Switching Transition Research Articles

Analytical Model to Study Turn-OFF Soft Switching Dynamics of SiC MOSFET in a Half-Bridge Configuration

Switching transients of SiC MOSFET are fast compared to its Si counterpart. Fast switching transient reduces switching loss but may induce prolonged oscillations, spurious turn-on, high device stress, and electromagnetic interference (EMI)-related issues, etc. In soft switched converters, use of external drain source capacitance can reduce these adverse effects along with the reduction in switching loss. However, the selection of external drain source capacitance is not straightforward. A large external capacitance reduces switching loss, (dv/dt), (di/dt), and transient over-voltage but may also result in higher dead-time loss and reduced switching frequency. This article presents an analytical model that captures the soft turn-off switching dynamics of SiC MOSFET using parameters obtained from device datasheet along with the values of external circuit parasitics. Unlike linear approximation, a nonlinear channel current model is used along with a comprehensive model of transfer capacitance. The effect of external gate drain capacitance is also considered. This leads to a better estimation of switching transition time, actual loss, (dv/dt), (di/dt), and transient over voltage. Also, a method to select an optimal value of external drain source capacitance is presented. The proposed model is validated through behavioral simulation and experiment for two 1.2-kV discrete SiC MOSFETs.

Aperiodic sampled-data controller design for switched Itô stochastic Markovian jump systems

In this paper, aperiodic sampled-data control for a class of Itô stochastic Markovian jump systems with switching transition rate matrix containing partially known elements is investigated. By introducing a loop-based Lyapunov functional, mean square exponential stability criteria are presented and mode-dependent aperiodic sampled-data controllers are designed. Due to the constraint on the upper bound of the sampling interval is no greater than the dwell time, the transition rate matrix may switch in a sampling interval. The issue concerning the asynchronization between the sampled-data controller mode and the system mode is hence considered. A practical RLC electrical circuit example is presented to illustrate the effectiveness of the method.

(Invited) Understanding Dynamic RDS(on) in GaN Devices

In this article, we expand on the wide body of experimental and theoretical knowledge of charge trapping phenomena in eGaN devices that cause dynamic on-resistance shifting (dRDS(on)). In previous publications, we advanced a first-principles model to explain this effect, based on the physics of hot carrier scattering. The model led to a set of equations to predict dRDS(on) under different operating conditions of drain voltage, junction temperature, switching frequency and current. In addition, the model has led to iterative improvements in device design, culminating in the near elimination of dynamic on-resistance effects in eGaN devices when operated within datasheet limits.Several groups have studied RDS(on) shifts in GaN FETs that result from single switching waveforms such as in the double-pulse test. EPC’s approach has been to quantify RDS(on) over relatively long time intervals, ranging from billions to trillions of switching transitions. This long-term data is more relevant to practical applications. Furthermore, the resistance rise versus time can be fit to a physics-based model equation. Using these fits, dRDS(on) can be projected out to years of continuous operation, providing an invaluable tool for users to assess lifetime against their mission profile.An example of this kind of long-term data and model fits is provided in Figure 1. The data was taken on the EPC2045 (5th generation 100V eGaN FET). The graph on the left shows the evolution of resistance versus time at different switching voltages (all at a junction temperature of 75 °C). Note that for operation below (and including) the datasheet maximum, dRDS(on) is negligible, even when projected out to 10 years of continuous operation. When operated above datasheet VDSmax, RDS(on) growth is observed, and the evolution is in good agreement with the model. The graph on the right shows data at 150V and two different temperatures. The trapping phenomenon is seen to have a negative temperature activation, whereby on-resistance increases faster at lower temperature. This counter-intuitive result is consistent with the physics of hot carrier scattering, because an electron can travel further between scattering events at lower temperature and therefore gain greater kinetic energy in a given electric field. These highly energetic electrons scatter into unintended regions in the device, where they trap and degrade on-resistance.In this work, we expand on previous results with the following new data and analyses: Long-term dynamic RDS(on) data and model fits for 5th generation 100V and 200V eGaN FETs at various temperatures and voltages extending well beyond datasheet limits.High speed measurements of RDS(on) less than 100 ns after a switching transition, seeking out possible trap states that recover on short timescales but may nonetheless increase switching losses. To within our measurement resolution, we find that eGaN FETs switch to a low resistance state instantly, with no evidence for such “fast” dynamic RDS(on) A comparison of hard-switching versus soft-switching. In contrast to some other GaN technologies, we find that eGaN is essentially immune to dRDS(on) under soft-switching conditions, consistent with the underlying physics of hot carrier scattering.A comparison of inductive versus resistive hard-switching. Despite the different loci in current-voltage space traversed during these two types of switches, we find the impact on dRDS(on) to be minor. This result affirms that the simpler resistive hard-switching circuit is an equally valid method to characterize dRDS(on) in eGaN.Effect of switching speed, with transitions ranging from 1-50 ns.Effect of third quadrant operation. Some GaN technologies suffer from adverse trapping effects when operated in reverse conduction, as can occur during dead time or synchronous operation in a dc-dc converter. We see no evidence for these effects in eGaN. Figure 1

