Introduction

Seasonic revamped their S12II power supply series, adding 80 Plus Bronze certification and promising higher efficiency. This new series is called S12II Bronze and let’s see if the 520 W model is a good pick.

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Figure 1: Seasonic S12II Bronze 520 W power supply.

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Figure 2: Seasonic S12II Bronze 520 W power supply.

Seasonic S12II Bronze 520 W is a short power supply, being only 5 ½” (140 mm) deep, using a 120 mm fan on its bottom and active PFC circuit, of course.

Being an entry-level product, it doesn’t have a modular cabling system. All cables have nylon protections, that come from inside the power supply housing. All cables use 18 AWG wires, which is the minimum recommended. The cables included are:

• Main motherboard cable with a 20/24-pin connector (21 ¼” or 54 cm long).
• One cable with one EPS12V connector (21 ¼” or 54 cm long).
• One cable with two ATX12V connectors that together form an EPS12V connector (21 ¼” or 54 cm long).
• One cable with one six-pin video card power connector (21 ¼” or 54 cm long).
• One cable with one six/eight-pin video card power connector (21 5/8” or 55 cm long).
• One cable with three SATA power connectors (16 ½” or 42 cm to the first connector and 3 ½” or 9 cm between connectors).
• One cable with three SATA power connectors (20 ½” or 52 cm to the first connector and 3 ½” or 9 cm between connectors).
• One cable with three peripheral power connectors (16 ½” or 42 cm to the first connector and 4” or 10 cm between connectors).
• One cable with three peripheral power connectors (20 ½” or 52 cm to the first connector and 4” or 10 cm between connectors).

Although the cable configuration is compatible with a unit from this power range, we think Seasonic should have put a greater distance between the SATA and peripheral power connectors.

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Figure 3: Cables.

Now let’s take an in-depth look inside this power supply.

A Look Inside The Seasonic S12II Bronze 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.

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

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Figure 4: Overall look.

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Figure 5: Overall look.

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Figure 6: Overall look.

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. 

This power supply is flawless on this stage, with four Y capacitors and one ferrite coil more than the minimum required, plus one X capacitor after the rectifying bridge.

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Figure 7: Transient filtering stage (part 1).

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Figure 8: Transient filtering stage (part 2).

In the next page we will have a more detailed discussion of the components used in the Seasonic S12II Bronze 520 W.

Primary Analysis

On this page we will take an in-depth look at the primary stage of Seasonic S12II Bronze 520 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU806 rectifying bridge in its primary, which can deliver up to 8 A at 100º C. At 115 V this unit would be able to pull up to 920 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 736 W without burning this component. Of course we are only talking about this component and the real limit will depend on all other components from the power supply.

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Figure 9: Rectifying bridge.

On the active PFC circuit two FDP18N50 power MOSFET transistors are used, each one capable of delivering up to 18 A at 25º C or up to 10.8 A at 100º C in continuous mode (note the difference temperature makes), or up to 72 A in pulse mode at 25º C. These transistors present a maximum resistance of 265 mΩ when turned on, a characteristic called RDS(on). This number indicates the amount of power that is wasted, so the lower this number the better, as less power will be wasted thus increasing efficiency.

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Figure 10: One of the switching transistors, active PFC diode and active PFC transistors.

This power supply uses a Japanese capacitor from Chemi-Con labeled at 105º C to filter the output from the active PFC circuit. This is great because Japanese capacitors are better and being labeled at 105º C means a higher life-span. At Seasonic’s website there is something fishy, though. The manufacturer added a comparison graph between solid capacitors and conventional electrolytic capacitors, but this power supply doesn’t have any solid capacitor in it. The presence of this chart is very misleading.

In the switching section, another two FDP18N50 power MOSFET transistors are used. The main specifications for these transistors were already published above.

The primary is controlled by an ICE1CS02 PWM/PFC combo controller.

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Figure 11: PWM/PFC combo Controller.

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

Secondary Analysis

This power supply has five Schottky rectifiers attached to its secondary heatsink.

