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[nextpage title=”Introduction”]

Seasonic has just released a series of fanless power supplies with the 80 Plus Gold certification, full modular cabling system, and single +12 V rail. They released two models so far: 400 W and 460 W. Let’s take an in-depth look at their 400 W model.

The new X Fanless series shares the same design concepts from the “standard” Seasonic X series, like the use of a resonant switching circuit, the use of a synchronous design in the secondary with DC-DC converters for the +5 V and +3.3 V outputs, the installation of the DC-DC converters directly on the modular cabling system, and some connectors of the modular cabling system soldered directly on the main printed circuit board.

Seasonic X-400 Fanless power supplyFigure 1: Seasonic X-400 Fanless power supply

Seasonic X-400 Fanless power supplyFigure 2: Seasonic X-400 Fanless power supply

The Seasonic X-400 Fanless is 6.3” (160 mm) deep and, as the name implies, it doesn’t have any kind of fan, being a product target to users that want to build the quietest computer possible.

This unit features active PFC, of course.

The new Seasonic X-400 Fanless has a full modular cabling system, meaning that even the main motherboard cable is modular. This system has seven connectors and the 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, 25.6” (65 cm) long
  • One cable with one six/eight-pin connector for video cards, 23.6” (60 cm) long
  • One cable with three SATA power connectors, 21.3” (54 cm) to the first connector, 5.9” (15 cm) between connectors
  • One cable with two SATA power connectors, 21.3” (54 cm) to the first connector, 5.9” (15 cm) between connectors
  • One cable with three standard peripheral power connectors, 21.3” (54 cm) to the first connector, 5.9” (15 cm) between connectors
  • One cable with two standard peripheral power connectors, 21.3” (54 cm) to the first connector, 5.9” (15 cm) between connectors
  • One adapter to convert one standard peripheral power connector into two floppy disk drive power connectors

All wires are 18 AWG, except the ones used on the ATX12V/EPS12V  and on the video card auxiliary power cables, which are thicker (16 AWG).

The cable configuration is satisfactory for a 400 W product, and the cables are very long for a 400 W unit.

Seasonic X-400 Fanless power supplyFigure 3: Cables

Let’s now take an in-depth look inside this power supply.

[nextpage title=”A Look Inside The Seasonic X-400 Fanless”]

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.

This page will be an overview, and then in the following pages we will discuss in detail the quality and ratings of the components used.

Seasonic X-400 Fanless power supplyFigure 4: Top view

Seasonic X-400 Fanless power supplyFigure 5: Rear quarter view

Seasonic X-400 Fanless power supplyFigure 6: Front quarter view

Seasonic X-400 Fanless power supplyFigure 7: 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. 

The AC receptacle used in this power supply isn’t a simple connector, but a complete filtering circuit. The Seasonic X-400 Fanless has all the required components, as you can see in Figure 9.

Seasonic X-400 Fanless power supplyFigure 8: Transient filtering stage (part 1)

Seasonic X-400 Fanless power supplyFigure 9: Transient filtering stage (part 2)

In the next page we will have a more detailed discussion about the components used in the Seasonic X-400 Fanless.

[nextpage title=”Primary Analysis”]

On this page we will take an in-depth look at the primary stage of the Seasonic X-400 Fanless. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses two GBJ1506 rectifying bridges, which are attached to an individual heatsink. Each bridge supports up to 15 A at 100° C so, in theory, you would be able to pull up to 3,450 W from a 115 V power grid. Assuming 80% efficiency, the bridges would allow this unit to deliver up to 2,760 W without burning themselves out. Of course, we are only talking about these components, and the real limit will depend on all the other components in this power supply.

Seasonic X-400 Fanless power supplyFigure 10: Rectifying bridges

The active PFC circuit uses three SPP20N60C3 MOSFETs, each one capable of delivering up to 20.7 A at 25° C or up to 13.1 A at 100° C (note the difference temperature makes) in continuous mode, or up to 62.1 A in pulse mode at 25° C. These transistors present a 190 mΩ resistance when turned on, a characteristic called RDS(on). The lower this number the better, meaning that the transistors will waste less power and the power supply will achieve a higher efficiency.

Seasonic X-400 Fanless power supplyFigure 11: Active PFC diode and transistors

The electrolytic capacitor used to filter the output of the active PFC circuit is Japanese, from Chemi-Con, and labeled at 105° C.

The active PFC circuit is controlled by an NCP1654 integrated circuit.

