XFX 850 W Black Edition Power Supply Review
By Gabriel Torres on September 14, 2009


Introduction

Hardware Secrets Golden Award

XFX, the traditional video card manufacturer, is now entering the power supply arena. Their first release is a high-end 850 W power supply manufactured by Seasonic and based on their award-winning M12D model. Let’s take a look at this new release.

Externally XFX 850 W Black Edition has a very aggressive looks, with the fan and connectors from the modular cabling system in lime yellow, matching the color pattern used on other products from XFX.

XFX 850 W Black Edition power supply
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Figure 1: XFX 850 W Black Edition power supply.

XFX 850 W Black Edition power supply
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Figure 2: XFX 850 W Black Edition power supply.

XFX 850 W Black Edition isn’t a very long power supply, being 6 19/64” (160 mm) deep, using a 135 mm fan on its bottom and featuring active PFC, of course. As mentioned the reviewed unit has a modular cabling system, with five cables permanently attached to the power supply:

These cables have a nylon protection that comes from inside the power supply.

The modular cabling system has eight connectors and the unit comes with nine cables:

All cables use 18 AWG wires, except the main motherboard cable, which use thicker 16 AWG wires, which is always nice to see.

XFX 850 W Black Edition power supply
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Figure 3: Cables.

The number of cables is terrific for the high-end user, however if you want to install more than two very high-end video cards you will need to use adapters, since each very high-end card takes two auxiliary power connectors each and this power supply comes with “only” four of them.

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

A Look Inside The XFX 850 W Black Edition

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. The first thing that caught our attention was that all capacitors used are Japanese from Chemi-Con and the secondary filtering stage uses some solid capacitors.

XFX 850 W Black Edition power supply
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Figure 4: Overall look.

XFX 850 W Black Edition power supply
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Figure 5: Overall look.

XFX 850 W Black Edition power supply
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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.

On this power supply this stage is flawless. It has two extra ferrite coils, one extra X capacitor and two extra Y capacitors.

XFX 850 W Black Edition power supply
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Figure 7: Transient filtering stage (part 1).

XFX 850 W Black Edition power supply
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Figure 8: Transient filtering stage (part 2).

In the next page we will have a more detailed discussion about the components used in the XFX 850 W Black Edition.

Primary Analysis

On this page we will take an in-depth look at the primary stage of XFX 850 W Black Edition. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses two GBU806 rectifying bridges in its primary, which one feeding a separated active PFC circuit. Each bridge supports up to 8 A at 100° C, so in theory, you would be able to pull up to 1,840 W from the power grid; assuming 80% efficiency, the bridges would allow this unit to deliver up to 1,472 W without burning them. Of course, we are only talking about these components, and the real limit will depend on all the other components in this power supply.

XFX 850 W Black Edition power supply
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Figure 9: Rectifying bridges.

As mentioned, there are two active PFC circuits, and each one uses two TK20A60U power MOSFET transistors, so we have a total of four MOSFETs on the active PFC stage. Each MOSFET is capable of delivering up to 20 A at 25° C in continuous mode (unfortunately the transistor manufacturer doesn’t say how much each transistor can deliver at 100° C) or 40 A in pulse mode at 25° C. These transistors present a 165 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.

XFX 850 W Black Edition power supply
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Figure 10: Active PFC transistors.

This power supply uses two electrolytic capacitors to filter the output from the active PFC circuit. The use of more than one capacitor here has absolute nothing to do with the “quality” of the power supply, as laypersons may assume (including people without the proper background in electronics doing power supply reviews around the web). Instead of using one big capacitor, manufacturers may choose to use two or more smaller components that will give the same total capacitance, in order to better accommodate space on the printed circuit board, as two or more capacitors with small capacitance are physically smaller than one capacitor with the same total capacitance. XFX 850 W Black Edition uses two 390 µF x 400 V in parallel; this is equivalent of one 780 µF x 400 V capacitor.

These capacitors are Japanese, from Chemi-Con and are labeled at 105° C. This is good for two reasons, first, Japanese capacitors do not leak; and second, usually manufacturers use 85° C capacitors here, so it is good to see a manufacturer using a capacitor with a higher temperature rating.

