Please reference the Test Protocol for more information. Generalized Test Protocol for Calculating the Energy Efficiency of Internal Ac-Dc and Dc-Dc Power Supplies, section 6.1.1 Proportional allocation method for loading multiple and singleoutput ac- dc and dc-dc power supplies
Given:
- Overall rated DC output power: 1600W @ 230V, if we were to test this at 115V, rated wattage is 1000W. For this example we will have the rating at 1600W
Current Ratings:
- +55V: 29.1 A
- +12V: 33.3 A
 Figure 13: Multi-Rail Power Supply Label |
Table 5: Output Variable Labels with Multi-Rail Output Voltage Bus
Step 1: Calculate derating factors DS1 to DS6 for each of the subgroups as shown in Eq. 6-4.
55V has a max current of 29.1A, an equation you would use for this. Derating = 1
12V has a max current of 33.34A, an equation you would use for this. Derating = 1
If the derating factor DS ≥ 1, then it is clear that when the subgroup is loaded to the rated dc output currents, the subgroup rated output powers will not be exceeded and there is no need for derating. However, if one or more DS factors are less than 1 then the subgroup power will be exceeded if the outputs are loaded to their full output currents and there is a need for derating
Step 2: There is also a need to check whether the sum of the subgroup maximum rated powers is greater than the total maximum power rating of the power supply (PT). If the sum of the subgroup maximum rated powers is greater than the overall power rating of the power supply then a second derating factor DT must be applied. This factor is calculated as shown below: If DT ≥ 1 then no derating is needed. If DT < 1 then the derating for each of the outputs has to be applied and is shown below.
For example,
The total derating factor, Dt = 0.79996
55V rail: 29.1 A x 0.79996 Dt x 100% (load)= 23.279
12V rail: 33.34 A x 0.79996 Dt x 100% (load) = 26.639
Here is a screenshot of what this specific loading would be at each loading point.
 Figure 14: Loading Guidelines for Multi-Rail |