We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
[nextpage title=”Introduction”]
The Seasonic Platinum Fanless 520 W (a.k.a. SS-520FL) is, as the name suggests, a fanless power supply with the 80 Plus Platinum certification, targeted to users building a quiet computer. It also comes with a fully modular cabling system. Let’s see if this new release deserves our recommendation.
Figure 1: Seasonic Platinum Fanless 520 W power supply
Figure 2: Seasonic Platinum Fanless 520 W power supply
The Seasonic Platinum Fanless 520 W is 6.3” (160 mm) deep.
The modular cabling system from this power supply has 10 connectors: two for the main motherboard power connector, four for video card and ATX12V/EPS12V connectors, and four for peripheral and SATA connectors. This power supply comes with the following cables:
- Main motherboard cable with a 20/24-pin connector, 23.6” (60 cm) long
- One cable with two ATX12V connectors that together form an EPS12V connector, 25.2” (64 cm) long
- Two cables, each with one six/eight-pin connector for video cards, 23.6” (60 cm) long
- One cable with four SATA power connectors, 15.7” (40 cm) to the first connector, 4.7” (12 cm) between connectors
- One cable with two SATA power connectors, 11.8” (30 cm) to the first connector, 4.7” (12 cm) between connectors
- One cable with three peripheral power connectors, 15.7” (40 cm) to the first connector, 4.7” (12 cm) between connectors
- One cable with two peripheral power connectors, 11.8” (30 cm) to the first connector, 4.7” (12 cm) between connectors
- One adapter to convert a standard peripheral power connector into a floppy disk drive power connector
All wires are 18 AWG, which is the minimum recommended gauge.
The number of connectors is outstanding for a 520 W power supply.
Figure 3: Cables
Let’s now take an in-depth look inside this power supply.
[nextpage title=”A Look Inside the Seasonic Platinum Fanless 520 W”]
We decided to disassemble this power supply to see what it looks like inside, how it is designed, and what components are used. Please read our “Anatomy of Switching Power Supplies” tutorial to understand how a power supply works and to compare this power supply to others.
On this page we will have an overall look, and then in the following pages we will discuss in detail the quality and ratings of the components used.
Figure 4: Top view
Figure 5: Front quarter view
Figure 6: Rear quarter view
Figure 7: The printed circuit board
[nextpage title=”Transient Filtering Stage”]
As we have mentioned in other articles and reviews, the first place we look when opening a power supply for a hint about its quality, is its filtering stage. The recommended components for this stage are two ferrite coils, two ceramic capacitors (Y capacitors, usually blue), one metalized polyester capacitor (X capacitor), and one MOV (Metal-Oxide Varistor). Very low-end power supplies use fewer components, usually removing the MOV and the first coil.
In the transient filtering stage, this power supply is flawless, with two X capacitors, four Y capacitors, and one ferrite coil more than the minimum required.
Figure 8: Transient filtering stage (part 1)
Figure 9: Transient filtering stage (part 2)
On the next page, we will have a more detailed discussion about the components used in the Seasonic Platinum Fanless 520 W.
[nextpage title=”Primary Analysis”]
On this page, we will take an in-depth look at the primary stage of the Seasonic Platinum Fanless 520 W. For a better understanding, please read our “Anatomy of Switching Power Supplies” tutorial.
This power supply uses two GBJ2506 rectifying bridges connected in parallel, which are attached to an individual heatsink. Each bridge supports up to 25 A at 100° C. In theory, you would be able to pull up to 5,750 W from a 115 V power grid. Assuming 80% efficiency, the bridges would allow this unit to deliver up to 4,600 W without burning themselves out (or 5,175 W at 90% efficiency). Of course, we are only talking about these particular components. The real limit will depend on all the components combined in this power supply.
