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[nextpage title=”Introduction”]

The Seasonic X-Series brings the 80 Plus Gold certification and a full modular cabling system. It was the first power supply series where the DC-DC converter was installed on the same printed circuit board as the modular cabling system. We’ve already reviewed the 560 W, 650 W, and 850 W models, and they all got great results. Let’s see if the X-Series 750 W is also a winner.

Seasonic X-Series 750 W power supplyFigure 1: Seasonic X-Series 750 W power supply

Seasonic X-Series 750 W power supplyFigure 2: Seasonic X-Series 750 W power supply

The Seasonic X-Series 750 W is 6.3” (160 mm) deep, using a 120 mm Japanese ball-bearing fan on its bottom (Sanyo Denki San Ace 120, model 9S1212P4M61).

The reviewed power supply has a fully modular cabling system, meaning that even the main motherboard cable is removable. All cables are protected with nylon sleeves. This power supply comes with the following cables:

  • Main motherboard cable with a 20/24-pin connector, 22” (56 cm) long
  • One cable with one ATX12V connector, 22” (56 cm) long
  • Two cables, each with one EPS12V connector, 22” (56 cm) long
  • Four cables, each with one six/eight-pin connector for video cards, 21.6” (55 cm) long
  • Two cables, each 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, 13.8” (35 cm) to the first connector, 5.9” (15 cm) between connectors
  • Two cables, each 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, 13.8” (35 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, which is the minimum recommended gauge. The number of connectors is adequate for a 750 W power supply, allowing you to install two high-end video cards that require two auxiliary power connectors each without the need for adapters.

Seasonic X-Series 750 W power supplyFigure 3: Cables

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

[nextpage title=”A Look Inside the Seasonic X-Series 750 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.

Seasonic X-Series 750 W power supplyFigure 4: Top view

Seasonic X-Series 750 W power supplyFigure 5: Front quarter view

Seasonic X-Series 750 W power supplyFigure 6: Rear quarter view

Seasonic X-Series 750 W power supplyFigure 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 has all required components. The metallic part you see in Figure 8 is a complete filtering module.

Seasonic X-Series 750 W power supplyFigure 8: Transient filtering stage (part 1)

Seasonic X-Series 750 W power supplyFigure 9: Transient filtering stage (part 2)

On the next page, we will have a more detailed discussion about the components used in the Seasonic X-Series 750 W.

[nextpage title=”Primary Analysis”]

On this page we will take an in-depth look at the primary stage of the Seasonic X-Series 750 W. For a better understanding, please read our “Anatomy of Switching Power Supplies” tutorial.

This power supply uses two GBJ1506 rectifying bridges connected in parallel and 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, these bridges would allow this unit to deliver up to 2,760 W without burning themselves out (up to 3,105 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. These are the same components used on the 650 W and 850 W versions of this power supply. 

Seasonic X-Series 750 W power supplyFigure 10: Rectifying bridges

The active PFC circuit uses three SPP20N60C3 MOSFETs, each supporting up to 20.7 A at 25° C or 13.1 A at 100° C in continuous mode (see the difference temperature makes) or 62.1 A at 25° C in pulse mode. These transistors present a maximum 190 mΩ 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. These are the same transistors used on the 650 W version of this power supply, but the 850 W model uses stronger transistors here. 

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

Seasonic X-Series 750 W power supplyFigure 11: Active PFC controller

The output of the active PFC circuit is filtered by two 390 µF x 400 V Japanese electrolytic capacitors, from Chemi-Con, labeled at 105° C. These capacitors are connected in parallel and are the equivalent of a single 780 µF x 400 V capacitor.

In the switching section, two STP26NM60 MOSFETs are employed using a resonant configuration. Each transistor supports up to 20 A at 25° C or 12.6 A at 100° C in continuous mode; or up to 80 A at 25° C in pulse mode, with a maximum RDS(on) of 165 mΩ. These are the same transistors used in the 850 W model. The 650 W version uses different transistors here, but with similar specifications.

Seasonic X-Series 750 W power supplyFigure 12: One of the switching transistors, the active PFC diode, and the three active PFC transistors

The switching transistors are managed by a CM6901 resonant controller.

