Guía Técnica

TECHNICAL GUIDE

> Back

4.2. Reliability

A power supply’s failure rate, as a function of time, is similar to that of any electronic device. Three stages can be distinguished , as shown in figure 22:
 
(A) Premature failure or “child mortality”. During this stage of the device’s service life, the failure probability is higher. This is due to the fact that some imperfections may remain undetected in the components used. Their influence is minimized by carrying out a burn-in of all units before being marketed.
 
(B) Random failure. This is the stage of the service life after the premature failure period has elapsed. During this time period, the failure rate is minimum.
 
(C) Ageing failure. Once the device’s service life is ended, the components featuring faster ageing start to degrade causing the failure rate to increase.
A power supply’s failure rate, as a function of the ambient temperature, also has a similar behaviour to that of any electronic device. The common way to refer to a reliability forecast is by using the term MTBF (Mean Time Between Failure) expressed in hours.
 
As shown in figure 23, the temperature effect upon MTBF is dramatic, since it features an exponential dependency on temperature, which is obtained from the Arrhenius formula. As a consequence of this, a noticeable increase of MTBF and service life may well reward investments in resources to decrease, even by just a few degrees, the power supply ambient temperature, such as, for example, improving ventilation, etc.

Figure 22

Figure 22

Figure 23

Figure 23