DC Output Current – REQUIRED
Maximum Step Size
(% of rated output amps)
Maximum Step Size (A)
40% (Required)70% (Recommended)
85% of CPU supported in Table 2-12
Steps from 100% à 300%
30% à 100% 3
- Example of how to use this table, for a rated +5 VDC output of 14A, the transient step would be 30% x 14 A = 4.2 A. Testing for a 4.2 A step size would result in testing starting at 9.8A going up to 14A.
- 12V2 rails are typically used for CPU power. CPU step size will have more updated values in the Power Supply Design Guide Addendum (# 621484) which will be used to determine the 85% value
- 12V3/V4 rails are typically used for PCIe* Add-in Card connectors. This recommendation is based on Chapter Chapter 3 where PCIe* Add-in Card needs are discussed. The step size will come from the amount of PCIe* Add-in Card power supported based on the size of the PSU in Table 3-2.For more detail reference the Desktop Platform Form Factor Power Supply Test Plan (Doc # 338448)
- Power supplies that have one combined 12V rail shall perform Dynamic testing on the one 12V rail with multiple tests which simulate different system level workloads: 12V1 (total system), 12V2 (CPU Load), and 12V3/V4 (PCIe AIC).
- Simultaneous load steps on the +12 VDC, +5 VDC, and +3.3 VDC outputs (all steps occurring in the same direction)
- Load-changing repetition rate of 50 Hz to 10 kHz
- AC input range per Section Section 2.1 and Capacitive loading per Table 4-7
The transient load slew rate is defined in Table 4-5 based on whether the PSU supports the PCIe* 12VHPWR Connectors. This usually can be correlated to the PSU’s Rated Wattage, which is listed as a guidance.
PSU without PCIe* 12VHPWR Connectors (Rated Size ≤450 Watts)
PSU with PCIe* 12VHPWR Connector(Rated Size >450 Watts)