ATX12V Power Supply Design Guide
Version 2.0
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 ATX12V power supplies must conform exactly to the content of this document. The design specifics described herein are not intended to support all possible system configurations. 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.Key Changes for ATX12V Version 2.0 as Compared with ATX Power Supply
This section briefly summarizes the major changes made to this document that now defines ATX12V power supply. With the move to 12V voltage regulators for the processor, ATX guidelines for 5V as main power are no longer provided.
1.2.1. Increased +12 VDC output capability
System components that use 12V are continuing to increase in power. In cases where expected current requirements is greater than 18A a second 12 V rail should be made available. ATX12V power supplies should be designed to accommodate these increased +12 VDC currents.
1.2.2. Minimum Efficiency
Minimum measured efficiency is required to be 70% at full and typical (~50%) load and 60% at light (~20%) load. New recommended guidance has been added to provide direction for future requirements.
†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.
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