Seasonic Platinum Fanless 520W PSU

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The casing is unchanged from the X-series fanless models, as far as I could tell. Like all the X-series PSUs, instead of the conventional double U-shaped parts that clamshell together, the main casing is a 5-sided box, to which the top perforated cover is secured with four small screws. It remains about the most mechanically robust PSU casing I've come across. There are hex-hole vents on all sides except the bottom. The top and back panels are almost entirely vented.

Technically, Seasonic says the 520W uses full-bridge topology on the primary and an LLC resonant controller for increased efficiency. The previous Gold-level X-400 and X-460 used a half-bridge topology. The MOSFETs for +12V regulation have also been moved from the trace side of the primary PCB to a secondary plug-in board for better cooling. The secondary side is said to be a synchronous design. The DC-DC converters are on the modular daughter PCB with the output connectors solder directly on it. This improves efficiency and eliminates losses to connecting wires. This aspect is unchanged from the X-series.

A completely modular cable setup.

Inside, compared to the X-400 and X-460 fanless models, the 520W's heatsinks have been beefed up, though they are still small compared to earlier, lower efficiency PSUs. Seasonic's usual high standards of workmanship, layout and parts quality apply.

As with the X series, the main PCB contains the circuitry to filter and convert the AC voltage to 12VDC, and the conversion from 12VDC to the lower DC lines is done in the PCB on the output panel, to reduce internal soldering/wiring and shorten the paths for lower voltages for minimal loss.

Seasonic compares its patented output board with integrated low voltage line VRM against traditional modular design.

FEATURE & BRIEF Our comment
80+ Platinum
The Platinum Series, certified in accordance to the highest 80PLUS standards, offers the newest technology and innovation for performance and energy savings with up to 92% efficiency and a true power factor of greater than 0.9PF.
Patented DC Connector Panel with Integrated VR Module*
Seasonic’s Patented Fully Modular Design while minimizing voltage drops and impedance, greatly maximizes efficiency and cooling.
Highly Reliable 105°C Japanese Aluminum Electrolytic Capacitors OK
Conductive Polymer Aluminum Solid Capacitors
Gold Plated High Current Terminals OK
Multi-GPU Technology Support This means 2 pairs of PCIe power cables
Full Modular Cabling Design OK
DC to DC Converter Design
Fanless - 0dBA OK
High +12V Output OK
Safety: CE, CB, TÜV, Nemko, Semko, Fimko, Demko, FCC, cRUus, cTUVus OK
7 year warranty Great!
160 x 150 x 86 mm
3.5 kg
Fairly modest in size & weight.

AC Input
100~240VAC, 7~4A, 50/60Hz
DC Output

The operating temperature limit for rated performance is said to be 50°C, although this information did not seemed to be specified on any of their product pages. My torture testing of the Seasonic X-400 (in 2010) for 15 hours at full power in a 53~57°C hot box through which the X-400 came with with flying colors, suggests users not concern themselves unduly about this PSU's ability to take the heat — the X-520 has larger heatsinks and even higher efficiency for less heat generation.


As mentioned earlier, only the main ATX cable is "normal", nicely sleeved. All the other output cables are flat data-style. This is the first time such cables have appeared in a Seasonic PSU, although many products made by Seasonic for other brands (such as Corsair and bequiet!) have featured them for years. My guess is that there is some small savings in labor cost; the flat cables do not require sleeving.

1 - Main ATX (24/20 pin), 60cm
1 - EPS12V/ATX12V (8/4 pin), 65cm
2 - PCIe (6/8 pin) connector, 60cm
1 - 4 SATA connectors, 70cm
1 - 2 SATA connectors, 40cm
1 - 3 4-pin peripheral connectors, 60cm
1 - 2 4-pin peripheral connectors, 40cm
1 - Floppy drive Y-adapter

The inclusion of only one pair of PCIe connectors seems indicative of Seasonic's typical conservatism. With improved energy efficiency in the latest generation of GPUs, 520W will easily power a modern PC with a couple of mid/mid-high performance cards. A pair of nVidia GTX670s, for example will pull a maximum peak of 340W together. Current Intel socket 1155 CPUs don't go much past 65W in real apps, so the maximum peak demand for an Intel CPU SLI system using the GTX670 would not run higher than 450W. Eager users can probably buy additional cables with dual PCIe connectors, though.

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