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[nextpage title=”Introduction”]

Seasonic is releasing the third generation of their power supplies with the 80 Plus Gold certification, dubbed the X-Series KM3, using a completely different internal design. So far, three versions were released, 650 W, 750 W, and 850 W, all with a single +12 V rail and a fully modular cabling system. Let’s see how the 650 W model fared on our tests.

Seasonic X-Series KM3 650wFigure 1: Seasonic X-Series KM3 650 W power supply

Seasonic X-Series KM3 650wFigure 2: Seasonic X-Series KM3 650 W power supply

The Seasonic X-Series KM3 650 W is 6.3” (160 mm) deep. It uses a 120 mm ball-bearing fan on its bottom (Sanyo Denki San Ace 120 9S1212F404). This fan is different from the one used on the Seasonic X-Series KM3 650 Wi. The power supply has a “hybrid/normal” switch that allows you to configure the fan to turn on only when the power supply load reaches 30% of the unit’s labeled wattage (i.e., 195 W), so the power supply won’t make any noise when the computer doesn’t demand a lot of power. Under the “hybrid” mode, between 30% and 50% load the fan will spin at a lower speed, generating lower noise than usual.

Seasonic X-Series KM3 650wFigure 3: Fan

The modular cabling system from this power supply has 13 connectors: two for the main motherboard power connector, six for video card and ATX12V/EPS12V connectors, and five 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, 25.6” (65 cm) long
  • One cable with one EPS12V connector, 25.6” (65 cm) long
  • Two cables, each with two six/eight-pin connectors for video cards, 21.6” (55 cm) to the first connector, 3.9” (10 cm) between connectors
  • Two cables, each 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, 12.6” (32 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, 5.1” (13 cm) between connectors
  • One cable with two peripheral power connectors, 11.8” (30 cm) to the first connector, 5.1” (13 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 very good for a 650 W power supply, allowing you to install up to two high-end video cards that require two auxiliary power connectors each.

Seasonic X-Series KM3 650wFigure 4: Cables

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

[nextpage title=”A Look Inside the Seasonic X-Series KM3 650 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 KM3 650wFigure 5: Top view

Seasonic X-Series KM3 650wFigure 6: Front quarter view

Seasonic X-Series KM3 650wFigure 7: Rear quarter view

Seasonic X-Series KM3 650wFigure 8: 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.

Seasonic X-Series KM3 650wFigure 9: Transient filtering stage (part 1)

Seasonic X-Series KM3 650wFigure 10: 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 KM3 650 W.

[nextpage title=”Primary Analysis”]

On this page, we will take an in-depth look at the primary stage of the Seasonic X-Series KM3 650 W. For a better understanding, please read our “Anatomy of Switching Power Supplies” tutorial.         

This power supply uses two GBJ1506 rectifying brid
ges, which are attached to an individual heatsink. Each bridge supports up to 15 A at 100° C. 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 (or 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. 

Seasonic X-Series KM3 650wFigure 11: Rectifying bridges

The active PFC circuit uses two IPP60R250CP MOSFETs, each one supporting up to 12 A at 25° C or 8 A at 100° C in continuous mode (note the difference temperature makes), or 40 A at 25° C in pulse mode. These transistors present a 250 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.

Seasonic X-Series KM3 650wFigure 12: The active PFC diode and transistors

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

Seasonic X-Series KM3 650wFigure 13: Active PFC controller

The output of the active PFC circuit is filtered by two 220 μF x 420 V Japanese electrolytic capacitors, from Hitachi, labeled at 105° C. These capacitors are connected in parallel and are the equivalent of a single 440 μF x 420 V capacitor.

Seasonic X-Series KM3 650wFigure 14: Capacitors

In the switching section, four IPP50R399CP MOSFETs are employed using a full-bridge, resonant configuration. Each transistor supports up to 9 A at 25° C or 6 A at 100° C in continuous mode or up to 20 A at 25° C in pulse mode, with a maximum RDS(on) of 399 mΩ. 

Seasonic X-Series KM3 650wFigure 15: The switching transistors

The switching transistors are controlled by a CM6901 resonant controller, which is physically located on the same printed circuit board as the +12 V transistors.

Seasonic X-Series KM3 650wFigure 16: 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 X-Series KM3 650 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 PSMN2R6-40YS MOSFETs, each one supporting up to 100 A at 100° C in continuous mode, or up to 651 A at 25° C in pulse mode, with a maximum RDS(on) of 3.7 mΩ. 

