Airflow And Fans - Recommended; Fan Location And Direction; Fan Size And Speed; Figure 5-5: Serial Ata* Power Connector - Intel ATX 3.0 Design Manual

Mechanical

Figure 5-5: Serial ATA* Power Connector

5.3

Airflow and Fans - RECOMMENDED

The designer's choice of a power supply cooling solution depends in part on the
targeted end-use system application(s). At a minimum, the power supply design
should ensure its own reliable and safe operation.
5.3.1

Fan Location and Direction

In general, exhausting air from the system chassis enclosure via a power supply fan
at the rear panel is the preferred, most common, and most widely applicable system-
level airflow solution. However, some system/chassis designers may choose to use
other configurations to meet specific system cooling requirements.
5.3.2

Fan Size and Speed

A thermally sensitive fan speed control circuit is recommended to balance system-
level thermal and acoustic performance. The circuit typically senses the temperature
of the secondary heatsink and/or incoming ambient air and adjusts the fan speed as
necessary to keep power supply and system component temperatures within
specification. Both the power supply and system designers should be aware of the
dependencies of the power supply and system temperatures on the control circuit
response curve and fan size and should specify them carefully.
Fan should not turn on at the same time as PS_ON# is Asserted. This is because of
power optimization at low levels and Alternative Low Power Modes. Two options to
consider:
1. Wait for at least 2 seconds before the fan turns on.
2. Fan needs to be only turned on when the PSU needs the thermal cooling.
The power supply fan should be turned off when PS_ON# is de-asserted (high). In this
state, any remaining active power supply circuitry must rely only on passive
convection for cooling.
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