XFX 750 W Black Edition Power Supply Review
By Gabriel Torres on February 23, 2010
XFX may be a newcomer on the power supply market, but so far the other two models from them we reviewed, 650 W XXX Edition and 850 W Black Edition proved to be outstanding products. Let’s see if their latest model, 750 W Black Edition, follows the same path.
Like 850 W Black Edition, the 750 W version is manufactured by Seasonic and, in fact, it is a relabeled Seasonic M12D, which proved to be one of the best 750 W power supplies on the market today. Therefore XFX 750 W Black Edition enters the market to fight against this model from Seasonic and Corsair HX750W, as they all use a DC-DC design, i.e., the power supply is basically a +12 V model, with +5 V and +3.3 V outputs being produced by two smaller power supplies attached to the power supply main +12 V rail.
XFX 750 W Black Edition isn’t a long power supply, being 6 19/64” (160 mm) deep, using a 135 mm fan on its bottom and featuring active PFC, of course.
The reviewed power supply has a modular cabling system with eight connectors (two for video cards and six for SATA/peripheral cables) and it comes with five cables permanently attached to the unit. This cables included are the following:
The main motherboard cable, the CPU cable (ATX12V/EPS12V) and the video card cables use thicker 16 AWG wires, which is excellent. SATA and peripheral cables use 18 AWG wires.
The number of cables is terrific for the high-end user, supporting two very high-end video cards that require two power connectors each.
Now let’s take an in-depth look inside this power supply.
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.
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 ferrite coils, one X capacitor and two Y capacitors more than the minimum required, plus one X capacitor after each rectifying bridge.
In the next page we will have a more detailed discussion about the components used in the XFX 750 W Black Edition.
On this page we will take an in-depth look at the primary stage of XFX 750 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, each one feeding a separated active PFC circuit, just like on Seasonic M12D and S12D units. 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.
As mentioned, there are two active PFC circuits, each one using two FQP13N50C power MOSFET transistors, so we have a total of four MOSFETs on the active PFC stage. Each MOSFET is capable of delivering up to 13 A at 25° C or 8 A at 100° C in continuous mode (note the difference temperature makes) or 52 A in pulse mode at 25° C. These transistors present a 480 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.
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 750 W Black Edition uses two 390 µF x 400 V capacitor connected 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 IPW50R140CP power MOSFET transistors are used on the traditional two-transistor forward configuration. Each transistor supports up to 23 A at 25° C or 15 A at 100° C (note the difference temperature makes) or 56 A in pulse mode at 25° C, presenting an RDS(on) of 140 mΩ. These transistors are different from the ones used on M12D but have similar specs.
This power supply uses a CM6802 active PFC/PWM combo controller.
Now let’s take a look at the secondary of this power supply.
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., two small switching power supplies) located on a small printed circuit board. This design is the current trend among high-efficiency power supplies. This is exactly the same configuration from Seasonic M12D.
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. Of course these are theoretical numbers and are being used just as an exercise.
Some power supplies based on the DC-DC converter use two separated printed circuit boards for generating the +5 V and +3.3 V outputs. XFX 750 W Black Edition uses a single printed circuit board to generate these two outputs. This board has solid aluminum caps and two APW7073 PWM controllers, one for each output, with seven APM2556N MOSFETs, which present a maximum RDS(on) of only 7.2 mΩ.
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).
Electrolytic capacitors from the secondary are also Japanese, from Chemi-Con and labeled at 105° C.
In Figure 18, you can see the power supply label containing all the power specs.
This power supply has a single-rail design, so there is not much to talk about here. This is one of the main differences between XFX 750 W Black Edition and Seasonic M12D: on the Seasonic-braded model the unit has two +12 V virtual rails.
Now let’s see if this power supply can really deliver 750 W.
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 the reviewed unit has a single +12 V rail, both inputs were connected to the power supply single +12 V rail (+12VB was connected to the power supply EPS12V connector and all other cables were connected to the load tester +12VA input).
5 A (60 W)
11 A (132 W)
16 A (192 W)
22 A (264 W)
27 A (324 W)
5 A (60 W)
10 A (120 W)
16 A (192 W)
21 A (252 W)
27 A (324 W)
2 A (10 W)
4 A (20 W)
6 A (30 W)
8 A (40 W)
10 A (50 W)
2 A (6.6 W)
4 A (13.2 W)
6 A (19.8 W)
8 A (26.4 W)
10 A (33 W)
1 A (5 W)
1 A (5 W)
1.5 A (7.5 W)
2 A (10 W)
2.5 A (12.5 W)
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)
% Max Load
Ripple and Noise
XFX 750 W Black Edition, like Seasonic M12D and S12D, achieved very high efficiency, staying above 84% all times, including when you pull its maximum labeled power. If you pull between 40% and 60% from its labeled capacity (i.e., between 300 W and 450 W) you will get efficiency between 87% and 88%.
This unit has 80 Plus Silver certification, and in theory would present efficiency of at least 85% at light (20%) and full (100%) loads and 88% at typical (50%) load. Our tests are tougher than the ones conducted by Ecos Consulting (the company behind 80 Plus certification) because they test power supplies at 23° C, while we test them at double this temperature, and the higher temperature is, the lower efficiency is. That is why we got efficiency below 85% during full load (test five).
Voltage stability was another highlight from XFX 750 W Black Edition, with all 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). This includes the -12 V output, which usually doesn’t like to stay within a tolerance this tight.
And finally we have noise and ripple, which were low all the time: noise level at +12 V was below 30% 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.
Now let’s see if we could pull more than 750 W from this unit.
Below you can see the maximum we could pull from this power supply with it still working within ATX12V specs. If we tried to pull more than that, noise level on +12 V would jump above the maximum allowed (during this test noise level at +12 V was around 105 mV). See how under this extreme configuration efficiency was still around 83%.
33 A (396 W)
33 A (396 W)
15 A (75 W)
15 A (49.5 W)
3 A (15 W)
0.5 A (6 W)
% Max Load
XFX 750 W Black Edition power supply specs include:
* Researched at Newegg.com on the day we published this review.
Being based on Seasonic M12D, XFX 750 W Black Edition is as good as this model from Seasonic: very high efficiency, voltages very close to their nominal values (3% voltage regulation instead of 5%) and very low noise and ripple on its outputs. Plus we could pull over 900 W from it! The main difference between these two power supplies is the presence of a single +12 V rail on the XFX version. On pricing, XFX has the absolute advantage. Seasonic M12D 750 W is being harder to find these days, and costs USD 10 more than this model from XFX.
But it faces a hard competition from Corsair HX750W, which is also being sold for USD 150 and has similar performance. Therefore choosing between XFX 750 W Black Edition and Corsair HX750W is just a matter of personal taste for one brand or the other: both are terrific products.
In summary, XFX 750 W is an outstanding 750 W power supply, with a nice price tag for the user that is looking for a high-end power supply.