The maximum theoretical current each line can deliver is given by the formula I / (1 - D), where D is the duty cycle used and I is the maximum current supported by the rectifying diode. Just as an exercise, we can assume a typical duty cycle of 30%.

The +12 V output is produced by three SBR30A50CT Schottky rectifiers, each one capable of delivering up to 30 A (15 A per internal diode at 125º C with a maximum voltage drop of 0.55 V). From the six diodes available (two per device), two are used for the direct rectification path and four are used for the “freewheeling” path. This gives us a maximum theoretical current of 43 A or 514 W for the +12 V output.

The +5 V output is produced by one SBR40U45CT Schottky rectifier, which can handle up to 40 A (20 A per internal diode at 110º C, maximum voltage drop of 0.52 V). This gives us a maximum theoretical current of 29 A or 143 W for the +5 V output.

The +3.3 V output is produced by one STPS30L30CT Schottky rectifier, which can handle up to 30 A (15 A per internal diode at 140º C, maximum voltage drop of 0.46 V). This gives a maximum theoretical current of 21 A or 71 W for the +3.3 V output.

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Figure 12: +12 V, +5 V and +3.3 V rectifiers.

The outputs are monitored by an HY-510N integrated circuit, which supports only over voltage (OVP) and under voltage (UVP) protections.

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Figure 13: Monitoring integrated circuit.

The secondary capacitors are also Japanese, from Chemi-Con.

Power Distribution

In Figure 14, you can see the power supply label containing all the power specs.

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Figure 14: Power supply label.

As you can see, the label says this unit has two +12 V rails, but this do not correspond to the reality. Inside the power supply all +12 V (yellow) wires are connected to the same place and the monitoring circuit doesn’t support over current protection (OCP), which is a prerequisite to have more than one virtual rail. Therefore, this power supply has a single-rail design. The manufacturer lists OCP as a feature from this unit on the text present on their website, but not on the feature list available on the same page, so they probably just copied and pasted the text without paying attention (just to clarify, this unit doesn’t have OCP).

On the manufacturer website it says that this unit is based on a single-rail design. So the label is definitely wrong.

Now let’s see if this power supply can really deliver 520 W.

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 how the reviewed unit behaved 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. On 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. Since this power supply in reality has only one +12 V rail (see explanation in the previous page), both inputs were connected to the single rail present. The +12VB input was connected to the power supply EPS12V connector, while other connectors where installed on the +12VA input.

Input	Test 1	Test 2	Test 3	Test 4	Test 5
+12VA	4 A (48 W)	7.5 A (90 W)	11 A (132 W)	14.5 A (174 W)	18 A (216 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)
+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)	2.5 A (12.5 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	110.4 W	205.3 W	313.6 W	417.2 W	520.1 W
% Max Load	21.2%	39.5%	60.3%	80.2%	100.0%
Room Temp.	44.1º C	43.8º C	44.9º C	47.3º C	45.9º C
PSU Temp.	45.0º C	45.2º C	46.0º C	48.1º C	50.3º C
Voltage Regulation	Pass	Pass	Pass	Pass	Pass
Ripple and Noise	Pass	Pass	Pass	Pass	Pass
AC Power	129.4 W	237.3 W	365.9 W	494.6 W	631.0 W
Efficiency	85.3%	86.5%	85.7%	84.4%	82.4%
AC Voltage	114.2 V	113.2 V	111.8 V	110.5 V	108.9 V
Power Factor	0.996	0.996	0.997	0.997	0.996
Final Result	Pass	Pass	Pass	Pass	Pass

Seasonic S12II Bronze 520 W can really deliver its labeled wattage at high temperatures.

Efficiency was very high all the times, staying between 85.3% and 86.55% when we pulled up to 60% of the power supply labeled wattage (i.e., up to 312 W). At 80% load (416 W) efficiency was still high at 84.4%. And when delivering its full 520 W the reviewed unit achieved 82.4% efficiency. Therefore this unit can really maintain the 80 Plus Bronze minimum requirements under real-world temperatures. If you follow our reviews you know by now that not all 80 Plus-certified power supplies can deliver the efficiency that they promise because 80 Plus certification is done at a room temperature of only 23º C and efficiency drops with temperature.

