I read some documents like the PoE application, it used ORing to protect the reverse input current. I would like to know what ORing is. I googled it, but I cannot find the answer. It seems like a diode or something the datasheet uses diode to protect, but I am not sure what this is.

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    \$\begingroup\$ Can you provide a reference? \$\endgroup\$
    – Frog
    Jul 14, 2021 at 9:47
  • \$\begingroup\$ In the power supply context, ORing uses a logic term to describe an analogue circuit function, described well by @TomCarpenter answer below. \$\endgroup\$
    – TonyM
    Jul 14, 2021 at 9:52
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    \$\begingroup\$ Or-ing, not O-Ring, in case that's how you were reading it. \$\endgroup\$ Jul 14, 2021 at 9:55
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    \$\begingroup\$ @AndrewMorton I have seen O-Ring mentioned in a presentation in front of the entire engineering department. \$\endgroup\$
    – user253751
    Jul 14, 2021 at 10:39

1 Answer 1


OR is a logical function - the output is high when either input is high. ORing is simply a way of saying perform the logical OR of a set of signals.

In the context of power supplies, when ORing is used, the output (the device) is powered by whichever supply typically has the highest voltage.

A simple power OR gate can be made by diodes in series with each supply, which prevent power from the higher voltage supply backflowing into the lower voltage supply.

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    \$\begingroup\$ EEC- No, there are other techniques besides diodes that can be used. FETs are used quite often as they offer lower ON resistance and so lower voltage drop than a diode. \$\endgroup\$
    – SteveSh
    Jul 14, 2021 at 11:17
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    \$\begingroup\$ @EEC this might be a good read. Product specific, but it gives some insight. Keyword: "Ideal Diode" and "Load switch" \$\endgroup\$ Jul 14, 2021 at 11:29
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    \$\begingroup\$ I parsed it a O-Ring and wondered what it was talking about. \$\endgroup\$
    – Joshua
    Jul 14, 2021 at 20:01
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    \$\begingroup\$ @Joshua - I couldn't decide between or-ing, o-ring and 0-ring. These all sound just like they could be a specific technical term. :D \$\endgroup\$
    – Vilx-
    Jul 15, 2021 at 6:58
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    \$\begingroup\$ @Joshua O-ring, usually used as a seal to couple two parts. Very common part. \$\endgroup\$
    – Mast
    Jul 15, 2021 at 9:07

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