Seasonic X-Series KM3 650wFigure 17: 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 located on the same printed circuit board as the modular cabling system. The two converters are controlled by the same PWM controller, an APW7159, and each exit makes use of three BSC0906NS MOSFETs, each one supporting up to 63 A at 25° C or 50 A at 100° C in continuous mode and up to 252 A at 25° C in pulse mode, with a maximum RDS(on) of 4.5 mΩ. 

Seasonic X-Series KM3 650wFigure 18: The DC-DC converters

Seasonic X-Series KM3 650wFigure 19: 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. There are four OCP channels, one for +3.3 V, one for +5 V, and two for +12 V. The manufacturer, however, decided to use only one of the +12 V channels available, resulting in this unit having a single +12 V rail. 

Seasonic X-Series KM3 650wFigure 20: Monitoring circuit

This power supply uses a mix of solid and electrolytic capacitors in its secondary. The electrolytic capacitors are also Japanese, from Chemi-Con, and labeled at 105° C, as usual.

Seasonic X-Series KM3 650wFigure 21: Capacitors

[nextpage title=”The +5VSB Power Supply”]

The +5VSB (a.k.a. standby) power supply is independent of the main power supply, since it is on co
ntinuously.

The +5VSB power supply uses an ICE2QR4765 integrated circuit, which incorporates the PWM controller and the switching transistor into a single chip.

Seasonic X-Series KM3 650wFigure 22: The +5VSB integrated circuit with an integrated switching transistor

The rectification of the +5VSB output is performed by an SBR30A40CT Schottky rectifier, which supports up to 30 A (15 A per internal diode at 110° C, 0.50 V maximum voltage drop).

Seasonic X-Series KM3 650wFigure 23: The +5VSB rectifier

[nextpage title=”Power Distribution”]

In Figure 24, you can see the power supply label containing all the power specs.

Seasonic X-Series KM3 650wFigure 24: Power supply label

As you can see, this unit has a single +12 V rail configuration.

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 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, 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 5 A (60 W) 10 A (120 W) 14.5 A (174 W) 19 A (228 W) 23.5 A (282 W)
+12VB 5 A (60 W) 10 A (120 W) 14 A (168 W) 19 A (228 W) 23.5 A (282 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 139.8 W 270.8 W 391.4 W 523.7 W 649.8 W
% Max Load 21.5% 41.7% 60.2% 80.6% 100.0%
Room Temp. 45.3° C 44.5° C 44.9° C 48.1° C 45.6° C
PSU Temp. 46.6° C 46.7° C 47.0° C 49.4° C 49.0° C
Voltage Regulation Pass Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power 154.9 W 296.2 W 431.0 W 583.5 W 736.0 W
Efficiency 90.3% 91.4% 90.8% 89.8% 88.3%
AC Voltage 117.5 V 116.4 V 115.0 V 113.5 V 112.4 V
Power Factor 0.991 0.986 0.990 0.993 0.994
Final Result Pass Pass Pass Pass Pass

The Seasonic X-Series KM3 650 W presented outstanding efficiency, way above the minimum set by the 80 Plus Gold certification. The 80 Plus Gold certification promises efficiency of at least 87% under light (i.e., 20%) load, 90% under typical (i.e., 50%) load, and 87% under full (i.e., 100%) load.

Let’s discuss voltage regulation on the next page.

[nextpage title=”Voltage Regulation Tests”]

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. We consider a power supply as “flawless” if it shows voltages within 3% of its nominal values. In the table below, you can see the power supply voltages during our tests and, in the following table, the deviation, in percentage, of their nominal values.

The Seasonic X-Series KM3 650 W presented outstanding voltage regulation, with all its main positive voltages within 1% of their nominal values. (Seasonic promises 2% voltage regulation for this power supply.)