Seasonic X-400 Fanless power supplyFigure 12: Active PFC controller

In the switching section, two IPP60R190C6 MOSFET transistors are used, each one capable of delivering up to 20.2 A at 25° C or up to 12.8 A at 100° C, in continuous mode, or up to 59 A at 25° C in pulse mode, with an RDS(on) of 190 mΩ.

Seasonic X-400 Fanless power supplyFigure 13: Switching transistors

The switching transistors are connected using a design called “LLC resonant,” also known as series parallel resonant converter, being controlled by a CM6901 integrated circuit, which operates under PWM (Pulse Width Modulation) mode when the power supply is operating under light load but under FM (Frequency Modulation) mode under other loads.

Seasonic X-400 Fanless power supplyFigure 14: LLC resonant controller

Now let’s take a look at the secondary of this power supply.

[nextpage title=”Secondary Analysis”]

This power supply uses a synchronous design in its secondary, meaning that the Schottky rectifiers were replaced by MOSFET transistors in order to increase efficiency. On top of that, this unit uses a DC-DC design, meaning that this unit is basically a +12 V power supply, with the +5 V and +3.3 V outputs being generated by two small power supplies attached to the +12 V output.

The +12 V output is generated by four IPD036N04L MOSFETs, each one capable of handling up to 90 A at 25° C or up to 87 A at 100° C in continuous mode or up to 400 A at 25° C in pulse mode, with an RDS(on) of only 3.6 mΩ. These transistors are soldered directly on the solder side of the printed circuit board, and the power supply housing is used as a heatsink for them. The +5 V and +3.3 V are produced from the +12 V output, but just as an exercise if all power from this unit was pulled exclusively from the +12 V rail, this unit would have a maximum theoretical current of 249 A or 2,983 W.

Seasonic X-400 Fanless power supplyFigure 15: +12 V transistors

Usually power supplies that use DC-DC converters in the secondary to generate the +5 V and +3.3 V outputs have two separate printed circuit boards installed in the secondary, one for each output. Like other “X-Series” power supplies from Seasonic, in the X-400 Fanless these converters are installed on the modular cabling printed circuit board.

Seasonic X-400 Fanless power supplyFigure 16: The DC-DC converter

Seasonic X-400 Fanless power supplyFigure 17: The DC-DC converter

Both outputs are managed by an APW7159 PWM controller, and each output is generated by four IPD060N03L MOSFETs, each one capable of handling up to 50 A at 100° C in continuous mode, or 350 A at 25° in pulse mode, with an RDS(on) of only 6 mΩ.

In Figure 18, you can see how there are several solid capacitors in the secondary (and the capacitors that aren’t solid are made in Japan, by Chemi-Con), and how Seasonic added some interesting heatsinks connected straight to the printed circuit board.

Seasonic X-400 Fanless power supplyFigure 18: Heatsinks and solid capacitors

The secondary is monitored by a PS223 integrated circuit. This chip supports OCP (over current protection), over voltage protection (OVP), under voltage protection (UVP) and over temperature protection (OTP).

Seasonic X-400 Fanless power supplyFigure 19: Monitoring circuit

[nextpage title=”Power Distribution”]

In Figure 20, you can see the power supply label containing all the power specs.

Seasonic X-400 Fanless power supplyFigure 20: Power supply label

This power supply has a single +12 V rail, so ther
e is not much to talk about here.

Let’s now see if this power supply can really deliver 400 W.

[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 the 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 power listed for each test, you may find a different value than what is posted under “Total” below. Since each output can vary slightly (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 our tests, both were connected to the power supply’s single +12 V rail.

Input Test 1 Test 2 Test 3 Test 4 Test 5
+12VA 2.5 A (30 W) 5.5 A (66 W) 8 A (96 W) 10.5 A (126 W) 14 A (168 W)
+12VB 2.5 A (30 W) 5.5 A (66 W) 8 A (96 W) 10.5 A (126 W) 13 A (156 W)
+5V 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 A (5 W) 1.5 A (7.5 W) 2 A (10 W) 2 A (10 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 80.2 W 161.3 W 240.6 W 319.3 W 401.4 W
% Max Load 20.1% 40.3% 60.2% 79.8% 100.4%
Room Temp. 44.8° C 43.2° C 42.2° C 42.4° C 43.8° C
PSU Temp. 59.0° C 58.2° C 58.6° C 58.7° C 59.5° C
Voltage Regulation Pass Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power 91.5 W 176.2 W 263.5 W 352.5 W 449.8 W
Efficiency 87.7% 91.5% 91.3% 90.6% 89.2%
AC Voltage 114.0 V 113.0 V 112.7 V 111.9 V 111
Power Factor 0.969 0.991 0.998 0.988 0.991
Final Result Pass Pass Pass Pass Pass

The Seasonic X-400 Fanless can really deliver its labeled wattage at high temperatures.

