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Results for “Pulse circuits”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Performance Evaluation and Loss Modeling of WBG Devices based on a Novel Double-Pulse Test Method for Current Source Inverter

Careful measurements of the power device characteristics are necessary to accurately estimate a power converter's losses and efficiency. The conventional double-pulse test (DPT) circuit is a well-known method to implement this laboratory characterization of power devices and power modules. However, the switching characteristics of a power device depend on the power electronics circuit in which it is connected as well as the power circuit's physical layout, in addition to the device's internal structure. Hence, the conventional DPT circuit configuration, which is tailored for a standard voltage-source inverter (VSI), is not well-suited for a current-source inverter (CSI). This paper demonstrates a previously-proposed CSI-based DPT measurement technique that is appropriate for normal CSI operation. The characteristics of SiC MOSFETs and series-connected SiC Schottky diodes used in a CSI are measured using this improved technique while taking temperature effects into account to yield more accurate loss predictions. The CSI losses, including the switching and conduction losses of SiC MOSFETs and SiC Schottky diodes, have been modeled using this approach. The total CSI losses and efficiency have been estimated based on the CSI DPT results and loss models.

42 ENGINEERING↗
DOE OSTI2023

Signal processing to reduce dark noise impact in precision timing

We introduce a technique to mitigate the effects of low frequency noise on precision timing. The example of Dark Count Noise Rate (DCR) in Silicon Photomultipliers (SiPMs) is emphasized. This technique exploits the correlation between time shifts on the leading edge of a signal and the residual slope of the baseline (due to noise) which remains after baseline subtraction. In fast timing applications (such as for Time-of-flight particle ID) the signal arrival time is typically captured on the signal leading edge. The signal risetime is often fixed by the physics of the sensor and input circuit. Then accurate pulse timing can be achieved by correcting a leading edge threshold time (depending on a slope proportional to both the Amplitude and the risetime) to a “constant fraction” time. This compensation for time walk due to amplitude fluctuations breaks down once we introduce interference from low frequency noise on the leading edge. In this paper we demonstrate that an additional measurement of the slope at threshold can be used to correct for this noise jitter.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

SiC and GaN Devices With Cryogenic Cooling

This article presents the cryogenically cooled application for wide bandgap (WBG) semiconductor devices. Characteristics of silicon carbide (SiC) and gallium nitride (GaN) at cryogenic temperatures are illustrated. SiC MOSFETs exhibit increased on-state resistance and slower switching speed at cryogenic temperatures. However, cryogenic cooling provides low ambient temperature environment and thus enables the SiC converter to operate at lower junction temperature to achieve higher efficiency compared to room temperature cooling. A cryogenically cooled MW-level SiC inverter prototype is developed and demonstrated the feasibility of operating high-power SiC converter with cryogenic cooling. GaN HEMTs exhibit more than five times on-state resistance reduction and faster switching speed at cryogenic temperatures which makes GaN HEMTs an excellent candidate for cryogenic power electronics applications. The significantly reduced on-state resistance of GaN devices provides the possibility to operate them at a current level much higher than rated current at cryogenic temperatures. A GaN double pulse test (DPT) circuit is constructed and demonstrated that GaN HEMTs can operate at nearly four times of rated current at cryogenic temperatures. Challenges of utilizing WBG device with cryogenic cooling are discussed and summarized.

42 ENGINEERING↗
DOE OSTI2024

Magnetics, Inc. 0077894A7 (Datasheet)

Description of Core Under Test (CUT). Magnetics, Inc. 0077894A7 is a powder core material having low loss and high saturation fields. Known for the marketing name Kool Mu, was transformed by taking the known magnetic material, Sendust, and altered the manufacturing process to lower core losses. Possessing these specific properties makes it ideal for power factor correction circuits as well Pulse and Flyback Transformers. In-Line Noise Filters and Inductors are also common due to the near zero magnetostriction. Exhibits a potential saturation induction of 1 T.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Low-Jitter Clock Receivers for Fast Timing Applications

