Effects of combined stressing on the electrical properties of film and ceramic capacitors
Advanced power systems which generate, control and distribute electrical power to many large loads are a requirement for future space exploration missions. The development of high temperature insulating materials and power components constitute a key element in systems which are lightweight, efficient, and are capable of surviving the hostile space environment. In previous work, experiments were carried out to evaluate film and ceramic capacitors for potential use in high temperature applications. The effects of thermal stressing, in air and without electrical bias, on the electrical properties of the capacitors as a function of thermal aging up to 12 weeks were determined. In this work, the combined effects of thermal aging and electrical stresses on the properties of teflon film and ceramic power capacitors were examined. The ceramic capacitors were thermally aged for 35 weeks and the teflon capacitors for 15 weeks at 200/spl deg/C under full electrical bias and were characterized, on a weekly basis, in terms of their capacitance stability and electrical loss in the frequency range of 50 Hz to 100 kHz. DC leakage current measurements were also obtained. The results obtained represent the influence that short-term thermal aging and electrical bias, have on the electrical properties of the power capacitors characterized.<<ETX>>
Design approach and analysis of a MOSFET with monolithic integrated EMI snubber for low voltage automotive applications
The trend of integration is continuously increasing in order to reach higher power densities. One promising way is the monolithic integration of RC snubber circuits into power semiconductors. This work describes a new way of monolithic integration of an RC snubber in the power semiconductor to improve electromagnetic interference (EMI). The snubber circuit is built of additional trenches next to the power semiconductor. This approach is analyzed on the basis of electrical simulations with an automotive low voltage power MOSFET. Electrical simulations prove a comparable behavior of the monolithic integrated snubber to discrete variants in the time domain during transitions as well as in the frequency domain. The monolithic integration of snubber circuits has several advantages in terms of cost efficiency and overcoming thermo-mechanical and electromechanical problems which can occur in conventional surface-mounted devices (SMDs).
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.