Q&A(FAQ) How to read derating curve?
1． Meaning of the Derating Curve
The allowable output current of the power supply depends on the ambient temperature and the mounting method. In addition, for some products, the allowable output current varies with the input voltage. These conditions are shown in the instruction manual and specification sheet as a derating curves. Please refer to Fig. 1.1 and Fig. 1.2 for examples of derating curves.
2． How to calculate when two derating curves must be considered?
When two derating curves must be considered, the allowable load factor is obtained by multiplying the derating ratios of the two curves.
(Available load factor) = (Input voltage derating) x (Ambient temperature derating)
Example
- Model (example)
- Model C (on Fig.1.2)
- Input voltage
- 100Vac
- Ambient temp
- 40℃
- Mounting
- B mounting
- Cooling
- Convection
Calculation
- Ambient temperature derating
- = 73%
- Input voltage derating
- = 90%
↓
Available load factor = 73% x 90%
= 65.7%
*In the case of multiple-output power supplies, the ambient temperature derating must be applied to all output currents.