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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Shunt Diode Designs in Li/cf Shuttle Batteries

Although Li/CF cells and batteries have an excellent safety record, they are included with other battery systems that require additional safety precautions. One precaution suggested is the inclusion of shunt diodes into these batteries. The benefits of this addition are examined. All cells tested at elevated temperatures vent regardless of length of time between being fully discharged and reversed or inclusion of the diode in the system. Cells discharged at ambient temperatures all show a relatively quick reversal, but stabilize at voltages that are high enough that the diodes are not functioning. Cells tested at depressed temperatures reverse the deepest of all cells tested, with the deepest reversal occurring very early in the test and voltages recovering to above -0.60 volts near the end of the tests. Anode limited cells will eliminate the venting during hot reversal.

Miller, D.↗
NASA NTRS1974

High performance dc-dc conversion with voltage multipliers

The voltage multipliers using capacitors and diodes first developed by Cockcroft and Walton in 1932 were reexamined in terms of state of the art fast switching transistors and diodes, and high energy density capacitors. Because of component improvements, the voltage multiplier, used without a transformer, now appears superior in weight to systems now in use for dc-dc conversion. An experimental 100-watt 1000-volt dc-dc converter operating at 100 kHz was built, with a component weight of about 1 kg/kW. Calculated and measured values of output voltage and efficiency agreed within experimental error.

Harrigill, W. T.↗
NASA NTRS2004

Silicon Carbide Diodes Characterization at High Temperature and Comparison With Silicon Devices

Commercially available silicon carbide (SiC) Schottky diodes from different manufacturers rated at 200, 300, 600, and 1200 V, were electrically tested and characterized as a function of temperature up to 300 C. Electrical tests included both steady state and dynamic tests. Steady state tests produced forward and reverse I-V characteristic curves. Transient tests evaluated the switching performance of the diodes in either a hard-switched DC to DC buck converter or a half-bridge boost converter. For evaluation and comparison purposes, the same tests were performed with current state-of-the-art ultra fast silicon (Si) pn-junction diodes of similar ratings and also a Si Schottky diode. The comparisons made were forward voltage drop at rated current, reverse current at rated voltage, and turn-off peak reverse recovery current and reverse recovery time. In addition, efficiency measurements were taken for the buck DC to DC converter using both the SiC Schottky diodes and the Si pn-junction diodes at different temperatures and frequencies. The test results showed that at high temperature, the forward voltage drop for SiC Schottky diodes is higher than the forward drop of the ultra fast Si pn-junction diodes. As the temperature increased, the forward voltage drop of the SiC Schottky increased while for the ultra fast Si pn-junction diodes, the forward voltage drop decreased as temperature increased. For the elevated temperature steady state reverse voltage tests, the SiC Schottky diodes showed low leakage current at their rated voltage. Likewise, for the transient tests, the SiC Schottky diodes displayed low reverse recovery currents over the range of temperatures tested. Conversely, the Si pn-junction diodes showed increasing peak reverse current values and reverse recovery times with increasing temperature. Efficiency measurements in the DC to DC buck converter showed the advantage of the SiC Schottky diodes over the ultra fast Si pn-junction diodes, especially at the higher temperatures and higher frequencies.

Lebron-Velilla, Ramon C.↗
NASA NTRS1979

Data reduction and analysis of graphite fiber release experiments

The burn and burn/explode effects on aircraft structures were examined in a series of fifteen outdoor tests conducted to verify the results obtained in previous burn and explode tests of carbon/graphite composite samples conducted in a closed chamber, and to simulate aircraft accident scenarios in which carbon/graphite fibers would be released. The primary effects that were to be investigaged in these tests were the amount and size distribution of the conductive fibers released from the composite structures, and how these various sizes of fibers transported downwind. The structures included plates, barrels, aircraft spoilers and a cockpit. The heat sources included a propane gas burner and 20 ft by 20 ft and 40 ft by 60 ft JP-5 pool fires. The larger pool fire was selected to simulate an aircraft accident incident. The passive instrumentation included sticky paper and sticky bridal veil over an area 6000 ft downwind and 3000 ft crosswind. The active instrumentation included instrumented meteorological towers, movies, infrared imaging cameras, LADAR, high voltage ball gages, light emitting diode gages, microwave gages and flame velocimeter.

Lieberman, P.↗
NASA NTRS1981

Direct current ballast circuit for metal halide lamp

A direct current ballast circuit for a two electrode metal halide lamp is described. Said direct current ballast circuit includes a low voltage DC input and a high frequency power amplifier and power transformer for developing a high voltage output. The output voltage is rectified by diodes and filtered by inductor and capacitor to provide a regulated DC output through commutating diodes to one terminal of the lamp at the output terminal. A feedback path from the output of the filter capacitor through the bias resistor to power the high frequency circuit which includes the power amplifier and the power transformer for sustaining circuit operations during low voltage transients on the input DC supply is described. A current sensor connected to the output of the lamp through terminal for stabilizing lamp current following breakdown of the lamp is described.

