Search

In this paper, a Phase-shift-modulated (PS) Resonant Two-switch Boosting Switched-capacitor Converter (RTBSC) and its modulation map are proposed. Compared with the traditional RTBSC, all diodes are replaced by active switches and then phase-shift modulation is applied. The advantages of the modified topology are obtained as follow. 1) The voltage gain can be regulated efficiently either below or above the nominal value even at light-load condition, making it suitable for applications with voltage fluctuations; 2) The conduction loss is reduced by replacing all diodes in RTBSC with low turn-on resistance transistors, especially for high-order and high-gain configuration; 3) All switches achieve the zero-voltage-switching (ZVS) turn-on operation; 4) The soft-charging property smooths the current profile. Aside from the topology modification, a comprehensive analysis of operation principle, voltage gain, component stress and ZVS region is given. On the basis, a modulation map with the optimal operation region is proposed. It provides a guideline to operate and design such converters in the target gain range, low component stress and ZVS region, making up for the lack of modulation map and design guideline in aforementioned literatures. A 120W prototype with low-voltage side 43-60V and high-voltage side 150V was designed to verify the above analyses.

A gallium nitride (GaN)-based resonant step-up converter is proposed for the application in the satellite electric propulsion (EP) system. This converter consists of a full-bridge inverter, a resonant tank and a multi-stage Cockcroft-Walton (CW) voltage multiplier to provide a high gain. Additionally, the air-core transformer is introduced due to the megahertz switching frequency allowed by the GaN device. Thus, the limited magnetizing inductance of transformer and the remarkable junction capacitance of diode have to be carefully considered in the resonant tank design, especially after considering that this converter normally operates at the light load in the EP system. In this work, the 4-order LCLC resonant converter is investigated. The recommended parameter selection for the 4-order resonant tank is also provided. A 1.2-MHz, 23-V/2.5-kV, and 6-W prototype is demonstrated. It achieves a low harmonics distortion and a low power loss with the zero voltage switching (ZVS).

Multiplexing circuits in pixelated PET detectors are being studied with the goal of minimizing the degradation of detector performance. The purpose of this study was to develop a diode-based symmetric charge division (SCD) circuit with reducing the crosstalk caused by the leakage currents of adjacent channels connected in rows and columns. Four different SCD circuits (diode-based SCD with grounding path, diode-based SCD, resistor-based SCD with grounding path and resistor-based SCD) were constructed and their performance was evaluated and compared after being combined with a PET detector consisting of LYSO crystals optically coupled with SiPM. The diode-based SCD circuit with grounding path achieved a crosstalk ratio, energy resolution, coincidence timing resolution (CTR) and mean peak to valley ratio of 0.02, 14.3%, 0.5 ns and 27.9: 1, respectively; the diode-based SCD circuit achieved 0.03, 15.9%, 0.7 ns and 19.4: 1, respectively; the resistor-based SCD circuit with grounding path achieved 0.04, 14.5%, 0.9 ns and 19.4: 1, respectively; the resistorbased SCD circuit achieved 0.05, 17.8%, 1.8 ns and 17.7: 1, respectively. These results indicate that the proposed SCD has the potential to improve not only the crosstalk but also the energy linearity, energy resolution, and coincidence timing resolution characteristics in PET detectors.

Following the continuous development of wide bandgap (WBG) devices and multilevel converter technology, medium voltage (MV) active front ends (AFEs) are becoming promising in future high-power-density and high-power applications. However, the cost issue is one of the major drawbacks, which stops the WBG devices from being widely applied in high-power areas. This paper proposes a silicon carbide (SiC) and silicon (Si) hybrid five-level unidirectional rectifier. It requires only four SiC MOSFETs with relatively low blocking voltage and four Si diodes. Meanwhile, by adding snubber capacitors, all the Si devices are with low-speed switching, and the voltage stresses of fast SiC MOSFETs are minimized. In this paper, operational analysis and carrier-based phase-disposition PWM scheme for this circuit are discussed in detail. The capacitor voltage balancing and unity power factor are both realized. Simulation and scaled-down experimental results are demonstrated to verify the proposed rectifier. Furthermore, the comparison of the hybrid five-level rectifiers is given to show the advantages of the proposed rectifier in terms of voltage stress, efficiency, and cost.

Recently, inverters with a common ac and dc ground are gaining significant interest due to their zero common-mode voltage that made them particularly attractive for the solar photovoltaic application. However, the dc source current of the existing topologies is discontinuous, and their voltage gains are limited. This article proposes a novel common-ground-type boost inverter that achieves continuous dc source current with significantly enhanced dynamic voltage gain. It consists of one boost inductor, four capacitors, nine power MOSFETs, and two power diodes. Voltage boosting and generation of nine-level ac voltage are achieved concurrently within a single-stage operation. The operation of the proposed CGT-9L-BI inverter is analyzed. Simulation and experimental results are presented for validation.

Reliable and affordable AC/AC power conversion plays a key role in supplying various electrical equipment. Among the options available, direct matrix converter (DMC) outperforms its counterparts (e.g. AC/DC/AC), in terms of lifespan and compactness, due to its omission of fragile and bulky dc-link capacitors. However, most off-the-shelf DMC modules suffer from high input current spikes, which if unresolved, can noticeably increase current stresses and lower efficiency. Origin of the spikes and a mechanism for reducing them are hence studied in the paper, before developing a low-cost SiC-Si hybrid module for implementing DMC reliably and compactly. The developed module consists of 18 Si insulated gate bipolar transistors (IGBTs) and 18 SiC junction barrier Schottky (JBS) diodes connected in a common-collector structure. The improved reverse recovery property of the SiC JBS diodes then permits the hybrid module to operate with mitigated current spikes. To demonstrate, the hybrid module has been fabricated, tested and compared with two counterparts in terms of their input current spikes and power losses over different output voltages and switching frequencies. Experimental results have proven the expected performances of the hybrid DMC module, which collectively, can accelerate large-scale emergence of small all-semiconductor drives for industrial pumps, cooling and refrigeration systems, and others widely needed in developing economies.

