Maximum Duty Cycle Research Articles

Loop gain and margins of stability of inner-current loop of peak current-mode-controlled PWM dc–dc converters in continuous conduction mode

A general expression for the loop gain of the inner-current loop of peak current-mode-controlled PWM dc–dc converters operating in continuous conduction mode (CCM) is derived as a function of perturbation ratio and switching frequency. It is shown that this expression is identical for all conventional PWM dc–dc converters in CCM, such as buck, boost and buck–boost converters. However, the value of perturbation ratio is dependent on the converter topology. Also, an expression for required slope compensation at a specified phase margin and a maximum duty cycle is presented. The general expression of the loop gain enables the investigation of the margins of stability of the inner loop of peak current-mode-controlled PWM dc–dc converters irrespective of the converter topology.

High-Power High-Performance Low-Cost Capacitor Charger Concept and Implementation

A 20-kJ/s 10-kV 1-kHz repetition rate capacitor charger design and testing are described. The goal of the development was to combine high performance and versatility with low-cost design and good manufacturability. This goal was met using an energy-dosing converter topology with smart controls adapting the switching frequency in such a way as to ensure zero-current switching for all possible scenarios, keeping maximum duty cycle for high power. The switching is accomplished at a frequency of up to 55 kHz, employing relatively slow insulated-gate bipolar transistors with low conduction losses. High efficiency allows all-air cooled design that fits into a 19 × 10 × 24 rack. Design guidelines are reviewed. Comprehensive PSpice models accounting for numerous parasitic parameters and mimicking controls for the frequency variation were developed and simulation results are presented. Worst-case repeatability analysis has been performed. Both PSpice simulations and analytical tools predicted pulse-to-pulse repeatability of 0.3%; the measured figures are 0.8% and 1% for short- and long-term operations, respectively, at peak charging and repetition rates. Typical current and voltage traces and results of thermal runs are presented.

Steady-State Stability of Current Mode Active-Clamp ZVS DC–DC Converters

Active-clamp dc-dc converters are pulsewidth-modulated converters having two switches featuring zero-voltage switching at frequencies beyond 100 kHz. Generalized equivalent circuits valid for steady-state and dynamic performance have been proposed for the family of active-clamp converters. The active-clamp converter is analyzed for its dynamic behavior under current control in this paper. The steady-state stability analysis is presented. On account of the lossless damping inherent in the active-clamp converters, it appears that the stability region in the current-controlled active-clamp converters get extended for duty ratios, a little greater than 0.5 unlike in conventional hard-switched converters. The conventional graphical approach fails to assess the stability of current-controlled active-clamp converters, due to the coupling between the filter inductor current and resonant inductor current. An analysis that takes into account the presence of the resonant elements is presented to establish the condition for stability. This method correctly predicts the stability of the current-controlled active-clamp converters. A simple expression for the maximum duty cycle for subharmonic-free operation is obtained. The results are verified experimentally.

The influence of strain and activation on the locomotor function of rat ankle extensor muscles

The ankle extensor muscles of the rat have different mechanical and physiological properties, providing a means of studying how changes in locomotor demands influence muscle fascicle behaviour, force and mechanical power output in different populations of muscle fibre types. Muscle fascicle strain, strain rate and activation patterns in the soleus, plantaris and medial gastrocnemius muscles of the rat were quantified from sonomicrometric and myoelectric data, collected during treadmill locomotion under nine velocity/incline conditions. Significant differences in peak-to-peak muscle fascicle strains and strain rates were identified between the three muscles (P<0.001, all cases), with much smaller strains (<0.1) and strain rates (<0.5 s(-1)) occurring in soleus and plantaris compared with medial gastrocnemius (>0.2 and >1.0 s(-1), respectively). The proportion of stride duration that each muscle was active (duty cycle) differed between locomotor conditions as did the timing of the activation and deactivation phases. A simple Hill-based muscle model was used to determine the influence of muscle activation relative to maximum fascicle strain and duty cycle on total force production and mechanical power output, from a slow and a fast muscle fibre, simulated through two peak-to-peak strain cycles (0.1 and 0.3). The predictions of the model did not complement conclusions that may be drawn from the observation of myoelectric timing and fascicle strain trajectories in each of the muscles. The model predicted that changes in mechanical power output were more sensitive to changes in activation parameters than to changes in strain trajectories, with subtle changes in activation phase and duty cycle significantly affecting predicted mechanical power output.