Seasonic X-Series 750 W power supplyFigure 13: Resonant controller

In summary, the primary of the X-Series 750 W is identical to the primary of the 650 W model, but the 850 W model uses stronger active PFC transistors.

Let’s now take a look at the secondary of this power supply.

[nextpage title=”Secondary Analysis”]

The Seasonic X-Series 750 W uses a synchronous design, meaning that the rectifiers were replaced with MOSFETs. Also, this power supply uses a DC-DC design, meaning that it is basically a +12 V power supply, with the +5 V and +3.3 V outputs being generated through two smaller switching power supplies connected to the +12 V rail. Both designs are used to increase efficiency.

The +12 V output uses four IPD031N06L3 G MOSFETs, each 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 3.1 mΩ. These transistors are located on the solder side of the main printed circuit board, using the power supply case as a heatsink. These transistors are identical to the ones used in the 850 W model, which are stronger than the ones used in the 650 W version of this power supply. 

Seasonic X-Series 750 W power supplyFigure 14: The +12 V transistors

The DC-DC converters are located on the same printed circuit board as the modular cabling system. Both are managed by an APW7159 PWM controller, with each output using a pair of APM2510N MOSFETs, each supporting up to 50 A at 25° C or 35 A at 100° C in continuous mode, with a maximum RDS(on) of 8.5 mΩ, and a pair of APM2556N MOSFETs, each supporting up to 160 A at 25° C or 90 A at 100° C in continuous mode, with a maximum RDS(on) of 4.5 mΩ.

Seasonic X-Series 750 W power supplyFigure 15: The DC-DC converter

Seasonic X-Series 750 W power supplyFigure 16: The DC-DC converter

The outputs of this power supply are monitored by a PS223 integrated circuit, which supports over voltage (OVP), under voltage (UVP), and over current (OCP) protections. There are two +12 V over current protection channels; however, the manufacturer decided to configure this power supply as a single-rail model.

Seasonic X-Series 750 W power supplyFigure 17: Monitoring circuit

This power supply uses a mix of Japanese electrolytic capacitors, from Chemi-Con, and solid capacitors to filter its outputs.

In summary, the secondary of the X-Series 750 W is identical to the one from the X-Series 850 W, with stronger transistors than the secondary of the X-Series 650 W.

[nextpage title=”Power Distribution”]

In Figure 18, you can see the power supply labe
l containing all the power specs.

Seasonic X-Series 750 W power supplyFigure 18: Power supply label

As you can see, this power supply has a single +12 V rail, so there is not much to talk about here.

How much power can this unit really deliver? Let’s find out.

[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 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, both inputs were connected to the power supply’s single +12 V rail. (The power supply’s EPS12V connector was installed on the +12VB input of the load tester.)

Input Test 1 Test 2 Test 3 Test 4 Test 5
+12VA 5.5 A (66 W) 11 A (132 W) 16.5 A (198 W) 21.5 A (258 W) 27.5 A (330 W)
+12VB 5.5 A (66 W) 11 A (132 W) 16 A (192 W) 21.5 A (258 W) 27.5 A (330 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 153.4 W 297.2 W 448.1 W 585.7 W 748.2 W
% Max Load 20.5% 39.6% 59.7% 78.1% 99.8%
Room Temp. 47.9° C 47.5° C 48.6° C 45.6° C 45.2° C
PSU Temp. 50.1° C 50.2° C 50.6° C 50.8° C 50.7° C
Voltage Regulation Pass Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power 175.3 W 327.9 W 498.2 W 660.0 W 859.0 W
Efficiency 87.5% 90.6% 89.9% 88.7% 87.1%
AC Voltage 114.6 V 112.6 V 111.2 V 109.6 V 107.8 V
Power Factor 0.986 0.995 0.993 0.995 0.996
Final Result Pass Pass Pass Pass Pass

The Seasonic X-Series 750 W graduated from our tests with the highest honors. It presented efficiency between 87.1% and 90.6%, perfectly matching the levels promised by the 80 Plus Gold certification.

