Articles: Cases/PSU

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ZM400A-APF, like the previous PSU, features active correction of the power factor: the circuit board is visible in the second snapshot of the internal structure of the device, to the left of the big capacitor of the high-voltage rectifier.

This unit comes with a more expensive fan from NMB (Minebea Co., Ltd.), the 3110GL-B4W-B30 model. The maximum speed of this fan is 2700rpm and it is pumping 31.78 cubic feet per minute producing 28dB of noise at the same time.

Our measurements showed that the rotational speed of the fan is smoothly changing from 1200 to 2250rpm depending on the temperature. The thermal diode sits on the end of the heatsink – you can see it in the first snapshot of the internal unit construction. The fan is absolutely silent under the minimal load, as its speed is very low (so don’t be afraid if it doesn’t spin up at all when you turn your system on). According to the manufacturer, after a “burning” test with a load of 375W, the fan reached the speed of 2250rpm, but was modestly loud – about 23-24dB.

The unit has seven IDE power connectors, two mini-plugs for floppy drives, ATX12V, AUX and 20-pin ATX connectors. Most cables have a 16AWG section, which is the norm for high-quality units of 300W wattage and up.

The oscillograms of the +5V voltage show no considerable fluctuations: in fact, we have only noise here.

Small fluctuations appear in the oscillogram of the +12V voltage and sometimes short voltage surges appear when the inverter transistors are switched. However, these fluctuations are much below the maximum acceptable level. Thus, the PSU shows excellent results in this aspect, too.

The stability of the voltages is somewhat poorer than we had with the previous model, but this is caused by the increased load: such behavior is usual for PSUs of different wattages, but assembled according to similar circuit schemes. However, this instability is not catastrophic – the unit still shows excellent performance. The test graph shows no serious artifacts, save for the higher +12V surges when the load changes, but this is explained by the fact that the +5V power bus has a wider load range now due to the higher wattage of this unit.

I’m sure this model deserves your attention. As its predecessor, ZM400A-APF is a high-quality product, showing excellent results in our tests. Add also such nice features as an effective thermal control and a very quiet fan – the last feature is really rare in PSUs of such high wattage as manufacturers often prefer to put a powerful fan to solve the cooling problem altogether. On the other hand, if your computer experiences problems with its current 300W PSU, ZM400A-APF won’t help you in all cases. Particular bus that cannot provide enough power to the components of your system.

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