Voltages regulation is another highlight from Seasonic S12II Bronze 520 W: all voltages were closer to their nominal voltages than required, staying within a 3% tolerance, while ATX12V specification allows a 5% tolerance. This includes the -12 V output.

And noise and ripple were amazingly low, as you can see below. The maximum allowed is 120 mV for the +12 V output and 50 mV for the +5 V and +3.3 V outputs. All numbers are peak-to-peak figures.

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Figure 15: +12VA input from load tester at 520.1 W (22.8 mV).

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Figure 16: +12VB input from load tester at 520.1 W (21.0 mV).

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Figure 17: +5V rail with power supply delivering 520.1 W (11.6 mV).

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Figure 18: +3.3 V rail with power supply delivering 520.1 W (18.4 mV).

Let’s see if we can pull more than 520 W from this unit.

Overload Tests

Below you can see the maximum we could pull from this unit with it still working. If we increased one amp at any output voltages would drop below the minimum allowed (for example, +12 V output at +10.42 V).

Input	Overload Test
+12VA	21 A (252 W)
+12VB	21 A (252 W)
+5V	8 A (40 W)
+3.3 V	8 A (26.4 W)
+5VSB	2 A (24 W)
-12 V	0.5 A (6 W)
Total	588.2 W
% Max Load	113.1%
Room Temp.	39.9º C
PSU Temp.	37.2º C
AC Power	720.0 W
Efficiency	81.7%
AC Voltage	108.3 V
Power Factor	0.996

Main Specifications

Seasonic S12II Bronze 520 W power supply specs include:

• Nominal labeled power: 520 W at 40º C or 416 W at 50º C (“the rated power will reduce from 100% to 80% from 40º C to 50º C”)
• Measured maximum power: 588.2 W at 39.9º C.
• Labeled efficiency: Up to 87%. 80 Plus Bronze certified
• Measured efficiency: Between 82.4% and 86.5% at 115 V (nominal, see complete results for actual voltage).
• Active PFC: Yes.
• Modular Cabling System: No.
• 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: One six-pin connector and one six/eight-pin connector in separated cables.
• SATA Power Connectors: Six in two cables.
• Peripheral Power Connectors: Six in two cables.
• Floppy Disk Drive Power Connectors: None.
• Protections: Over voltage (OVP), over power (OPP) and short-circuit (SCP). Under voltage (UVP) not listed but present.
• Warranty: Five years
• More Information: http://www.seasonicusa.com
• Average price in the US*: USD 90.00

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

Conclusions

Seasonic S12II Bronze 520 W is an excellent power supply. It passed with flying colors in our tests: efficiency between 82.4% and 86.5%, voltages closer to their nominal voltages than required (3% voltage regulation instead of the standard 5%) and ultra-low noise and ripple levels. Plus we could pull up to 588 W from it with efficiency still at 81.7%.

Of course there are power supplies on the same power range from well-known manufacturers that cost less, like Enermax Tomahawk 500 W (USD 70) and OCZ StealthXStream 500 W (USD 40 at Newegg.com, around USD 60 everywhere else), but they provide lower efficiency.

So the real competitor to S12II Bronze 520 W is Zalman ZM500-RS, which costs a little bit more (USD 100), provides lower efficiency at higher loads and has very high ripple and noise levels.

We still think that USD 90 is a little bit too much for this power supply – we’d like it better if it were being sold for USD 80 –, but it is definitely a better product than its competitors. If you are a savvy user looking for a flawless power supply on the 500 W range, this is the unit you should buy.

As a final note, although Seasonic manufacturing quality is flawless, they should take care of the mistakes they are doing on the product label (listing two +12 V rails when in fact the unit has a single-rail design) and product page on their website (chart comparing solid capacitors against regular electrolytic capacitors, which can make users to believe that this unit uses solid caps, which is not the case; listing features that this unit doesn’t have, like OCP).