BFG MX-550 Power Supply Review
By Gabriel Torres on December 3, 2008


Introduction

Hardware Secrets Silver Award

The new MX series of power supplies from BFG features a modular cabling system, one 120 mm fan and one 80 mm fan that only kicks in when the temperature on the secondary heatsink is above 50° C. Let’s see if the 550 W model (MX-550 or BFGI550WMXPSU) is a good product.

BFG MX-550 Power Supply
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Figure 1: BFG MX-550.

By the way, power supplies from BFG MX series are internally identical to the ones from LS series. The difference between the two series lies on the presence of the modular cabling system and on the auxiliary 80 mm fan on the MX series, and also on the size of the main fan (120 mm on MX series but 135 mm on the LS series).

This power supply is 6 11/16” deep (17 cm), while we’ve seen some products on the same power range using a smaller form factor, 6 19/64” (160 mm) or even 5 ½” (140 mm) deep, but it is hard to make it smaller when a modular cabling system is used.

BFG MX-550 Power Supply
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Figure 2: BFG MX-550.

This unit has its main motherboard cable (20/24-pin connector) and the ATX12V/EPS12V cable (two ATX12V connectors that together form an EPS12V connector) coming directly from inside the power supply housing. They have a nylon sleeving that comes from inside the housing.

The modular cabling system has eight connectors, two reserved for the video card auxiliary power cables (lime green) and six for SATA and peripheral power connectors.

The unit comes with eight cables: one auxiliary power cable for video cards with a 6-pin connector, one auxiliary power cable for video cards with a 6/8-pin connector, one cable with three SATA power connectors, two cables with two SATA power plugs each, one cable with two standard peripheral power plugs and two cables with two standard peripheral power plugs and one floppy disk drive power plug each.

BFG MX-550 Power Supply
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Figure 3: Cables from the modular cabling system.

All wires used on this power supply are 18 AWG, which are adequate for a product on this power range.

MX-550 features active PFC, allowing BFG to sell it in Europe. As for efficiency, BFG says this unit has a minimum 80% efficiency.

This power supply is manufactured by Fore Point (one of the factories from Fortrex) and according to our contact at BFG it is based on their FP-165 design. This same design is currenty used by BFG LS series, so right now internally power supplies from these two series are identical. However, BFG will change the vendor from their LS series to Enhance Electronics in the near future, so they won't be internally identical forever.

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

A Look Inside The MX-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.

BFG MX-550 Power Supply
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Figure 4: Overall look.

BFG MX-550 Power Supply
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Figure 5: Overall look.

BFG MX-550 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.

This power supply is flawless on this stage, having two extra X capacitors and two extra Y capacitors.

BFG MX-550 Power Supply
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Figure 7: Transient filtering stage (part 1).

BFG MX-550 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 MX-550.

Primary Analysis

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

This power supply uses one GBU1006 rectifying bridge in its primary, capable of delivering up to 10 A at 100° C if a heatsink is used, which is the case. This is more than adequate rating for a 500 W power supply. The reason why is that at 115 V this unit would be able to pull up to 1,150 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 920 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.

BFG MX-550 Power Supply
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Figure 9: Rectifying bridge.

MX-550 uses two SPP16N50C3 power MOSFET transistors on its active PFC circuit, each one capable of delivering up to 10 A at 100° C (or 16 A at 25° C, see the difference temperature makes) in continuous mode, or up to 48 A in pulse mode.

The active PFC capacitor is Japanese from Matsushita (Panasonic) and labeled at 85° C.

BFG MX-550 Power Supply
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Figure 10: Active PFC transistors and diode.

This power supply uses two SPA16N50C3 power MOSFET transistors on the traditional two-transistor forward configuration on its switching section. These transistors are identical to the ones used on the active PFC circuit except for the packaging (TO220 vs. TO220FP).

BFG MX-550 Power Supply
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Figure 11: Switching transistors.

The primary is controlled by a CM6800 integrated circuit installed on a small printed circuit board. This component is the most popular PWM/PFC combo controller.

BFG MX-550 Power Supply
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Figure 12: PFC/PWM controller.

Secondary Analysis

BFG MX-550 has four Schottky rectifiers on its secondary, two for the +12 V output, one for the +5 V output and one for the +3.3 V output.

