Electronic – ATX Power supply 5V rail Peak Current

5vatx

We have setup, where 16-24, 2.5" Drives will be arranged in mobile racks of( 8 or 12 each).

We are selecting ATX SMPS to satisfy these needs.

We need to power these drives with a ATX Power Supply.

As these drives only takes current from 5V rail only. 12V and other rails were just not much required (12V required upto 100W).

I have seen specifications suggest maximum current from 5V rail close to 20A for 500W/600W ATX SMPS, and mainly(largely) power is mentioned on 12V rails.

If we are using only 5V on ATX SMPS of 500W, whether complete 500W or maximum portion of power can be taken from 5V? if no, How to find what is the peak current (for short duration) can be taken from 5V rail?

Best Answer

You should rely on the specifications of your PSU.

The ATX standard has several versions. The power allocation between 3.3 V, 5 V and 12 V rails are very different between older and newer ATX PSU designs.

The original ATX (1995)

The power distribution specification defined that most of the PSU's power should be provided on 5 V and 3.3 V rails, because most of the electronic components (CPU, RAM, chipset, PCI, AGP and ISA cards) used 5 V or 3.3 V for power supply. The 12 V rail was only used by fans and motors of peripheral devices (HDD, FDD, CD-ROM, etc.)

In ATX12V 2.0:

Most power is now provided on 12 V rails. The standard specifies that two independent 12 V rails (12 V2 for the 4 pin connector and 12 V1 for everything else) with independent overcurrent protection are needed to meet the power requirements safely (some very high power PSUs have more than two rails, recommendations for such large PSUs are not given by the standard).

The power on 3.3 V and 5 V rails was significantly reduced.

Update:

In "ATX12V Power Supply Design Guide, v2.31"(It's published in 2008, a little old, but you may take it as a reference), it gives the power distribution of 3.3V/5V and 12V rails from 180W to 450W, and their related max. current limit. In page 69, it gives: for a ATX 450W PSU, the typical 5V+3.3V power < 120W, and 5V rail has a max. curren 15A. .

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