Articles: Cases/PSU

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Etasis ET850 (850W)

We have already tested products from Etasis in an unobvious way. This firm develops and manufactures Zeus series units for SilverStone. This time Etasis plays under its own brand in our roundup. The sample for our review was provided by Sundial Micro.

It’s impossible not to register at least an external resemblance of this PSU to the Zeus series. It is the same case design with the cover opening backwards. The fan is in the back part of the case again, making you wonder at first whether the PSU is cooled actively at all. The On/Off switch, mains connector and operation mode indicator are all placed in the same way, too. The only difference is the color of the case. Zeus PSUs are black while the ET850 is painted a somewhat unusual matte dark-gray color.

Internally, the PSU consists of two full-size PCBs facing one another. This helps reduce the component density of each separate PCB, but also limits the size of the heatsinks and makes the PSU more crowded overall, which hinders proper cooling.

The top PCB carries most of the high-voltage components: an active PFC device (its choke is in the top left of the photo and its controller chip resides on the small upright PCB in the center) and a rectifier with two parallel-connected 390µF electrolytic capacitors on the output. The standby +5Vsb source is placed here as well (in the bottom right of the PCB in the photo above).

An interesting thing in this particular PSU, there is a seat for a relay on the PCB (a little below its center) which is, however, not soldered in. The purpose of this relay would be to close thermistors that would limit the current when the PSU is started up. In its cold state, the thermistor (it is the large green disc standing near the fuse and the 6-pin connector) has a rather high resistance. So when the PSU is plugged into the wall socket, this resistor limits the inrush of current, protecting the PSU’s input circuitry. This current heats the resistor up and its resistance lowers as the consequence. After that, it has no effect on power supply operation. The relay must have been meant to close the thermistors so that after they have done their job in the first second, their heating up wouldn’t contribute to increasing the PSU temperature and their resistance wouldn’t affect the PSU’s input resistance.

Well anyway, the developer chose not to install the relay at all.

The other PCB carries the power transformer with transistors as well as the low-voltage section of the PSU. The latter is interesting since the ET850 is one of the few PSUs with truly independent regulation of voltages. The two small additional cards you can see in the photo above to the left of the output cables are switching regulators based on an L6730 chip with synchronous rectifiers. These regulators are compact thanks to their high operating frequency (400kHz) and synchronous rectification. Each of them resides on a card the size of a matchbox and does with a tiny heatsink for cooling.

It’s hard to tell if this design is better than the regulator with a saturable choke that is traditionally employed in PSUs. The latter has an excellent efficiency and a good regulation coefficient, but is not exactly independent. It can only work in pair with a “senior” full-featured regulator. Perhaps the reason for choosing this design is that Etasis drew from their earlier engineering solutions when developing this PSU.

The PSU can yield almost all of its output power (840W out of 850W) via the +12V rail which is split into four outputs by means of 18A current limiters.

The PSU offers the following cables and connectors:

  • Mainboard cable with a 24-pin connector (44cm)
  • CPU cable with a 4-pin connector (49cm)
  • CPU cable with an 8-pin connector (53cm)
  • Four graphics card cables with 6-pin connectors (48cm)
  • One cable with two Molex connectors and one FDD mini-plug on each (49+14+14cm)
  • Two cables with three Molex connectors on each (45+14+14cm)
  • Four cables with two SATA power connectors on each (51+10cm)
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