Diode Conduction Research Articles

Single-Phase Grid-Connected Motor Drive System With DC-Link Shunt Compensator and Small DC-Link Capacitor

The single-phase diode rectifier system with small dc-link capacitor shows wide diode conduction time and it improves the grid current harmonics. By shaping the output power, the system meets the grid current harmonics regulation without any power factor corrector or grid filter inductor. However, the system has torque ripple and suffers efficiency degradation due to the insufficient dc-link voltage. To solve this problem, this paper proposes the dc-link shunt compensator (DSC) for small dc-link capacitor systems. DSC is located on dc-node in parallel and operates as voltage source, improving the system performances. This circuit helps the grid current-shaping control during grid-connection time, and reduces the flux-weakening current by supplying the energy to the motor during grid-disconnection time. This paper presents a power control method and the design guideline of DSC. The feasibility of DSC is verified by simulation and experimental results.

A study of thermal conductivity in graphene diodes and transistors with intrinsic defects and subjected to metal impurities

In this paper, the effect of the presence of cavities resulting from the fabrication process and the effect of common metal impurities added during the synthesis process on the thermal conductivity of single-layer graphene sheets, diodes and transistors have been investigated by using the Reverse Non Equilibrium Molecular Dynamics (RNEMD) method. The obtained results show that thermal conductivity generally diminishes by increasing the concentration of nanoparticles and increases when porosities and impurities are at the edges of sheets. Regarding a better thermal management in graphene with the addition of nanoparticles, and considering its existing porosity, a lower thermal conductivity is achieved by adding more nanoparticles. By increasing the diameter of pores from 0.5 nm to 4.4 nm in a specific single-layer graphene sheet, thermal conductivity diminishes from 67 W/mk to 1.43 W/mk; while it diminishes from 45 to 1.0 W/mk for the same structure containing both the defects and nanoparticles over the defects. In evaluating the influences of cavities and metallic nanoparticles on thermal conductivity, it was observed that changing the share of cavities or nanoparticles has a significant effect on the thermal conductivity of graphene diodes and transistors. The rectification efficiency of diodes diminished from about 100% for the defect-free diode to about 19% for the diode containing 2 nm cavities and then increased to 75% for the diode with 5 nm cavities. While, with the increase in the concentration of iron nanoparticles, the rectification efficiency increased from about 100% for the diode with no iron particles to about 255% for the diode containing 13 wt % of iron particles. Final results demonstrate that the metallic nanoparticles and also defects with specific diameters can be effectively exploited to increase or decrease the efficiency of nanodiodes and nanotransistors. This leads to engineered design of nanodiodes and nanotransistors for various applications.

An 18 V Input 10 MHz Buck Converter With 125 ps Mixed-Signal Dead Time Control

A highly integrated synchronous buck converter with a predictive dead time control for input voltages ${ > } 18\,\text{V}$ with 10 MHz switching frequency is presented. A high resolution dead time of ${\sim} 125\,\text{ps}$ allows to reduce dead time dependent losses without requiring body diode conduction to evaluate the dead time. High resolution is achieved by frequency compensated sampling of the switching node and by an 8 bit differential delay chain. Dead time parameters are derived in a comprehensive study of dead time depended losses. This way, the efficiency of fast switching DCDC converters can be optimized by eliminating the body diode forward conduction losses, minimizing reverse recovery losses and by achieving zero voltage switching. High-speed circuit blocks for fast switching operation are presented including level shifter, gate driver, PWM generator. The converter has been implemented in a 180 nm high-voltage BiCMOS technology. The power losses were measured to be reduced by up to 31% by the proposed dead time control, which results in a 5.3% efficiency increase at ${V_{\rm IN} = } 18\,\text{V}$ , ${V_{\rm OUT} = } 5\,\text{V}$ , and 0.45 A load. At ${V_{\rm IN} = }12\,\text{V}$ , the peak efficiency is 81.2% with an efficiency improvement of 6% with dead time control.