In the switching section, two IPW60R125CP power MOSFET transistors are used on the traditional two-transistor forward configuration. Each transistor supports up to 25 A at 25° C or 16 A at 100° C (note the difference temperature makes) or 82 A in pulse mode at 25° C, presenting an RDS(on) of 125 mΩ.

XFX 850 W Black Edition power supply
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Figure 11: Switching transistors and active PFC diodes.

This power supply uses a CM6802 active PFC/PWM combo controller.

XFX 850 W Black Edition power supply
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Figure 12: Active PFC/PWM combo controller.

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

Secondary Analysis

This power supply uses eight SBR40S45CT Schottky rectifiers on its secondary and each one is capable of handling up to 40 A (20 A per internal diode at 110° C, maximum voltage drop of 0.55 V). All rectifiers are in charge of producing the +12 V output, with +5 V and +3.3 V being generated from the +12 V output using a DC-DC converter (i.e., a small switching power supply) located on a small printed circuit board. This design is the current trend among high-efficiency power supplies. This is exactly the same configuration used on the Seasonic M12D and S12D 750 W models.

Three of the rectifiers are in charge of the direct rectification, while the remaining five are in charge of the “freewheeling” part of the rectification process (i.e., discharging the coil).

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%.

For our math we need to assume the path that has the lower limit, which is the direct rectification path. This would give us a maximum theoretical current of 171 A (40 A x 3 / 0.70). This maximum theoretical current limit is for the whole secondary, since +5 V and +3.3 V are also produced from the +12 V output. The practical limit will depend on other factors, but mainly on the coils used and on the design from the small DC-DC converter used to generate the +5 V and +3.3 V outputs. If this 171 A was solely pulled from the +12 V outputs, this would give us 2,052 W.

XFX 850 W Black Edition power supply
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Figure 13: Rectifiers.

The DC-DC converter uses solid aluminum caps and two APW7073 controllers, one for each output, with seven APM2556N MOSFETs, which present a maximum RDS(on) of only 7.2 mΩ.

XFX 850 W Black Edition power supply
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Figure 14: DC-DC converter in charge of generating +5 V and +3.3 V outputs from the +12 V output.

XFX 850 W Black Edition power supply
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Figure 15: DC-DC converter in charge of generating +5 V and +3.3 V outputs from the +12 V output.

This power supply uses a PS223 monitoring integrated circuit, which is in charge of the power supply protections, like OCP (over current protection), over voltage protection (OVP), under voltage protection (UVP) and over temperature protection (OTP, not implemented on this unit).

XFX 850 W Black Edition power supply
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Figure 16: Monitoring circuit.

Electrolytic capacitors from the secondary are also Japanese, from Chemi-Con and labeled at 105° C.

Power Distribution

In Figure 17, you can see the power supply label containing all the power specs.

XFX 850 W Black Edition power supply
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Figure 17: Power supply label.

This power supply uses a single-rail design, so there is not much to talk about here.

Now let’s see if this power supply can really deliver 850 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 +12V1 and +12V2 inputs listed below are the two +12 V independent inputs from our load tester and during our tests they were connected to the single +12V rail from the power supply.

Input

Test 1

Test 2

Test 3

Test 4

Test 5

+12V1

6 A (72 W)

13 A (156 W)

20 A (240 W)

25 A (300 W)

29 A (384 W)

+12V2

6 A (72 W)

12 A (144 W)

17 A (204 W)

25 A (300 W)

29 A (384 W)

+5V

2 A (10 W)

4 A (20 W)

6 A (30 W)

8 A (40 W)

16 A (80 W)

+3.3 V

2 A (6.6 W)

4 A (13.2 W)

6 A (19.8 W)

8 A (26.4 W)

16 A (52.8 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

174.5 W

351.6 W

515.8 W

690.1 W

853.4 W

% Max Load

20.5%

41.4%

60.7%

81.2%

100.4%

Room Temp.

