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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 heat sink be used? These questions are answered by using the technical tip below.

Technical Tip: Vicor's DC-DC converters are rated for operation at full output power at baseplate temperatures up to a maximum of 100°C (85°C 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), Application Manuals (VI-200 and VI-J00) and Vicor’s online Thermal Design Calculator. As Vicor DC-DC converter efficiency is relatively flat over the input voltage range and from 20% to maximum power, power dissipation of the converter is determined primarily by knowing the output power required from the converter and the efficiency.

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°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).
  

Figure 1 – 1-up FlatPAC, 12–48 V output

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 the VI-200 and VI-J00 Design Guide.