Precision timing is a key requirement for emerging 4D particle tracking, Positron Emission Tomography (PET), beam and fusion plasma diagnostics, and other systems. Time-to-Digital Converters (TDCs) are commonly used to provide digital estimates of the relative timing between events, but the jitter performance of a TDC can be no better than the performance of the circuits that acquire the pulses and deliver them to the TDC. Several clock receiver and distribution circuits were evaluated, and a differential amplifier with resistive loads driving a pseudo-differential clock distribution network, developed using design guidelines for radiation tolerance and cryogenic compatibility, was fabricated as part of three prototypes: an analog front-end testbed chip for high-precision timing pixel readout, a dedicated TDC evaluation chip, and a Low-Gain Avalanche Detector (LGAD) readout circuit. Based on TDC measurements of the prototypes, we infer that the jitter added by the clock receiver and distribution circuits is less than 2.25 ps-rms. This performance meets the requirements of many future precision timing systems. The clock receiver and on-chip pseudo-differential driver were fabricated in commercial 28-nm CMOS technology and occupy 2288 µm 2 .

47 OTHER INSTRUMENTATION↗
NASA NTRS1967

TV synchronization system features stability and noise immunity

Horizontal jitter in the video presentation in television systems is prevented by using an additional sync level. This circuitry uses simultaneous signals at both sync and porch frequencies, providing a sync identification from which a coincidence circuit can generate pulses having the required stability and noise immunity.

Landauer, F. P.↗
NASA NTRS1969

Constant-frequency, variable-duty-cycle multivibrator

Circuit provides a pulse source of constant frequency with a duty cycle that is adjustable by an external input signal. It could serve as a switching mode voltage regulator or as a switching source for control systems.

Johnson, J. E.↗
NASA NTRS1972

The UHURU X-ray instrument.

On Dec. 12, 1970, the UHURU X-ray observatory was launched into equatorial orbit with the prime mission of conducting an all-sky survey of astronomical X-ray sources with intensities of 0.00005 Sco-X1 or greater. The X-ray detection system contains 12 gas-filled proportional counters, 6 behind each collimator. The aspect system is discussed together with the structure, the pulse height analyzer, the command system, the calibration system, and the power distribution system. Pulse shape discrimination circuits used on UHURU use the same technique that was used on the system originally developed for large area proportional counters described by Gorenstein and Mickiewicz (1968).

Jagoda, N.↗
NASA NTRS1965

Analog-to-digital converter

An analog to digital converter circuit arrangement is reported that is suitable for use in ultra fast pulse height analysis. The circuit uses series connected tunnel diodes to quantize a voltage signal into discrete levels.

Lewyn, L. L.↗
NASA NTRS1975

Voltage monitoring system

A description is given of a system for monitoring the voltage at a remote location and determining when the voltage exceeds upper and lower levels. The system includes transmission lines for transmitting the voltage back to a central station and applying such to an amplifier having a pair of outputs. One of the outputs of the amplifier is applied to an oscillograph. The other output is fed through an isolation transformer, a full wave rectifier, to a pair of unijunctional transistor circuits for producing pulses when the voltage exceeds or drops below a predetermined level. These pulses, in turn, energize a relay which turns on the oscillograph for recording the voltages being monitored.

Canicatti, C. L.↗
NASA NTRS1979

Hybrid ECG signal conditioner

Circuit with high common-mode rejection has ability to filter and amplify accepted analog electrocardiogram (ECG) signals of varying amplitude, shape, and polarity. In addition, low power circuit develops standardized pulses that can be counted and averaged by heart/breath rate processor.

Rinard, G. A.↗
NASA NTRS1988

Frequency-Accommodating Manchester Decoder

No adjustment necessary to cover a 10:1 frequency range. Decoding circuit converts biphase-level pulse-code modulation to nonreturn-to-zero (NRZ)-level pulse-code modulation plus clock signal. Circuit accommodates input data rate of 50 to 500 kb/s. Tracks gradual changes in rate automatically, eliminating need for extra circuits and manual switching to adjust to different rates.