Input Test 1 Test 2 Test 3 Test 4 Test 5
+12VA +12.06 V +12.04 V +12.02 V +12.00 V +11.98 V
+12VB +12.06 V +12.03 V +12.00 V +11.97 V +11.94 V
+5 V +5.03 V +5.02 V +5.02 V +5.01 V +5.01 V
+3.3 V +3.33 V +3.31 V +3.31 V +3.31 V +3.30 V
+5VSB +5.08 V +5.05 V +5.02 V +4.99 V +4.96 V
-12 V -11.41 V -11.54 V -11.66 V -11.84 V -12.01 V
Input Test 1 Test 2 Test 3 Test 4 Test 5
+12VA 0.50% 0.33% 0.17% 0.00% -0.17%
+12VB 0.50% 0.25% 0.00% -0.25% -0.50%
+5 V 0.60% 0.40% 0.40% 0.20% 0.20%
+3.3 V 0.91% 0.30% 0.30% 0.30% 0.00%
+5VSB 1.60% 1.00% 0.40% -0.20% -0.80%
-12 V 5.17% 3.99% 2.92% 1.35% -0.08%

Let’s discuss the ripple and noise levels on the next page.

[nextpage title=”Ripple and Noise Tests”]

Volta
ges 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 KM3 650 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 15.0 mV 21.2 mV 25.0 mV 28.8 mV 33.2 mV
+12VB 15.8 mV 23.0 mV 27.2 mV 32.2 mV 38.4 mV
+5 V 10.0 mV 10.4 mV 10.8 mV 11.6 mV 12.8 mV
+3.3 V 7.8 mV 8.6 mV 9.8 mV 11.2 mV 12.0 mV
+5VSB 5.0 mV 6.0 mV 7.0 mV 7.2 mV 7.4 mV
-12 V 14.0 mV 18.4 mV 22.4 mV 24.0 mV 31.8 mV

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

Seasonic X-Series KM3 650wFigure 25: +12VA input from load tester during test five at 649.8 W (33.2 mV)

Seasonic X-Series KM3 650wFigure 26: +12VB input from load tester during test five at 649.8 W (38.4 mV)

Seasonic X-Series KM3 650wFigure 27: +5V rail during test five at 649.8 W (12.8 mV)

Seasonic X-Series KM3 650wFigure 28: +3.3 V rail during test five at 649.8 W (12.0 mV)

Let’s see if we can pull more than 650 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 extremely low, with all outputs still within their tighter-than-usual range.

Input Overload Test
+12VA 28 A (336 W)
+12VB 28 A (336 W)
+5 V 13 A (65 W)
+3.3 V 13 A (42.9 W)
+5VSB 3 A (15 W)
-12 V 0.5 A (6 W)
Total 786.8 W
% Max Load 121.0%
Room Temp. 42.8° C
PSU Temp. 49.5° C
AC Power 914.0 W
Efficiency 86.1%
AC Voltage 110.0 V
Power Factor 0.995

[nextpage title=”Main Specifications”]

The main specifications for the Seasonic X-Series KM3 650 W power supply include:

  • Standards: ATX12V 2.3 and EPS12V 2.91
  • Nominal labeled power: 650 W
  • Measured maximum power: 786.8 W at 42.8° C
  • Labeled efficiency: 80 Plus Gold certification (87% at light/20% load, 90% at typical/50% load, and 87% at full/100% load)
  • Measured efficiency: Between 89.2% and 92.0% 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 EPS12V connector, and two ATX12V connectors that together form an EPS12V connector
  • Video Card Power Connectors: Four six/eight-pin connectors on two cables
  • SATA Power Connectors: 10 on three 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), over current (OCP), over power (OPP), over temperature (OTP), and short-circuit (SCP) protections
  • Are the above protections really available? Yes.
  • Warranty: Seven years
  • Real Manufacturer: Seasonic
  • More Information: https://www.seasonicusa.com
  • Average Price in the U.S.*: USD 130.00

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

[nextpage title=”Conclusions”]

The new X-Series KM3 650 W is another flawless power supply from Seasonic, targeted to users who demand only “the best.” Its efficiency surpassed the numbers promised by the 80 Plus Gold certification, noise and ripple levels were very low, and voltage regulation was outstanding, with the main positive voltages (+12 V, +5 V, and +3.3 V) within 1% of their nominal values. The ATX12V specification allows a 5% deviation, and we usually consider units with 3% voltage regulation as “flawless.”

Other highlights of the Seasonic X-Series KM3 650 W include the fully modular cabling system and the semi-passive mode of operation, where you can configure the power supply to turn on its fan only when you pull above 30% of its labeled wattage, and at low speed between 30% and 50% load, thereby making the power supply silent when the computer is not demanding a lot of power.

Costing USD 130, it is more expensive than the other 650 W power supplies around. However, we think the peace of mind of using a flawless power supply is worth every cent.