High Current Mode Research Articles

Research of growth mechanism of ceramic coatings fabricated by micro-arc oxidation on magnesium alloys at high current mode

Abstract Micro-arc oxidation (MAO) coatings of ZK60 magnesium alloys were formed in a self-developed dual electrolyte composed of sodium silicate and phosphate at the high constant current of 1.8 A (15 A/dm 2 ). The MAO process and growth mechanism were investigated by scanning electron microscopy (SEM) coupled with an energy dispersive spectrometer (EDS), confocal laser scanning microscopy and X-ray diffraction (XRD). The results indicate that the growth process of MAO coating mainly goes through “forming → puncturing → rapid growth of micro-arc oxidation →large arc discharge → self-repairing”. The coating grows inward and outward at the same time in the initial stage, but outward growth of the coating is dominant later. Mg, Mg 2 SiO 4 and MgO are the main phases of ceramic coating.

Catalytic hydrogen–oxygen reaction in anode and cathode for cold start of proton exchange membrane fuel cell

Fuel cell vehicles (FCVs) have shown the potential of commercialization in recent years. The concerns on the startup ability of proton exchange membrane (PEM) fuel cell stack from subfreezing temperature have risen. The hydrogen–oxygen catalytic reactions assisted cold start method is developed and analyzed in this study. It utilizes a small amount of hydrogen/air mixture to react at low temperature in the catalyst layers (CLs) through platinum catalyst. The interactions between this assisted method and various startup modes are the major issue to be discussed. Anode catalytic reaction with air mole fraction higher than 16% is effective to assist a 30-cell stack starting from −25 °C within 13 s in maximum power mode. However, cathode catalytic reaction cannot sustain a successful startup. The anode humidification effect plays an important role to reduce the stack resistance, and to increase the inherent heat generation rate. In maximum power mode and high current density constant power mode, anode catalytic reaction assisted cold start can be achieved within 10–20 s from −40 °C. Anode air mole fraction must be higher than 18% to ensure the successful cold start in these two modes. For constant power mode, the operating power must be lower than 12 W per cell. In constant current mode, when the current density is low, there would be less demand for anode catalytic reaction to achieve successful startup from −40 °C, indicating that lower current density operations have better survivability in low temperature. Nevertheless, much longer start duration is required for lower operating current. Generally, high current density operating mode with high air mole fraction is a more practical and energy efficient cold start strategy, as the startup time can be reduced significantly. Cold start from about −20 °C without ice accumulation is feasible using this method, which may have reduced concern about degradation. Increasing the volume of CL (porosity and thickness) also helps reduce the ice formation.

A high linearity current mode second IF CMOS mixer for a DRM/DAB receiver**Project supported by the National Natural Science Foundation of China (No. 61306069), and the National High Technology Research and Development Program of China (No. 2011AA010301).

A passive current switch mixer was designed for the second IF down-conversion in a DRM/DAB receiver. The circuit consists of an input transconductance stage, a passive current switching stage, and a current amplifier stage. The input transconductance stage employs a self-biasing current reusing technique, with a resistor shunt feedback to increase the gain and output impedance. A dynamic bias technique is used in the switching stage to ensure the stability of the overdrive voltage versus the PVT variations. A current shunt feedback is introduced to the conventional low-voltage second-generation fully balanced multi-output current converter (FBMOCCII), which provides very low input impedance and high output impedance. With the circuit working in current mode, the linearity is effectively improved with low supply voltages. Especially, the transimpedance stage can be removed, which simplifies the design considerably. The design is verified with a SMIC 0.18 μm RF CMOS process. The measurement results show that the voltage conversation gain is 1.407 dB, the NF is 16.22 dB, and the IIP3 is 4.5 dBm, respectively. The current consumption is 9.30 mA with a supply voltage of 1.8 V. This exhibits a good compromise among the gain, noise, and linearity for the second IF mixer in DRM/DAB receivers.

Current-voltage Characteristics of the high Pressure Reflex Discharge in Helium

In this paper the high pressure reflex discharge is investigated. Conditions for the discharge transition from a low-current to a high-current mode are considered. The study of the discharge is carried out in the atmosphere of helium at pressures from 1 to 35 mTorr, with a magnetic field up to 2.1 kG and voltage up to 1.2 kV. The radial profile of the potential distribution in the central plane of the discharge (perpendicular to the axis) was obtained by the isolated probe method.