Dependence of the conductivity on the active-region thickness in GaAs thin-film Schottky diodes

The dependences of the electrical characteristics of thin-film structures with Schottky barrier on gallium arsenide are studied using Monte Carlo numerical simulation in the kinetic approximation with the main scattering mechanisms taken into account. The dependences of the diode conductivity on the voltage and channel thickness are obtained. It is shown that the relation between the diode voltage and conductivity changes at a small channel thickness, which is explained by barrier field expulsion to the substrate.

A 10-MHz Isolated Synchronous Class-Φ2 Resonant Converter

Because of the forward recovery, the performance of the diodes degrades seriously at multimegahertz, causing extremely high power loss. So, the synchronous rectification (SR) is strongly desired in the multimegahertz resonant converters. This paper proposes a self-driven level-shifted resonant gate driver (RGD) for the SR FET in a 10-MHz isolated class-Φ2 resonant converter. The proposed RGD provides precise switching timing for the SR so that the body diode conduction loss can be minimized. A control stage is introduced to the proposed RGD to block the circulating current and the low-impedance path in the driver to realize ON–OFF control of the converter with high efficiency. The proposed RGD also generates a tunable dc bias to increase the peak gate voltage and extend the conduction time with the optimal $R_{{\rm DS}({\rm on})}$ so that the average $R_{{\rm DS}({\rm on})}$ and the associated conduction loss can be reduced significantly. A 10-MHz prototype with 18-V input and 5-V/2-A output was built. At full load of 2 A, the proposed RGD improves the efficiency from 80.2% using the conventional RGD to 82% (an improvement of 1.8%). Compared to the efficiency of 77.3% using the diode rectification, the efficiency improvement is 4.7% at full load.

On the Impact of Timer Resolution in the Efficiency Optimization of Synchronous Buck Converters

Excessive dead time in complementary switches causes significant energy losses in DC-DC power conversion. The optimization of dead time prevents the degradation of overall efficiency by minimizing the body diode conduction of power switches and, as a consequence, also reduces reverse recovery losses. The present work aims at analyzing the influence of one of the most important characteristics of a digital controller, the timer resolution, in the context of dead-time optimization for synchronous buck converters. In specific, the analysis quantifies the efficiency de-pendency on the timer resolution, in a parameter set that comprises duty-cycle and dead-time, and also converter frequency and analog-to-digital converter accuracy. Based on a sensorless optimization strategy, the relationship between all these limiting factors is described, such as the number of bits of timer and analog-to-digital converter. To validate our approach experimental results are provided using a 12-to-1.8V DC-DC converter, controlled by low- and high-resolution pulse-width modulation signals generated with an XMC4200 microcontroller from Infineon Technologies. The measured results are consistent with our analysis, which predicts the power efficiency improvements not only with a fixed dead time approach, but also with the increment of timer resolution.

Enabling High-Frequency High-Efficiency Non-Isolated Boost Converters With Quasi-Square-Wave Zero-Voltage Switching and On-Chip Dynamic Dead-Time-Controlled Synchronous Gate Drive

This paper presents techniques to enable non-isolated boost converters to achieve high power efficiencies under high switching frequency and high-voltage conditions. A quasi-square-wave zero-voltage switching (QSW-ZVS) boost converter topology is proposed to achieve high-frequency soft switching without any coupled inductors in the power stage and, thus, minimize the switching power loss of the converter. An on-chip dynamic dead-time controller is developed to provide near-optimum dead time for power FETs during switching transitions under different output voltage and load current conditions in order to achieve ZVS with minimal body diode conduction loss of power FETs. A synchronous gate driver is also proposed to provide fast propagation delays and output signal rise/fall time, enabling megahertz operation of the converter. A hardware boost converter prototype is built with the synchronous gate driver circuitry implemented in a 0.5-μm high-voltage CMOS process. The proposed QSW-ZVS boost converter provides an output voltage of 150 V and delivers an output power of 130 W. The peak power efficiency of the proposed converter achieves 92.7% at the switching frequency of 1 MHz. Compared with state-of-the-art gate drivers, the worst-case propagation delay of the proposed synchronous gate driver is improved by at least 7.6 times. The operation frequency of the proposed non-isolated boost converter is also improved by at least 15 times compared with other state-of-the-art counterparts.

