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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1Can you provide a reference? – Frog Jul 14 '21 at 09:47
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In the power supply context, ORing uses a logic term to describe an analogue circuit function, described well by @TomCarpenter answer below. – TonyM Jul 14 '21 at 09:52
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20Or-ing, not O-Ring, in case that's how you were reading it. – Andrew Morton Jul 14 '21 at 09:55
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4@AndrewMorton I have seen O-Ring mentioned in a presentation in front of the entire engineering department. – user253751 Jul 14 '21 at 10:39
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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.
Tom Carpenter
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4EEC- 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. – SteveSh Jul 14 '21 at 11:17
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3@EEC [this](https://www.analog.com/en/technical-articles/a-low-loss-replacement-for-an-oring-diode.html) might be a good read. Product specific, but it gives some insight. Keyword: "Ideal Diode" and "Load switch" – Tom Carpenter Jul 14 '21 at 11:29
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3@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 – Vilx- Jul 15 '21 at 06:58
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2@Joshua [O-ring](https://i.imgur.com/o1rhMOO.jpg), usually used as a seal to couple two parts. Very common part. – Mast Jul 15 '21 at 09:07
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And it's named `OR`ing because the result is high if input 1 **OR** input 2 is high. Compare with `AND`ing where the result is hight if input 1 **AND** input 2 are high. There's also `XOR` (exclusive OR: result is high if input 1 **OR** input 2 is high, **but not both**), and negations (`NAND`, `NOR`)... Of course in this specific case where it's not really the logic but the power that matters, those probably wouldn't make much sense. – jcaron Jul 15 '21 at 13:57