Small and low-cost chlorophyll sensors are popular in agricultural sector and food-quality control.Combining such sensors with silicon CMOS electronics is challenged by the absence of silicon-integrated light-sources.We experimentally achieve optical absorption sensing of chlorophyll based pigments with silicon (Si) micro light-emitting diodes (LED) as light-source, fabricated in a standard SOI-CMOS technology.By driving a Si LED in both forward and avalanche modes of operation,we steer its electroluminescentspectrum between visible (400-900 nm) and near-infrared (1120 nm). For detection of chlorophyll in solution phase, the dualspectrum light from the LED propagates vertically through glycerol micro-droplets containing sodium copper chlorophyllin at varying relative concentrations. The transmitted light is detected via an off-chip Si photodiode. The visible to near-infrared color ratio (COR) of the photocurrent yields the effective absorption coefficient. We introduce the LED-specificmolar absorption coefficient as ametric to compute the absolute pigment concentration (0.019 ± 0.006 mol L-1) and validate the results by measurements with a hybrid spectrophotometer. With the same sensor, we also show noninvasive monitoring of chlorophyll in plant leaves. COR sensitivities $\sim 3.9 \times 10^{4}$ mol-1L and $\sim 5.3 \times 10^{4}$ mol-1L are obtained for two leaf species, where light from the LED propagates diffusely through the thickness of the leaf prior to detection by the photodiode. Our work demonstrates the feasibility of realizing fully CMOS-integrated optical sensors for biochemical analyses in food sector and plant/human health.

The snappy reverse recovery (SRR) and failure of high-voltage non-punch-through (NPT)-PIN diodes under extreme working conditions is of great significance to the reliability evaluation of operating diodes in actual power electronic devices. In this paper, the analysis of the physical mechanism of the diode SRR and the restrictions of the traditional PT-PIN diode model are made. Then, the traditional model for soft recovery is improved in order to accurately describe the diode SRR characteristics. Simulations of key dynamic performances of the established model agree well with the testing results. Furthermore, a suppression method for diode SRR based on the optimal RC snubber circuit is proposed. A high-voltage NPT-PIN diode used in the DC-DC converter with different RC snubber circuits is simulated using the proposed diode snappy model and tested. The comparison results show good consistency between the simulated and measured voltage and current peaks and the diode SRR can be suppressed effectively. The model developed and the results are of much importance to the prediction of the safe operation area of the diode and to the reliability improvement of power electronic device.

In renewable energy micro-source applications, a wide range of voltage conversion of the step-up converter is an essential part to equalize the typical low voltage of micro-source with DC-bus voltage of Inverter or motor drives. In order to meet this purpose, an ultra-voltage gain step-up DC-DC converter is proposed in this paper. The proposed converter has made an arrangement of the regenerative-boost fed switched inductor and capacitor configurations. Thereby, due to such an organization of structure, the proposed converter can develop an extremely high voltage-gain even at lower duty ratios. In addition, it has advantages of lesser switching stress across all power semi-conductive diodes. Furthermore, this paper describes the steady-state analysis and comparative features of the converter with existing recent literature. Finally, to validate theoretical analysis and test feasibility and suitability of the proposed ultra-gain converter, the experimental results were observed by a 500 W fabricated prototype.

Two-switch converters (TSC) are widely used and are more efficient at high power levels with lower component stress than the single-switch topologies. These converters have flexible operations in both boost and buck modes, and are applicable to onboard battery chargers in the power factor correction (PFC) converter stage. The intermediate output voltage at PFC can be greater or lesser than the peak of input voltage (variable DC-link voltage) resulting in higher switching losses across the boost switch. An auxiliary circuit proposed in the paper comprises of an active switch, a diode with a pair of resonant inductor’s and capacitor that are applied across the main switch to operate with loss-less switching. Though the conduction time of the proposed auxiliary circuit is small compared to the main converter operation but it attains the main switch to turn-ON with zero voltage transition (ZVT) and turn-OFF with zero current transition (ZCT). Also, the auxiliary switch involved in the converter operation is also subjected to SS. Additionally, the proposed converter has no extra component stress and switching losses. With this, it can enhance the overall converter efficiency. The various operating modes involved in different time intervals are analyzed and presented in the paper. Moreover, the design criteria of auxiliary circuit and the main converter parameters are also discussed in the paper. As proof-of-concept, a hardware prototype of 1 kW is implemented with the proposed control structure and the results are presented in the paper. Maximum efficiency of 97.4% has been achieved from the implemented hardware prototype.

In this paper we demonstrate a high wall-plug efficiency and low threshold current for heterogeneously integrated III-V-on-Silicon distributed feedback (DFB) lasers. Above 12% wall plug efficiency is achieved for a 200 µm long DFB laser diode at 25 °C. Up to two times 6 mW of optical power is coupled into the silicon waveguide and more than 40 dB side-mode suppression ratio is obtained. We also discuss the non-return-to-zero on-off keying modulation at 20 Gb/s and the transmission over a 2 km long optical fiber.

