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

When evaluating product reliability, failure probability or damage probability is also commonly used. Failure probability is the probability of an event corresponding to reliability. Reliability and failure probability are very simple and intuitive for evaluating the reliability of components, switching power supplies, transformers, chargers or complex systems. The greater the reliability, the smaller the failure probability, 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 irrepairable products and repairable products.

For non-repairable products, the average life 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 mean working time between failures, 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 the product at any time t is defined as: the probability of failure of the product within unit time after the product works to time t. It can also be said that the failure rate is equal to the ratio of the number of product failures in one unit time after time t to the number of products that are still working at time t.

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 abroad as the unit of failure rate, that is, one failed component occurs after 1 million components work for 1,000 hours, which is called 1 Fit.

4. Failure density: The failure density of a product (refers to the ratio of the number of failed products per unit time to the initial number of products under test. Products that fail during the test will not be replaced.