Real Exchange Rates and Fundamentals in a new Markov‐STAR Model*

AbstractWe propose a new nonlinear Markov‐STAR model to capture both the Markov switching and smooth transition dynamics for real exchange rates. We derive stationarity conditions for the model and apply it to the real exchange rates of 17 countries. We relate switching equilibrium rates and volatilities to a set of relevant macroeconomic variables and find, consistent with economic intuitions, that an economy deteriorating relative to the US economy tends to see a significantly increased likelihood of real exchange rate depreciation. Moreover, we document significant connections between rising economic uncertainties and real exchange rate changes as well as exchange rate volatility.

Decision trees within a molecular memristor.

Profuse dendritic-synaptic interconnections among neurons in the neocortex embed intricate logic structures enabling sophisticated decision-making that vastly outperforms any artificial electronic analogues1-3. The physical complexity is far beyond existing circuit fabrication technologies: moreover, the network in a brain is dynamically reconfigurable, which provides flexibility and adaptability to changing environments4-6. In contrast, state-of-the-art semiconductor logic circuits are based on threshold switches that are hard-wired to perform predefined logic functions. To advance the performance of logic circuits, we are re-imagining fundamental electronic circuit elements by expressing complex logic in nanometre-scale material properties. Here we use voltage-driven conditional logic interconnectivity among five distinct molecular redox states of a metal-organic complex to embed a 'thicket' of decision trees(composed of multiple if-then-else conditional statements) having 71 nodes within a single memristor. The resultant current-voltage characteristic of this molecular memristor (a 'memory resistor', a globally passive resistive-switch circuit element that axiomatically complements the set of capacitor, inductor and resistor) exhibits eight recurrent and history-dependent non-volatile switching transitions between two conductance levels in a single sweep cycle. The identity of each molecular redox state was determined with in situ Raman spectroscopy and confirmed by quantum chemical calculations, revealing the electron transport mechanism. Using simple circuits of only these elements, we experimentally demonstrate dynamically reconfigurable, commutative and non-commutative stateful logic in multivariable decision trees that execute in a single time step and can, for example, be applied as local intelligence in edge computing7-9.

Field-controlled tunability of novel multifunctional phenomena in Tb-substituted La2CoMnO6: Role of antisite disorder

Multifunctional materials have gained huge attention owing to their great possibility in device applications. However, producing single-phase multifunctional materials, associated with various novel properties, has been proved to be a serious challenge. A simple yet effective way to overcome this barrier, is therefore of great importance. Here, we report the evolution of temperature- and magnetic field-dependent novel multifunctional phenomena in polycrystalline La2-xTbxCoMnO6. Substitution of Tb in ferromagnetic La2CoMnO6, induces antiferromagnetic ordering through development of antisite disorder and antiphase boundaries, and results in a phase separation between ferromagnetic/antiferromagnetic layers. This originates the coexistence of conventional and inverse magnetocaloric effects in this system. The switching between them, with its tunability with temperature and magnetic field, suggests a huge potential of this compound. In addition, a clear correlation is established between the magnetocaloric switching and field-induced metamagnetic transitions. Furthermore, the discovery of tunable giant exchange bias (~1.8 kOe) at very low cooling field (500 Oe), a reasonable self-exchange bias (270 Oe), and a large negative magnetoresistance (~14%), makes this system enormously attractive for practical applications and fundamental research. The present study proposes a novel and effective route for successfully preparing essential multifunctional compounds to open a new pathway toward room-temperature applications.

High-Performance Computing-in-Memory Architecture Using STT-/SOT-Based Series Triple-Level Cell MRAM

Spin-torque-based magnetic random access memories (MRAMs) have emerged as a promising option for next-generation data-centric computing systems. Multi-level cell (MLC) configuration is an efficient method to increase storage density. In this article, we propose a series triple-level cell (sTLC) architecture based on spin-transfer torque (STT) and spin-orbit torque (SOT) switching mechanisms. The proposed hybrid STT/SOT sTLC MRAM architecture is capable of storing 3 bits of data using a maximum of two writing steps. However, most of the switching transitions (72%) use only single-step writing. The simulation results of the sTLC MRAM showed 82% and 68% saving in the write energy compared with previously published STT and STT-/SOT-based TLC structures, respectively. One-step parallel read operation for sTLC is presented in this work that enables ultra-fast reading of 3 bits of data. Furthermore, a novel sTLC-based computing-in memory (CiM) architecture is proposed, and high-performance AND/OR/XOR and magnetic full-adder (MFA) logic circuits have been implemented. The proposed sTLC-based CiM MFA shows 33% lesser transistor counts with nearly equivalent energy performance in comparison to the recently published spin-Hall effect (SHE)-based CiM MFA.

