Sharif Digital Repository

In conventional high-voltage power supplies used for driving the microwave tubes, the shunt crowbar, which generally consists of series-connected thyristors, protects the microwave tube against the vacuum arc fault. In the case of arc fault, the thyristor-based crowbar is closed as a parallel path and diverts the fault current through itself. It avoids serious damage to the microwave tube. However, thyristor switches usually have a limited rate of rise of ON-state current (di/dt), which necessitates placing a series inductor in the crowbar path. Thus, satisfying all protection limits of microwave tubes-including the injected fault energy and the fault current interruption time-is a... 

High voltage power supplies are widely used in telecommunication systems. To better utilize these power supplies, voltage should be stabilized at a certain level. In this application, in case of changing voltage, the desired output parameters will change, such as RF output power quality. Various methods have been proposed to stabilize the voltage at acceptable levels. One of the most commonly used methods is use of switching regulators that are considered for high efficiency in comparison with linear regulators. But the use of these regulators also has problems. One of these problems is electromagnetic interference which is very important in telecommunication systems. Therefore, the need for... 

High-voltage power supplies (HVPSs) are widely used to drive vacuum tubes, inherently susceptible to vacuum arc faults. Owing to the considerable cost of vacuum tubes, the HVPS should enjoy a reliable, fast protection mechanism. A common protection mechanism against vacuum arc faults is the shunt crowbar. The crowbar diverts the energy stored in the elements of the HVPS through itself as a parallel path, thereby protecting vacuum tubes from irrecoverable damages. Among all types of the shunt crowbar, the thyristor-based crowbar along with the fault current limiter (FCL) resistors attracts more attention because of its more reliable operation. The absence of the comprehensive design procedure... 

This article describes the development of an 18 kV, 30 kW power supply for a pulsed current load with the maximum current of 20 A and a di/dt equal to 100 A/μs. The achieved output ripple is less than 0.01%. In such a high level of precision, the most important issues are considerable difference between the instantaneous and average output powers, as well as insufficient reaction speed of the converter to the fast load change. Very low level of the voltage feedback and its sensitivity to the noise. The first issue necessitates a notable overdesign of the converter switches if the output voltage precision is dedicated to the converter. The second issue raises the problems relevant to... 

High-voltage power supplies (HVPSs) are widely used to supply vacuum tubes. The amount of delivered energy from the HVPS to the tube is an important issue during the vacuum arc in the tube. The conventional protection mechanism consists of a shunt crowbar which diverts the fault current from the tube to itself as a parallel path. The crowbar circuit is usually built of the devices without the turn-off capability. It is a drawback since the output of the power supply is shortened for a long time. Thus, the restoration time of these power supplies is excessive. This demerit can have detrimental effects on mission-critical applications. In this paper, the insulated-gate bipolar transistor... 

High voltage power supplies (HVPS) are widely used to supply vacuum tubes. Regarding to their high efficiency, resonant converters are a choice of HVPS structure. In this application, HVPS is faced with wide variation of the load power. On the other hand, output voltage regulation over wide load range is essential. However, there are several problems dealing with resonant converters such as output voltage regulation and low-efficient performance in a light load. In this paper, a control scheme for a series-parallel resonant converter is presented. This scheme regulates the output voltage of the converter over load variation range. A variable inductor placed as the series inductor in the... 

Vacuum tubes are widely used for various applications. These vacuum tubes are supplied by high voltage power supplies. The amount of delivered energy from the high voltage power supply to the vacuum tube is an important issue during the vacuum arc in the tube. The protection mechanism consists of a shunt crowbar which diverts the fault current from the tube to itself as a parallel path. Detection of the vacuum arc is crucial and only one sensor is usually employed to detect the vacuum arc. This characteristic intensifies the interference susceptibility of the vacuum arc diagnosis system in a noisy environment. As a result of the noise, the arc detection system can report false alarms. False... 

Electrospray technique is one of the commonly used methods for generating nanoparticles. In this method, the chemical solution which consists of a polymer and its solvent are injected into an electric field via a nozzle. At the end of this nozzle, due to electric forces, a certain part of this liquid is separated. Then, the separated part is divided into smaller particles and the solvent is evaporated and hence, the nanoparticles are acquired. Produced nanoparticales are collected in deionized water placed under the certain distant from nozzle. However, construction of this method is generally based on practical results. In this paper, modeling and performance evaluation of high voltage... 

Stray capacitance of transformer winding is an important parasitic element influencing the behavior of the switching power converters, especially for high-voltage transformers. There are various methods for calculating the stray capacitance in transformers and inductors with ordered windings. However, an ordered winding is less likely with an increased number of turns and layers. In this paper, it is shown that a slight disorderliness in winding leads to a considerable difference between the value of winding stray capacitance of the former ordered winding and its slightly disordered scheme. Therefore, regular methods for calculating the stray capacitance have significant errors in a...