High-Temperature SOI/SiC-Based DC-DC Converter Suite

A complete design strategy (mechanical and electrical) for a 25 W 28 V/5 V dc-dc converter utilizing SiC and SOI electronics is presented. The converter includes a high-temperature SOI-based PWM controller featuring 150 kHz operation, a PID feedback loop, maximum duty cycle limit, complementary or symmetrical outputs, and a bootstrapped high-side gate driver. Several passive technologies were investigated for both control and power sections. Capacitor technologies were characterized over temperature and over time at 300C∘, power inductors designed and tested up to 350C∘, and power transformers designed and tested up to 500C∘. Northrop Grumman normally-off SiC JFETs were used as power switches and were characterized up to 250C∘. Efficiency and mass optimization routines were developed with the data gained from the first prototype. The effects of radiation on SiC and SOI electronics are then discussed. The results of the first prototype module are presented, with operation from 25C∘ up to an ambient temperature of 240C∘.

SU‐GG‐T‐175: Analysis of Inter‐ and Intra‐Fraction Breathing Patterns Using the Varian Real Time Position Management System

Purpose: To analyse respiratory waveforms for key parameters that may be used to characterise patients' breathing patterns for the purpose of distinguishing between patients, tailoring gated treatment for individuals and determining the suitability of patients for gated radiotherapy. Method and Materials: The Varian Real time Position Management (RPM) system was used to record the breathing waveforms of three volunteers. The RPM marker was placed on the volunteers': chest, sternum and abdomen. Waveforms were captured for 1min on several days in each position, and a 5min waveform captured in the sternum position. From the resulting waveforms, four key parameters were determined using customised software, and compared between inter‐ and intra‐fraction measurements. Also, the breathing waveforms of three patients were captured for 1min over several days and analysed similarly. Results: The key parameters investigated were: frequency of breathing, maximum amplitude of inhale and exhale, asymmetry of the breathing pattern and the maximum potential duty cycle of both inhale and exhale. The intra‐fractional differences were smaller than the inter‐fraction differences for the volunteers, although this was not the case for the patients. The frequency of breathing ranged from 8 to 16, and 4 to 12 for the patients and volunteers respectively. The maximum amplitudes were noticeably different between the volunteers for both inhale and exhale, although the patient group showed marked differences only on the maximum exhale amplitude. The volunteers' and patients' waveforms were reasonably symmetric and the longest duty cycles were observed on the inhale for both patients and volunteers. Conclusion: The breathing patterns of the volunteers and patients indicate that the differences within a subject are smaller than the differences between subjects. We conclude that the RPM can be used to reproducibly record the waveforms from which these four key parameters may be derived to tailor gated radiotherapy for an individual.

Asymmetrical zero-voltage-switching PWM DC–DC converter employing two transformers and current doubler rectification

A new zero-voltage-switching (ZVS) PWM DC–DC converter with two switches driven by asymmetrical duty cycles is presented. Two small transformers with the same turns ratio instead of one large transformer are used to fulfil the low-profile design. The current doubler rectifier can reduce the current ripple in the output capacitors. The leakage inductance of the transformer or an additional resonant inductance helps to achieve ZVS during the dead times. Therefore high conversion efficiency can be obtained. The maximum duty cycle can be extended to be above 50%. Thus, the proposed converter is suitable for the applications with a wide input voltage range. Detailed analysis and design of the presented ZVS PWM DC–DC converter are described. Experimental results are recorded for a prototype converter with a DC input voltage of 120–190 V, an output voltage of 12 V and a load current of 12 A, operating at a switching frequency of 180 kHz.

Blazar duty-cycle at γ-ray frequencies: constraints from extragalactic background radiation and prospects for AGILE and GLAST

We take into account the constraints from the observed extragalactic γ-ray background to estimate the maximum duty cycle allowed for a selected sample of WMAP Blazars, in order to be detectable by AGILE and GLAST γ-ray experiments. For the nominal sensitivity values of both instruments, we identify a subset of sources which can in principle be detectable also in a steady state without over-predicting the extragalactic background. This work is based on the results of a recently derived Blazar radio LogN-LogS obtained by combining several multi-frequency surveys.

Violet‐emitting diode lasers on low defect density GaN templates

We compare the electro-optical characteristics of violet-emitting ridge waveguide (AlGaIn)N quantum well diode lasers with etched laser facets, grown on GaN templates with a homogeneously reduced defect density, with those of reference devices grown on sapphire using conventional low-temperature GaN nucleation layer technology. Defect densities of the former and latter laser structures were around 1 × 108 cm–2 and 2 × 109 cm–2, respectively. In on-wafer pulsed-mode operation a 35% reduction in threshold current density and 40% reduction in injected electrical power at threshold was achieved upon reduction of defect density. Minimum values for threshold current density and injected electrical power at threshold are 7.5 kA/cm² (500 µm × 4 µm) and 0.9 W (500 µm × 2 µm), respectively, for a ridge laser with uncoated facets. For improved heat sinking the sapphire substrate of selected laser diodes on GaN template was removed using laser lift-off, followed by n-side down soldering on copper heat sinks. This way, the maximum duty-cycle, limited by premature thermal rollover, could be increased by a factor of three for the substrate-less lasers. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

HEV maximum power performance simulation and duty cycle generation

Generic duty cycles have been used to design and evaluate powertrains of hybrid electric vehicles. Our research indicates that a duty cycle depends on a powertrain's configuration. Thus, using a generic duty cycle may result in an overestimation on the selection of power sources and a false estimate on vehicle performance. A simulation tool based on powertrain dynamics, configuration and component specifications was created to generate configuration dependent duty cycles. A comparison between the generated duty cycle and a generic one is presented. The effect of using different duty cycles on selection of power sources is discussed.

