What’s the Opposite of Derating?

July 31, 2015
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Engineers are very familiar with the concept of derating: under certain circumstances, such as elevated temperatures, devices are unable to deliver their full performance. Data sheets or application notes provide the information to derate the device – i.e. calculate how much performance is lost in this particular situation. This approach is particularly common in applications such as military systems where the component must deliver reliability in extreme environments.

In the Vicor application note 29: Single DCM as an Isolated, Regulated DC-DC Converter, however, there is a very interesting note:

Power Dissipation Graph for DCMs

Graph from DCM Datasheet used to Calculate max. Power Dissipation

The DCM is also capable of sustained operation above rated power, up to the current limit threshold with no derating or overstress to the module, provided it is sufficiently cooled. Figure 25 “Thermal Specified Operating Area: Max Power Dissipation vs. Case Temp for arrays or current limited operation” is an extension of Figure 1, which relates maximum dissipated power to environmental temperature for same the three heat extraction paths. Any time the DCM is used above rated power, for example at current limit, the thermal design must be based on the operating efficiency and the appropriate Figure 25 curve.

So in the right thermal conditions, you can safely run a DCM above its rated output. This is very unusual: manufacturers rarely say that their products can safely exceed the data sheet parameters over a sustained period. In fact there isn’t even a word that means the opposite of derate!

For engineers using DCMs, however, this is great news. The robust electrical design is an indication of the quality of this power component, something that is good to know even if the application isn’t one where it is possible to exceed the data sheet power rating.

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