Lutus, P.↗
NASA NTRS2004

Advanced Electrical Materials and Components Being Developed

All aerospace systems require power management and distribution (PMAD) between the energy and power source and the loads. The PMAD subsystem can be broadly described as the conditioning and control of unregulated power from the energy source and its transmission to a power bus for distribution to the intended loads. All power and control circuits for PMAD require electrical components for switching, energy storage, voltage-to-current transformation, filtering, regulation, protection, and isolation. Advanced electrical materials and component development technology is a key technology to increasing the power density, efficiency, reliability, and operating temperature of the PMAD. The primary means to develop advanced electrical components is to develop new and/or significantly improved electronic materials for capacitors, magnetic components, and semiconductor switches and diodes. The next important step is to develop the processing techniques to fabricate electrical and electronic components that exceed the specifications of presently available state-of-the-art components. The NASA Glenn Research Center's advanced electrical materials and component development technology task is focused on the following three areas: 1) New and/or improved dielectric materials for the development of power capacitors with increased capacitance volumetric efficiency, energy density, and operating temperature; 2) New and/or improved high-frequency, high-temperature soft magnetic materials for the development of transformers and inductors with increased power density, energy density, electrical efficiency, and operating temperature; 3) Packaged high-temperature, high-power density, high-voltage, and low-loss SiC diodes and switches.

Schwarze, Gene E.↗
NASA NTRS1981

High-frequency high-voltage high-power DC-to-DC converters

The current and voltage waveshapes associated with the power transitor and the power diode in an example current-or-voltage step-up (buck-boost) converter were analyzed to highlight the problems and possible tradeoffs involved in the design of high voltage high power converters operating at switching frequencies in the range of 100 Khz. Although the fast switching speeds of currently available power diodes and transistors permit converter operation at high switching frequencies, the resulting time rates of changes of current coupled with parasitic inductances in series with the semiconductor switches, produce large repetitive voltage transients across the semiconductor switches, potentially far in excess of the device voltage ratings. The need is established for semiconductor switch protection circuitry to control the peak voltages appearing across the semiconductor switches, as well as to provide the waveshaping action require for a given semiconductor device. The possible tradeoffs, as well as the factors affecting the tradeoffs that must be considered in order to maximize the efficiency of the converters are enumerated.

Wilson, T. G.↗
NASA NTRS1999

Study of Bulk and Elementary Screw Dislocation Assisted Reverse Breakdown in Low-Voltage (<250 V) 4H-SiC p+n Junction Diodes - Part 1: DC Properties

Given the high density (approx. 10(exp 4)/sq cm) of elementary screw dislocations (Burgers vector = lc with no hollow core) in commercial SiC wafers and epilayers, all appreciable current (greater than 1 A) SiC power devices will likely contain elementary screw dislocations for the foreseeable future. It is therefore important to ascertain the electrical impact of these defects, particularly in high-field vertical power device topologies where SiC is expected to enable large performance improvements in solid-state high-power systems. This paper compares the DC-measured reverse-breakdown characteristics of low-voltage (less than 250 V) small-area (less than 5 x 10(exp -4) sq cm) 4H-SiC p(+)n diodes with and without elementary screw dislocations. Compared to screw dislocation-free devices, diodes containing elementary screw dislocations exhibited higher pre-breakdown reverse leakage currents, softer reverse breakdown I-V knees, and highly localized microplasmic breakdown current filaments. The observed localized 4H-SiC breakdown parallels microplasmic breakdowns observed in silicon and other semiconductors, in which space-charge effects limit current conduction through the local microplasma as reverse bias is increased.

Neudeck, Philip G.↗
NASA NTRS1998

Study of Bulk and Elementary Screw Dislocation Assisted Reverse Breakdown in Low-Voltage (less than 250 V) 4H-SiC p(+)n Junction diodes: DC Properties - Part 1

Given the high density (approx. 10(exp 4)/sq cm) of elementary screw dislocations (Burgers vector = 1c with no hollow core) in commercial SiC wafers and epilayers, all appreciable current (greater than 1 A) SiC power devices will likely contain elementary screw dislocations for the foreseeable future. It is therefore important to ascertain the electrical impact of these defects, particularly in high-field vertical power device topologies where SiC is expected to enable large performance improvements in solid-state high-power systems. This paper compares the DC-measured reverse-breakdown characteristics of low-voltage (less than 250 V) small-area (less than 5 x 10(exp -4)/sq cm) 4H-SiC p(+)n diodes with and without elementary screw dislocations. Compared to screw dislocation-free devices, diodes containing elementary screw dislocations exhibited higher pre-breakdown reverse leakage currents, softer reverse breakdown I-V knees, and highly localized microplasmic breakdown current filaments. The observed localized 4H-SiC breakdown parallels microplasmic breakdowns observed in silicon and other semiconductors, in which space-charge effects limit current conduction through the local microplasma as reverse bias is increased.