At present, solid-state laser-driven lighting fabricated with blue laser diode (LD) and phosphor has been greatly developed in high-power lighting applications. The major obstacle is the luminescence saturation threshold of the fluorescence conversion material (YAG:Ce). In this work, we successfully prepared a series of high-quality and robust YAG:Ce single crystals. With high quantum efficiency (QE = 92%), regular crystal structure and high thermal conductivity, the single-crystal has excellent ability to deal with high radiation flux and thermal accumulation generated by high power. Matching the single-crystal with the laser, the luminous efficiency up to 274 lm/W and saturation threshold of 12 W/mm2 were obtained. In addition, the influence of Ce doping concentration and sample processing conditions on the indicators in laser-driven white lighting was systematically studied. The results are of great significance and are believed to promote the development of solid-state laser-driven lighting.

In order to suppress the crosstalk in gallium nitride (GaN)-based bridge configuration, a novel negative voltage self-recovery gate drive (NVSRGD) is proposed in this paper. The resistor-capacitor-diode voltage divider is applied to establish the negative gate-source voltage and suppress the impact of positive crosstalk. The antiparallel diode is added to constitute low-impedance Miller current path from the driver integrated circuit (IC) to the GaN device. It works together with the self-recovery gate-source voltage to suppress the negative crosstalk, which not only prevents the GaN device from the negative overstress but also reduces the reverse conduction loss during the dead time. The NVSRGD is composed of a few passive components, which are suitable for integrating into the driver IC. The capacitors and resistors of the NVSRGD are designed to determine the negative voltage level and the restore time. Additive separate negative voltage power supplies or active devices are not needed. The double pulse test based on GS66508B verifies the effectiveness of the proposed method for suppressing the positive and negative crosstalk of GaN devices.

The series resonant dc-dc converter (SRC) which features zero current switching (ZCS) and open-loop control is widely used for providing galvanic isolation and voltage scaling. However, output short-circuit (OSC) fault is a challenge for SRC because it will cause dramatically high current in the low-impedance resonant tank. To address this issue, a resonant full-bridge dc-dc converter only using small dc-side capacitors to resonate with the resonant inductor Lr is proposed. Under normal condition, ZCS can be achieved. When OSC fault occurs, the output dc-side capacitor can be bypassed by the anti-paralleled diodes of the full bridge and the resonant current can be limited automatically by the resonant inductor Lr without additional control. The operation principle of the converter under normal and faulty condition is analyzed. Based on these analyses, the switching frequency to achieve ZCS is designed. The resonant inductor Lr and dc-side resonant capacitors Cr design considerations are provided. The ZCS characteristics and the current limiting capability of the converter are verified on an experimental prototype.

We firstly propose the integration of heterogeneous Tm:YAG and Ho:YAP crystals into a single bulk structure for a compact, diode-pumped passively Q-switched (PQS) Ho laser. Efficient 2129 nm laser, with maximum CW power of 6.67 W was obtained from the Tm:YAG/Ho:YAP gain medium, with slope efficiency of 38.3% and optical conversion efficiency of 27.4% by considering the incident diode power at 785 nm. Modulated by a Cr:ZnSe saturable absorber inside a hybrid cavity, characteristic self-pulsing of the integrated Ho laser can be suppressed for a stable PQS process, where average output power of 743 mW at 2053.3 nm was obtained with shortest pulse duration of 123 ns at 14.2 kHz. As the maximum thermal stress of 48.2 MPa is far below the fracture limits of each integrated section (~160 MPa), higher laser power can be expected. The results pave the way to explore the integration of other existing Tm-doped and Ho-doped hosts for an accessible 2.1 m source.

The correct parameter determination of the photovoltaic module and the solar cell is considered an important phase to deliver a reliable simulation for the PV system characteristics. The triple diode model (TDM) has been examined to model the PVM 752 GaAs thin-film PV solar cell (SC), STM6 PV module, and RTC SC. A set of the measured I-V data at various levels of the weather conditions has been considered for the studied PV solar cell/modules. A new marine predators algorithm (MPA) is used to identify the TDM parameters based on measured datasets. Throughout the optimization procedure, the nine undetermined parameters of TDM are employed as decision variables but the fitness function requires to be least is the RMSE between the experimental and calculated datasets. The achieved results by MPA are compared with different algorithms. The comparison confirmed the superiority of MPA.

Switched-capacitor-based multilevel inverters for boost-type dc–ac power conversions usually exhibit a trade-off between the switch count and switch-voltage rating, i.e., a reduction of one necessitating an increase of the other. Such a dilemma is well addressed in this article by proposing a novel single-phase nine-level inverter based on a switched-capacitor network with a single switch. The proposed inverter then reduces the number of switches while generating a boosted dc-link voltage. A unique six-switch full-bridge cooperating with a low-frequency half-bridge further steps-up the output voltage with a quadruple gain. The voltage stresses on the power devices are, however, maintained low even under the boosted high output voltage, as all the switches/diodes can be clamped to any of the low-voltage capacitors. Consequently, low-voltage power devices can be utilized, reducing the overall power loss. Detailed theoretical analysis, calculations, and design considerations of the proposed inverter are provided. Comparisons with the prior-art inverters illustrate its advantages. Simulations and experimental tests on a 1-kVA inverter prototype verify the above-claimed benefits.

This paper presents an improved full-bridge converter with a five-diode rectifier. The primary side circuit is composed of a full bridge with two transformers and two split capacitors. On the secondary side, five diodes are employed in the rectifier stage. By using the asymmetrical PWM signals, this converter can realize the ZVS of all switches and reduce the circulating current. The two transformers share the load power equally in whole load range. Compared with the other dual-transformer-isolated-full-bridge converters, the transformers in the proposed converter are easy to optimize because of the load power equal sharing. Furthermore, the output filter inductance is reduced, which reduces the loss and volume. According to the loss analysis, the proposed converter has higher efficiency compared with some other DC-DC converters. The experimental results of a prototype with 300-400V input voltage and 250V/4A output verify the performance of the proposed converter.

