Power Supply Basics

Goodbye MTBF hello Design life

Posted by Martin on April 15, 2011
Posted in: Power Supply Basics

In the world of AC-DC power supplies, it deeply concerns me how many people misunderstand MTBF – thinking it means product life and making design in decisions without qualifying the MTBF numbers on a datasheet. An MTBF of say 100,000 hours may look good but statistically it actually means that 63% will have failed by then !

Users of AC-DC power supplies should be asking manufacturers for detailed information about the design life instead – usually this comes down to the worst case electrolytic capacitor life under a given set of operating conditions and/or the fan (if used). ( I have seen design life calculations from a manufacturer who selected the best case capacitor !)

That assumes, of course, that the basic design is sound, component deratings are adequate, rigorous component qualification methods are employed and extensive design verification testing (DVT) is carried out.

Any reputable power supply manufacturer will be able to provide the information required to support the stated design life .