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[nextpage title=”Introduction”]

LS and MX are sister power supply series from BFG, with models from MX series coming with a modular cabling system, a 120 mm fan and an auxiliary 80 mm fan on the rear, while models from LS series use a 135 mm fan and no modular cabling system or second fan. Initially both series used the same internal design, however this is not entirely true anymore. All models from MX series are manufactured by Fore Point (one of the factories from Fortrex), but LS-450 and the new version of LS-550 (marked as “LS-550 (New)” on their website, being the model we are reviewing today) are manufactured by Enhance. The old LS-550 and LS-680 are manufactured by Fore Point with the same design as models from MX series. According to BFG they will move all models from MX and LS to Enhance in the future, and when this happens units will be either released with new wattages (e.g., LS-700 instead of LS-680) or will have the name “New” added to their name.

Enhance Electronics is the manufacturer behind power supplies from Akasa, Real Power Pro series from Cooler Master and TruePower Quattro series from Antec. Keep in mind that not all models from these two brands are manufactured by Enhance.

We have already reviewed LS-450, so we will be able to provide a comparison between LS-450 and LS-550.

BFG LS-550 (New) power supplyFigure 1: BFG LS-550 (New) power supply.

BFG LS-550 (New) power supplyFigure 2: BFG LS-550 (New) power supply.

LS-550 is bigger than LS-450, being 6 19/64” (160 mm) deep, basically because it uses a bigger fan (135 mm vs. 120 mm). The reviewed unit has active PFC, of course.

All cables use a nylon protection and all come from inside the power supply housing, as you can see in Figure 2. The included cables are:

  • Main motherboard cable with a 20/24-pin connector.
  • ATX12V/EPS12V cable with two ATX12V connectors that together form one EPS12V connector.
  • One auxiliary power cable for video cards with one six-pin video card power connector and one six/eight-pin video card power connector.
  • Two SATA power cables with three SATA power connectors each.
  • One peripheral power cable with three standard peripheral power plugs and one floppy disk drive power connector.
  • One peripheral power cable with three standard peripheral power plugs.

The only difference between LS-450 and LS-550 (New) here is the presence of a second video card power cable attached to the only cable available. Of course having these connectors on separated cables is better.

All cables have 20 ½” (52 cm) between the power supply housing and the first connector on the cable, and on cables with more than one connector there is 5 ½” (140 mm) between connectors. All wires are 18 AWG, which is the correct gauge to be used.

This unit presents a satisfactory number of connectors for an entry-level or mainstream PC with only one video card installed.

BFG LS-550 (New) power supplyFigure 3: Cables.

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

[nextpage title=”A Look Inside The LS-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.

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.

BFG LS-550 (New) power supplyFigure 4: Overall look.

BFG LS-550 (New) power supplyFigure 5: Overall look.

BFG LS-550 (New) power supplyFigure 6: Overall look.

[nextpage title=”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, with two X capacitors, one X capacitor after the rectifying bridge and two Y capacitors more than required.

BFG LS-550 (New) power supplyFigure 7: Transient filtering stage (part 1).

BFG LS-550 (New) power supplyFigure 8: Transient filtering stage (part 2).

In the next page we will have a more detailed discussion about the components used in the BFG LS-550 (New).

[nextpage title=”Primary Analysis”]

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

This power supply uses one GBU1006 rectifying bridge in its primary, which can deliver up to 10 A at 100° C. This component is clearly overspec’ed: 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 a
bout this component and the real limit will depend on all other components from the power supply. LS-450 uses an 8 A bridge.

BFG LS-550 (New) power supplyFigure 9: Rectifying bridge.

On the active PFC circuit one SPW47N60C3 power MOSFET transistors is used, capable of delivering up to 47 A at 25° C or 30 A at 100° C in continuous mode (note the difference temperature makes) or 141 A in pulse mode at 25° C, presenting a resistance of 70 mΩ when turned on, a characteristic called RDS(on) – the lower this number the higher efficiency is. Like LS-450, this unit uses only one transistor on the active PFC circuit. The transistor used on LS-450 has lower current specs (to 32 A at 25° C or 20 A at 100° C).

The active PFC capacitor is Japanese from Chemi-Con and labeled at 105° C. This is good for two reasons. Usually manufacturers use 85° C capacitors here, so it is good to see a manufacturer using a capacitor with a higher temperature rating. Secondly, Japanese capacitors don’t suffer from leakage problems.

