Keeping One’s Cool

May 7, 2005

To provide a long service life, power supplies require adequate cooling. Heat is removed from the supply using conduction, convection and radiation cooling. The equipment casing is sometimes used to conduct heat away. Often additional cooling is required and ambient air (convection) or moving air, e.g. from a fan, is used to remove excess heat. What airflow is required and should an additional heatsink be used? These questions are answered by using Vicor’s Thermal Design Calculator or graphically by using our published charts. The Technical Tip below explains how to use this data.

Technical Tip: Vicor’s DC-DC converters are rated for operation at nominal output power at baseplate temperatures up to a maximum of 100 Degrees Celsius (85C for VI-200) without de-rating. One can easily determine the thermal design required to cool Vicor products by using the thermal charts in our Design Guides (Maxi, Mini and Micro series) and Application Manuals (VI-200 and VI-J00). As Vicor DC-DC converter efficiency is almost independent of input voltage the maximum total power dissipation in the converter is determined primarily by knowing the output power required from the converter.

Vicor’s system products are based on our DC-DC converters and their thermal performance is determined in the same manner as DC-DC converters by using the appropriate thermal charts.

For example: Verify that a 200 W, 28 Vdc output AC-DC FlatPAC does not exceed the maximum allowable chassis temperature at an ambient temperature of 55 degrees C.

  • For delivered output powers of up to 150 W reference to the datasheet shows that airflow of 100 LFM (200 LFM = 1 meter/sec) is required (see the red line in the chart below).
  • Increasing the airflow to 250 LFM will increase the available output power to 200 W while ensuring that the baseplate of the internal converter does not exceed its maximum temperature (see the green line in the chart below)

Knowing the baseplate temperature and the environmental conditions of the power supply Vicor’s application engineering team can provide designers with the MTBF (Mean Time Between Failures) reliability data.

By optimizing thermal design early in the design process it is possible to significantly improve product reliability and hence increase product life times.

Further information on thermal considerations may be found in the thermal section of our website



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