Rise time

About: Rise time is a research topic. Over the lifetime, 4748 publications have been published within this topic receiving 47512 citations.

Time to failure of medium-voltage form-wound machine turn insulation stressed by unipolar square waves

Abstract: The lifespans of enamelled turn insulation samples are studied when stressed with square waves characterized by different rise times, duty cycles, switching frequencies, and applied voltages. Partial discharge activities under these test conditions have also been recorded using an RF antenna in an effort to correlate the time to breakdown with material degradation under fast repetitive pulse aging. The aging and PD features were independent of rise time for a 50 % duty cycle; however, slightly faster times to failure were observed at a 15 % duty cycle for the faster rise times, for the considered range. The higher duty cycle and the higher number of applied cycles accelerated the aging.

A thyristor switch with a subnanosecond switching time

Abstract: The possibility of triggering thyristors by an overvoltage pulse with a short rise time was investigated. Low-frequency thyristors of pellet design with diameters of semiconductor structures of 32 and 40 mm and an operating voltage of 2 kV were used in the experiments. An external overvoltage pulse that increased from 2 to 5–8 kV within a time of 0.8–1 ns was applied to the thyristors. Under such conditions, the time of switching a thyristor into a conducting state was no longer than 200 ps. An assembly of six thyristors connected in series switched a capacitor with a capacitance of 2 μF, which was charged to a voltage of 13 kV, to a resistive load of 0.25 Ω. The following results were obtained: a discharge-current amplitude of 27 kA, an initial current-rise rate of 110 kA/μs, a FWHM pulse duration of 1 μs, and a peak power in the load of 190 MW. The circuit diagram of the experiment and the obtained results are described.

Carbon-Nanotube-Triggered Pseudospark Switch

Abstract: Pseudospark switches are fast-closing low-pressure gas discharge switches with a hollow-cathode geometry. They can be triggered optically or by electron injection, where electrons emitted from a cold cathode emitter are accelerated in the electric field and initiate breakdown. The efficiency of charge carrier accumulation in the hollow-cathode structure determines the performance of the switch operation. The advantages of such switches include high hold-off voltage, high conduction current, fast current rise time, low delay and jitter time, and long lifetime. In this paper, the operating characteristics of a pseudospark switch, triggered by a carbon-nanotube (CNT)-coated electron emitter, are presented. The electron emitter is fabricated by coating randomly oriented CNTs on silicon substrate using chemical vapor deposition method. Field emission characteristics of CNTs are determined and then used as part of the trigger electrode which is integrated into an in-house constructed pseudospark switch. The operating characteristics of the switch are tested under different background pressures and different trigger voltages. Delay and jitter time under different working conditions are analyzed. Hold-off voltage and current rise time are also presented.

High-Power Ultrafast Current Switching by a Silicon Sharpener Operating at an Electric Field Close to the Threshold of the Zener Breakdown

Abstract: A new principle of high-power ultrafast current switching by Si sharpener based on a successive breakdown of the series-connected structures has been experimentally implemented and theoretically studied. A voltage pulse with an amplitude of 180 kV and a rise time of 400 ps was applied to a semiconductor device containing 44 series-connected diode structures located in a 50- transmission line. Due to a sharp nonuniformity of the applied voltage distribution across the length of the device, the structures operate in the successive breakdown mode. Each successive structure breaks down with a shorter time interval as the electromagnetic shockwave builds. In the experiments in a 50- transmission line, we have obtained 150-kV output pulses having a 100-ps rise time. The maximum current and voltage rise rates amount to 30 kA/ns and 1.5 MV/ns, respectively. In the numerical simulations, the ionization rate of the process-induced deep-level centers, as well as the band-to-band tunneling, is taken into account. The calculations show that, at a reverse voltage rise rate across the structure of over 10^13 nV/s, the electric fields that are close to the threshold of the Zener breakdown can be achieved even if the structure contains deep-level centers with a concentration of 1011 to 1012 cm-3.

Switching of Vertical Alignment Liquid Crystal Cell Doped with Carbon Nanotubes

Abstract: We investigate switching characteristics of a vertical alignment (VA) liquid crystal (LC) cell doped with minute amounts of carbon nanotubes (CNTs). The doped CNTs increase the effective elastic constant of the LC–CNT mixture, decreasing the fall time of the cell. However, the doped CNTs disturb the LC alignment, generating complex defects in the cell under voltage supply. The flow motion of the defects generates an optical bounce on the rising edge of the optical response curve of the cell, increasing the rise time of the cell. A step-voltage driving scheme is demonstrated to eliminate the optical bounce and effectively improve the rise time of the cell. Under the CNT doping condition and the step-voltage driving scheme, the response time of the VA LC cell can be reduced to 50% of that of the pristine cell under the conventional driving scheme.