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I am working on an application that requires isolated power inputs.

Wondering if the standard ATX PSU has any isolated outputs?

Why are we having multiple ground pins on the Connector?

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The outputs of the ATX power supply are isolated from the mains. The outputs of the ATX power supply are not isolated from each-other. In other words, +5V and +12V output "share" the same ground.

Multiple ground pins increase current carrying capacity. I bet, you will see continuity between them if you check with a meter.

My information comes from several ATX power supply reference designs that can be found on the web (such as this one). Such reference designs contain detailed schematics. A complete schematic would be a bit too detailed for the purposes of this conversation. But here's a block diagram.

enter image description here

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Per this link, the ATX provides isolation from the wall power supply. But their outputs share a common, the link also gives the simplified circuit of a PC PSU.

enter image description here

And the ATX standard defined the connector pin-out. There are many "COM"s on a connector, beside the reason for interconnecting, there are reasons to increasing the current carrying capability. Because connectors usually has a rated current carrying per contact, if your output current greater than this, you need more contacts.

Refs:

  1. http://www.formfactors.org/developer/specs/Power_Supply_Design_Guide_Desktop_Platform_Rev_1_2.pdf
  2. http://www.smpspowersupply.com/connectors-pinouts.html
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