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1 2 3 4 5 NextNovember 27, 2007 by Mike
Chin with Devon Cooke
Product

Sparkle Power SPI220LE
220W FlexATX 80Plus Power Supply 
Manufacturer

Sparkle
Power Inc. 
Market Price

??? 
Conversion efficiency as a measure of performance has been part and parcel of SPCR's power supply assessment for years. Our interest arose originally from the simple fact that higher efficiency means less heat needs to be dissipated, which usually means that a slower, quieter fan can be used for PSU cooling. Quieter is better; ergo, we're interested in high efficiency.
A little over two years ago, Intel's ATX12V power supply design guide began recommending higher efficiency, and the emerging 80 Plus program underscored the benefits of high efficiency power conversion. All this due partly to the increasing power demands of CPUs and GPUs, but also because of the increasing awareness of the need for energy conservation in our day. Now, conversion efficiency is firmly established as a core measure of performance for computer power supplies.
For those still not familiar with power conversion efficiency, it's a simple matter: A computer power supply takes AC from the wall outlet and converts it to several DC voltages required by the components. The conversion process is not 100% efficient; some of the power is lost as heat during the conversion to DC. The AC/DC conversion efficiency is expressed in percentage. An 80% efficient power supply loses 20% of the AC input as heat. This means that to deliver 80W in DC, the power supply draws 100W from the wall. Conversely, if it draws 100W from the wall, the DC output is 80W.
AC/DC conversion efficiency varies with the actual load. As with most machines (electronic or otherwise), there is an optimum load where highest efficiency is achieved. For computer power supplies, peak efficiency is usually reached somewhere between 50% and 75% of rated power, and the broad high efficiency range is about 25%~75% of full load. A power supply that's approved by 80 Plus has reached 80% efficiency at 20%, 50% and 100% of rated power. This means, for example, a 400W 80 Plus approved power supply should reach 80% efficiency at all loads higher than 80W.
There are many power supplies today that are 80 Plus approved. The vast majority of them are rated for 300W or higher, the mean being somewhere around or over the 400W mark. This is significant if you're trying to achieve the lowest power consumption with very low power computer components. A 300W 80 Plus power supply is assured to reach 80% efficiency at 60W or higher output. What if your system only draws 30W? Chances are, that 300W PSU will do no better than perhaps 50~60% efficiency at this low output. It gets much worse for higher rated PSUs, as the graph below of real power supplies tested by SPCR demonstrates. Note how efficiency in the 600W PSU starts dropping off at a much higher power level than the 300W model. This difference continues and even increases as output level drops.
Note expanded and limited vertical scale. The graph shows the relative efficiency difference at lower power for two PSUs that achieve the same maximum efficiency.

Are there many systems today that have low power demand? No, there aren't many super low power prebuilt computers, but for the doityourselfer, there is a surprisingly large number of component options for assembling such low power systems. Very low power CPUs that idle at just a few watts are available from from AMD, Intel and VIA. The single biggest power bottleneck in such systems is the power supply, where upwards of 50% of incoming AC power can be lost.
The unusual picoPSU with a high efficiency AC/DC power adapter has been the power supply of choice among ultra low power, silent system builders, but it's not cheap and it has some limitations. Could this new 80 Plus approved 220W power supply from Sparkle be a viable alternative? The Sparkle SPI220LE has just about the lowest rated power of all 80 Plus approved power supplies. (There is one PSU on the 80 Plus approved list rated for 200W, but it's by a manufacturer we've never heard of before.) To achieve 80 Plus approval, the Sparkle SPI220LE must reach 80% efficiency at just 44W output. It seemed too promising for us not to investigate after we read about it .
The Sparkle SPI220LE is a power supply meant for use in small FlexATX systems.
It comes only in bulk, free of fancy retail packaging and is 80 Plus approved.
Some of you may recognize this PSU from a Shuttle SFF system; note the similarity of the Shuttle PSU on the left to the SPI220LE on the right. The Shuttle has nowhere near the same efficiency however; it's a 2~3 year old model.

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