ZVS PWM昇圧チョッパ・ZVSフルブリッジDC-DCコンバータ構成の2ステージ電力変換システム

The high-frequency isolated power supply with low-voltage large-current output and widely fluctuating input voltage is discussed in this paper. It is described that it is difficult to achieve high efficiency of the power supply with ZVS phase-shift PWM controlled DC-DC power converter mainly due to high conduction power losses in the rectifier stage. The 2-stage DC-DC converter system configuration, which consists of boost ZVS-PWM DC-DC chopper and ZVS full-bridge high-frequency isolated DC-DC converter operating with maximum duty cycle, is presented. An ability to improve efficiency of the power conversion by using 2 stages DC-DC circuit configuration is discussed. 900W-100kHz DC-DC conversion system prototypes were built and tested. An efficiency comparison between full-bridge ZVS phase-shift PWM DC-DC power converter and 2-stage soft-switching DC-DC converter has been made. It is proved that using 2-stage DC-DC converter can improve efficiency under full load.

Tension-time index, fatigue, and energetics in isolated rat diaphragm: a new experimental model.

The tension-time index (TTI) has been used to estimate mechanical load, energy utilization, blood flow, and susceptibility to fatigue in contracting muscle. The TTI can be defined, for a rhythmically contracting muscle, as the product of average force development divided by maximum tetanic force times duty cycle [contraction time / (contraction + relaxation time)]. In this study, the TTI concept was applied to isolated diaphragm via a method that allowed TTI to be clamped at a predetermined value. The hypothesis tested was that, at constant TTI, muscle energetics and the extent of fatigue would vary with stimulation frequency. Isolated diaphragm strips were stimulated at 25, 50, 75, or 100 Hz for 4 min, one per second. Duty cycle was continuously adjusted to maintain TTI at 0.07, which was near the highest TTI tolerated for 4 min, at 20-Hz stimulation. At the end of the fatigue run, muscles were either immediately frozen for determination ATP, creatine, and creatine phosphate concentrations (n = 6) or stimulated for evaluation of low- and high-frequency fatigue (n = 5). Results demonstrated no difference in the extent of fatigue or in the final ATP and creatine phosphate concentrations between groups. Large within-run increases in duty cycle were required at low stimulation frequencies, but only small increases were required at the highest frequencies. The results demonstrate that, at a constant TTI, similar fatigue properties predominate at all stimulation frequencies with no clear distinction between high- and low-frequency fatigue. The method of clamping TTI during fatigue may be useful for evaluating energetics and contractile function between treatment groups in isolated muscle when treatment influences baseline contractile characteristics.

Analysis and design of asymmetrical half bridge flyback converter

The detailed circuit behaviour of the asymmetrical half bridge flyback converter is analysed. The specific relationships between the duty cycle and the different types of energy in the energy storage elements are thoroughly investigated. From the analytical results, the maximum duty cycle is not bounded by 50%, which means that the converter can now be optimally used for the different applications. The zero voltage switching (ZVS) conditions of the power switches are derived. Mathematical equations and design considerations are also given. According to the presented design guidelines, the ZVS operations of the power switches can be maintained from no-load to full-load conditions. A 5V/20A prototype has been built to verify the analytical results under real life conditions.

Buried heterostructure quantum cascade lasers with a large optical cavity waveguide

We report the fabrication and characterization of buried heterostructure quantum cascade (BH-QC) lasers formed by selective lateral regrowth of InP on the laser ridge by metal organic chemical vapor deposition (MOCVD). A fivefold improvement in maximum average power (up to 10 mW) and a twofold improvement in maximum operation duty cycle (up to 17%) are measured at 273 K and are attributed to lower lateral waveguide losses and a better heat dissipation.

