; dividing the peak-to-peak output current of 1.1658 milliamps by the average value of 38.57 milliamps yields a current ripple factor of 3.02%.

Figure 15 shows the measured waveforms of AC input voltage v_AC and input current i_AC. From the figure, it can be indicated that the AC input current follows the input voltage and the phases of the two waveforms are the same; therefore, the prototype of the proposed single-stage driver circuit for supplying the deep ultraviolet LED disinfecting and sterilizing lamp has the effect of power factor correction. The power factor and the total harmonic distortion factor of the input current were measured to be 0.9236 and 17.401%, respectively, using a power analyzer. In addition, the measured input power of the prototype drive circuit is 3.901 W and the output power is 3.583 W, and the efficiency of the prototype circuit is 91.85%.

Table 5. Comparisons between the existing AC-DC LED driver in [19] and the proposed one.

Item	Existing AC-DC LED Driver in Reference [19]	ProposedAC-DC LED Driver
Circuit topology	Integration of an inverse buck-boost converter with a lossless snubber	Integration of a buck converter and a flyback converter
Input AC voltage	110 V	110 V
Output power	18 W (60 V/0.3 A)	3.6 W (90 V/0.04 A)
Number of required switch	1	1
Number of required capacitors	4	3
Number of required magnetic element	3	2
Number of required diodes	7	6
Measured power factor	0.9737	0.9236
Measured current THD	18.422%	17.401%
Measured circuit efficiency	85.01%	91.85%

shows a comparison between the existing AC-DC LED driver in [19] which integrates an inverse buck-boost converter with a lossless snubber and supplies an 18 W-rated (60 V/0.3 A) power, and the proposed one which integrates a buck converter and a flyback converter and supplies a 3.6 W-rated (90 V/0.04 A) power. As can be seen from Table 3, both LED drivers are supplied by an input AC voltage of 110 V and use a single power switch. The proposed AC-DC LED driver circuit saves a capacitor, a magnetic element and a diode compared to the ones in [19]. In addition, the current THD and circuit efficiency of the proposed AC-DC LED driver is better than that of the existing driver.

4. Conclusions

This paper proposes a single-stage electronic lighting prototype driver circuit utilizing SiC Schottky didoes for a deep ultraviolet LED disinfection and sterilization lamp, which integrates a buck converter and a flyback converter to form a single-stage, single-power-switch AC-DC power converter circuit architecture with a factor correction function. By designing the inductor in the AC-DC power converter to operate in discontinuous conduction mode, the effect of power factor correction can be achieved naturally. In addition, the proposed single-stage electronic lighting driver circuit employs a majority-carrier Schottky diode made of silicon carbide wide-bandgap semiconductor material and recovers the energy from the leakage inductance of the transformer, thereby improving the conversion efficiency of the driver circuit. In this paper, a 3.6 watt deep ultraviolet LED electronic lighting prototype driver circuit for a disinfection and sterilization lamp has been developed and tested. At an AC input voltage of 110 volts RMS and at rated output power, the results were: output voltage ripple factor less than 1%, output current ripple factor less than 4%, power factor greater than 0.9, input current total harmonic distortion factor less than 18%, and circuit efficiency greater than 90%. The single-stage deep ultraviolet LED electronic lighting prototype driver circuit proposed in this paper can simplify the number of power switches required in the driver circuit and has high circuit efficiency.