Articles: Cases/PSU

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Of course, two diode packs allow using a simpler and cheaper heatsink, but cost more by themselves than a single diode pack. Thus, the manufacturer always chooses between two options: they can put more expensive diodes and save on the heatsink or they can save on the diodes but put down a more expensive heatsink. The latter way is more common, but FSP’s engineers took the former approach. You might say it would be well to have both expensive diodes and a good heatsink all at once, but this would inevitably affect the end cost of the power supply. For example, FSP’s fan-less power supply called Zen uses the same YM3045N diodes and the heatsinks occupy almost the entire free space inside the case, too, but that PSU is priced appropriately high, even though it is one of the cheapest fan-less solutions available.

The engineers followed the same approach with the rest of the semiconductors. Take note of the tidy row of three transistors on the PFC heatsink or of the two diode bridges on both sides of the central heatsink.

So, it’s now clear with the diodes, but the smaller heatsinks are not only the consequence of the developer’s using more diode packs. Their size alone may improve the cooling efficiency. A smaller heatsink offers less resistance to the incoming stream of air. The speed of the air stream is higher then and its temperature gets lower. Of course, this effect is not very big, but you shouldn’t dismiss it altogether.

Another interesting feature of this power supply is the increased frequency of the PWM regulator. It is usually near 30kHz (this looks like fluctuations at 60kHz in oscillograms of a PSU’s output voltages since the push-pull inverter doubles the frequency). In the Epsilon this frequency is 55kHz or almost two times higher than usual. The higher PWM frequency permits to use smaller ferrites (coils and transformers) keeping the same maximum output power or, on the contrary, to increase the power while keeping their size the same. This explains the rather small (for a 700W power supply) dimensions of the power transformer and of the group regulation coil.

The main PWM regulator and the active PFC device are assembled on one chip, Champion Microelectronics CM6800G, which is installed on a small separate card to the right of the PFC coil and next to the central heatsink of the PSU. The standby voltage source is based on a Fairchild FSDM311 chip which is a full-featured PWM controller for low-power sources. And finally, there is a supervisor of the output voltages and currents on yet another small card installed near the spot where the output cables are soldered to the PSU (you can identify it in the snapshots by the long white connector on its edge). The PSU follows the traditional design with group voltage regulation.

The power supply offers you the following cables and connectors:

  • Mainboard cable with a 24-pin connector (with a detachable 4-pin part), 55cm long
  • CPU cable with a 8-pin connector that splits in two 4-pin parts, 56cm long
  • Two graphics card cables with a 6-pin connector, 57cm long
  • Two cables with three Molex connectors and one mini-plug for the floppy drive (53cm from the PSU to the first connector and 20cm more to each next connector)
  • Two cables with three SATA power connectors on each, 57cm from the PSU to the first plug and 22cm more to the next connector

You can’t really complain that this is an insufficient selection of cables. Almost any modern configuration can be attached to the Epsilon without any adapters or splitters. The cables are all sleeved.

The declared characteristics are truly impressive. The FX700-GLN has four +12V lines with a current of 15A each, and the only limitation to their combined load is the overall wattage of the unit, i.e. 680W for the main rails. In other words, the manufacturer promises you can load this power supply through one 12V power rail only.

The PSU label also shows you how the power channels are wired to the output connectors: one channel powers up the first processor (meaning one 4-pin half of the 8-pin EPS12V connector; you will plug in only this half on your ATX12V system which only has one 4-pin power connector on the mainboard); the second channel powers one of the graphics cards and the second processor; the third channel is for the mainboard and all the peripherals; the fourth is for the second graphics card. It is easy to identify the connectors and tell which is for the first graphics card and which is for the second one because different channels are coded with strips of different colors on the wires (a black, blue or green strip goes against the yellow background of the 12V cable).

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