In this paper, we classify the instantaneous response of resistors with memory into three types: linear (L), separable nonlinear (SN), and non-separable nonlinear (NSN). A particular model of an NSN-type memristive device is introduced and used to demonstrate the possibility of rich dynamics in the memristor-capacitor circuit subjected to a sinusoidal voltage. In particular, our numerical simulations reveal the regimes of double period oscillations, multiple period oscillations, and chaotic oscillations. The comparison with L-type and SN-type memristive devices described by the same differential state equation indicates the importance of the NSN-type response to achieve such complex dynamics in the memristor-capacitor circuit with a first-order memristive device. Moreover, we demonstrate that a compound NSN-type memristive device can be assembled using one L-type memristive device, two resistors, and two diodes. The complex behavior of such compound devices is verified using SPICE modeling.

InGaN light-emitting diodes (LEDs) grown with an asymmetric multiple quantum well (MQW) are proposed for use in an optical link with an avalanche photodiode (APD) based receiver. In contrast to the high photoresponse of red AlGaInP LEDs in APDs, the proposed blue LEDs provide improved light output and enhanced system bandwidth for directed line-of-sight optical links passing through a 100-cm-long water tank. This improvement is due to the nonuniform carrier distribution within the InGaN MQWs being mitigated by using a thin GaN barrier near the n-GaN to facilitate hole transport capacity. In addition, bandwidth degradation resulting from APD module saturation can also be avoided by using these blue LEDs, successfully establishing a 300 Mbit/s LED-based underwater data link. The proposed InGaN LEDs (zero bias) under illumination exhibit a peak responsivity of 0.133 at λ = 370 nm, an ultraviolet (UV)-to-visible rejection ratio of 4849 and a 3-dB cut-off frequency of 33.3 MHz. Using violet UV laser diodes and the proposed LEDs respectively as the optical transmitter and receiver, an underwater optical link (L = 100 cm) with a data transmission rate of up to 130 Mbit/s and a bit error rate of 4.2 × 10−9 is also demonstrated.

Hollow cathodes are used as thermionic emitters in a variety of electric propulsion devices, such as the Hall thruster. This work studies the derivation and discusses the results of a phenomenological (zero-dimensional) plasma model for a hollow cathode with open-end emitter and orificed keeper. This represents the first attempt at modeling the plasma in the three regions of hollow cathodes with open-end emitter geometry, namely, the keeper orifice, the cathode-keeper gap, and the insert. The current continuity, ion balance, and plasma power balance equations are solved to compute the main plasma property in each of the aforementioned regions. One novelty of this work is the definition of ready-to-use expressions for the dynamic viscosity and ionization and excitation rates for krypton. Moreover, the resistive losses in the cathode–anode region are computed to model the cathode standalone diode testing with an external anode. The model delivers cathode operational parameters, such as the discharge power and potential, which are compared to experimental data for both xenon- and krypton-fed cathodes. Furthermore, the influence of the geometry of the three regions as well as the propellant flow rate and the discharge current on plasma property and cathode power budget of sample cathodes is discussed at length.

We demonstrate hole-transport-layer-free light-emitting diodes (LEDs) based on solution-processed multiple-quantum-well (MQW) perovskite. The MQW perovskite can self-assemble to a unique structure of vertically graded distribution with two-dimensional layered perovskite covered by three-dimensional-like perovskite at top, which can naturally form a barrier of electron transporting to the anode interface, thereby enhancing the charge capture efficiency. This leads to hole-transport-layer-free MQW perovskite LEDs reaching an external quantum efficiency (EQE) of 9.0% with emission peak at 528 nm, which is over 6 times of LEDs based on three-dimensional perovskite with the same device structure, representing the record EQE of hole-transport-layer-free perovskite LED.

Naphthalene diimides (NDIs) are a promising material for n-type polymer acceptors in thin-film devices such as organic light-emitting diodes. The intersystem crossing (ISC) pathway of NDIs has been...

In the solar cells under the open-circuit condition, the carriers charges emits the external luminescence for balancing the incoming solar radiations. The generation of such external luminescence represents the optical losses in the solar cells. Efficient external luminescence ensures the state of approaching the maximum limit of the SQ (Shockley-Queisser) equation. In this way in solar cell’s need of getting high efficiency is fulfilled if it is also responding as an efficient light-emitting diode. This article focus on achieving a high external luminescence efficiency under the standard solar spectrum with optimum value of fill factor using the optimum values of GaAs solar cell parameters by applying Genetic algorithm. Different geometries based on physics of light absorption are considered for optimum parameter search that can give high external luminiscence efficiency as well as high Value of fill factor.

Yellow light-emitting diodes (LEDs) are widely utilized in high-quality lighting, light communication, indicator lamps, etc. Owing to their outstanding material properties and device performance, the metal halide perovskites have demonstrated a significant potential for LED applications. However, the performance of the yellow perovskite LEDs (PeLEDs) is inferior to that of their green and red counterparts, with the maximum external quantum efficiency (EQE) limited to ∼3.1%. Further, a majority of the yellow PeLEDs are fabricated using the spin-coating methods. The current study reports the development of the yellow CsPbBr2I PeLEDs based on an all-vacuum deposition approach, which has been widely employed in the commercial organic LEDs (OLEDs). By controlling the co-evaporation rate of CsI and PbBr2, the growth kinetics of the perovskite layer are regulated to achieve a small grain size of ∼31.8 nm. Consequently, an improved radiative recombination rate (8.04 × 10−9 cm3/s) is obtained owing to the spatial confinement effect. The PeLEDs based on the optimal perovskite film demonstrate the yellow electroluminescence (574 nm) with a maximum EQE of ∼3.7% and luminance of ∼16,200 cd/m2, thus, representing one of the most efficient and bright yellow PeLEDs. Overall, this study provides a useful guideline for realizing the efficient PeLEDs based on the thermal evaporation strategy and highlights the potential of PeLED as an efficient and bright yellow light source.