A Charge Coupled Device Array Detector for Single-Wavelength and Multiwavelength Ultraviolet Absorbance in Capillary Electrophoresis

A fundamental limitation to the use of single-point absorbance detection for capillary electrophoresis is irradiance, since it is not possible to create an image at the detection point on capillary that is brighter than the light source. This limitation may be overcome by illuminating a length of the capillary using a fiber-optic bundle and using a charge coupled device (CCD) camera that can image the full length of the illuminated zone. The present paper describes design and development of a CCD detector for UV absorbance that can be used in both multiwavelength and single-wavelength modes. The CCD camera images analyte peaks in the capillary dimension, together with wavelength-resolved absorbance in the dimension perpendicular to the capillary. Successive snapshots of the peaks are added together, after appropriate correction for time-dependent peak displacement, without sacrificing spatial resolution. Measured baseline rms noise values at 200 nm are 34 μAU using a holographic grating in multiwavelength mode and 8 μAU with the addition of a band-pass filter. Both values are in excellent agreement with calculations of limiting shot noise. Performance in multiwavelength mode is constrained by the 470-ms readout time of the CCD used, which sets a maximum duty cycle of 2.3%. Noise contributions from source intensity fluctuations are reduced by using a portion of the CCD image to provide a baseline reference signal. With 4-hydroxybenzoate as test analyte, the linear dynamic range in multiwavelength mode is shown to be between 3 and 4 orders of magnitude. High-quality spectra of 2-, 3-, and 4-methylbenzoates are obtained on capillary and used in deconvolution of closely migrating peaks of the 2- and 3-isomers.

Chopper-stabilized amplifiers with a track-and-hold signal demodulator

The conventional signal demodulator of a chopper amplifier can be substituted by track-and-hold (T/H) and averaging functions. This arrangement provides offset cancellation without requiring low-pass filters and can ignore the residual offset generated by input spikes. A noise analysis shows that this T/H demodulator degrades the white noise signal-to-noise ratio (SNR), although degradation can be minimized by using maximum duty cycle and minimum amplifier bandwidth.

Multivalent Acceptor-Doped Germanium Lasers: a solid-state tunable source from 75 to 300 μm

AbstractWe report on the performance of far-infrared hole inversion lasers made from germanium doped with the multivalent acceptors beryllium and copper. Commonly used hole inversion lasers are made from Czochralski-grown Ga-doped Ge single crystals and show emission from 75 to 125 and 170 to 300 μm. The emission gap between 125 and 170 μm, originating from absorption of the far-infrared light due to internal hole transitions in the neutral Ga acceptor, is absent in the new Be and Cu-doped lasers. We also find a mechanism for inversion depopulation through neutral Ga which hinders lasing at low electric fields. This same mechanism is shown to cause population inversion in the Be-doped laser and allows lasing at lower fields. This reduces the power input into the germanium crystal and has allowed us to increase the duty cycle up to 2.5% which is one order of magnitude higher than the maximum duty cycle reported for Ga-doped Ge lasers. These new lasers may offer an opportunity for achieving continuous-wave operation.In addition we have performed preliminary studies on the effect of uniaxial stress on the lasing in these new materials. We demonstrate that small uniaxial stress increases laser action in Ge:Cu. We propose that this is due to an increased population inversion because under these conditions two separate mechanisms cause heavy holes to enter the light hole band.

Maximum soliton-train duty cycle in harmonically mode-locked fiber lasers

We analyze the main methods for high-repetition-rate soliton generation in fiber lasers in view of the applications to fiber transmission. Particular emphasis is given to the problem of intracavity soliton interactions and stabilization methods. Because of the interactions we find that the maximum duty cycle achievable in a soliton source is 0.22. We also find that the relative phase difference between adjacent solitons may be controlled by means of an intracavity etalon, whereas without the etalon the solitons are stable only when they are out of phase. Moreover the introduction of the intracavity etalon has led to a strong reduction in the fluctuations of the soliton parameters induced by quantum noise.

Auger, zero-energy photoelectron, coincidence spectroscopy: Chemical-site-selective Auger electron spectroscopy

The Auger electron spectrum associated with decay of a core-hole on the terminal nitrogen and that associated with the central nitrogen of nitrous oxide, N 2O, are obtained individually through the use of a coincidence technique. Specifically, each of the two Auger electron spectra is obtained by detection of Auger electrons in coincidence with near zero energy (threshold) photoelectrons at the respective ionization thresholds. These zero energy electrons serve to identify the core-ionization continuum associated with the different Auger electrons. The salient features of the experimental spectra are in good agreement with theoretical calculations. The low counting rate generally associated with coincidence experiments, especially in the gas phase, is not encountered because the low energy electrons are collected over a 4π solid angle. Also, velocity discrimination is accomplished by a spatial filter rather than by time-of-flight to utilize the maximum duty cycle of the synchrotron source. These data are believed to be the first examples of chemical-site-selective molecular Auger spectra.

High-power microwave pulse generator

An inexpensive alternative to commercial high-power microwave pulse generators is described. The present high-power microwave pulse generator utilizes a surplus MIT model 3 Mark II hard tube modulator and 2J51 magnetron. The basic design and technical details of the pulse generator are presented. The pulse generator is designed to produce 8.5–9.6 GHz pulses with pulse lengths ranging from 2 to 4 μs, with a nominal power output of 20 kW and a maximum duty cycle of 0.001.