الفهرس 
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Abstract
Systems and products are composed of a group of interrelated individual components. Each component or subsystem has a specific function within the system. If any component fails to perform its intended function, the overall system can fail and therefore any improvement in components reliability will increase the overall system reliability. System reliability improvement may be achieved by several approaches. Standby redundancy is a flexible approach to improve system reliability.
This study investigates how to improve system reliability by modifying redundancy components configuration. An electronic circuit with +5 volts regulated power supply is used as an application to apply the suggested approach using standby redundancy. The circuit is built up using four main components, transformer, rectifier, capacitor and voltage regulator.
The voltage regulator is considered as the least reliable component of the system due to its high failure frequency. The effect of three different design modifications on the overall system reliability is studied. The three modifications are one-level series redundancy design, one-level parallel redundancy design and parallel-series redundancy design. The voltage regulator, in each design, is subjected to an accelerated life test. It is tested at three stress levels of 25, 20 and 12 volts. For each suggested design, the accelerated test is repeated ten times. The Weibull distribution is proposed to describe system performance. A single variable linear regression model with median rank is used to evaluate the shape and scale parameters of a Weibull distribution. Weibull ++7 software package is used to emphasis the results. Three reliability measures are used to compare reliability of each of the three modified designs with those of the initial one. The inverse power law model is used to characterize the relationship between system lifetime (L) and stress (voltage) level (V). All three design modifications rendered some improvement in the average Time- To- Failure of the voltage regulator however; the parallel-series design has the highest reliability improvement followed by the series design and the parallel design. At 12V stress level, the relative improvement of all three design modifications is significantly small when compared to the other accelerating stress levels. However, the parallel-series design has a significant enhancement in system reliability by 75% in system reliability at 12 volts stress level.