Assessing the Reliability of MEAN WELL Power Supplies

30 November 2021

MEAN WELL was established in 1982 and has gained a global reputation for the design and manufacture of superior quality and high cost-performance power supplies.

With switch-mode power supplies, the number of components used in the design can be anything from dozens to hundreds, depending on the power output and topology.  

Of course, each component is designed in due to necessity.  

Ensuring a long service life and assessing reliability are priorities in the power supply industry. 

There are two parameters that are usually cited in product data sheets that enable you to assess the anticipated service life and reliability of a power supply. 

These are: 

  • Meantime Between Failure (MTBF) 
  • Lifecycle 

In this blog post we discuss both the MTBF and the lifecycle parameters  

MTBF and Lifecycle are not a guarantee of how long a single power supply will last. Rather, the give an average expectation.  


Lifecycle is determined by measuring the temperature rise of the electrolytic capacitors under their maximum operating temperature under a full load to estimate the approximate life of the power supply.  

This is usually expressed in the data sheet in 1000’s of hours. 

Mean Time Between Failure 

The calculation to derive the MTBF data is more involved than that to determine the Lifecycle value. MTBF can be calculated using two different methodologies: "part count" and "stress analysis".  

The standards MIL-HDBK-217F Notice 2 and TELCORDIA SR/TR-332(Bellcore) are commonly used to calculate MTBF and you will see these referenced in most MEAN WELL data sheets. 

MIL-HDBK-217F is a United States military standard, and TELCORDIA SR/TR-332(Bellcore) is a commercial regulation.  

The only difference is that they are derived from differential equations. 

The MTBF equation for electrical component failure rate contains many variations, including quality factor, environment factor, basic failure factor…etc.  

The advancements in the design of components and the processes used to manufacture them results in better quality and stability.  

Therefore, if a power supply is updated to use a newer component of a higher quality, it is possible to adjust the pQ parameter in the above equation to enhance the MTBF value of the power supply.  

To ensure the relevance of the MTBF, MEAN WELL uses the below table to establish which pQ factor should be used in the above MTBF equation. 

Quality Level Quality Factor (πQ=) Description
0 6

Commercial grade reengineered, remanufactured, reworked, salvaged, grey market sourced components. 

Primary manufacturer has no device qualification, lot-to-lot controls, or an effective feedback and corrective action program, or these are outsourced to a lower-level design or manufacturing subcontractor. 

However, steps have been taken to ensure that the components are compatible with the design application. 

I 3 Commercial grade components that are procured and used without thorough device qualification or lot-to-lot controls by the manufacturer. However, (a) steps must have been taken to ensure that the components are compatible with the design application and manufacturing process, and (b) an effective feedback and corrective action program must be in place to resolve problems that arise during manufacture and in the field. 
II 1 Components that meet requirements (a) and (b) of quality level I, plus the following: (c) purchase specifications must explicitly identify important characteristics (electrical, mechanical, thermal, and environmental) and acceptable quality levels (i.e., AQLs, DPMs, etc,) for lot control; (d) devices and device manufacturers must be qualified and identified on approved part numbers/manufacturers list (device qualification must include appropriate life and endurance tests); (e) lot-to-lot controls either by the equipment manufacturer or device manufacturer, must be in place at adequate AQls/DPMs to ensure consistent quality. 
III 0.8 Components that meet (a) through to (e) of quality levels I and II, plus the following: (f) device families must be requalified periodically; (g) lot-to lot controls must include early life reliability control of 100% screening (temperature cycling and burn-in), which, if the results warrant, may be reduced to a “reliability audit” (i.e., a simple basis) or to an acceptable “reliability monitor” with demonstrated and accepted cumulative early failure values of less than 200 ppm out to 10,000 hours; (h) where burn-in screening is used, the Percent Defective Allowed (PDA) shall be specified and shall not exceed 2%; and (i) an ongoing, continuous reliability improvement program must be implemented by both the device and equipment manufacturers. 

The continuous pursuit of innovation and optimisation is an ongoing mission for MEAN WELL. As a result, MEAN WELL’s quality is continuously evolving as newer components and suppliers are selected.  

This is why you will see many power supplies offered by MEAN WELL with warranty periods of 5 years or longer.  

For further information on MEAN WELL power supplies, please do not hesitate to contact MEAN WELL Australia.  

Author: Simon Kuo / MEAN WELL Technical Service Centre 
Editor: Stephen Lilley / ADM