Rise time

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

A Multigap Multiaperture Pseudospark Switch and Its Performance Analysis for High-Voltage Applications

Abstract: In this article, the development and switching characterization of a coaxial three-gap demountable multigap multiaperture pseudospark switch (MGMA-PSS) prototype is presented. The investigated MGMA-PSS geometry has three gaps which are separated by two cavity drift space regions. A high dielectric constant ferroelectric-based single plasma trigger unit, located within the hollow cathode of the first gap, is used for effective discharge initiation and subsequent synchronous breakdown of the three gaps of the MGMA-PSS. To guarantee long lifetime with high currents and high hold-off voltages and optimized plasma coupling, kidney-shaped ring slot electrodes with baffles are used. Each of the gaps is designed for a minimum voltage hold-off up to 30 kV, with a total voltage hold-off for the MGMA-PSS of approximately 70 kV. Studies of switching behavior are carried out at different operating conditions, such as operating voltages (5–40 kV), hydrogen gas pressures (10–40 Pa), various trigger configurations, and change of circuit parameters [charging capacitance (36, 200, and 380 nF), load resistance (2.7 and $8.3~\Omega $ )]. The short time-scale analysis of the breakdown voltage waveform shows steps in the voltage fall at low gas pressure (< 20 Pa) and low hold-off voltages (< 15 kV), which indicates a too-long time delay in plasma formation and coupling within the drift regions. This effect could not be observed at higher voltages (≥15 kV) and gas pressure (≥20 Pa). The overall performance of the three-gap prototype PSS has been analyzed in terms of hold-off voltage, fall time, current rise time, peak current, delay time, and related parameters.

Bistable operation of two semiconductor lasers in an external cavity: Rate-equation analysis

Abstract: The steady-state and dynamic behavior of a bistable laser resonator containing two semiconductor elements is examined theoretically. We derive necessary conditions for the bistable operation of the cavity and the constraints on the amplifier and absorber element characteristics imposed by these conditions. Our rate equation model demonstrates turn-on and turn-off of the output via current pulses, overshoot and ringing using fast rise time pulses, and critical slowing down when either the absorber or amplifier is switched. We give numerical results on switching.

Characterisation of voltage shapes acting on the insulation of rotating machines supplied by inverters

Abstract: Use of frequency inverters for supply of electrical rotating machine is becoming more usual, particularly for applications needing a rotating speed variation. New semiconductors, like Gate Turn-off thyristor (GTO) or Insulated Gate Bipolar Transistor (IGBT), can work at very high frequency, up to 10 kHz, with very short rise times down to less than 0.1 /spl mu/s. In order to study the ageing associated with these voltage shapes, we have first tried to characterise them. The inverter is a Pulse Width Modulated one (PWM) feeding a 220 V squirrel cage induction motor modified to observe the propagation of voltage shape in the winding. This adaptation results in 36 shielded coaxial wires distributed on the 6 coils and the 17 turns. Turn-to-turn and turn-to-ground voltages are recorded. A spectral analysis shows that the driving frequency is the main frequency propagating in the winding with no attenuation. On the other hand, the motor input turn-to-turn voltages show very short rise time voltage waves (typically 2000V//spl mu/s) which are very attenuated and a delay growing during propagation in the winding. Moreover, on the input coils, high frequency oscillations and overvoltages are observed, depending on supply cable length. >

A Method for Generating High-Current, Ultrashort, and Square-Wave Pulses Based on a Photoconductive Switch Operating in the Quenched High-Gain Mode

Abstract: The quenched high-gain mode of semi-insulation photoconductive semiconductor switch (PCSS) is a new operating mode. It has many advantages over the traditional modes, such as ultrafast rise time (mainly determined by the laser), high power, short pulsewidth, ultrafast fall time (mainly determined by the carrier lifetime), and so on, making it possible to generate high-power ultrashort pulses. To approximate square waveforms, a method for controlling PCSS is presented in this paper. First, a physical model of PCSS is established, which depends on the electronic negative differential mobility, the high-voltage impact ionization, the characteristic of luminous current filament, and the continuity equation of current. Second, constraint equations of circuit parameters are deduced to hold the dynamic balance of the tendency of current to increase or decrease for obtaining the flat top of output pulses. Finally, the control circuits of GaAs:EL2 PCSS operating in the quenched high-gain mode are designed, the parameters of which are the solutions to the constraint equations. The experimental results demonstrate that the method can generate square-wave pulses of kiloampere amplitude and about 50-ns pulsewidth on a subohm load.

EMI reduction by optimizing the output voltage rise time and fail time in high-frequency soft-switching converters

Abstract: In order to ensure the compatibility between devices, several electromagnetic compatibility (EMC) standards specify the maximum permitted levels of radiated noise. To comply with these standards, hard switching power converters need to use expensive solutions, namely shielding, Filtering techniques and snubbers, because the voltages have low values of rise and fall times. This fact leads into significant harmonic content at high frequencies. In this case, the most cost effective way to deal with radiated noise is to reduce it at the source. A way to achieve this goal is to impose moderate values of output voltage rise and fall times. This paper theoretically and experimentally explains, that the harmonic content at high frequencies can be significantly reduced with a selection of a suitable value of voltage rise time and fall time. Based on the study of a generic trapezoidal waveform, simple but precise equations, that permit to easily evaluate the envelope of the frequency spectrum, are derived. These equations also permit to analyze the importance and the influence of the rise and fall times in the spectrum envelope. Finally, with this simple analysis, the influence of the values of rise time and fall time in more complex waveforms are shown, as the output voltage waveform of a high frequency cycloconverter. The validity of the theoretical analysis is confirmed by experimental results.