Vasquez, Mario J.↗
NASA NTRS1992

Broadband millimeter-wave GaAs transmitters and receivers using planar bow-tie antennas

We report broadband monolithic transmitters and receivers IC's for mm-wave electromagnetic measurements. The IC's use nonlinear transmission lines (NLTL) and sampling circuits as picosecond pulse generators and detectors. The pulses are radiated and received by planar monolithic bow-tie antennas, collimated with silicon substrate lenses and off-axis parabolic reflectors. Through Fourier transformation of the received pulse, 30-250 GHz free space gain-frequency measurements are demonstrated with an accuracy approximately = 0.17 dB, RMS.

Konishi, Y.↗
NASA NTRS1994

High-Performance X-ray Detection in a New Analytical Electron Microscope

X-ray detection by energy-dispersive spectrometry in the analytical electron microscope (AEM) is often limited by low collected X-ray intensity (P), modest peak-to-background (P/B) ratios, and limitations on total counting time (tau) due to specimen drift and contamination. A new AFM has been designed with maximization of P. P/B, and tau as the primary considerations. Maximization of P has been accomplished by employing a field-emission electron gun, X-ray detectors with high collection angles, high-speed beam blanking to allow only one photon into the detector at a time, and simultaneous collection from two detectors. P/B has been maximized by reducing extraneous background signals generated at the specimen holder, the polepieces and the detector collimator. The maximum practical tau has been increased by reducing specimen contamination and employing electronic drift correction. Performance improvments have been measured using the NIST standard Cr thin film. The 0-3 steradian solid angle of X-ray collection is the highest value available. The beam blanking scheme for X-ray detection provides 3-4 times greater throughput of X-rays at high count rates into a recorded spectrum than normal systems employing pulse-pileup rejection circuits. Simultaneous X-ray collection from two detectors allows the highest X-ray intensity yet recorded to be collected from the NIST Cr thin film. The measured P/B of 6300 is the highest level recorded for an AEM. In addition to collected X-ray intensity (cps/nA) and P/B measured on the standard Cr film, the product of these can be used as a figure-of-merit to evaluate instruments. Estimated minimum mass fraction (MMF) for Cr measured on the standard NIST Cr thin film is also proposed as a figure-of-merit for comparing X-ray detection in AEMs. Determinations here of the MMF of Cr detectable show at least a threefold improvement over previous instruments.

Lyman, C. E.↗
NASA NTRS1997

Development of Power Electronics for a 0.2kW-Class Ion Thruster

Applications that might benefit from low power ion propulsion systems include Earth-orbit magnetospheric mapping satellite constellations, low Earth-orbit satellites, geosynchronous Earth-orbit satellite north-south stationkeeping, and asteroid orbiters. These spacecraft are likely to have masses on the order of 50 to 500 kg with up to 0.5 kW of electrical power available. A power processing unit for a 0.2 kW-class ion thruster is currently under development for these applications. The first step in this effort is the development and testing of a 0.24 kW beam power supply. The design incorporates a 20 kHz full bridge topology with multiple secondaries connected in series to obtain outputs of up to 1200 V(sub DC). A current-mode control pulse width modulation circuit built using discrete components was selected for this application. An input voltage of 28 +/- 4 V(sub DC) was assumed, since the small spacecraft for which this system is targeted are anticipated to have unregulated low voltage busses. Efficiencies in excess of 91 percent were obtained at maximum output power. The total mass of the breadboard was less than 1.0 kg and the component mass was 0.53 kg. It is anticipated that a complete flight power processor could weigh about 2.0 kg.

Pinero, Luis R.↗
NASA NTRS2017

Methods and Apparatus for Pulsed-DC Dielectric Barrier Discharge Plasma Actuator and Circuit

A plasma generating device intended to induce a flow in a fluid via plasma generation includes a dielectric separating two electrodes and a power supply. The first electrode is exposed to a fluid flow while the second electrode is positioned under the dielectric. The power supply is electrically coupled to a switch and the first and second electrodes. When the power supply is energized by repeated action of the switch, it causes a pulsed DC current between the electrodes which causes the fluid to ionize generating a plasma. The generation of the plasma induces a force with a velocity component in the fluid.

Corke, Thomas C.↗