Figure 10: Rectifying bridges
The active PFC circuit uses two IPP60R160C6 MOSFETs, each one supporting up to 23.8 A at 25°
; C or 15 A at 100° C in continuous mode (note the difference temperature makes), or 70 A at 25° C in pulse mode. These transistors present a 160 mΩ maximum resistance when turned on, a characteristic called RDS(on). The lower the number the better, meaning that the transistor will waste less power, and the power supply will have a higher efficiency.
Figure 11: The active PFC diode and the two active PFC transistors
The active PFC circuit is managed by an NCP1654 active PFC controller.
Figure 12: Active PFC controller
The output of the active PFC circuit is filtered by one 330 µF x 420 V Japanese electrolytic capacitor, from Hitachi, labeled at 105° C.
Figure 13: Capacitor
In the switching section, four IPP50R250CP MOSFETs are employed using a full-bridge, resonant configuration. Each transistor supports up to 13 A at 25° C or 9 A at 100° C in continuous mode or up to 31 A at 25° C in pulse mode, with a maximum RDS(on) of 250 mΩ.
Figure 14: The four switching transistors
The switching transistors are controlled by a CM6901 controller.
Figure 15: Resonant controller
Let’s now take a look at the secondary of this power supply.
[nextpage title=”Secondary Analysis”]
As one would expect in a high-efficiency power supply, the Seasonic Platinum Fanless 520 W uses a synchronous design, where the Schottky rectifiers are replaced with MOSFETs. Also, the reviewed product uses a DC-DC design in its secondary. This means that the power supply is basically a +12 V unit, with the +5 V and +3.3 V outputs produced by two smaller power supplies connected to the main +12 V rail. Both designs are used to increase efficiency.
The +12 V output uses two BSC018N04LS G MOSFETs, each one supporting up to 100 A at 100° C in continuous mode, or up to 400 A at 25° C in pulse mode, with a maximum RDS(on) of only 1.8 mΩ. These transistors are located on the same printed circuit board as the resonant controller.
Figure 16: One of the +12 V transistors
As explained, the +5 V and +3.3 V outputs are produced by two DC-DC converters, which are situated on the same printed circuit board as the modular cabling system. The converters are controlled by a single APW7159 integrated circuit. Each output uses three RJK0332DPB-01 MOSFETs, each one supporting up to 35 A at 25° C in continuous mode and up to 140 A at 25° C in pulse mode, with a maximum RDS(on) of 3.6 mΩ.
Figure 17: The DC-DC converters
Figure 18: The DC-DC converters
The outputs of the power supply are monitored by a WT7527 integrated circuit, which supports over voltage (OVP), under voltage (UVP), and over current (OCP) protections. This chip offers two +12 V channels, but the manufacturer decided to use only one of them, resulting in this unit having a single +12 V rail.
Figure 19: Monitoring circuit
The electrolytic capacitors available in the secondary are also Japanese, from Chemi-Con and Rubycon, and labeled at 105° C, as usual. As you can see in Figure 20, several solid capacitors are also used.
Figure 20: Capacitors
[nextpage title=”Power Distribution”]
In Figure 21, you can see the power supply label containing all the power specs.
Figure 21: Power supply label
As you can see, this unit has a single +12 V rail configuration, so there is not much to talk about here.
Let’s find out how much power this unit can deliver.
[nextpage title=”Load Tests”]
We conducted several tests with this power supply, as described in the article, “Hardware Secrets Power Supply Test Methodology.”
First, we tested this power supply with five different load patterns, trying to pull around 20%, 40%, 60%, 80%, and 100% of its labeled maximum capacity (actual percentage used listed under “% Max Load”), watching the behavior of t
he reviewed unit under each load. In the table below, we list the load patterns we used and the results for each load.
If you add all the powers listed for each test, you may find a different value than what is posted under “Total” below. Since each output can have a slight variation (e.g., the +5 V output working at 5.10 V), the actual total amount of power being delivered is slightly different than the calculated value. In the “Total” row, we are using the real amount of power being delivered, as measured by our load tester.