Investigation of gate-diode degradation in normally-off p-GaN/AlGaN/GaN high-electron-mobility transistors

Gate diode conduction mechanisms were analyzed in normally-off p-GaN/AlGaN/GaN high-electron mobility transistors grown on Si wafers before and after forward bias stresses. Electrical characterization of the gate diodes indicates forward current to be limited by channel electrons injected through the AlGaN/p-GaN triangular barrier promoted by traps. On the other hand, reverse current was found to be consistent with carrier generation-recombination processes in the AlGaN layer. Soft breakdown observed after ∼105 s during forward bias stress at gate voltage of 7 V was attributed to formation of conductive channel in p-GaN/AlGaN gate stack via trap generation and percolation mechanism, likely due to coexistence of high electric field and high forward current density. Possible enhancement of localized conductive channels originating from spatial inhomogeneities is proposed to be responsible for the degradation.

High efficiency DCM buck converter with dynamic logic based adaptive switch-time control

This paper presents a dynamic logic based adaptive switch-time control circuit (DASTC) for fast control to minimize body diode conduction losses and dead-time of a buck regulator operating in discontinuous conduction mode. Dead-time is an important metric for improving efficiency of low voltage converters. DASTC provides instant sensing and feedback based on the load to minimize dead-time significantly compared to prior-art and scales low side power switch pulse width adaptively across load currents, just enough to discharge the stored inductor energy fully. Furthermore, the converter has inherent pulse skipping mode to lower the switching frequency at light loads to enhance light load efficiency. The proposed 1.5 V buck regulator was fabricated in 0.35 $$\upmu$$μm CMOS process with an input voltage range of 1.8---3 V and load current range of 1---200 mA. Measurement results demonstrate a peak power efficiency of 94.6 % and a high overall power efficiency ( >~89 %) for load currents greater than 5 mA for $${V_{IN}}$$VIN = 1.8 V. The proposed scheme achieves 4× (~5 ns) better dead-time and 4---5.5 % better power efficiency compared to prior-art over the load current range.

Charge equalisation for series‐connected LiFePO 4 battery strings

LiFePO4 batteries are suitable for high power applications because of their advantages of large discharge current and high efficiency. Owing to the characteristics of LiFePO4 batteries, it may cause overcharge/over-discharge and reduce the cycle life of the battery when series-connected batteries are used. This study proposes a charge equaliser based on an interleaved active clamp flyback converter. The interleaved topology reduces the output ripple current. Therefore the rectifier diode conduction loss can be reduced. With a clamp capacitor and leakage inductance, the switches are turned on with zero-voltage switching while the voltage stress of switch is reduced. Furthermore, a constant switching frequency and duty ratio are designed to achieve a simple control for the proposed system. The simulations and experimental results are provided to verify the performance of the proposed charge equaliser.

Reducing Switching Losses in BLDC Motor Drives by Reducing Body Diode Conduction of MOSFETs

This paper presents a new power electronic topology that aims to reduce switching losses in hard-switched inverters for brushless dc (BLDC) motor drives. This is achieved by extending the benefits of synchronous rectification used in low-voltage switch-mode dc-dc conversion to high-voltage motor drive applications and by minimizing the reverse conduction behavior of the intrinsic body diode of the synchronous rectifier MOSFET. The proposed topology for reducing body diode conduction includes the addition of a MOSFET in series with the rectifying switch and a SiC Schottky diode around the series switch combination. This paper focuses on theory, simulations, and experimental results and validates the benefits of proposed new topology for BLDC motor drive applications. An extension of this topology for sinusoidal back electromotive force permanent-magnet motors is also presented.

