On Figure 18 you can see HX620W label stating all its power specs.

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Figure 18: Power supply label.

As you can see the label says this power supply has three +12V rails. These rails are “virtual” as all of them are connected together to the single +12 V “real” rail coming from the +12 V rectifiers thru a series of jumpers (a.k.a. “shunts”).

Each virtual rail, at least in theory, has its own over current protection (OCP) and that is why they are listed as individual rails even though they are all connected to the same place inside the power supply. From what the label says the over current protection is configured to shut down the power supply if you pull more than 18 A in any of the three rails (usually the over current protection circuit is set with a value a little bit higher than what is written on the label). At least in theory, as during our tests we pulled a lot more than 18 A on +12V1 rail and the power supply didn’t shut down (but let’s not get ahead of ourselves; more about this on the next page).

This power supply, however, has only two virtual rails (+12V1 and +12V2), not three, as you can see on Figures 19, 20 and 21 (Figures 19 and 20 were taken with the version of Corsair HX620W we looked in Sep 2006; the version currently on the market – Feb 2008 – uses a  slight different wire configuration, as shown on Figure 21). Corsair explained to us that the OCP connection wasn’t being made on the printed circuit board like it is normally done, but directly on the +12 V wires, and that we shouldn’t consider what was on the printed circuit board. We, however, couldn’t find any evidence of this happening (if OCP was connected to the +12 V wires instead of to the jumpers located on the PCB we should see one wire connecting each claimed +12 V virtual rail to the OCP circuit, which we couldn’t find).

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Figure 19: +12 V wires are separated into two groups (there is no 12V3 virtual rail inside the PSU).

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Figure 20: But they are connected to the same +12 V line on the PCB.

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Figure 21: +12 V wire distribution on the model currently on the market (Feb 2008).

On the model currently on the market, +12V distribution is the following:

• +12V1: Modular cabling system, EPS12 V.
• +12V2: Main motherboard connector, ATX12V.

Unless, of course, Corsair is right and there are three virtual rails using an exotic configuration we weren’t able to figure out. If we are right, we would like to see EPS12V on the second rail for better power distribution.