DC Output Current (Required)
The below table summarizes the expected output transient step sizes for each output. All items in the below table are REQUIRED, unless specifically called out as RECOMMENDED.
Table 4-3: DC Output Transient Step Sizes
Output | Maximum Step Size (% of Rated Output Amps) | Maximum Step Size (A) |
+12V1DC | 40% (Required)70% (Recommended) | - |
+12V2DC | 85% of CPU supported in Table 2-1 | - |
+12V3/4 | Steps from 100% 300% 30% 100% 2 | |
+12VSB | - | 0.5 |
- 12V2 rails are typically used for CPU power. CPU step size will have more updated values in the Power Supply Design Guide Addendum (# 621485) 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 Section 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).
Output voltages should remain within the regulation limits of Table 4-2, for instantaneous changes in load as specified in Table 4-3 and for the following conditions:
- Simultaneous load steps on the +12 VDC output (all steps occurring in the same direction)
- Load-changing repetition rate of 50 Hz to 10 kHz
- AC input range as per Section 2.1 and Capacitive loading per Table 4-7.
The transient load slew rate is defined in the Table 4-4 based on PSU supporting any PCIe* Auxiliary Power Connectors. This usually can be correlated to the PSU’s Rated Wattage, which is listed as a guidance.
Table 4-4: DC Output Transient Slew Rate
Output | PSU without PCIe* 12VHPWR Connectors (Rated Size ≤450 Watts) | PSU with PCIe* 12VHPWR Connector(Rated Size >450 Watts) |
All +12V | 2.5 A/µS | 5.0 A/µS |
+12VSB | 0.1 A/µS | 0.1 A/µS |