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TFX12V Power Supply Design Guide
Thin Form Factor with 12 V Connector
Version 2.0
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1.2.2 Improved Acoustics
As desktop systems become smaller, they are placed in more exposed areas in the home and work place.
The smaller systems are no longer confined to the floor or under the desk, but are placed on the desktop next
to the user. In these situations, noise becomes an important factor to the end user. Thin Form Factor with 12
Volt connector (TFX12V) supplies should use fan speed control techniques to provide a low acoustic profile,
while providing ample cooling to internal components when required.
1.3 Key Changes for TFX12V Version 2.0
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.
1.3.1 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.
1.3.2 Minimum Efficiency
Minimum measured efficiency is required to be 70% at full, typical (50%) load and 60% at light (20%) load.
New recommended guidance has been added to provide direction for expected future requirements.
1.3.3 Main Power Connector
The 2 x 12 main power connector replaces the 2 x 10 connector. This change was made to support 75 watt
PCI Express* requirements.
1.3.4 Separate Current Limit for 12V2 on the 2x2 Connector
The 12V rail on the 2 x 2 power connector should be a separate current limited output to meet the
requirements of UL and EN 60950.