43.8° C

43.9° C

49.9° C

48.4° C

46.0° C

PSU Temp.

44.2° C

44.5° C

49.8° C

58.0° C

46.3° C

Voltage Stability

Pass

Pass

Pass

Pass

Pass

Ripple and Noise

Pass

Pass

Pass

Pass

Pass

AC Power

201.0 W

400.6 W

593.0 W

808.0 W

1031.0 W

Efficiency

86.8%

87.8%

87.0%

85.4%

83.0%

AC Voltage

112.5 V

110.5 V

109.1 V

107.7 V

104.7 V

Power Factor

0.963

0.971

0.977

0.977

0.982

Final Result

Pass

Pass

Pass

Pass

Pass

XFX 850 W Black Edition achieved very high efficiency just like Seasonic M12D and S12D, achieving up to 87.8% during our tests. Efficiency dropped to 83% while the unit was delivering 850 W, but this is quite normal to happen and we can’t say that 83% is a bad number. It is important to keep in mind that 80 Plus says that this unit present efficiency of at least 85% when delivering 850 W. Our numbers are usually a couple of points below that because we test power supplies at a room temperature of at least 45° C, while 80 Plus test them at 23° C – the higher the temperature, the lower efficiency is.

Voltage stability was another highlight from XFX 850 W Black Edition, with all positive voltages inside 3% of their nominal values(i.e., voltages were closer to their nominal value than needed, as ATX spec allows voltages to be up to 5% from their nominal values, 10% for -12 V). The -12 V output was outside this range during test five, at -12.4 V, but still very close to its nominal value.

And finally we have noise and ripple, which were low all the time: noise level at +12 V was below 25% of the maximum allowed. Below you can see the results for test number five. As we always point out, the limits are 120 mV for +12 V and 50 mV for +5 V and +3.3 V and all numbers are peak-to-peak figures.

XFX 850 W Black Edition
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Figure 18: +12V1 input from load tester at 856.0 W (27.0 mV).

XFX 850 W Black Edition
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Figure 19: +12V2 input from load tester at 856.0 W (29.4 mV).

XFX 850 W Black Edition
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Figure 20: +5V rail with power supply delivering 856.0 W (11.0 mV).

XFX 850 W Black Edition
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Figure 21: +3.3 V rail with power supply delivering 856.0 W (19.4 mV).

Now let’s see if we could pull more than 850 W from this unit.

Overload Tests

Below you can see the maximum we could pull from this power supply with it still working within specs. If we tried to pull one more amp from any of the outputs the ripple would go out of range, showing that the power supply stopped working correctly. The idea behind of overload tests is to see if the power supply will burn/explode and see if the protections from the power supply are working correctly. This power supply didn’t burn or explode.

Input

Maximum

+12V1

32 A (384 W)

+12V2

32 A (384 W)

+5V

25 A (125 W)

+3.3 V

25 A (82.5 W)

+5VSB

3 A (15 W)

-12 V

0.5 A (6 W)

Total

996.8 W

% Max Load

117.3%

Room Temp.

47.5° C

PSU Temp.

56.9° C

AC Power

1,250 W

Efficiency

79.7%

AC Voltage

100.6 V

Power Factor

0.986

Main Specifications

XFX 850 W Black Edition power supply specs include:

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

Conclusions

XFX 850 W Black Edition is identical to Seasonic M12D 850 W, but with a more aggressive looks and costing a little bit less (USD 210 vs. USD 230 on the day we published this review).

Like M12D, XFX 850 W Black Edition is a high-efficiency power supply presenting extremely low ripple and noise levels and great voltage regulation.

The only negative point we can see on this power supply is the presence of “only” four video card auxiliary power connectors, preventing you from installing three high-end video cards without the use of adapters. Since this is a power supply targeted to high-end users that may be interested in running three-way SLI we would prefer to see six video card connectors on this unit.

Nevertheless, this is a terrific product for users looking for a high-end, high-quality 850 W power supply.

Originally at http://www.hardwaresecrets.com/article/XFX-850-W-Black-Edition-Power-Supply-Review/808


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