Introduction

Seasonic offers four models under their G series: 360 W, 450 W, 550 W, and 650 W, all featuring the 80 Plus Gold certification. We’ve already reviewed the 360 W model, which proved to be a winner. Let’s see if the 550 W version follows in the same footsteps.

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Figure 1: Seasonic G-550 power supply

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Figure 2: Seasonic G-550 power supply

The Seasonic G-550 is 6.3” (160 mm) deep, using a 120 mm ball-bearing fan on its bottom (ADDA AD1212MB-A70GL, the same used on the 360 W model).

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Figure 3: Fan

Differently from the 360 W model, the Seasonic G-550 has a modular cabling system with six connectors: two for video card power cables and four for peripheral and SATA power cables. The unit comes with the main motherboard cable and an ATX12V/EPS12V cable permanently attached to it. They use nylon sleeves that come from inside the unit. This power supply comes with the following cables:

• Main motherboard cable with a 20/24-pin connector, 21.2” (54 cm) long, permanently attached to the power supply
• One cable with two ATX12V connectors that together form an EPS12V connector, 21.2” (54 cm) long, permanently attached to the power supply
• Two cables, each with one six/eight-pin connector for video cards, 23.6” (60 cm) long, modular cabling system
• One cable with four SATA power connectors, 16.9” (43 cm) to the first connector, 5.1” (13 cm) between connectors, modular cabling system
• One cable with two SATA power connectors, 13” (33 cm) to the first connector, 5.1” (13 cm) between connectors, modular cabling system
• One cable with three standard peripheral power connectors, 16.9” (43 cm) to the first connector, 5.1” (13 cm) between connectors, modular cabling system
• One cable with two standard peripheral power connectors, 13” (33 cm) to the first connector, 5.1” (13 cm) between connectors, modular cabling system
• One adapter to convert a standard peripheral power connector into a floppy disk drive power connector

All wires are 18 AWG, which is the correct gauge to be used.

The number of connectors is perfect for a 550 W power supply.

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Figure 4: Cables

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

A Look Inside the Seasonic G-550

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.

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Figure 5: Top view

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Figure 6: Front quarter view

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Figure 7: Rear quarter view

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Figure 8: The printed circuit board

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 one X capacitor, four Y capacitors, and one ferrite coil more than the minimum required.

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Figure 9: Transient filtering stage (part 1)

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Figure 10: Transient filtering stage (part 2)

On the next page, we will have a more detailed discussion about the components used in the Seasonic G-550.

Primary Analysis

On this page, we will take an in-depth look at the primary stage of the Seasonic G-550. For a better understanding, please read our “Anatomy of Switching Power Supplies” tutorial.

This power supply uses one GBU10JL rectifying bridge, which is attached to an individual heatsink. This bridge supports up to 10 A at 100° C. In theory, you would be able to pull up to 1,150 W from a 115 V power grid. Assuming 80% efficiency, the bridge would allow this unit to deliver up to 1,380 W without burning itself out (or 1,553 W at 90% efficiency). Of course, we are only talking about this particular component. The real limit will depend on all the components combined in this power supply. This is exactly the same bridge used in the 360 W model.

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Figure 11: Rectifying bridge

The active PFC circuit uses two SPP20N60C3 MOSFETs, which support up to 20.7 A at 25° C or 13.1 A at 100° C in continuous mode (note the difference temperature makes) or 62.1 A at 25° C in pulse mode. These transistors present a 190 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.

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Figure 12: The active PFC transistors and diode

The active PFC circuit is managed by an ICE3PCS01 active PFC controller.

The output of the active PFC circuit is filtered by one 390 µF x 420 V Japanese electrolytic capacitor, from Chemi-Con, labeled at 105° C.

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Figure 13: Capacitor

In the switching section, two FDP18N50 MOSFETs are employed using a resonant configuration. Each transistor supports up to 18 A at 25° C or 10.5 A at 100° C in continuous mode or up to 72 A at 25° C in pulse mode, with a maximum RDS(on) of 265 mΩ.