The +12VA and +12VB inputs listed below are the two +12 V independent inputs from our load tester. During this test, the +12VA and +12VB inputs were connected to the power supply’s single +12 V rail. (The +12VB input was connected to the power supply EPS12V connector.)
| Input | Test 1 | Test 2 | Test 3 | Test 4 | Test 5 |
| +12VA | 3.5 A (42 W) | 7.5 A (90 W) | 11 A (132 W) | 15 A (180 W) | 18.5 A (222 W) |
| +12VB | 3.5 A (42 W) | 7.5 A (90 W) | 11 A (132 W) | 14.5 A (174 W) | 18 A (216 W) |
| +5 V | 1 A (5 W) | 2 A (10 W) | 4 A (20 W) | 6 A (30 W) | 8 A (40 W) |
| +3.3 V | 1 A (3.3 W) | 2 A (6.6 W) | 4 A (13.2 W) | 6 A (19.8 W) | 8 A (26.4 W) |
| +5VSB | 1 A (5 W) | 1.5 A (7.5 W) | 2 A (10 W) | 2.5 A (12.5 W) | 3 A (15 W) |
| -12 V | 0.5 A (6 W) | 0.5 A (6 W) | 0.5 A (6 W) | 0.5 A (6 W) | 0.5 A (6 W) |
| Total | 104.4 W |
209.4 W |
313.3 W | 422.8 W | 525.4 W |
| % Max Load | 20.1% | 40.3% | 60.3% | 81.3% | 101.0% |
| Room Temp. | 46.9° C |
46.4° C |
46.5° C | 46.6° C | 48.0° C |
| PSU Temp. | 48.5° C |
48.8° C |
49.0° C | 52.5° C | 55.1° C |
| Voltage Regulation | Pass | Pass | Pass | Pass | Pass |
| Ripple and Noise | Pass | Pass | Pass | Pass | Pass |
| AC Power | 114.0 W |
224.5 W |
338.0 W | 460.3 W | 579.0 W |
| Efficiency | 91.6% | 93.3% | 92.7% | 91.9% | 90.7% |
| AC Voltage | 117.2 V |
116.9 V |
116.2 V | 114.7 V | 113.4 V |
| Power Factor | 0.976 | 0.995 | 0.990 | 0.993 | 0.995 |
| Final Result | Pass | Pass | Pass | Pass | Pass |
We were really impressed by the efficiency results of the Seasonic Platinum Fanless 520 W, always above 90% at high temperatures.
Voltage regulation was also outstanding, with all voltages within 3% of their nominal values. The ATX12V specification states that positive voltages must be within 5% of their nominal values, and negative voltages must be within 10% of their nominal values.
Let’s discuss the ripple and noise levels on the next page.
[nextpage title=”Ripple and Noise Tests”]
Voltages at the power supply outputs must be as “clean” as possible, with no noise or oscillation (also known as “ripple”). The maximum ripple and noise levels allowed are 120 mV for +12 V and -12 V outputs, and 50 mV for +5 V, +3.3 V and +5VSB outputs. All values are peak-to-peak figures. We consider a power supply as being top-notch if it can produce half or less of the maximum allowed ripple and noise levels.
The Seasonic Platinum Fanless 520 W provided extremely low ripple and noise levels, as you can see in the table below.
| Input | Test 1 | Test 2 | Test 3 | Test 4 | Test 5 |
| +12VA | 13.0 mV | 17.6 | 23.0 mV | 25.4 mV | 27.8 mV |
| +12VB | 13.4 mV | 18.2 | 24.0 mV | 26.8 mV | 31.0 mV |
| +5 V | 9.8 mV | 10.4 | 10.0 mV | 11.2 mV | 11.4 mV |
| +3.3 V | 10.4 mV | 10.4 | 10.4 mV | 10.8 mV | 12.6 mV |
| +5VSB | 5.0 mV | 5.8 | 6.0 mV | 6.4 mV | 6.8 mV |
| -12 V | 13.4 mV | 17.2 | 21.4 mV | 22.4 mV | 27.4 mV |
Below you can see the waveforms of the outputs during test five.