Neudeck, Philip G.↗
NASA NTRS1978

Regulated high efficiency, lightweight capacitor-diode multiplier dc to dc converter

A voltage multiplier having a capacitor-diode voltage multiplying network is disclosed which is fed with voltage pulses from a dc source through a first switching means. Pulses of a second polarity are also supplied through a second switching means to the input of the capacitor-diode voltage multiplier from a second dc source whose voltage is adjustable to change the voltage of the pulses of second polarity. The switching means are alternately rendered conducting by signals from a control circuit. The second dc source may be controlled by a voltage comparator which compares the output voltage of the capacitor-diode voltage multiplier to the reference source.

Harrigill, W. T., Jr.↗
NASA NTRS2012

Forward voltage short-pulse technique for measuring high power laser array junction temperature

The present invention relates to a method of measuring the temperature of the P-N junction within the light-emitting region of a quasi-continuous-wave or pulsed semiconductor laser diode device. A series of relatively short and low current monitor pulses are applied to the laser diode in the period between the main drive current pulses necessary to cause the semiconductor to lase. At the sufficiently low current level of the monitor pulses, the laser diode device does not lase and behaves similar to an electronic diode. The voltage across the laser diode resulting from each of these low current monitor pulses is measured with a high degree of precision. The junction temperature is then determined from the measured junction voltage using their known linear relationship.

Meadows, Byron L.↗
NASA NTRS2014

High Input Voltage Discharge Supply for High Power Hall Thrusters Using Silicon Carbide Devices

A power processing unit for a 15 kW Hall thruster is under development at NASA Glenn Research Center. The unit produces up to 400 VDC with two parallel 7.5 kW discharge modules that operate from a 300 VDC nominal input voltage. Silicon carbide MOSFETs and diodes were used in this design because they were the best choice to handle the high voltage stress while delivering high efficiency and low specific mass. Efficiencies in excess of 97 percent were demonstrated during integration testing with the NASA-300M 20 kW Hall thruster. Electromagnet, cathode keeper, and heater supplies were also developed and will be integrated with the discharge supply into a vacuum-rated brassboard power processing unit with full flight functionality. This design could be evolved into a flight unit for future missions that requires high power electric propulsion.

Electric Propulsion↗
NASA NTRS1970

Thermionic triode generates ac power

Electrostatic grid controls conduction cycle of thermionic diode to convert low dc output voltages to high ac power without undesirable power loss. An ac voltage applied to the grid of this new thermionic triode enables it to convert heat directly into high voltage electrical power.

Kniazzeh, A. G. F.↗
NASA NTRS2004

Microfluidic Devices for Chemical and Biochemical Analysis in Microgravity

One often touted benefit of "Lab-on-a-Chip" devices is their potential for use in remote environments. The ultimate remote environment is outer space, and NASA has multiple needs in the area of analytical sensing capability in such an environment. In particular, we are interested in integrating microfluidic devices with NASA bioreactor systems. In such an integrated system, the microfluidic device will serve as a biosensor and be used for both feedback control and for detecting various bioproducts produced by cells cultured in the NASA bioreactors. As a first step in demonstrating the ability of microfluidic devices to operate under the extreme environmental conditions found in outer space, we constructed a portable, battery operated platform for testing under reduced gravity conditions on a NASA KC-135 reduced gravity research aircraft, (AKA "the vomit comet"). The test platform consisted of a microchip, two 0-8kV high voltage power supplies, a high voltage switch, a solid-state diode-pumped green laser, a channel photomultiplier, and an inertial mass measurement unit, all under the control of a laptop computer and powered by 10 D-cell alkaline batteries. Over the course of 4 KC-135 flights, 1817 fast electrophoretic separations of 4 amino acids and/or proteins were performed in a variety of gravitational environments including zero-G, Martian-G, lunar-G, and 2-G. Results from these experiments will be presented and discussed.

Roman, Gregory T.↗
NASA NTRS1976

High voltage compliance constant current ballast

A ballast circuit employing a constant current diode and a vacuum tube that can provide a constant current over a voltage range of 1000 volts. The simple circuit can prove useful in studying voltage breakdown characteristics.

Rosenthal, L. A.↗
NASA NTRS1992

Barrier/n/n+ Varactor Frequency Multipliers

Barrier/n/n+ (BNN+) varactor diodes developed as frequency multipliers at millimeter and submillimeter wavelengths. Devices required to serve as frequency triplers or quintuplers to provide powers of order of milliwatts at frequencies from 0.1 THz to about 1 THz. Feature Mott or heterojunction barriers and back-to-back diode configuration, which make it possible to obtain symmetrical capacitance-versus-voltage characteristics with high ratio between maximum and minimum capacitances. Extension of barrier/intrinsic/n+ (BIN+) concept described in "BIN Diode for Submillimeter Wavelengths" (NPO-17258).

Lieneweg, Udo↗
NASA NTRS1967

Transistor biased amplifier minimizes diode discriminator threshold attenuation

Transistor biased amplifier has a biased diode discriminator driven by a high impedance /several megohms/ current source, rather than a voltage source with several hundred ohms output impedance. This high impedance input arrangement makes the incremental impedance of the threshold diode negligible relative to the input impedance.

Larsen, R. N.↗