COTS: Some General Considerations

July 28, 2014

This is the final part of the blog series about COTS power systems, highlighting some general considerations that should be taken into account when developing power systems using COTS products.

Previous posts in the series are:

  • What is COTS?
  • EMI Requirements for COTS Power Supplies
  • Environmental Requirements for COTS Power Supplies
  • Variations in Input Power: COTS Power Supply Holdup

There are a few general rules that will help to ensure that a power system using COTS components will meet the demanding requirements set out by the Mil-STD specifications we have discussed in this series. The most important thing is to understand the application: how the unit is used is critical. A COTS power supply may well meet the requirements while being tested as a stand-alone item, but fail in the system

Mounting of the unit is a particularly important factor as this may impact shock, vibration and temperature results to a significant degree. For example, consider a unit that is firmly mounted on its bottom plate on the floor of a system. In this case, the impact of vibration, particularly on taller, heavier items such as hold up caps, will be quite different than if the unit is mounted by its side on a vertical surface. Adequate clearance for airflow is a must on both input and output sides.

EMI performance can be dramatically changed by the cabling. Improper cabling, such as bad routing and inadvertent loops, may impact both emissions and susceptibility.

Another potential source of confusion is variations in requirements. A clear understanding of exactly what requirements apply is key: if you hear reference to Mil-STD 810 without specificity as to exactly what procedure and levels, raise the alarm!


This series has shown that when selecting and designing-in COTS power supplies, engineers must be aware of complex standards, and the factors that can influence performance in the applications. For more information about the standards and how to design systems that will pass the tests required for your application, contact your local Vicor applications engineer.

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