Formation of silicon nanocrystal films at low temperature during capacitive radio frequency discharge transition to the high-current mode

In this paper, silicon nanocrystal (Si-nc) films were synthesized via capacitive radio frequency (rf) discharge plasma with silane diluted in helium and hydrogen. The plasma conditions were chosen to simultaneously deposit both Si-ncs and amorphous silicon matrix. The structure and photoluminescence of Si-nc films have been studied. By changing the power delivered to the reactor, the transition from amorphous to crystalline growth in the gas phase can be systematically varied. This transition has been confirmed by detecting the change of current and voltage characteristics of the discharge. The results are interpreted in terms of rf discharge transition to the high-current mode. At high-current mode, plasma density will have a sharp rise by hot electron injection. The high plasma density and hot electrons will increase coupling parameter and cause the transition from amorphous particles to crystal particles.

Modified current‐fed full‐bridge isolated power factor correction converter with low‐voltage stress

One drawback of the conventional current-fed full-bridge (CFFB) power factor correction (PFC) converters is extremely high-voltage spikes on metal oxide semiconductor field effect transistors (MOSFETs), which cause many problems such as high-voltage high-cost devices used, unreliability and burdensome magnetising components imposed. To overcome above shortcomings, a new isolated CFFB PFC converter featuring efficiency improvement, high input current quality and good common mode (CM) noise performance is proposed in this study. The voltage spikes are effectively eliminated by using a non-dissipative clamping structure resulting of no-loss consumption and low-voltage MOSFETs used. Additionally, to evaluate the conducted electromagnetic interference behaviour, the differential mode loop and CM loop models are also presented. Two testing hardware systems with 180–240 V input, 380 V/1 kW output of the conventional CFFB PFC and proposed PFC were built and inspected to compare their performances. The experimental results showed that the proposed topology completely eliminated the voltage spike on MOSFETs. The efficiency was largely improved by utilising of high-performance MOSFETs. In consequence, the experimental results reveal the preponderance of the proposed PFC converter to the previous researches on this topic.

Automated Systems.

Automated Systems.

A Driving Scheme Using a Single Control Signal for a ZVT Voltage Driven Synchronous Buck Converter

This paper deals with the optimization of the driving techniques for the ZVT synchronous buck converter proposed in [1]. Two new gate drive circuits are proposed to allow this converter to operate by only one control signal as a 12V voltage regulator module (VRM). Voltage-driven method is applied for the synchronous rectifier. In addition, the control signal drives the main and auxiliary switches by one driving circuit. Both of the circuits are supplied by the input voltage. As a result, no supply voltage is required. This approach decreases both the complexity and cost in converter hardware implementation and is suitable for practical applications. In addition, the proposed SR driving scheme can also be used for many high frequency resonant converters and some high frequency discontinuous current mode PWM circuits. The ZVT synchronous buck converter with new gate drive circuits is analyzed and the presented experimental results confirm the theoretical analysis.

Time-synchronized continuous wave laser-induced fluorescence axial velocity measurements in a diverging cusped field thruster

Measurements are presented of time-synchronized axial ion velocities at three positions in the discharge channel and plume of a diverging cusped field thruster operating on xenon. Xenon axial ion velocities for the thruster are derived from laser-induced fluorescence measurements of the 5d[4]7/2–6p[3]5/2 xenon ion excited state transition centred at λ = 834.72 nm. The thruster is operated in a high-current mode, where the anode discharge current is shown to oscillate quasi-periodically. A sample-hold scheme is implemented to correlate ion velocities to phases along the current cycle. These time-synchronized measurements show that median axial ion velocities decrease as discharge current increases, and that the widths of ion velocity distributions increase with increases in discharge current for positions at the exit plane and outside the thruster channel.

Effect of the chemical nature of the ionogenic groups of ion-exchange membranes on the size of the electroconvective instability region in high-current modes

The size of the electroconvective instability region on the membrane-solution boundary at currents exceeding the limiting diffusion current was measured by laser interferometry. The influence of the chemical nature of the ionogenic groups of ion-exchange membranes on the development of electroconvective instability was studied. The thickness of the electroconvection region decreased as the catalytic activity of the ionogenic groups of commercial and pilot membrane samples with respect to the heterolytic water dissociation increased. The maximum size of the electroconvective instability region and the minimum currents at which it was recorded for the anion-exchange membranes under study were determined for the highly basic modified anion-exchange membrane MA-41M with an almost completely suppressed water dissociation function. A correlation was found between the size of the convective instability region and the characteristic points on the current-voltage curves.

