Reliability index of switching power supply adapter

　　Reliability is a very important quality index of switching power supply adapter products. The quantification of reliability is conducive to putting forward clear and unified indexes for the reliability of various products. The quantification of reliability can adopt different indexes according to needs.

　　Reliability indicators mainly include reliability, average life, failure rate and failure density.

　　1. Reliability: The reliability of the product is the probability of normal operation, which refers to the probability that the product will complete the specified function under the specified conditions and within the specified time. When calculating the reliability, the larger the number of products at the beginning of the test and the smaller the test interval, the higher the accuracy of the reliability.

　　When evaluating product reliability, failure probability or damage probability is also often expressed. The failure probability is the probability of the corresponding event of the reliability. Reliability and failure probability are very simple and intuitive to assess the reliability of components, switching power supplies, transformers, chargers or complex systems. The greater the reliability, the lower the probability of failure and the higher the reliability.

　　2. Average life: The average life of a product refers to the average normal working time of the product, which has different meanings for unrepairable products and repairable products.

　　For non-repairable products, the average life span refers to the average working time before the product fails, usually called MTTF, which is the average time before failure.

　　For repairable products, the average life span refers to the average working time between two adjacent failures, that is, the average trouble-free working time, usually called MTBF, which is the average time between failures.

　　The meanings of MTTF and MTBF are similar, and their mathematical expressions are also consistent.

　　3. Failure rate: The failure rate (failure rate, failure intensity) of a product at any time t is defined as the probability of failure in a unit of time after the product works at time t. It can also be said that the failure rate is equal to the ratio of the number of product failures in a unit time after time t to the number of products still working at time t.

　　The failure rate is often used to indicate the reliability index of electronic products and components. The lower the failure rate, the higher the reliability. The unit of failure rate is the percentage of time, such as %/h, %/kh, which represents the percentage of the number of failures of the tested product within 1 hour (or 1000 hours). Fit is commonly used in foreign countries as the unit of failure rate, that is, 1 failure component occurs after 1 million components work for 1000 hours, which is called 1 fit.

　　4. Failure density: Product failure density (fault frequency) refers to the ratio of the number of failed products per unit time to the initial number (total) of the tested products. Products that fail during the test will not be replaced.

　　The unit of failure density is 1/h, which is the ratio of the number of failed products per hour to the total number of tested products.

　　When evaluating the reliability of different products, one or two of the above four indicators for characterizing reliability can be selected. Which indicator is used depends on the convenience of use. For general switching power adapters, electronic equipment or systems, reliability (probability of failure) can be used; for complex electronic equipment or systems, average life can be used, because such products cannot be tested in large quantities; for components The failure rate obtained through a large number of test statistics is used to characterize the reliability; for the equipment that is one-time use or that fails to be repaired, the failure density is used to characterize its reliability.

　　The reliability of switching power supply products can be quantitatively evaluated with mean time between failures (MTBF). At present, the electronics industry at home and abroad has taken the mean time between failures as one of the main criteria for evaluating and measuring product quality. The mean time between failures of civil electronic products usually refers to the average working time from the time the product leaves the factory to the first failure; the mean time between failures of industrial electronic products is usually the average operating hours.

　　To improve the reliability and mean time between failures of the switching power supply adapter, first determine the most basic factors affecting the mean time between failures, and then solve them according to their causes. Most of the failures of switching power supply products are caused by damage to the components. The average trouble-free working time of an electronic component is its life cycle. Once an electronic component fails, it marks the end of the life of the power adapter. The more the number of components used in the switching power supply machine, the higher the failure rate, the lower the reliability, and the shorter the average trouble-free working time. Therefore, when designing a switching power supply, try to use integrated components to reduce the number of components in the complete machine and simplify the circuit structure. At the same time, components with low failure rates should be selected as much as possible, and components that meet national quality standards should be selected. In the stage of developing switching power supply adapters, self-made or non-standard components should be avoided as much as possible.

　　In addition to the components, the failure of the welding point is another important factor that causes the failure of the switching power supply product. Because mistakes are unavoidable in the process of printed circuit board production, assembly, and soldering. Therefore, if the number of product solder joints is large, the soldering technology or the quality of the flux is poor, the mean time between failures of the switching power supply unit will inevitably change short.

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