How to read derating curve?

1.Meaning of derating curve

The available output current of the power supply depends on the ambient temperature and mounting method. In addition, the available output current changes by the input voltage depending on a product. This condition is shown on the instruction manual and specification sheet as a derating curve. Please refer to the Fig.1.1 and Fig.1.2 for the example of derating curve.

Fig.1.1 Example of Ambient temperature derating curve

Fig.1.2 Example of Input voltage derating curve

2.How to calculate if two derating curves shall be considered?

In case of two derating curves should be considered, available load factor can be calculated by multiplying both derating ratios.

(Available load factor) = (Input voltage derating) x (Ambient temperature derating)


Model Model C (on Fig.1.2)
Input voltage 100Vac
Ambient temp 40℃
Mounting B mounting
Cooling Convection


Ambient temperature derating = 73%
Input voltage derating = 90%

Available load factor = 73% x 90%
= 65.7%

  • ※In the case of multiple supply, the ambient temperature derating must be applied to all output current.

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