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Figure 14: The switching transistors

The switching transistors are controlled by an ICE2HS01G resonant controller.

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Figure 15: Resonant controller (left) and active PFC controller (right)

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

Secondary Analysis

As one would expect in a high-efficiency power supply, the Seasonic G-550 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 5.3 mΩ. These transistors are located on the solder side of the printed circuit board, using the power supply case as their heatsink.  

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Figure 16: 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 a single printed circuit board located in the secondary section of the power supply. The converters are controlled by an APW7159 integrated circuit and use seven IPD060N03L G MOSFETs: four of them are used by the +5 V output and three of them are used by the +3.3 V output. Each transistor supports up to 50 A at 100° C in continuous mode and up to 350 A at 25° C in pulse mode, with a maximum RDS(on) of 6 mΩ.

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Figure 17: The DC-DC converters

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Figure 18: The DC-DC converters

The outputs of the power supply are monitored by a PS223 integrated circuit, which supports over voltage (OVP), under voltage (UVP), over current (OCP), and over temperature (OTP) protections. There are four OCP channels available, but the manufacturer decided to use only one of them, making the reviewed unit use a single +12 V rail configuration.

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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. A few solid capacitors are also used.

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Figure 20: Capacitors

The +5VSB Power Supply

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

On the Seasonic G-550, the +5VSB power supply uses an ICE2QR1765 integrated circuit, which includes the PWM controller and the switching transistor in the same chip.

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Figure 21: The +5VSB PWM controller with integrated switching transistor

The rectification of the +5VSB output is performed by an SBR10U45 Schottky rectifier, which supports up to 10 A (5 A per internal diode at 110° C, 0.57 V maximum voltage drop). This rectifier is located on the solder side of the printed circuit board.

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Figure 22: The +5VSB rectifier

Power Distribution

In Figure 23, you can see the power supply label containing all the power specs.

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Figure 23: Power supply label

As you can see, there is only one +12 V rail, so there is not much to talk about here.

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

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 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	4 A (48 W)	8 A (96 W)	12 A (144 W)	16 A (192 W)	19.5 A (234 W)
+12VB	4 A (48 W)	8 A (96 W)	12 A (144 W)	16 A (192 W)	19.5 A (234 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	0.3 A (3.6 W)	0.3 A (3.6 W)	0.3 A (3.6 W)	0.3 A (3.6 W)	0.3 A (3.6 W)
Total	115.0 W	221.4 W	372.9 W	453.3 W	555.4 W
% Max Load	20.9%	40.3%	67.8%	82.4%	101.0%
Room Temp.	45.6° C	45.3° C	45.9° C	47.9° C	49.8° C
PSU Temp.	45.5° C	45.9° C	46.4° C	47.4° C	49.9° C
Voltage Regulation	Pass	Pass	Pass	Pass	Pass
Ripple and Noise	Pass	Pass	Pass	Pass	Pass
AC Power	131.7 W	246.0 W	421.4 W	510.9 W	638.0 W
Efficiency	87.3%	90.0%	88.5%	88.7%	87.1%
AC Voltage	117.3 V	116.1 V	114.2 V	113.3 V	112.2 V
Power Factor	0.994	0.997	0.998	0.998	0.998
Final Result	Pass	Pass	Pass	Pass	Pass

The 80 Plus Gold certification guarantees minimum efficiencies of 87% at 20% load, 90% at 50% load, and 87% at 100% load. In our tests, the Seasonic G-550 met these requirements at high temperatures, which is terrific.

Let’s discuss voltage regulation on the next page.

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.

As you can see, the positive voltages of the Seasonic G-550 were always within 3% of their nominal values.