Figure 22: +12VA input from load tester during test five at 525.4 W (27.8 mV)
Figure 23: +12VB input from load tester during test five at 525.4 W (31.0 mV)
Figure 24: +5V rail during test five at 525.4 W (11.4 mV)
Figure 25: +3.3 V rail during test five at 525.4 W (12.6 mV)
Let’s see if we can pull more than 520 W from this unit. [nextpage title=”Overload Tests”]
Below you can see the maximum we could pull from this power supply. The objective of this test is to see if the power supply has its protection circuits working properly. This unit passed this test, since it shut down when we tried to pull more than what is listed below. During this test, noise and ripple levels were still low, with all outputs still within 3% of their nominal values.
| Input | Overload Test |
| +12VA | 22 A (264 W) |
| +12VB | 22 A (264 W) |
| +5 V | 12 A (60 W) |
| +3.3 V | 12 A (39.6 W) |
| +5VSB | 3 A (15 W) |
| -12 V | 0.5 A (6 W) |
| Total | 651.4 W |
| % Max Load | 125.3% |
| Room Temp. | 49.4° C |
| PSU Temp. | 56.1° C |
| AC Power | 762.2 W |
| Efficiency | 85.5% |
| AC Voltage | 111.8 V |
| Power Factor | 0.996 |
[nextpage title=”Main Specifications”]
The main specifications for the Seasonic Platinum Fanless 520 W power supply include:
- Standards: NA
- No
minal labeled power: 520 W - Measured maximum power: 651.4 W at 49.4° C
- Labeled efficiency: 80 Plus Platinum certification (90% at light/20% load, 92% at typical/50% load, and 89% at full/100% load)
- Measured efficiency: Between 90.7% and 93.3%, at 115 V (nominal, see complete results for actual voltage)
- Active PFC: Yes
- Modular Cabling System: Yes, full
- Motherboard Power Connectors: One 20/24-pin connector and two ATX12V connectors that together form an EPS12V connector
- Video Card Power Connectors: Two six/eight-pin connectors on two cables
- SATA Power Connectors: Six on two cables
- Peripheral Power Connectors: Five on two cables
- Floppy Disk Drive Power Connectors: One, through an adapter
- Protections (as listed by the manufacturer): Over voltage (OVP), under voltage (UVP), over current (OCP), over power (OPP), over temperature (OTP), and short-circuit (SCP) protections
- Are the above protections really available? Yes.
- Warranty: Seven years
- More Information: https://www.seasonicusa.com
- Average Price in the U.S.*: USD 150.00
* Researched at Newegg.com on the day we published this review.[nextpage title=”Conclusions”]
We were really impressed with the Seasonic Platinum Fanless 520 W. It achieved the feat of being the best power supply we’ve ever reviewed.
Efficiency was always above 90%, surpassing the requirements of the 80 Plus Platinum certification by a good margin. Most power supplies we test can’t deliver the promised efficiency at high temperatures, since the tests for the 80 Plus certification are conducted at 23° C, and efficiency drops as temperature increases.
The efficiency numbers are more incredible when you take into consideration that this is a fanless power supply. Power supplies without a fan may work internally at higher temperatures, meaning lower efficiency.
Voltage regulation was superb, with all outputs within 3% of their nominal values. Noise and ripple levels were extremely low, making this unit a flawless product.
Even the price of this power supply (USD 150) is more than right when you compare it to its competitors. For example, the SilverStone Nightjar 500 W is a fanless power supply with the 80 Plus Bronze certification and is sold for USD 185.
If you are building a quiet computer and want “the best,” the Seasonic Platinum Fanless 520 W is the power supply you should buy.