X-bit labs

ATX Power Supply Units Roundup. Part VIII (page 8)

Category: Other

by Oleg Artamonov

[ 12/11/2007 | 10:04 AM ]

The cross-load diagram looks good overall but the +12V voltage sags 3-4% below the nominal value under load. That’s quite a lot. A top-end graphics card may prove sensitive to such sagging even though it remains within the allowable 5% limit. On the other hand, I don’t think anyone will use a junior model of an inexpensive PSU to power up a top-performance graphics card. The +5V voltage bottoms out under high loads as well, yet that’s not critical since there just can’t be a high load on the +5V rail in a modern PC.

The diagrams for the 350W and 400W models are almost the same. It is only at greatly misbalanced loads that the voltages violate the allowable limits, but the +12V and +5V voltages sag when the respective power rail is under high load.

The output voltage ripple is similar between the PSUs, so the diagram above is for the senior model at its full load of 400W. The ripple is within the norm, twice lower than the permissible limit on every power rail.

The PSUs are equipped with identical fans (ARX FD1212-S3112E) and have identical noise characteristics as the consequence. By the way, that’s another refutation of the myth that a higher-wattage PSU is always quieter than a lower-wattage one.

The fan is working at a constant speed at loads below 200W and then accelerates in a linear manner. The PSUs are average in terms of noisiness. The initial speed of the fan is rather low (yet it is lower by some 200rpm in the really quiet PSUs) but, unfortunately, ARX fans are rarely good quality. You often get a sample with noisy bearings or an imprecisely balanced impeller.

The PSUs have an efficiency of slightly over 80% at the maximum, but the average efficiency is good, especially for inexpensive entry-level PSUs. The power factor is a little over 0.65 as you can expect from PSUs without power factor correction.

So, InWin has begun a mass production of power supplies that comply with today’s requirements such as the ATX 12V 2.0 standard, a modern circuit design including a specialized PWM controller in the standby source, an acceptable selection of cables and connectors. Still, these PSUs are rather meant for mainstream and entry-level PC systems. They are not exceptional in terms of electrical parameters or noise level, but can do quite well in an office PC or in a home PC of an undemanding user especially as they sell not only individually but also in InWin system cases, which have an appealing price/quality ratio.