The +12 V output is produced by two STPS30L60CT Schottky rectifiers connected in parallel, each one capable of handling up to 30 A at 130° C (15 A per internal diode). The maximum theoretical current the +12 V 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 (which in this case is made by two 15 A diodes in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 43 A or 514 W for the +12 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.

The +5 V output is produced by one SBR30U30CT Schottky rectifier, which is capable of handling up to 30 A at 140° C (15 A per internal diode). The maximum theoretical current the +5 V 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 (which in this case is made by one 15 A diode). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 21 A or 107 W for the +5 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.

The +3.3 V output is produced by one SPR30L40CT Schottky rectifier, which is capable of handling up to 30 A at 110° C (15 A per internal diode). The maximum theoretical current the +12 V 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 (which in this case is made by one 15 A diode). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 21 A or 71 W for the +3.3 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.

It is always good to remember that the real current/power limit for each output will depend on other factors, like the coils and the width of the printed circuit board traces.

BFG MX-550 Power Supply
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Figure 13: +12 V rectifier and +5 V rectifier.

BFG MX-550 Power Supply
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Figure 14: +3.3 V rectifier and +12 V rectifier.

The +5VSB output is rectified by an SR560 diode (5 A limit).

This power supply uses a PS223 monitoring integrated circuit, which features the following protections: over current (OCP), over temperature (OTP, although this power supply does not implement this protection), over voltage (OVP) and under voltage (UVP). As you see the only protection missing is over power protection (OPP).

BFG MX-550 Power Supply
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Figure 15: Monitoring integrated circuit.

As you can see in Figure 13, this power supply has two thermal sensors, one for each fan. We don’t understand why the manufacturer didn’t implement over temperature protection (OTP), as the monitoring integrated circuit has this protection, the only thing that would be needed was an additional thermal sensor.

All the electrolytic capacitors from the secondary are from JunFu and labeled at 105° C, as usual.

Power Distribution

In Figure 16, you can see the power supply label containing all the power specs.

BFG MX-550 Power Supply
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Figure 16: Power supply label.

This power supply features four +12 V virtual rails distributed like this:

We think this distribution is perfect.

Now let’s see if this power supply can really deliver 550 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.

+12V1 and +12V2 are the two independent +12V inputs from our load tester and during out tests the +12V1 input was connected to the power supply +12V1 (main motherboard cable and peripheral power connectors) and +12V3 rails (video card auxiliary power connector), while the +12V2 input was connected to the power supply +12V1 rail (EPS12V connector).

Input

Test 1

Test 2

Test 3

Test 4

Test 5

+12V1

4 A (48 W)

8 A (96 W)

12 A (144 W)

16 A (192 W)

20 A (240 W)

+12V2

4 A (48 W)

8 A (96 W)

12 A (144 W)

16 A (192 W)

20 A (240 W)

+5V

1 A (5 W)

2 A (10 W)

4 A (20 W)

5 A (25 W)

6 A (30 W)

+3.3 V

1 A (3.3 W)

2 A (6.6 W)

4 A (13.2 W)

5 A (16.5 W)

6 A (19.8 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

115.9 W

223.3 W

338.0 W

442.0 W

544.9 W

% Max Load

21.1%

40.6%

61.5%

80.4%

99.1%

Room Temp.

46.9° C

46.9° C

47.3° C

47.3° C

50.1° C

PSU Temp.

49.1° C

49.1° C

50.3° C

50.3° C

53.1° C

Voltage Stability

Pass

Pass

Pass

Pass

Pass

Ripple and Noise

Pass

Pass

Pass

Pass

Pass

AC Power

134 W

254 W

391 W

523 W

668 W

Efficiency

86.5%

87.9%

86.4%

84.5%

81.6%

Final Result

Pass

Pass

Pass

Pass

Pass

BFG MX-550 showed to be an excellent product. It could deliver its labeled power at 50° C.

If you pull up to 80% (440 W) from it, it will deliver at least 84.5% efficiency. Working with it at up to 60% (330 W) from its labeled maximum capacity you will see efficiency between 86% and 88%, which is terrific. Pulling its full labeled power efficiency dropped to 81.6% – not as great as the other results but still above the 80% mark.

