On Figure 15 you can see TX750W label stating all its power specs.

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Figure 15: Power supply label.

As you can see Corsair labeled this unit as having only one +12 V rail. If you open the power supply, however, you will see that the +12 V wires are separated in four groups (+12V1 thru +12V4) and may think that this power supply has in fact four virtual rails (see Figure 16).

Here is the deal. As we have exhaustively explained on other articles, on power supplies with more than one rail these +12 V “virtual rails” are connected to the single +12 V real rail the power supply has – there is only +12 V output coming from the rectifiers. The exact same thing happens on this power supply from Corsair. The difference lies on the OCP (Over Current Protection) mechanism. On power supplies with multiple rails, the OCP circuit has several inputs and is set to shut down the power supply whenever any of the rails pulls more than a given current – 16 A, 18 A, 20 A are some good examples. So on power supplies with four rails, for example, the OCP circuit will be monitoring the four rails.

On this power supply, however, the OCP circuit monitors the entire current pulled by all +12 V wires, so it has only one input. If your system pulls more than 60 A (actually the OCP circuit is usually set a little higher than the current printed on the power supply label), then your unit will shut down.

There is a lot of discussion of what design is the best, but we will leave this discussion to a tutorial we are planning to write.

So even though you see four labels on the printed circuit board this unit uses in fact a single rail design.

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Figure 16: Four rails labeled on the printed circuit board, but they are wrong and should be ignored (see text).

What is important is that the power and currents labeled are inside the specs from the semiconductors used on this power supply.

Once again we’d like to remind that this power supply is labeled at 50º C, which is outstanding. Usually when no temperature is stated, the manufacturers assume 25º C, which is a temperature far below the power supply real working temperature. Keep in mind that the maximum power a power supply can deliver drops as its internal temperature increases. We have a suggestion to Corsair, to post this information on their website, because it is printed only on the product box. Anyway, we will see if this power supply can really deliver its labeled power on the next page.

The only thing we really didn’t like about this power supply is how the +12 V wires from the video card cables are connected. As you can see on Figure 17 each video card cable has three +12 V wires but two of them are connected together to a single wire. We think that the three wires should be connected directly to the printed circuit board without any splitting in the middle of the way, as the configuration used can limit the maximum amount of current (and thus power) the power supply can deliver to each video card, theoretically speaking.

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Figure 17: Two of the +12 V wires from the video card cables are connected together to a single wire.