In this article, a novel ultrahigh voltage gain dc–dc boost converter with expandable diode-capacitor voltage multiplier (VM) cells is presented. The diode-capacitor VM cells and coupled inductors are employed in the presented topology to provide a higher voltage gain. Also, the main and the auxiliary power switches of the presented converter operate with zero voltage switching. The coupled inductors' leakage inductances control the rates of the current drop in the voltage multiplier diodes, which decreases their reverse recovery losses markedly. Moreover, the voltage stresses on all capacitors and semiconductors are reduced significantly. In this converter, the number of voltage multiplier cells, and the coupled inductors turn ratios provide three degrees of design freedom. These degrees of freedom are used to set the desired voltage stresses of the semiconductors within the desired range and to provide a high voltage gain at optimum duty cycles. The design and theoretical analysis of the presented converter are discussed. Finally, the performance of the presented converter is validated using a 500 W, 40 V/380 V laboratory prototype converter, and the experimental results confirm the theoretical calculation.

An efficient continuous-wave (CW) mid-infrared laser with a tunable wavelength range from 3 to 4.5 μm is demonstrated by using intracavity optical parametric oscillator (ICOPO). An optically pumped semiconductor laser (OPSL) is applied as the parent pumped laser gain medium to eliminate self-modulation effect caused by Nd-doped gain medium with ICOPO for fulfilling true CW emissions. Simultaneously, the OPSL gain chip with flip-chip packaging method can avoid mode hopping resulted from internal heat spreader etalon when strong depletion in ICOPO was achieved. The diode pump criteria of the OPSL is first investigated to prevent thermal roll over. By observing the spectral and temporal dynamics of the parent pumped OPSL with and without OPO operation, the true CW and mode-hop-free quality of the laser is verified. A low diode pump threshold of 2.67 W is obtained for the mid-IR idler emission and a total extracted idler power is 250 mW at a diode pump power of 8 W. Finally, the wavelength tunability is confirmed by adjusting the horizontal location of the multiple channel MgO:PPLN crystal, which indicated the feasibility of practical application in such a compact configuration.

Resonant converter is a good solution as the isolated high step-up converter due to its soft-switching features and less component count. However, since the resonant tank is placed on the primary side (low-voltage side) in most traditional resonant converters, large input current still leads to a big proportion of power loss. Besides, synchronous rectification (SR) is also a big issue. The diode conducting time in a resonant converter is hard to be predicted so a current transformer or an analog SR chip is usually employed to detect the current zero-crossing point when the higher efficiency is required. In this article, an isolated high step-up converter with active secondary-side quasi-resonant tank is proposed. Since the whole resonant tank is placed on the high-voltage side, the current stress of the resonant capacitors and their power loss can be greatly alleviated. Besides, the analytical solution of the diode conducting time is derived and two SR control schemes are proposed, without the need to detect the current zero-crossing point. All the switches and diodes achieve the soft-switching so this leads to a good efficiency performance. The validity is confirmed by the experimental results of a 500 W prototype with 36–48 V input and 380 V output.

Experimental studies into the beam parameter product ( BPP ) of 940–980 nm GaAs-based high-power diode lasers are presented. Such lasers exhibit broadening far field and narrowing near field with increasing bias, with BPP increasing tenfold over the diffraction limit. First, spectrally-resolved beam profile measurements of lasers with monolithically-integrated gratings are presented, showing that a reproducible series of spatially-extended optical modes makes up the optical field. Then, changes to the device construction are presented, enabling effects limiting BPP to be inferred and addressed. Process- and package-induced effects can be minimized by design, while the effects of carrier, gain and temperature profiles dominate. Self-heating within the laser stripe raises the refractive index, forming a thermal lens, and the variation in curvature of this lens with bias and device construction directly affects BPP . Temperature non-uniformity along the resonator is also shown to strongly degrade BPP . Moreover, current spreading and the resulting lateral carrier accumulation (LCA) amplify high-order, high- BPP modes, thus degrading BPP for any given thermal lens. This LCA-induced degradation is shown to be suppressed by regrown lateral current-blocking structures. Finally, a flatter thermal lens and lower BPP can be achieved using thermal engineering, via changes to the epitaxial design or device layout.

Extracting the optimum parameters of the solar photovoltaic (PV) model based on measured current–voltage data accurately, reliably, and quickly is a vital step to simulating, evaluating, and optimizing the model PV. Although several meta-heuristics have been proposed to extract photovoltaic parameters using experimental data, it suffers from slow convergence and poor efficiency which leads to poor solution quality. In this paper, a multiple learning JAYA (MLJAYA) approach has been proposed to extract the PV parameters under different operating conditions. The main advantage of multiple learning strategies introduced in the MLJAYA proposed is its ability to balance exploration and exploitation capabilities. The chaos perturbation mechanism is employed to improve the quality of the population to escape the local optimum and improve the accuracy of the basic JAYA algorithm. The structure of MLJAYA is very simple and requires only the size of the population and stop criterion. The efficacy of the proposed MLJAYA has been verified by including different PV modules models such as single diode, double diode, and PV module, and the results obtained was compared with different variants of JAYA and other state-of-the-art optimization algorithms. The best results of root mean square error (RMSE), and absolute error generated by MLJAYA are (RMSE = 9.8602E−04, SIAE = 1.781248E−02), and (RMSE = 9.8248E−04, SIAE = 1.76E−02) for RTC solar cell single diode and double diode respectively, and (RMSE = 2.4250748E−03, SIAE = 4.686375E−02) for Photowatt-PWP201. The results show the superior performance in terms of accuracy and reliability. Since, the MLJAYA show is a potential approach for extracting parameters from photovoltaic models.