All voltages were closer to their nominal values during all tests (3% voltage regulation), making the X-Series 750 W a “flawless” power supply. 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 X-Series 750 W provided extremely low ripple and noise levels, making it a “flawless” unit here as well.

Input Test 1 Test 2 Test 3 Test 4 Test 5
+12VA 9.2 mV 14.0 mV 11.2 mV 9.8 mV 12.6 mV
+12VB 9.8 mV 14.4 mV 13.2 mV 13.0 mV 16.2 mV
+5 V 10.4 mV 11.2 mV 12.2 mV 12.8 mV 15.2 mV
+3.3 V 10.8 mV 11.2 mV 12.8 mV 15.4 mV 15.4 mV
+5VSB 11.4 mV 16.2 mV 15.6 mV 18.6 mV 20.6 mV
-12 V 25.2 mV 30.2 mV 32.4 mV 44.8 mV 54.6 mV

Below you can see the waveforms of the outputs during test five.

Seasonic X-Series 750 W power supplyFigure 19: +12VA input from load tester during test five at 748.2 W (20.2 mV)

Seasonic X-Series 750 W power supplyFigure 20: +12VB input from load tester during test five at 748.2 W (18.6 mV)

Seasonic X-Series 750 W power supplyFigure 21: +5V rail during test five at 748.2 W (9.2 mV)

Seasonic X-Series 750 W power supplyFigure 22: +3.3 V rail during test five at 748.2 W (12.2 mV)

[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, as it shut down when we tried to pull more than listed in the table below. Noise and ripple levels were still extremely low and voltages were still within 3% of their labeled values.

Input Overload Test
+12VA 33 A (396 W)
+12VB 33 A (396 W)
+5 V 16 A (80 W)
+3.3 V 16 A (52.8 W)
+5VSB 3 A (15 W)
-12 V 0.5 A (6 W)
Total 937.8 W
% Max Load 125.0%
Room Temp. 45.2° C
PSU Temp. 52.9° C
AC Power 1124.0 W
Efficiency 83.4%
AC Voltage 102.7 V
Power Factor 0.997

[nextpage title=”Main Specifications”]

The main specifications for the Seasonic X-Series 750 W power supply include:

  • Standards: NA
  • Nominal labeled power: 750 W
  • Measured maximum power: 937.8 W at 45.2° C
  • Labeled efficiency: 80 Plus Gold certification
  • Measured efficiency: Between 87.1% and 90.6%, 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, one ATX12V connector, and two EPS12V connectors
  • Video Card Power Connectors: Four six/eight-pin connectors on separate cables
  • SATA Power Connectors: Eight on three cables
  • Peripheral Power Connectors: Eight on three cables
  • Floppy Disk Drive Power Connectors: Two (converted from a peripheral power connector)
  • Protections (as listed by the manufacturer): Over voltage (OVP), under voltage (UVP), over power (OPP), and short-circuit (SCP)
  • Are the above protections really available? Yes. The unit also has over current protection (OCP).
  • Warranty: Five years
  • More Information: https://www.seasonicusa.com
  • Average Price in the U.S.*: USD 160.00

* Researched at Newegg.com on the day we published this review.

[nextpage title=”Conclusions”]

The X-Series 750 W is another flawless power supply from Seasonic. It has superb voltage regulation, with all its voltages within 3% of their nominal values, extremely low noise and ripple levels, and efficiency between 87.1% and 90.6%, correctly matching its 80 Plus Gold certification. The cable configuration is adequate for a 750 W unit.

Internally, the X-Series 750 W uses the same design as the X-Series 650 W and 850 W models. The primary of the 650 W and 750 W models uses the same components, while the 750 W model uses stronger transistors in its secondary. The secondary of the 750 W and 850 W models uses the same components, but the primary of the 850 W model uses stronger active PFC transistors.

The only negative we can say about this power supply is its price, USD 160. However, it is priced slightly below its direct competitors, namely the Corsair AX750, the SilverStone Strider Gold Evolution 750 W, and the Antec High Current Pro 750 W, making it a terrific buy if you are looking for the “perfect” 750 W power supply with the 80 Plus Gold certification.