High slew rate current mode transconductance error amplifier for low quiescent current output-capacitorless CMOS LDO regulator

This paper presents a CMOS low quiescent current output-capacitorless low-dropout regulator (LDO) based on a high slew rate current mode transconductance amplifier (CTA) as error amplifier. Using local common-mode feedback (LCMFB) in the proposed CTA, the order of transfer characteristic of the circuit is increased. Therefore, the slew rate at the gate of pass transistor is enhanced. This improves the LDO load transient characteristic even at low quiescent current. The proposed LDO topology has been designed and post simulated in HSPICE in a 0.18µm CMOS process to supply the load current between 0 and 100mA. The dropout voltage of the LDO is set to 200mV for 1.2–2V input voltage. Post-layout simulation results reveal that the proposed LDO is stable without any internal compensation strategy and with on-chip output capacitor or lumped parasitic capacitances at the output node between 10 and 100pF. The total quiescent current of the LDO including the current consumed by the reference buffer circuit is only 3.7µA. A final benchmark comparison considering all relevant performance metrics is presented.

Hysteresis effects in the formation of a neutralizing beam plasma at low ion energy

In this paper, the PEGASES II thruster prototype is used as an ion source generating low-energy positive Ar ion beam, extracted without an external neutralizer. The ions are extracted and accelerated from the source using a two-grid system. The extracted positive ion beam current is measured on a large beam target that can be translated along the acceleration axis. The ion beam current shows a stepwise transition from a low-current to a high-current extraction regime with hysteresis. The hysteresis region depends strongly upon the beam target position. Langmuir probe measurements in the plume show high plasma potentials and low plasma densities in the low-current mode, while the plasma potential drops and the density increases in the high-current mode. The ion energy distribution functions of the beam are measured for different regimes of ion extraction. The ion beam extracted in the high-current mode is indicated by the presence of an additional low-energy peak corresponding to ions from an ion-beam plasma created in the downstream chamber, as well as 10–20 times higher intensity of the primary ion beam peak. The hysteresis behavior is explained by the formation of a downstream neutralizing beam plasma, that depends on the target position and pressure in agreement with a Paschen-like breakdown by secondary electrons. The obtained results are of high relevance for further development of the PEGASES thruster, as well as for improving existing neutralizer-free concepts of the broad-beam ion sources.

Cold atomic beam ion source for focused ion beam applications

We report measurements and modeling of an ion source that is based on ionization of a laser-cooled atomic beam. We show a high brightness and a low energy spread, suitable for use in next-generation, high-resolution focused ion beam systems. Our measurements of total ion current as a function of ionization conditions support an analytical model that also predicts the cross-sectional current density and spatial distribution of ions created in the source. The model predicts a peak brightness of 2 × 107 A m−2 sr−1 eV−1 and an energy spread less than 0.34 eV. The model is also combined with Monte-Carlo simulations of the inter-ion Coulomb forces to show that the source can be operated at several picoamperes with a brightness above 1 × 107 A m−2 sr−1 eV−1. We estimate that when combined with a conventional ion focusing column, an ion source with these properties could focus a 1 pA beam into a spot smaller than 1 nm. A total current greater than 5 nA was measured in a lower-brightness configuration of the ion source, demonstrating the possibility of a high current mode of operation.

Minimizing matrix effects and spectral interferences produced by Fe absorption lines in the determination of cadmium by electrothermal atomic absorption spectrometry: Application to the fractionation of cadmium in moderated contaminated soils

Solutions, including the extracting solutions used in the sequential procedure recommended by the Standard, Measurements and Testing Program, with different cadmium and iron concentrations were prepared and analyzed using combined electrothermal atomic absorption spectrometry (ETAAS) and two background compensation techniques. The first was based on the deuterium background correction method in which a deuterium lamp was used in combination with a conventional Cd hollow-cathode lamp. For the second, a high-intensity boosted discharge hollow-cathode lamp (BDHCL) was used as in the Smith–Hieftje (S–H) background correction method, but this lamp was modulated with a low and a high current mode at a modulation frequency of 100Hz. In the present study, the modulation cycle was 10 times higher than in the S–H system. Therefore, the background correction method was called high-speed self-reversal method. Pseudo-total Cd concentrations were determined using ETAAS in five reference materials and fractionation was made in two reference soils. With regard to the results, the high-speed self-reversal background correction method provided a method of choice to eliminate or decrease the spectral interference due to the close positioning of the analytical lines of Cd and Fe in solutions containing high iron concentrations during the Cd determination by electrothermal atomic absorption spectrometry. It is worth noting that using the HSSR-method, the sensitivity losses were from 32% to 39% compared to the continuum source background corrector equipped with a deuterium lamp. The HSSR-method was successfully applied to the determination of Cd in contaminated samples. The results showed that interferences caused by absorption line overlapping of Cd and Fe could be compensated accurately for Fe/Cd=100,000 in 0.11M acetic acid and Fe/Cd<10,000 in 0.5M hydroxylamine hydrochloride.