Featuring a combination of size-tunable emission wavelengths, high thermal stability, and low cytotoxicity, carbon quantum dots (CQDs) have opened up a new possibility for next-generation displays. However, the theoretically highest external quantum efficiency (EQE) limit of electroluminescent light-emitting diodes (LEDs) based on fluorescent CQDs is 5% due to the spin-forbidden nature of triplet state transitions. Comparatively, phosphorescent or delayed fluorescence CQDs are expected to overcome this limitation and allow the EQE of the devices to reach nearly 25%. At present, the preparation of CQDs with good solution processability, narrow bandwidth emission, and full-color phosphorescence or delayed fluorescence still faces great challenges. Herein, this review aims to offer a materials-chemistry perspective to tailor highly efficient phosphorescent or delayed fluorescence CQDs and present their applications in electroluminescent LEDs for the display technology. The mechanism and design principle of pure organic phosphorescence and delayed fluorescence as well as their recent advances in electroluminescent devices are summarized. Furthermore, we focus on the prospects and challenges for phosphorescent and delayed fluorescence CQDs in displays. We hope that this review will further stimulate the development of high-performance CQD-based electroluminescent displays with a combined effort from different disciplines.

We present the design and experimental characterization of a CMOS sensor based on Single-Photon Avalanche Diodes for direct Time-Of-Flight single-point distance ranging, under high background illumination for short-range applications. The sensing area has a rectangular shape (40 W 10 SPADs) to deal with the backscattered light spot displacement across the detector, dependent on target distance, due to the non-confocal optical setup. Since only few SPADs are illuminated by the laser spot, we implemented a smart laser-spot tracking within the active area, so to define the specific Region-Of-Interest (ROI) with only SPADs hit by signal photons and a smart sharing of the timing electronics, so to significantly improve Signal-to-Noise Ratio (SNR) of TOF measurements and to reduce overall chip area and power consumption. The timing electronics consists of 80 Time-to-Digital Converter (TDC) shared among the 400 SPADs with a self-reconfigurable routing, which dynamically connects the SPADs within the ROI to the available TDCs. The latter have 78 ps resolution and 20 ns Full-Scale Range (FSR), i.e., up to 2 m maximum distance range. An on-chip histogram builder block accumulates TDC conversions so to provide the final TOF histogram. We achieve a precision better than 2.3 mm at 1 m distance and 80% target reflectivity, with 3 klux halogen lamp background illumination and 2 kHz measurement rate. The sensor rejects 10 klux of background light, still with a precision better than 20 mm at 2 m.

Design rules are proposed for UVA vertical-cavity surface-emitting laser diodes, and the modal gain and cavity properties are analyzed using an electro-optical numerical model. To achieve a low threshold current, it is important to align the gain-peak and resonance wavelengths, but the quantum-confined Stark effect makes that difficult because the former wavelength shifts with changing current density. The relationship between the gain peak and the injection current is discussed. Also, the quantum-well design affects the gain characteristics, and the gain properties with different quantum-well number, composition, and width are discussed.

In this letter, a high-power step-up dc/dc converter dedicated to dc offshore wind farms is proposed, with the combination of half-bridge submodules, thyristors, diodes, and transformer. Compared with the other promising dc/dc topologies, the device numbers, costs, losses, and energy storage requirement are greatly reduced. The operation principle is introduced. The effectiveness and validity are confirmed by simulation and experimental results.

It is a common knowledge that the efficiency of a PV solar device is very small chiefly as a result of the exhibition of non-linear characteristics of its output parameters. However, this paper presents an exploratory work on the comparison of a single diode model and double diode model based on InGaN that has better conversion efficiency than its silicon pairs. This work further illustrates how efficiency of a solar cell can be improved. MATLAB is employed as the simulation tool for modelling and analysing the two models, mathematical modelling is designed using a Simulink. The paper further explains in great details the various parameters of a PV module and under variable temperature and irradiance checks for the accurate performance of both double and single diode model using MSX60 solar module. Parameters like maximum voltage, maximum power and efficiency are used to evaluate the accuracy in order to justify better model. The results obtained portray that the models have the ability to extract PV parameters efficiently. It was also observed that both two models performed well at different conditions of temperature and irradiance, even though at higher temperature, double diode outperformed single diode. Hence, it can be concluded that double diode irrespective of computational complexity is better than single diode.

The process of marking the surface by laser provides advantages for applications in many fields due to its high processing speed, non-contact precision marking at constant quality with minimal human intervention. The produced laser marked objects are used for product identification and traceability and also to prevent illegal copying of products. In this regard, mark readability seems to be one of the factors responsible to produce good quality marks. The application of process parameters such as laser power, scanning speed and pulse frequency had a significant role for marking engineering materials surface for qualities and characteristics. The paper focused to generate good quality square shaped marked surface in a minimal possible time on the surface of stainless steel 304 using multi diode pumped fiber laser marking system. The studies provides the process parameters influence on marking characteristics for a single pass laser marked surface. Experimental results revealed that the application of process parameters such as laser power of 15 W, pulse frequency of 50 kHz, scanning speed of 35 mm/s and duty cycle of 99% produces better squared shaped marks on stainless steel 304.