An active‐clamping zero‐voltage‐switching flyback converter with integrated transformer

SummaryThis paper proposes an active‐clamping flyback converter using an integrated transformer. The proposed converter is composed of two active‐clamp flyback converters. The presented converter can balance the total load current between secondary sides of two transformers so that the rectifier diode conduction loss is reduced. Also, the main switch of one converter is the auxiliary switch for the other converter, so that only two switches are required and both can achieve zero‐voltage‐switching operation. The two transformers are integrated into one magnetic core; therefore, the volume and copper loss of transformer can be reduced. Detailed analysis and design of this integrated magnetic active‐clamping flyback converter are described. Experimental results are recorded for a prototype converter with an AC input voltage ranging from 85 to 135 V, an output voltage of 24 V and an output current of 5 A, operating at a switching frequency of 100 kHz. Copyright © 2014 John Wiley & Sons, Ltd.

Actively bias-controlled metamaterial to mimic and modulate electromagnetically induced transparency

We present an active microwave metamaterial composed of orthogonally arranged cut wires and positive-intrinsic-negative diodes, having capability of high-speed response. When a forward voltage is applied to turn the diodes on, analogue spectral response of a classical electromagnetically induced transparency is observed at 6.13 GHz for destructive interference between dipolar and quadrupolar resonances in the cut wires. Besides, experiments demonstrate that around the frequency, response amplitude is modulated continuously by sweeping the bias, and intensity modulation depth is up to 85%. Surface current distributions verify that the diode conductivity decides coupling efficiency of the resonant fields and consequent the amplitude. Simulated and measured spectra are in good agreement.

High efficiency and low electromagnetic interference boost DC–DC converter

A synchronous boost DC–DC converter with an adaptive dead time control (DTC) circuit and anti-ringing circuit is presented. The DTC circuit is used to provide adjustable dead time and zero inductor current detection for power transistors and therefore, a high efficiency is achieved by minimizing power losses, such as the shoot-through current loss, the body diode conduction loss, the charge-sharing loss and the reverse inductor current loss. Simultaneously, a novel anti-ringing circuit controlled by the switching sequence of power transistors is developed to suppress the ringing when the converter enters the discontinuous conduction mode (DCM) for low electromagnetic interference (EMI) and additional power savings. The proposed converter has been fabricated in a 0.6 μm CDMOS technology. Simulation and experimental results show that the power efficiency of the boost converter is above 81% under different load currents from 10 to 250 mA and a peak efficiency of 90% is achieved at about 100 mA. Moreover, the ringing is easily suppressed by the anti-ringing circuit and therefore the EMI noise is attenuated.

Space charge limited conduction in ultrathin PbS quantum dot solid diodes

As a simple and direct characterization of carrier transport in nanocrystal quantum dot (NQD) solids, current-voltage characterization of ultrathin diodes is proposed. We found the space charge limited conduction (SCLC) behavior in ultrathin PbS NQD diodes with active layer thickness half of the full depletion width; and extracted hole concentrations in the order of 1015 cm−3, hole mobilities from 10−4 to 10−5 cm2/Vs, trap energy depths varying from 140 meV to 200 meV, and volume trap density around 1017 cm−3 for thin films with NQDs of diameters 3.3 and 3.6 nm, respectively. We further discuss the validity of applying SCLC to the NQD solids based diodes and the implications of the extracted parameters extensively. Proposed characterization method here is a direct measure of carrier transport in solar cell structures which could provide exact directions in NQD solids based solar cell fabrication and modeling.

