Articles: Cases/PSU

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Unfortunately, AMD didn’t support Intel’s initiative, and many owners of Socket A mainboards, about 20-25 percent of which still don’t have an ATX12V connector, have suffered from the problems Intel was talking about four years ago. As soon as there appeared high-powered processors for the Socket A platform, users began to report of burned-out pins in the PSU’s connectors and a strong misbalance of its output voltages (as the above-shown CLC diagrams indicate, even cheaper PSUs are better at handling the load on the +12v rail)…

In fact, there is only one technical drawback from the introduction of ATX12V – the efficiency of the CPU’s voltage regulator has diminished somewhat since the efficiency of any switch-mode converter diminishes when there’s a bigger difference between the input and the output voltages. This, however, was well compensated by the increased efficiency of the PSU proper. Like for the mainboard developers, the decision to orient on the +12v power rail as the main source of power has simplified the construction of the PSU for the designers. 

You can see it in the diagrams that the versions of ATX12V up to 1.2 inclusive differ from the original ATX standard in a higher allowable consumption on the +12v power rail. Version 1.3 of the standard brought more serious changes: for the first time in the evolution of computer PSUs the required allowable load on the +5v rail was decreased, while the allowable load on the +12v rail was increased even higher. In fact, computer PSUs began to adapt to the more modern systems in which fewer consumers remain on the +5v rail (processors have long been feeding on the +12v, and graphics cards are now following the suit). Unlike earlier models, an ATX12V version 1.3-compliant power supply didn’t have to maintain stable voltages when there’s a high load on the +5v rail and a small on the +12v rail.

The last version of the standard for today is ATX12V 2.0. Easy to see, the allowable load on the +5v rail has been decreased even more, and now it is only 130 watts. Meanwhile, the allowable power load on the +12v has grown up further. Besides that, ATX12V 2.0-compliant PSUs acquired a 24-pin power connector for the mainboard instead of the older 20-pin one. Four years ago the older connector was found to be insufficient for power-supplying the CPU, and they invented ATX12V, but now the maximum allowable current in this connector is not enough to give juice to new graphics cards with the PCI Express interface. ATX12V-compliant PSUs also have two sources of the +12v voltage, which are actually the same source inside the PSU, but with independent over-current protection circuits – according to the safety requirements of the IEC-60950 standard, currents over 20amps are not allowable on the +12v rail, so this power rail has to be split in two. When there’s no need to comply with this standard, the manufacturers can just leave out the appropriate circuitry and an ATX12V 2.0 PSU with, say, 10- and 15-ampere currents on its +12v rail, can be considered as a PSU with one +12v rail with a max current of 25amps.

So, returning to the above-discussed PSUs, we can say that the MP-360AR Ver.2 complies with the ATX12V 2.0 standard, while the LC-B300 – with ATX12V version 1.2, hence the difference in their CLCs. Well, the problem is not only in a formal compliance with this or that version of the standard. I said above that the LC-B300 cannot provide the declared wattage on the +5v rail, and now let’s compare its CLC diagram with Intel’s recommended CLC for ATX12V 1.2 units:

As you see, this power supply just doesn’t meet the requirements to 300W models in the allowable load on the +5v rail, so we can only regard it as a 300W PSU with a reservation that these watts are not very honest. For comparison, here’s the diagram of the MP-360AR in comparison with the recommended CLC for 350W ATX12V 2.0 units:

As you see, we have almost a perfect coincidence here. I guess there’s no need to comment on the comparative quality of the two PSUs.

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