A fundamental law of physics is that for every 10°C that you are able to keep the power supply’s environment lower than 40°C, you double the mean time between failures (MTBF). Conversely, for every 10°C your power supply’s ambient temperature increases, your MTBF cuts in half (that is, your power supply is half as reliable). Many, but not all, of the failure mechanisms on this list are related to temperature.

More and more, we’re seeing the use of end-equipment plastic chassis compared to the metal chassis that have been used since time began, which impacts thermals as well as EMC. Anything you can do to enhance thermal management around your power supply in the system is of critical importance.

1. Fans

Fans are the number one failure mechanism of power supplies, as found by both military MTBF simulations as well as Belcore standards and as both simulated and demonstrated in reality. As the only electromechanical moving part incorporated into power supplies, fans are prone to fail even in the most properly designed power supplies. Often, we see a no-fans requirement for the power supply only to have the end user add fans to get rid of the heat of the entire system. But this approach just transfers the problem from one place to another.

A fanless system can be sealed, which also eliminates other issues, including ingress of moisture. In the case of outdoor applications, such as digital signage, a sealed system can keep out leaves, bugs, twigs, and bird nests, as well as rain and moisture and, in the case of maritime applications, salt and fog.  

Removing the fan increases reliability by 25% and is the best solution for avoiding failure. A good design that keeps the efficiency of the power supply high enough makes fans unnecessary. 

2. Capacitors

Despite popular thought, a lot of progress is being made in capacitor technologies every year; however, they are prone to failure if overstressed or if substitutes are made in production or by counterfeiting. 

Capacitors, especially electrolytics, can be found failed in many different failure states, including swollen, leaking, exploded, shorted, reduced-capacitance, or increased-in-circuit ESR. Sometimes excess heat causes capacitor damage. Electrolytic capacitors can leak chemicals, which can then cause further damage from corrosion, eating away PCB traces, and other problems. To prevent failures, use high-quality capacitors from name brands. Also, derate. Keep capacitors as cool as possible and watch the ripple currents to make sure they are not excessively stressed. It’s important to know that storage life of electrolytic capacitors is limited to two years without power on the power supply, which is something that usually gets overlooked. As power designers, we avoid electrolytic capacitors if we can, but if we can’t avoid them, we get the best that we can find.

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