Articles: Cases/PSU

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SLI and CrossFire Support

Yet another pretty-looking label that means two power connectors for graphics cards and an ability to yield as much power as is considered sufficient for a SLI graphics subsystem. Nothing else stands behind that label.

The PSU manufacturer can get some certificate from a graphics card maker but such a certificate means nothing but the mentioned connectors and high wattage. The latter is often much higher than a typical SLI or CrossFire system may need. After all, the manufacturer must explain the necessity of buying PSUs of indecently high wattage to the customer, so why not do that by simply putting a SLI Certified sticker on the product?

Industrial Class Components

One more pretty-looking sticker! Industrial class components are components that can work in a very wide range of temperatures. But what’s the purpose of installing a chip capable of working under -45°C into a PSU if this PSU will never be used in such cold weather?

Sometimes the term industrial class components refers to capacitors meant for operation under a temperature up to 105°C, but that’s all clear here, too. The capacitors in the PSU’s output circuits heat up by themselves and also located very close to the hot chokes are always rated for a temperature of 105°C max or their service life would be too short. Of course, there is a much lower temperature inside the PSU, but the problem is that the service life of a capacitor depends on the ambient temperature. Capacitors rated for higher max temperatures are going to last longer under the same thermal conditions.

The input high-voltage capacitors work almost at the temperature of ambient air, so the use of somewhat cheaper 85°C capacitors there doesn’t affect the PSU’s service life much.

Advanced Double Forward Switching Design

Alluring the potential customer with mysterious terms is a favorite trick of the marketing department.

Here, the term means the topology of the PSU, i.e. the general concept of its circuit design. There are quite a number of different topologies. Besides the double forward converter, PC power supplies may use a forward converter or a half-bridge converter. These terms are only interesting for a specialist and don’t mean much for an ordinary user.

The choice of the particular PSU topology is determined by a number of reasons like the availability and price of transistors with required characteristics (they differ greatly depending on the topology), transformers, controller chips, etc. For example, the single-transistor forward converter is simple and cheap but requires a high-voltage transistor and high-voltage diodes on the PSU output, so it is only used in inexpensive low-wattage models (high-voltage diodes and transistors of high power are too expensive). The half-bridge converter is somewhat more complex, but has a two times lower voltage on the transistors. So, this is generally a matter of availability and cost of the necessary components. We can predict, for example, that synchronous rectifiers will be sooner or later used in the secondary circuits of PC power supplies. There’s nothing new in that technology, but it is too expensive as yet and its advantages don’t cover its cost.

Dual-Transformer Design

The use of two power transformers – usually in high-wattage (1000W and higher) power supplies – is a purely engineering solution, too. It doesn’t affect the PSU’s characteristics but it may be just handier to distribute the huge wattage of modern PSUs between two transformers, for example when a full-wattage transformer just wouldn’t fit into the PSU housing. However, some manufacturers present the dual-transformer topology as a means to achieve more stability, reliability, etc, which is not exactly true.

RoHS (Reduction of Hazardous Substances)

This is a new European Union directive that limits the use of certain substances in electronic equipment since July 1, 2006. It restricts the use of lead, mercury, cadmium, hexavalent chromium, and two bromides. For power supplies this mainly means a transition to non-lead solders. Yes, we are all for ecology and against heavy metals, but a too hasty transition to new materials may have unpleasant consequences. You may have heard the story about Fujitsu’s MPG hard drives which would die due to a failure of Cirrus Logic controllers that had a packaging made of some new environment-friendly compound from Sumitomo Bakelite. The elements of the compound facilitated the migration of copper and silver that formed bridges between interconnects inside the chip case. As a result, the chip would fail almost certainly after 1 or 2 years of operation. The compound was abandoned eventually, and the involved companies exchanged lawsuits, but nothing could restore the data that were lost with the hard drives.

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