Improving water desalination by hydraulically coupling an osmotic microbial fuel cell with a microbial desalination cell

A system consisting of two membrane-based bioelectrochemical reactors was developed to treat artificial wastewater and desalinate saline water. In this system, an osmotic microbial fuel cell (OsMFC) containing a forward-osmosis (FO) membrane was hydraulically coupled with a microbial desalination cell (MDC) that had ion exchange membranes. The coupled system significantly improved desalination efficiency through both dilution (in the OsMFC) and salt removal (in the MDC), and achieved more organic removal than an individual MDC. It was found that the high-power operation mode was more suitable for the OsMFC than the open-circuit mode and the high-current mode, because of good desalination performance (95.9% conductivity reduction in the coupled system) and energy production (0.160kWh/m3 treated saline water). When the active layer of the FO membrane was facing the feed solution, more water flux was obtained than the reversal membrane orientation. The coupled system achieved high reduction of conductivity (>85%) from the salt solution containing 10–50g NaCl/L. The acidified water was more advantageous as a catholyte for the MDC because of the superior desalination performance. These results have collectively demonstrated the feasibility of a membrane-based bioelectrochemical system for simultaneous wastewater treatment and saline water desalination.

Real time monitoring weld quality of small scale resistance spot welding for titanium alloy

Titanium and its alloys have been identified as one of the best engineering metals for application in industrial fields. Whereas, there is limited research work on monitoring and controlling the small scale resistance spot welding (SSRSW) of titanium alloy. This paper performed a systematic research on the voltage curve, which turned out to be an indication for weld quality of SSRSW. It was obtained through clipping two leads onto the electrodes during SSRSW process. As the common equipment in SSRSW, the high frequency (HF) power supply and constant current mode were employed in this study. First voltage curves at different welding parameters were analyzed and then a probabilistic neural network (PNN) model using three factors extracted from the voltage curve was employed in order to classify the weld quality, and satisfied experiment results were acquired. It was demonstrated that the dynamic voltage during a welding process could be identified as a good signature for weld quality monitoring purpose.

Dynamic avalanche behavior of power MOSFETs and IGBTs under unclamped inductive switching conditions

The ability of high-voltage power MOSFETs and IGBTs to withstand avalanche events under unclamped inductive switching (UIS) conditions is measured. This measurement is to investigate and compare the dynamic avalanche failure behavior of the power MOSFETs and the IGBT, which occur at different current conditions. The UIS measurement results at different current conditions show that the main failure reason of the power MOSFETs is related to the parasitic bipolar transistor, which leads to the deterioration of the avalanche reliability of power MOSFETs. However, the results of the IGBT show two different failure behaviors. At high current mode, the failure behavior is similar to the power MOSFETs situation. But at low current mode, the main failure mechanism is related to the parasitic thyristor activity during the occurrence of the avalanche process and which is in good agreement with the experiment result.

Near-Threshold Computing of High Speed MOS Current Mode Logic Circuits

Near-Threshold Computing of High Speed MOS Current Mode Logic Circuits

A Multi-bit High Speed Current Mode Analog to Digital Conversion Algorithm

This paper proposes a generic algorithm for k-bit Analog to Digital Conversion. The proposed algorithm is very fast method of conversion of an analog signal into k-bit digital output in a multi-bit parallel fashion. The algorithm employs m stages, each of which is capable of producing bits such that k/m bits are converted at the same time. Thus, this algorithm can be considered a k = n X m conversion method. The algorithm proposed has been tested for a 4-bit current mode ADC implementation. The simulations have been performed in 0.18μm CMOS technology at the supply voltage of 1.8V using P-SPICE.

A high linearity current mode multiplier/divider with a wide dynamic range

A high linearity current mode multiplier/divider (CMM/D) with a wide dynamic range is presented. The proposed CMM/D is based on the voltage—current characteristic of the diode, thus wide dynamic range is achieved. In addition, high linearity is achieved because high accuracy current mirrors are adopted and the output current is insensitive to the temperature and device parameters of the fabrication process. Furthermore, no extra bias current for all input signals is required and thus power saving is realized. With proper selection of establishing the input terminal, the proposed circuit can perform as a multifunction circuit to be operated as a multiplier/divider, without changing its topology. The proposed circuit is implemented in a 0.25 μm BCD process and the chip area is 0.26 × 0.24 mm2. The simulation and measurement results show that the maximum static linearity error is ±1.8% and the total harmonic distortion is 0.4% while the input current ranges from 0 to 200 μA.