New ZVS DC--DC Converter With Series-Connected Transformers to Balance the Output Currents

A new zero-voltage switching (ZVS) dc converter for high input voltage and high output current applications is presented in this paper. Two three-level pulse-width modulation (PWM) circuits with the same active switches connected in parallel at the output side are adopted to achieve load current sharing and to decrease current stress of rectifier diodes. The center-tapped rectifiers are adopted at the secondary side to have only one diode conduction loss in the forward current path. The series resonant tank of three-level converter is used to achieve ZVS turn-on for all power switches and zero-current switching for all rectifier diodes within nearly entire load range. Thus, the switching losses of power switches are reduced and the reverse recovery losses of rectifier diodes are eliminated. In order to overcome the drawback of a wide range of switching frequency in conventional series resonant converters, the fixed frequency pulse-width modulation is adopted to regulate the output voltage. The series-connected transformers are used in the primary and secondary sides to share and balance the load current. Finally, experiments based on a laboratory prototype are provided to verify the operation principle and demonstrate the effectiveness of the proposed converter.

Amplification of microwave oscillations on harmonics of the Gunn diode conductivity

The results of studying microwave amplifiers on the second harmonic of the negative conductivity of Gunn diodes operating in the centimeter waveband are presented.

Nonisolated Flyback Switching Capacitor Voltage Regulator

This paper proposes a novel nonisolated flyback switching capacitor voltage regulator. The converter is a combination of a switching capacitor converter and a pulsewidth modulation voltage regulator, and it has the following advantages: 1) the switches achieve zero voltage switching (ZVS); 2) the self-driven method of the synchronous rectifier (SR) is applied to save the drive loss and the body diode conduction loss; 3) the transformer leakage inductor is utilized to realize the soft switching of the switches; and 4) single-phase option makes it more flexible. Its derivation, operation principle, and self-driven method are presented. A single-phase 700 kHz 1.2 V/35 A output point-of-load prototype was built to verify the analysis.

Enhanced x-ray detection sensitivity in semiconducting polymer diodes containing metallic nanoparticles

Semiconducting polymer X-radiation detectors are a completely new family of low-cost radiation detectors with potential application as beam monitors or dosimeters. These detectors are easy to process, mechanically flexible, relatively inexpensive, and able to cover large areas. However, their x-ray photocurrents are typically low as, being composed of elements of low atomic number (Z), they attenuate x-rays weakly. Here, the addition of high-Z nanoparticles is used to increase the x-ray attenuation without sacrificing the attractive properties of the host polymer. Two types of nanoparticles (NPs) are compared: metallic tantalum and electrically insulating bismuth oxide. The detection sensitivity of 5 µm thick semiconducting poly([9,9-dioctylfluorenyl-2,7-diyl]-co-bithiophene) diodes containing tantalum NPs is four times greater than that for the analogous NP-free devices; it is approximately double that of diodes containing an equal volume of bismuth oxide NPs. The x-ray induced photocurrent output of the diodes increases with an increased concentration of NPs. However, contrary to the results of theoretical x-ray attenuation calculations, the experimental current output is higher for the lower-Z tantalum diodes than the bismuth oxide diodes, at the same concentration of NP loading. This result is likely due to the higher tantalum NP electrical conductivity, which increases charge transport through the semiconducting polymer, leading to increased diode conductivity.

Pulsewidth Locked Loop (PWLL) for Automatic Resonant Frequency Tracking in LLC DC–DC Transformer (LLC -DCX)

In recently developed distributed power architecture, the LLC resonant converter has been widely used as a dc–dc transformer (DCX) to provide a semiregulated or unregulated bus voltage. In order to achieve the highest efficiency, this paper proposes a novel switching frequency control scheme for the LLC-DCX. First, the synchronous rectifier (SR) gate-driving signals are tuned by eliminating the body diode conduction. Then, the pulsewidth locked loop (PWLL) is presented, by minimizing the pulsewidth difference between the main switch and the well-tuned SR gate-driving signals, the LLC-DCX always runs at the $f_0$ point to achieve the highest efficiency. For rapid prototyping purposes, the PWLL used to track $f_{0}$ is realized in a Cyclone III field programmable gate array.