Articles: Cases/PSU

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This time around we got four power supply units (PSUs) of the high-end category (at least their manufacturers claimed them to be such): one model from each Antec and BeQuiet, and two models from OCZ Technology. But here we are not as much interested in the positioning of the PSUs or their retail price as in their design features. Three of these four units have dedicated voltage regulation of each of the main power rails (+5v, +12v, and +3.3v), which is a very rare thing indeed in today’s computer PSUs. You can only meet it in top-end models, and it is the first time we have such units in our test labs.

So I am the more eager to compare their characteristics with classic-design units (namely, the stability of the output voltages, since the rest of the characteristics of a PSU don’t depend on the additional voltage regulators).

The first part of this review is dedicated to the theory of the problem – the problem of stability of voltages and its possible solutions and the explanation why the developers prefer the design we will see in the tested PSUs.

Independent Voltage Regulation

As I said in my previous article called X-bit Presents: Power Supply Units Testing Methodology, we use to test computer power supplies, one of the problems of each computer PSU is the lack of independent regulation of the output voltages. In other words, if the load on one of the PSU’s outputs changes, the output voltages on the other power rails change, too. This comes as there’s physically just one regulator inside the PSU, and this regulator works basing to some averaged load on the output rails of the unit.

This problem has become the more urgent today now that the ATX12V 2.0 standard has been accepted in which the main load has shifted finally from the +5v rail to the +12v. That is, you won’t have any problems with a power supply that strictly complies with the ATX12V 2.0 standard except that this power supply won’t work with powerful computers of old production dates that put a heavy load on the +5v rail. While Intel’s platforms have mostly relied on the +12v for a few years already, many mainboards for AMD’s Socket A processors have powered up the processor from the +5v until quite recently, and top-end processors have put a very high load on this rail.

If the manufacturer wants to create a universal power supply, i.e. equally suitable for both +12v-oriented systems (computers with Intel’s processors and AMD’s Athlon 64 belong here) and for older +5v-oriented computers, the output voltages must be independently regulated. Otherwise, the PWM controller of the PSU has to be predisposed to a high load on either the +5v or the +12v power rail. Yes, it is possible to find a compromise between these two requirements, but it would rather mean that the PSU would regulate both voltages equally badly rather than equally well. Of course, bad regulation doesn’t satisfy the user as well as the manufacturer. So, again, independent regulation of the voltages is a must.

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