Articles: Cases/PSU

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The PSUs fully comply with the ATX12V 2.0 standard in their declared load characteristics. This means a very high load capacity of the +12V rail, but also low load capacities of the +5V and +3.3V rails (don’t even look at the current, but at the low total wattage of these two rails – it’s smaller than that of 250W units of the older version of the standard) since modern components are supposed – quite correctly, by the way – to tend to the +12V rail. As a side remark, the Power Supply Design Guide, the fundamental document on every thing concerning the parameters of power supplies, says the max combined load on the +5 and +3.3V rails should be 130 watts, but the declared current of 28 amperes on the +5V rail already gives a higher wattage, so the parameters of the FSP400-60THN – where this load is 150 watts – seem more logical. Anyway, law is law, and the current requirements of the standard are just as they are listed in the table at the beginning of this article.

The load current on the +12V rail is reduced by 1amp for the 400W model in the diagrams above since its protection would get to work as soon as 29 amperes was achieved. So I had to reduce the load a little to record the cross-load characteristic without problems. As you can see, the stability of the output voltages is good, especially with the senior model. This PSU is even among the few units whose cross-load characteristic fully covers the area recommended by the standard (the CLC of many units, including the FSP300-60THN-P, doesn’t meet the recommendation at high loads on the +5V rail; yet, this is such a common thing that I don’t regard it as a serious drawback but rather think that the standard is somewhat too strict here).

The oscillograms of the output voltages look neat, too. The two models produced almost identical oscillograms, so I publish only one picture. The ripple at the max load isn’t even as high as half of the acceptable peak.

The PSUs also use identical fans (Yate Loon D12BM-12) and identical fan-control circuits, so the diagram above shows you the senior model. The graph of the junior model coincides with that quite accurately (at loads below 300 watts, of course). We can see some progress over the PN(PF) series: the fan speed is now controlled flexibly and smoothly, so the speed reaches the maximum only when it is really needed. Overall, the THN series units are quieter at work, even though they use the same fans.

The new PSUs are better than the previous series from the efficiency standpoint, too. Their efficiency is now 80-82%. That’s not a record, but a good result anyway, since the standard recommends 80% and higher efficiency and demands no less than 70%. The two graphs also show the power factor difference between a PSU with passive PFC (its efficiency, but also the power factor are somewhat better than those of the previous models) and without PFC. As you see, there’s some gain from passive correction, although I have repeatedly complained about the small value of this gain.

Thus, the THN series is quite appealing. It includes powerful PSUs capable of meeting the needs of the absolute majority of modern computers. Externally designed like the previous PN(PF) series, and with the same fans, these power supplies turn to be quieter at work due to the improved control over the fan speed.

As for disadvantages, the 300W model has too short cables and only one SATA power cable and the total number of connectors is rather small for a PSU of such wattage. It would be better to have at least two SATA power connectors, six Molex connectors and, preferably, an additional 6-pin connector for the graphics card.

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