ATX/ATX12V Power Supply Design Guide
Version 1.1
Page 6
1. Introduction
1.1. Scope
This document provides design suggestions and reference specifications for a family of
power supplies that comply with the ATX Specification, Version 2.03
*
for motherboards
and chassis. It includes supplementary information not expressly detailed in the ATX
Specification, such as information about the physical form factor of the power supply,
cooling requirements, connector configuration, and pertinent electrical and signal timing
specifications.
This document is provided as a convenience only and is not intended to replace the user’s
independent design and validation activity. It should not be inferred that all ATX or
ATX12V power supplies must conform exactly to the content of this document. Neither
are the design specifics described herein intended to support all possible system
configurations, because system power supply needs vary widely depending on factors such
as the application (that is, for desktop, workstation, or server), intended ambient
environment (temperature, line voltage), or motherboard power requirements.
1.2. New for ATX12V as Compared with ATX Power Supply
This section briefly summarizes the major changes made to this document that now
includes the ATX12V power supply. An earlier design guide covered only the ATX power
supply. There are also a few changes from Version 1.0 to 1.1 (increased 3.3 V current,
more explanation for power sharing).
1.2.1. ATX12V
A new superset of the original ATX power supply has been defined. Named “ATX12V,”
this new power supply is comprised of a standard ATX unit plus the following
enhancements:
•
Inc12 VDC output capability. Motherboard components with unique voltage
requirements are increasingly expected to be powered via DC/DC converters off the
+12 VDC power supply output. This trend is due primarily to the higher power
conversion and transmission efficiencies of +12 VDC relative to +5 VDC or +3.3 VDC.
ATX12V power supplies should be designed to accommodate these inc12 VDC
current requirements and to address associated issues such as cross-regulation,
capacitive loading, transient surge tolerance, cable voltage drop, and cooling.
*
2.03 is the current version of the ATX Specification as of this writing. Future references to the ATX
Specification in this document imply version 2.03 or later, as applicable.