Canoe slalom C1 stroke technique during international competitions

ABSTRACT The purpose of this study was to compare the frequency and duration of on-side and off-side strokes and stroke transitions between male and female canoe slalom athletes during international competitions. We analysed 33 International Canoe Federation World Cup, World Championship and European Canoe Association Championship canoe slalom race videos, from 2018 to 2020, frame-by-frame. We recorded drive durations and transition durations for each race run. We also recorded the frequency of different stroke types and transition types used in each run. Stroke timing parameters differed between female and male athletes. We found that female athletes performed a significantly greater proportion of switch transitions and on-side strokes. Male athletes performed a significantly greater proportion of cross transitions and off-side strokes. Male athletes performed significantly faster cross transitions. On-on and off-off transition durations were significantly faster than cross transitions, and cross transitions were significantly faster than switch transitions. Females had a significantly longer drive duration and lower stroke frequency compared to males. Overall, stroke and drive durations of on-side strokes and off-side strokes were not significantly different. This study identifies stroke technique differences between male and female canoe slalom athletes which can be used as a basis for future research and training.

Mechanisms of Molecular Ferroelectrics Made Simple

Molecular ferroelectrics have captured immense attention due to their superiority over inorganic oxide ferroelectrics, such as environmentally friendly, low-cost, flexible, foldable. However, the mechanisms of ferroelectric switching and phase transition for the molecular ferroelectrics are still missing, leaving the development of novel molecular ferroelectrics less efficient. In this work, we have provided a methodology combining molecular dynamics (MD) simulation on a polarized force field named polarized crystal charge (PCC) and enhanced sampling technique, replica-exchange molecular dynamics (REMD) to simulate such mechanisms. With this procedure, we have investigated a promising molecular ferroelectric material, (R)/(S)-3-quinuclidinol crystal. We have simulated the ferroelectric hysteresis loops of both enantiomers and obtained spontaneous polarization of 7/8 \mu C cm-2 and a corresponding coercive electric field of 15 kV cm-1. We also find the Curie temperature as 380/385 K for ferro-/para-electric phase transition of both enantiomers. All of the simulated results are highly compatible with experimental values. Besides of that, we predict a novel Curie temperature of about 600 K. This finding is further validated by principal component analysis (PCA). Our work would significantly promote the future exploration of multifunctional molecular ferroelectrics for the next generation of intelligent devices.

Robust Self-Regulated Rectifier for Parallel-Resonant Rx Coil in Multiple-Receiver Wireless Power Transmission System

This paper presents a small, low-cost self-regulated rectifier for parallel-resonant receivers (Rxs) in the wireless power transmission (WPT) system to maintain the individual rectifier voltages of each Rx to be constant. The problem of the conventional rectifier-low-dropout regulator (LDO) for parallel-resonant Rx coil is analyzed. Specifically, although the LDO attempts to reduce the excessive voltage by increasing its dropout resistance, this increases the power delivered to the Rx coil and rectifier due to the current source behavior of parallel-resonant Rx coil. To solve the problem, the proposed regulation reduces the total resistance seen by Rx coil so that the power delivered to Rx coil itself is reduced, which is fundamentally different from conventional regulation where excessive received power had to be dissipated at LDO. The proposed regulation does not require complex analog or digital control blocks and abrupt switch transitions, allowing noiseless operation and the low-cost smaller volume with off-the-shelf components. The regulation is demonstrated with commercially available off-the-shelf components for applications of multiple distributed receivers. The proposed method increased the overall efficiency from 20.9% to 43.0% at 2.8-W load power in three individual Rxs.

Adaptive response of a metal-organic framework through reversible disorder-disorder transitions.