Polar GaInN and AlGaN quantum wells (QWs) are widely used in light emitting diodes and laser diodes (LDs). However, the widths of such QWs are usually limited to a few nanometers in order to ensure a sufficiently large overlap between the wave functions of the ground electron and the ground hole state. By increasing the QW width we enter the area of ‘dead’ width where, the overlap of the electron and hole wave functions decreases almost to zero and the luminescence efficiency drastically deteriorates. Therefore, it is assumed that wide QWs are not suitable for light emitters and very wide (8-15 nm) QWs are not considered as a promising gain medium for LDs. Hence such QWs are very rarely studied both experimentally and theoretically. In this work the material gain is calculated for Ga0.8In0.2N/GaN and Al0.8Ga0.2N/AlN QWs with a width varying in the range of 2-15 nm. We observed that the material gain at fixed carrier concentration for these QWs drops to zero with the increase in the QW width and reaches negative values in the width range of ∼4-8 nm even for high carrier concentrations, but after exceeding a certain width to ∼8-12 nm it begins to increase rapidly and reaches the values greater than those observed for narrow QWs. This phenomenon is related to the screening of the built-in electric field by carriers, which is easier for wide QWs, and the reduction of the distance between the energy levels for electrons and holes. For the latter reason, optical transitions between higher energy states make a very significant contribution to the positive material gain .

We present a high-resolution and large dynamic range π-phase-shifted fiber Bragg grating (π-PSFBG) temperature sensor. A current modulated laser diode with a linearized optical frequency sweep is used to interrogate the sensor. The sensor is comprised of a π-PSFBG sensing head and an HCN gas cell. The gas cell functions as an absolute frequency reference to compensate for the laser frequency drift. The reflection spectrum is sent to a lock-in amplifier to generate the error signal, proportional to the first order derivative of the spectrum. The center frequency difference that carries sensing information between the π-PSFBG and HCN gas cell is calculated by cross-correlation of their error signals. A sinusoidal modulation enables to move the data processing from low-frequency stage to high-frequency stage, by phase-sensitive detection and low-pass filtering, the interferences caused by laser intensity noises and electronic devices’ noises are significantly reduced. In the experiment, a frequency resolution of 3.696 MHz with a 55 GHz mode-hop-free tuning range, is achieved, corresponding to a temperature resolution of 2.6 mK with a dynamic range from 5 to 40 °C.

AlGaN based deep ultraviolet light-emitting diodes (DUV LEDs) have wide applications in many fields, such as air and water purification, disinfection, and biochemical inspection. However, the wall plug efficiency (WPE) of DUV LEDs is relatively low for these applications, which is due to the low light extraction efficiency (LEE) yielding limited light output from LED package. In this work, we proposed a quartz lens with three-dimensional (3D) structure to enhance the light extraction of DUV LEDs. The optical models of DUV LEDs were established and the optical performances of DUV LEDs were investigated by using optical simulation. The DUV LEDs with the 3D quartz lens exhibit higher light efficiency than those with traditional quartz lens structure. Compared with the traditional structure, the light output power of the 3D lens structure is enhanced by 25.93% at the current of 140 mA and the packaged DUV LED can achieve a wide light angle of 153.2°. It is attributed to the significant light extraction enhancement of the sidewall emission from DUV LED chip.

An anomalous aluminum-mediated material transport process was investigated in sets of Ge-on-Si photodiodes with broadband optoelectrical characteristics measured at wavelengths from 255 nm to 1550 nm. The diodes had “PureGaB” anode regions fabricated by depositing a Ga wetting layer capped with an 11-nm-thick B-layer on 0.5 µm-thick Ge islands grown on Si. The Al metallization was able to reach the Ge-Si interface through ~ 0.1-µm-wide holes inadvertently etched along the perimeter of the Ge-islands, and then traveled along the Ge-Si interface, displacing and recrystallizing Ge and Si. The rest of the Ge surface was protected from the Al contact metallization by the B-layer. For diodes that had received the standard 400°C Al alloying step, the responsivity was near-theoretical at 406 nm and 670 nm, but, at 1310 nm and 1550 nm, the proximity of Ge-Si interfacial defects caused significant attenuation. Extra annealing at 400°C or 500°C enhanced the formation of Si pits that were filled with modified Ge crystals alloyed with Si andp-doped with Al. All these diodes maintained low dark currents, below 50 µA/cm2at 2 V reverse bias, but the responsivity was degraded, particularly for the long wavelengths. On the other hand, neither responsivity nor degradation of current–voltage (I–V) characteristics was observed for prolonged exposure to normal operating temperatures up to 100°C. Since the direct Al contacting of the Ge sidewalls does not degrade the dark current, for large diodes it could be a low-cost method of obtaining low contact resistance to an anode withp-type sidewall passivation and high fill-factor.

This article presents a novel two-channel light emitting diode (LED) current balancing method using current-fed (CF) quasi-Z-source (qZS) dc–dc converter. The proposed LED driver is simple in structure and requires minimal number of component counts. Currents flowing through the two LED strings are automatically balanced owing to charge (amp–sec) balance condition on capacitors in the CF–qZS network. Since current balancing is achieved automatically by passive components, current control of the proposed converter is very simple. In addition, the proposed circuit uses only one active switch and one diode. The operating principle and characteristics of the proposed two-channel LED driver are analyzed in detail. To verify validity of the proposed converter, 80 W prototype is built and tested.