Voltage stability was impressive, with all outputs always within 3% from their nominal values (the maximum allowed is 5% – 10% for -12 V), including -12 V.

Noise level was always far below the maximum allowed. During test number five (550 W) this unit presented a noise level of 22.6 mV at +12V1, 24 mV at +12V2, 16.6 mV at +5 V and 13.4 mV at +3.3 V. Just to remember, the maximum allowed for the +12 V outputs is 120 mV and the maximum allowed for the +5 V and +3.3 V outputs is 50 mV. All these values are peak-to-peak figures.  

Now let’s see if we could pull even more power from MX-550.

Overload Tests

Before overloading power supplies we always test first if the over current protection (OCP) circuit is active and at what level it is configured.

OCP kicked in when we tried to pull more than 25 A from +12V2 input from our load tester (which was connected to the power supply +12V2 through the ATX12V/EPS12V cable). The label says that each rail has a limit of 20 A, so OCP was configured the way we like: close to the limit printed on the label.

The problem, however, was that whenever we tried to overload the reviewed power supply, it would shut down in less than one minute. If this power supply implemented over temperature protection (OTP) we would say that this was the protection that entered in action, but that was not the case. Our best guess was that over current protection (OCP) or over load (OPP) entered in action after currents increased with temperature.

Then we decreased the currents we were pulling with our load tester and tried again to overload the unit, with the same results.

On our third try the power supply silently died. After we disassembled the unit we could see that we burned one of the +12 V rectifiers.

So this power supply failed our overload tests.

Another thing that we noticed during our reviews was that the auxiliary 80 mm fan was not entering in action, even thought the temperature inside our “hot box” was at 50° C and the power supply housing was measuring 53° C. With the tip of a pencil we manually moved the blades of the fan and it started spinning. So we have to give BFG the benefit of the doubt and assume that this was a problem with the sample we’ve got.

Main Specifications

BFG MX-550 power supply specs include:

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

Conclusions

BFG MX-550 proved to be an excellent product if you stay inside its maximum labeled power.

If you pull up to 80% (440 W) from it, it will deliver at least 84.5% efficiency. Working with it at up to 60% (330 W) from its labeled maximum capacity you will see efficiency between 86% and 88%, which is terrific. Pulling its full labeled power efficiency dropped to 81.6% – not as great as the other results but still above the 80% mark.

Electrical noise level was very low, far below the maximum allowed, and the voltages were always within 3% from their nominal values.

We had two problems with this power supply. The first one was that it burned when we tried to overload it. It is good to remind, however, that the power supply protections entered in action and shut it down three times before we finally killed it. It is clear to us that this was an overheating issue and thus it would be better if BFG had used +12 V rectifiers with a bigger dissipation area (technical talk: used rectifiers with TO-247 packaging instead of TO-220).

The second issue was that the auxiliary fan didn’t kick in automatically: we had to manually rotate it with the tip of a pencil in order to turn in on. Maybe this was one of the reasons that lead the secondary heatsink to overheat and burn the +12 V rectifier.

These issues, however, won’t affect 99.99% of the users, so if you are a regular user you should not worry about them (we have to give BFG the benefit of the doubt on the fan issue and assume that we got a defective unit).

Another very important thing that affect all users: warranty. You have to register your power supply with BFG within 30 days of its purchase, otherwise you will only get a two-year warranty instead of the full five-year one. This is really tricky, as most users do not register their products with the manufacturer.

This power supply competes in price and features with Antec NeoPower 550 W, a power supply that achieved the same results as BFG MX-550 (high efficiency between 83.3% and 88%, low noise and ripple and perfect stability) in our tests and that we could overload up to 650 W with no problem (this model from Antec uses rectifiers with TO-247 packaging instead of TO-220 – in English: the rectifiers are physically biggers, allowing a better heat dissipation). Honestly, between the two our recommendation is the model from Antec , since we had no issues with it and it provides a little bit higher efficiency when delivering 550 W – plus no product registration is needed to get full 5-year warranty with Antec.

This does not mean that MX-550 isn’t a good product that will certainly please the average user.

Originally at http://www.hardwaresecrets.com/article/BFG-MX-550-Power-Supply-Review/665


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