The ultrahigh porosity and varied functionalities of porous metal-organic frameworks make them excellent candidates for applications that range widely from gas storage and separation to catalysis and sensing. An interesting feature of some frameworks is the ability to open their pores to a specific guest, enabling highly selective separation. A prerequisite for this is bistability of the host structure, which enables the framework to breathe, that is, to switch between two stability minima in response to its environment. Here we describe a porous framework DUT-8(Ni)-which consists of nickel paddle wheel clusters and carboxylate linkers-that adopts a configurationally degenerate family of disordered states in the presence of specific guests. This disorder originates from the nonlinear linkers arranging the clusters in closed loops of different local symmetries that in turn propagate as complex tilings. Solvent exchange stimulates the formation of distinct disordered frameworks, as demonstrated by high-resolution transmission electron microscopy and diffraction techniques. Guest exchange was shown to stimulate repeatable switching transitions between distinct disorder states.

A Novel Inertial Microswitch With Dynamic Acceleration Band-Pass Characteristics

This letter reports an inertial microswitch with an integrated filtering mechanism to realize acceleration band-pass characteristics. The switch is composed of a normal acceleration threshold switch (a high-pass mechanism) and a specially designed filtering mechanism. Only acceleration between the upper and lower cut-off thresholds can make the switch transition to its `on' state. Both dynamic finite element simulations and experiments were performed to study the dynamic behavior of the switch. The results indicate that the acceleration band-pass characteristics have been successfully achieved. The upper and lower cut-off thresholds and bandwidth varied with shock duration. The experimental data agreed well with the simulated results.

Field tunable spin switching in perovskite YbFeO3 single crystal

We report the spin reorientation transition and spin switching transition in perovskite structure YbFeO3 single crystal. A spin reorientation transition of type Г4→Г2 occurs in the temperature range of 6 ∼ 8 K, and a type-Ⅱ spin switching along c-axis is found at temperature about 20 K under an applied magnetic field of 100 Oe. In field-cooled-cooling (FCC) process, due to the spin reversal of Yb3+ magnetic moments, the magnetic moments coupling of Yb3+ and Fe3+ change from parallel to antiparallel, which leads to a significant drop in magnetization at the transition temperature. Interestingly, the Magnetization vs. magnetic field curves at various temperatures above 8 K–200 K show magnetic field induced spin switching, for which the magnetization switches from negative/positive value to positive/negative value but without change of magnitude at a magnetic field induced spin switching point. The intriguing interaction between the two magnetic sublattices of rare earth (Yb3+) and iron (Fe3+) ions is controllable by the applied magnetic field to regulate the spin switching transition temperature in YbFeO3 single crystal and make it possible as one of low field potential materials for future application in spin devices.

Open Circuit Switch Fault Detection in Flying Capacitor and Cascaded H-Bridge Multilevel Converters

This article proposes a simple and fast active power device open circuit fault detection and localization technique. The proposed technique applies to the family of flying capacitor multilevel converters (FCMCs), including dc/dc FCMCs, single or multi-phase H-bridge FCMCs, and cascaded H-bridge multilevel converters. The localization technique needs to sense the voltage and direction of current at the output terminals of converters to detect and localize the fault. A circuit with multiple window detectors is utilized to track the output voltage level and current direction with high bandwidth. The algorithm compares the measured and expected terminal voltage, considering the commanded switch states and the terminal current direction. Once potential fault locations are identified, healthy switches are filtered out from the set of potential faulty switches over successive switching transitions. The proposed technique is experimentally validated on a single phase H-bridge FCMC. The switch state commands and pulsewidth modulation (PWM) is handled by a DSP while the fault detection and localization algorithm is implemented on a separate field programmable gate array (FPGA). The asynchronous operation of the DSP and FPGA is discussed.

Stability and [formula omitted]-gain analysis of nonlinear positive Markov jump systems based on a switching transition probability

This paper focuses on mean exponential stability and L1-gain analysis for nonlinear positive Markov jump systems (NPMJSs) based on a switching transition probability (STP), where sector nonlinear functions and delays are adopted. By developing a nonlinear stochastic copositive Lyapunov–Krasovskii functional (NSCLKF) approach, a sufficient condition for mean exponential stability of nonlinear positive time-delay Markov jump system is first presented under mode-dependent average dwell time (MDADT) switching by using linear programming (LP) approach. Further, L1-gain performance analysis is obtained. Moreover, the corresponding results for NPMJSs are given under average dwell time (ADT) switching. Illustrative results are provided to verify the validity of the theoretical results.