This brief presents a novel switched-capacitor multilevel inverter (SCMLI). The inverter can produce a 7-level output voltage utilizing a dc source, nine switches, two series-connected diodes, and three capacitors. The capacitors are charged from the supply voltage directly by turning on appropriate switching states. The proposed structure realizes all the output voltage levels without an H-bridge circuit at the load-end. A detailed comparison study with other similar inverters has been presented. It shows that the proposed SCMLI requires a lower number of components and is more cost-effective as compared to other inverters. The circuit build-up, capacitor charging process, operating principle, voltage stress analysis, and capacitor selection procedure of the proposed inverter is presented in detail. Finally, an extensive experimental study validates the performance and effectiveness of the proposed inverter.

The presence of lateral leakage through organic semi-conductive layers in organic light-emitting diodes (OLEDs) array prevents excellent performance of display application especially in high resolution one. To mitigate the impact of lateral leakage and figure out the detailed mechanism, an accurate model involving simultaneous measurements of OLED and organic thin film transistor (OTFT) is proposed. The results establish that the lateral leakage generates to the adjacent off-state devices due to a p-type thin film transistor-like effects with the cathode playing a gate function. The proposed technique reveals that higher gate voltage and source voltage brings in more serious lateral leakage, corresponding to the electric field effect. It also shows a temperature dependence when the environment has changed. The research opens the possibility of considering the influences of semi-conductive layers and parallel structural devices on more self-luminous arrays for their actual application.

This article introduces a new single-phase five-level inverter with reduced switch count, composed by a coupled-inductor, four switches, and two diodes. Its detailed analysis is provided, including a space-vector pulsewidth modulation strategy and design of its components. Compared with the conventional three-level neutral-point clamped (NPC) inverter, the introduced converter generates an output waveform with five levels, while having the same number of devices. In addition, the topology uses less components and has lower conduction losses than other existing five-level inverters. The reduced number of devices leads to a fewer number of gate drives, decreasing the cost and complexity of the system. Simulation and experimental results validate the theoretical analysis of the introduced inverter.

We investigate the transport behavior of two-terminal graphene ballistic devices with bias voltages up to a few volts suitable for electronics applications. Four graphene devices based ballistic designs, specially fabricated from mechanically exfoliated graphene encapsulated by hexagonal boron nitride, exhibit strong nonlinear I-V characteristic curves at room temperature. A maximum asymmetry ratio of 1.58 is achieved at a current of 60 µA at room temperature through the ballistic behavior is limited by the thermal effect at higher bias. An analytical model using a specular reflection mechanism of particles is demonstrated to simulate the specular reflection of carriers from graphene edges in the ballistic regime. The overall trend of the asymmetry ratio depending on the geometry fits reasonably with the analytical model.

This paper presents the development and validation of a building integrated photovoltaic (BIPV) simulation platform which can introduce and characterise main faults of BIPV systems. The coupling of the electrical circuit with thermal balance, and the introduction of different faults and their interactions with broken/active protection diodes are among the main contributions of this study. Through comparison with the data measured from a real BIPV installation, it was found that this platform is able to provide an acceptable prediction of the performance of BIPV systems. The design and test of a series of scenarios demonstrated that this platform was capable to simulate and characterise dynamic faulty operations of BIPV systems influenced by various faults. It was found that short-circuit current, gradient information and inflection point in the current-voltage (I–V) curve can be utilised to discriminate the aging and medium partial shading faults with corresponding broken/active bypass diodes. The open-circuit voltage and inflection point in the I–V curve, and the PV cell temperature can be used to distinguish the short-circuit fault in a PV string and inter-string short-circuit fault, with corresponding broken/active blocking diodes. Hotspot phenomenon can also be observed if a minor partial shading fault was introduced in the simulation.

InP quantum dots (QDs)-based light-emitting diodes (QLEDs) are considered as one of the most promising candidates for environmentally cadmium (Cd)-free electroluminescence devices. However, the performance of InP QLEDs still lags far behind that of Cd-containing QLEDs, which limits their practical applications in next-generation displays and lighting. Here, we report an all-solution processed green InP QLED, which is enabled by an electron transport layer (ETL) of In-doped ZnO (IZO) nanoparticles (NPs). The ETL of IZO NPs can not only suppress the exciton quenching of InP QDs emitting layer due to the reduced defect states, but also improve the charge balance by partially blocking the injection of electrons, and thus the device performance. The optimized InP QLED exhibits a maximum external quantum efficiency (EQE) of 5.42% corresponding to a current efficiency (CE) of 21.22 cd A-1, which is three times higher than that of the control device based on ZnO ETL, respectively. Our work suggests that IZO NPs can function as a good ETL material in QLEDs and other optoelectronic devices.

Metal halide perovskites, as a new generation of semiconductor materials, have been widely applied in various optoelectronic devices, especially in the field of perovskite light-emitting diodes (PeLEDs). The external quantum efficiencies (EQEs) of green, red, and near-infrared PeLEDs have exceeded 20% for the last few years, which are comparable to those of the state-of-the-art organic light-emitting diodes (OLEDs) and quantum-dot light-emitting diodes (QLEDs). However, the performances of blue PeLEDs lag far behind those of their counterparts, presumably due to the low quantum yields of blue perovskite films, the instability of the emission spectra, and the difficulties in charge injection for the devices under operation conditions. In this review, the structures and physical properties of blue emissive perovskite materials and the preparation methods of the corresponding perovskite films are firstly addressed. Then, the recent advances and strategies to improve the efficiency of blue PeLEDs are outlined, and the main challenges faced with the blue PeLEDs are also discussed. Finally, an outlook on blue LEDs based on perovskite materials is proposed.