Efficiency was extremely high, above 87% at light load (20% load, 80 W) and above 89% at full load, peaking 91.5% at 40% load (160 W). Really impressive.

Voltage regulation was another highlight of this product, with all voltages within 3% of their nominal values – including the -12 V output. The ATX12V specification allows voltages to be up to 5% from their nominal values (10% for the -12 V output). Therefore this power supply presents voltages closer to their nominal values than necessary.

Noise and ripple levels were always extremely low. Below you can see the results for the power supply outputs during test number five. The maximum allowed is 120 mV for +12 V and -12 V outputs, and 50 mV for +5 V and +3.3 V outputs. All values are peak-to-peak figures.

Seasonic X-400 Fanless power supplyFigure 21: +12VA input from load tester during test five at 401.4 W (20.6 mV)

Seasonic X-400 Fanless power supplyFigure 22: +12VB input from load tester during test five at 401.4 W (20.4 mV)

Seasonic X-400 Fanless power supplyFigure 23: +5V rail during test five at 401.4 W (10.2 mV)

Seasonic X-400 Fanless power supplyFigure 24: +3.3 V rail during test five at 401.4 W (8.8 mV)

Let’s see if we can pull even more from the Seasonic X-400 Fanless.

[nextpage title=”Overload Tests”]

Below you can see the maximum we could pull from this power supply. Because of its incredibly overspec’ed components, we could pull 600 W from it and it was still presenting extremely high efficiency (88%), with low noise and ripple levels, and voltages still within 3% from their nominal values. Impressive.

Input Overload Test
+12VA 22 A (264 W)
+12VB 22 A (264 W)
+5V 8 A (40 W)
+3.3 V 8 A (26.4 W)
+5VSB 2 A (10 W)
-12 V 0.5 A (6 W)
Total 602.2 W
% Max Load 150.6%
Room Temp. 40.2° C
PSU Temp. 48.7° C
AC Power 683.0 W
Efficiency 88.2%
AC Voltage 107.8 V
Power Factor 0.993

[nextpage title=”Main Specifications”]

The specs of the Seasonic X-400 Fanless include:

  • Nominal labeled power: 400 W
  • Measured maximum power: 602.2 W at 40.2° C ambient
  • Labeled efficiency: 87% at light (20% or 80 W) and full loads, and 90% at typical load (50% or 200 W), 80 Plus Gold certification
  • Measured efficiency: Between 87.7% and 91.5% at 115 V (nominal, see complete results for actual voltage)
  • Active PFC: Yes
  • Modular Cabling System: Yes
  • Motherboard Power Connectors: One 20/24-pin connector and two ATX12V connectors that together form an EPS12V connector
  • Video Card Power Connectors: One six/eight-pin connector
  • SATA Power Connectors: Five on two cables
  • Peripheral Power Connectors: Five on two cables
  • Floppy Disk Drive Power Connectors: Two, if the included adapter is used
  • Protections: Over voltage (OVP), under voltage (UVP), over power (OPP), over current (OCP), over temperature (OTP),
    and short-circuit (SCP) protections
  • Warranty: Five years
  • More Information: https://www.seasonicusa.com
  • MSRP in the US: USD 140.00

[nextpage title=”Conclusions”]

The new Seasonic X-400 Fanless is an impressive power supply. During our tests it achieved efficiency always above 87%, peaking 91.5%, voltages very close to their nominal values (3% regulation instead of the traditional 5% regulation), and extremely low noise and ripple levels. On top of that, due to its highly overspec’ed components, we could easily pull 600 W from it with efficiency still above 88%. This is remarkable. Seasonic could easily sell this power supply as a 600 W product, if they added more connectors, of course.

The only “problem” with this power supply is its price. It is hard to explain to the average user why this power supply costs more than twice the price of a good 400 W unit.

If you are a user who wants to build a completely silent PC or HTPC (home theater PC) and only demands “the best in class,” the new X-400 Fanless is an option. The average user, however, will find a better cost/benefit ratio in products that cost less.