ATX12V and ATX12VO PSU
Design Guide Addendum
Power Supplies with 12V Rails Listed Together
Most of today’s power supplies have all of the 12V rails listed together. Figure 3-1 shows an example of a power supply label for this scenario.
Figure 3-1: PSU Label with One 12V Rail
To understand if a power supply supports a specific processor in this scenario, basic power budgeting must be calculated for the rest of the system to determine if there is sufficient 12 Volt Current available for the processor. For this type of evaluation, the rest of platform power will set a basic minimum level. There can be many other scenarios where the rest of platform power will be different which can affect what processor can be supported by a specific power supply.
A basic desktop system 12 Volt Power Budget includes power to fans, storage, PCIe Add-In-Cards, LEDs and other components on the motherboard – Rest of Platform (ROP). A basic system’s 12V Power requirement can range from 2 Amps to 30 Amps. For these calculations 4, 8, and 14 Amps for rest of 12V Platform power will be used as an example for Desktop systems. As noted, it is expected that each system configuration will be different.
- Example calculation with integrated graphics:
- CPU = 23A (Intel® 12th Gen Core™ Processor family 65 W TDP)
- ROP = 4A (Simple DT ROP)
- Total = 23A + 4A = 27 A
- Conclusion: Choose a power supply with at least 27 A in this example.
- Example calculation with discrete graphics card power (need to know expected sustained power of discrete graphics card):
- CPU = 26 A (Intel® 12th Gen Core™ Processor family 125 W TDP)
- dGFX = 300 W = 300w/12v = 25 A
- ROP = 8 A (median DT ROP)
- Total = 26 + 25 + 8 =59A
- Conclusion: Choose a PSU with at least 59 Amps for this example
- Example Calculation for Workstation processor with discrete graphics card power, Rest of Platform also increases:
- CPU = 31 A (Intel® Xeon® W-3300 Processors processor 250 W TDP)
- dGFX = 450 W = 450w/12v = 37.5 A
- ROP = 14 A (median WS ROP)
- Total = 31 + 37.5 + 14 =82.5A
- Conclusion: Choose a PSU with at least 82.5 Amps for this example