Input	Test 1	Test 2	Test 3	Test 4	Test 5
+12VA	+12.28 V	+12.26 V	+12.20 V	+12.20 V	+12.16 V
+12VB	+12.28 V	+12.25 V	+12.20 V	+12.18 V	+12.15 V
+5 V	+5.05 V	+5.05 V	+5.01 V	+5.01 V	+5.00 V
+3.3 V	+3.36 V	+3.34 V	+3.28 V	+3.30 V	+3.29 V
+5VSB	+4.98 V	+4.97 V	+4.92 V	+4.90 V	+4.86 V
-12 V	-12.28 V	-12.26 V	-12.20 V	-12.20 V	-12.16 V

Input	Test 1	Test 2	Test 3	Test 4	Test 5
+12VA	2.33%	2.17%	1.67%	1.67%	1.33%
+12VB	2.33%	2.08%	1.67%	1.50%	1.25%
+5 V	1.00%	1.00%	0.20%	0.20%	0.00%
+3.3 V	1.82%	1.21%	-0.61%	0.00%	-0.30%
+5VSB	-0.40%	-0.60%	-1.60%	-2.00%	-2.80%
-12 V	-5.33%	-3.92%	-1.33%	0.00%	2.08%

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

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 G-550 provided very 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	8.0 mV	10.4 mV	15.4 mV	17.8 mV	23.2 mV
+12VB	14.2 mV	18.8 mV	25.6 mV	28.8 mV	36.8 mV
+5 V	6.0 mV	6.2 mV	6.8 mV	8.2 mV	10.0 mV
+3.3 V	6.2 mV	6.6 mV	8.6 mV	12.6 mV	12.0 mV
+5VSB	7.2 mV	7.8 mV	9.2 mV	11.0 mV	12.8 mV
-12 V	9.8 mV	10.0 mV	14.8 mV	14.0 mV	19.4 mV

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

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Figure 24: +12VA input from load tester during test five at 555.4 W (23.2 mV)

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Figure 25: +12VB input from load tester during test five at 555.4 W (36.8 mV)

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Figure 26: +5V rail during test five at 555.4 W (10.0 mV)

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Figure 27: +3.3 V rail during test five at 555.4 W (12.0 mV)

Let’s see if we can pull more than 550 W from this unit.

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. In fact, we tried to pull 0.5 A from the -12 V output, to make this review comparable to the other power supply reviews we’ve published, and the power supply would shut down. This is the first time we’ve seen a power supply with a tight protection configuration on its -12 V output. During this test, noise and ripple levels stayed close to the numbers we’ve seen during test five. All outputs were still inside 3% of their nominal values.

Input	Overload Test
+12VA	21 A (252 W)
+12VB	21 A (252 W)
+5 V	11 A (55 W)
+3.3 V	8 A (26.4 W)
+5VSB	3 A (15 W)
-12 V	0.3 A (3.6 W)
Total	609.4 W
% Max Load	110.8%
Room Temp.	48.4° C
PSU Temp.	49.0° C
AC Power	706.0 W
Efficiency	86.3%
AC Voltage	111.3 V
Power Factor	0.998

Main Specifications

The main specifications for the Seasonic G-550 power supply include:

• Standards: NA
• Nominal labeled power: 550 W
• Measured maximum power: 609.4 W at 48.4° C
• Labeled efficiency: 80 Plus Gold certification; 87% minimum at light (20%) and full loads and 90% minimum at typical (50%) load
• Measured efficiency: Between 87.1% and 90.0%, 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, permanently attached to the power supply
• Video Card Power Connectors: Two six/eight-pin connectors on two cables, modular cabling system
• SATA Power Connectors: Six on two cables
• Peripheral Power Connectors: Four 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), and short-circuit (SCP) protections
• Are the above protections really available? Yes.
• Warranty: Five years
• More Information: http://www.seasonicusa.com
• Average Price in the U.S.*: USD 90.00

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

Conclusions

The G-550 is another flawless power supply from Seasonic, with terrific efficiency, very low noise and ripple levels, and voltages within 3% of their nominal voltages.

One of its main competitors is the Rosewill CAPSTONE-550M, which was more expensive when we reviewed it (this model is currently out of stock).

At USD 90, the Seasonic G-550 is the perfect power supply for the mainstream user who is looking for a flawless yet affordable power supply. You won’t regret buying it.