DC-DC converter with 50 kHz-500 kHz range of switching frequency for passive component volume reduction

This paper presents the relationship of switching frequency towards passive components volume of DC-DC boost converter. Principally, the inductor current ripple and capacitor voltage ripple must be considered in order to design the inductor and capacitor, respectively. By increasing the switching frequency, smaller size and volume of passive component can be designed. As the consequences, the switching loss increases during switching transition at turn-ON and turn-OFF conditions. This paper used soft-switching technique to reduce the switching loss at turn-ON condition. The soft-switching technique is realized by adding resonant circuit in DC-DC boost converter. The effectiveness of resonant circuit will be analysed, thus, the efficiency of the converter can be improved. The range of switching frequency considered in the experimental are 50 kHz to 500 kHz. A 100 W prototype has been developed and tested in order to verify the principle. The switching loss experimentally confirm reduced by implementing soft-switching technique with efficiency converter improved from 96.36% to 97.12% when 500 kHz of switching frequency is considered. The passive components volume reduction is achieved when high switching frequency is used where the total volume of passive component when 50 kHz and 500 kHz are 0.083 dm3 and 0.010 dm3, respectively.

A high-accuracy switching loss model of SiC MOSFETs in a motor drive for electric vehicles

Power loss estimation of power electronic devices is essential to the efficiency optimization of motor drives in electric vehicles. However, most existing power loss models of silicon carbide (SiC) metal-oxidesemiconductor field-effect transistors (MOSFETs) have a low accuracy due to the neglection of parasitic parameters in the motor drive circuitry. In this paper, the voltage and current trajectories of SiC MOSFETs in the switching transition of a motor drive system are analyzed in detail. Based on the analysis, the conduction and switching losses of SiC MOSFETs in the motor drive inverter are modeled. Compared with the traditional power loss models, the proposed analysis model includes parasitic inductances and capacitances in circuitry and the MOSFET, and the reverse recovery loss of the body diode, etc. The experimental results verified that the proposed power loss model has higher accuracy than the conventional model.

High-Speed Medium-Voltage SiC Thyristors for Pulsed Power Applications

The high peak current withstand capability of thyristors makes them extremely suitable for pulsed power applications. Silicon carbide (SiC) thyristors provide significant efficiency advantages compared with their silicon counterparts due to their very fast switching transitions. This article presents the development and characteristics of 3 kV SiC thyristors. A novel current-source gate driver is proposed to enhance their switching speed and, hence, maximize their benefits in pulsed power applications. The proposed driver provides a very high gate current slew rate while limiting the peak of the current pulse. The higher gate current slew rate achieves faster and, thus, more efficient device switching transition. Gate driver circuit description, variant topologies, and experimental results for a 3 kV SiC thyristor for a pulsed power application are presented to verify the proposed concepts.

Decoding of crystal synthesis of fcc-hcp reversible transition for metals: theoretical mechanistic study from facet control to phase transition engineering

The insightful understanding of the phase transition during crystal growth is of essential significance to the future development of functional nanomaterials. However, compared to the intensive efforts in the optimization of experimental synthesis, the decoding of the facet switch and phase transition is still lacking. In particular, the electroactivity difference between the common fcc and hcp phases has been a long-standing challenge for the design of catalysts. Herein, we present a preliminary study of the crystal structure in transition metals regarding the detailed operation strategy for facet control and phase transition within fcc and hcp lattices. Innovatively, we present the pathway of phase change from the most common phases of transition metal fcc to the potential electroactive hcp phase. The directional mapping of the facet switching is systematically investigated as a key reference for experimental synthesis and facet control. The flexible control and modification of high index surfaces are identified due to the subtle energy difference between different facets, where the introduction of strain further facilitates the stabilization and transformation of facets. To verify our proposed idea, the phase change and the corresponding influence on the proton binding have been interpreted for the electrocatalysis. This work supplies a significant reference to the understanding of crystal structure engineering of the scientific community, which paves the avenue to realize the practical phase control and modification of transition metal in broad applications.

Local conservation law of rubber elasticity in hydrogel networks undergoing microphase separation and toughening

Thermoresponsive polymer segments have been reported to induce lateral microphase separations due to their switching transitions from a hydrophilic state to a hydrophobic one in hydrogels, which result in shrinkage and collapse of the polymer networks and significantly improved mechanical strength. However, the route from which the hydrophobic segments are assembled into micelles during microphase separations, and their thermoresponsive toughening mechanisms are not fully understood. In this study, a local conservation law of rubber elasticity is firstly formulated to describe the micellization and collapse of polymer networks in hydrogels, during which the thermoresponsive segments undergo a microphase separation. Flory-Huggins theory, interfacial free-energy equation and the extended Maxwell model are then employed to model the thermodynamics of micellization and microphase separations in the hydrogel, in which the polymer networks are composed of both hydrophilic and thermoresponsive segments. The toughening mechanism is further explored and discussed based on the proposed models. Finally, the proposed models have been verified using the experimental results reported in the literature. This study provides a new mechanism of local conservation law for rubber elasticity in hydrogels and also critical insights into the physical principles which govern the molecular self-assembly.