Reliability Index of Switching Power Adapter

Reliability is a critical quality indicator of switching power adapter products. Quantifying reliability helps establish clear and unified standards for evaluating the reliability of various products. Different indicators can be used to quantify reliability based on specific needs.

The primary reliability indicators include reliability, average life, failure rate, and failure density.

 

1.Reliability:
The reliability of a switching power adapter is the probability of its normal operation, defined as the likelihood of the adapter performing its specified function under specific conditions and within a specified time. The accuracy of reliability calculations improves with a larger sample size at the start of testing and shorter test time intervals.

 

In evaluating the reliability of a switching power adapter, failure probability is also commonly used. Failure probability represents the complement of reliability. Reliability and failure probability are straightforward and intuitive measures for assessing components, switching power supplies, transformers, chargers, or complex systems. Higher reliability corresponds to a lower probability of failure, which indicates better performance.

 

2.Average Life:
The average life of a switching power adapter refers to its average normal working time, which varies in definition depending on whether the product is repairable or non-repairable.

• For non-repairable products, average life is the mean working time before failure, commonly referred to as MTTF (Mean Time to Failure).
• For repairable products, average life refers to the mean working time between two consecutive failures, often termed MTBF (Mean Time Between Failures).

Both MTTF and MTBF have similar meanings, and their mathematical expressions are consistent.

 

3.Failure Rate:
The failure rate (also called failure intensity) of a switching power adapter at any given time is defined as the probability of failure in a unit of time after it has been operating for time ttt. Alternatively, it can be described as the ratio of failures occurring in a unit of time after ttt to the number of products still functioning at ttt.

Failure rate is often used to characterize the reliability of electronic products and components. A lower failure rate indicates higher reliability. Failure rate units are expressed as percentages over time, such as %/h or %/kh, representing the percentage of failures per hour or 1,000 hours, respectively. Internationally, FIT (Failures in Time) is a common unit, where 1 FIT equals one failure per billion hours of operation.

 

 

4.Failure Density:
Failure density (failure frequency) is the ratio of the number of failed products per unit time to the initial number of products tested. Failed products are not replaced during the test.

Failure density is measured in units of 1/h, which represents the proportion of failures per hour relative to the total number of tested products.

 

When evaluating product reliability, one or two of these four indicators are usually selected based on practical convenience. For general switching power adapters, reliability (failure probability) is typically used; for complex electronic equipment or systems, average life is preferred since such products cannot be mass-tested. For components, failure rate obtained through extensive testing is commonly used. For one-time-use equipment or non-repairable products, failure density is often used.

 

The reliability of switching power adapter products can be quantitatively assessed using the MTBF metric. In the electronics industry, both domestically and internationally, mean time between failures is a critical measure of product quality. For consumer electronic devices, MTBF often refers to the time from the product leaving the factory to its first failure. For industrial electronic equipment, it generally refers to the average working time between two failures.

 

To improve the reliability and MTBF of switching power adapters, it is essential to identify the root causes affecting MTBF and address them effectively. Most failures in switching power supply products result from component damage. The lifespan of a switching power adapter is determined by the lifespan of its electronic components. As the number of components in a system increases, so does the failure rate, which reduces reliability and MTBF. Therefore, when designing a switching power supply, it is crucial to use integrated components, minimize the total number of components, and simplify the circuit design. Additionally, components with low failure rates and those meeting national quality standards should be prioritized, while non-standard or homemade components should be avoided during the development phase.

 

Apart from components, welding point failures are another significant cause of failures in switching power adapters. Mistakes during production, assembly, or soldering of printed circuit boards can lead to reliability issues. A high number of welding points, poor soldering techniques, or substandard flux can significantly reduce the MTBF of the product.