In the switching section, two STP20NM50FD power MOSFET transistors are used on the traditional two-transistor forward configuration. Each one is capable of delivering up to 20 A at 25° C or 14 A at 100° C in continuous mode (note the difference temperature makes) or 80 A in pulse mode at 25° C, with a maximum RDS(on) of 250 mΩ. BFG LS-450 uses transistors with lower current limits here (12 A at 25° C or 7.5 A at 100° C).

BFG LS-550 (New) power supplyFigure 10: One of the switching transistors, active PFC diode and active PFC transistor.

The primary is controlled by a CM6806A PFC/PWM combo controller.

BFG LS-550 (New) power supplyFigure 11: PFC/PWM combo controller.

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

[nextpage title=”Secondary Analysis”]

This power supply uses four Schottky rectifiers on its secondary.

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 two 40CPQ060 Schottky rectifiers, each one with a maximum current limit of 40 A (20 A per diode at 120° C, 0.49 V voltage drop). This gives us a maximum theoretical current of 57 A or 686 W for the +12 V output.

The +5 V output is produced by one STPS60L45CW Schottky rectifier, capable of delivering up to 60 A (30 A per internal diode at 135° C, voltage drop of 0.50 V). This means the +5 V output has a maximum theoretical current of 43 A or 214 W.

The +3.3 V output is produced by another STPS60L45CW Schottky rectifier, giving us a maximum theoretical current of 43 A or 141 W for the +3.3 V output.

BFG LS-550 (New) power supplyFigure 12: +3.3 V, +5 V and the two +12 V rectifiers.

The outputs are monitored by a PS223 integrated circuit, which supports the following protections: over current (OCP), under voltage (UVP), over voltage (OVP) and over temperature (OTP, not implemented on this power supply). Any other protection that this unit may have is implemented outside this integrated circuit.

BFG LS-550 (New) power supplyFigure 13: Monitoring integrated circuit.

Most electrolytic capacitors from the secondary are also Japanese, from Chemi-Con, but some models are from Teapo (Taiwanese company).

In summary, even though LS-450 and LS-550 (New) are based on the same project, all main components were upgraded on LS-550. This is really nice to see, because some manufacturers when releasing a power supply with a higher wattage only replaces the secondary rectifiers, not upgrading the primary.

[nextpage title=”Power Distribution”]

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

BFG LS-550 (New) power supplyFigure 14: Power supply label.

This power supply uses a single-rail design, so there is nothing to talk about here. Keep in mind that the difference between a single-rail design and a multiple-rail design is how the over current protection (OCP) circuit is connected. On single-rail design there is only one OCP circuit monitoring all outputs, while on multiple-rail design there are several OCP circuits, each one monitoring a group of wires called “rails.”

Now let’s see if this power supply can really deliver 550 W.[nextpage title=”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 our tests both were connected to the single +12 V provided by this power supply.

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 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 112.8 W 215.0 W 328.5 W 430.5 W 531.1 W
% Max Load 20.5% 39.1% 59.7% 78.3% 96.6%
Room Temp. 45.6° C 47.2° C 45.8° C 48.7° C 45.9° C
PSU Temp. 47.5° C 48.1° C 45.9° C 48.6° C 50.1° C
Voltage Stability Fail on -12 V Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power 133.4 W 250.8 W 388.8 W 520.6 W 661.0 W
Efficiency 84.6% 85.7% 84.5% 82.7% 80.3%
AC Voltage 113.1 V 111.7 V 110.3 V 109.5 V 107.4 V
Power Factor 0.956 0.950 0.961 0.969 0.976
Final Result Pass Pass Pass Pass Pass

The new version from BFG LS-550 presents a high efficiency between 84.5% and 85.7% if you pull between 20% and 60% (between 110 W and 330 W) from its labeled wattage. Delivering 80% from its labeled capacity (440 W) efficiency dropped to 82.7%, still a very decent number. At full load (550 W) efficiency dropped to 80.3%, still above the 80% mark.

The only problem we saw was voltage level at -12 V. This output has a higher 10% tolerance, so it can be anywhere between -13.2 V and -10.8 V. During test number one this output was at -10.78 V, passing this limit by 0.02 V. During test two it was touching the limit at -10.87 V, during test three it was at -10.99 V, during test four it was at -11.08 V and during test five it was at -11.19 V. We saw the same thing happening with LS-450.

Ripple and noise stayed inside specs, although they were higher than competing products. Below you see the waveforms during test number five. Just to remember, the maximum allowed is 120 mV at +12 V and 50 mV at +5 V and +3.3 V. All values are peak-to-peak.

BFG LS-550 (New) power supplyFigure 15: +12V1 rail with power supply delivering 531.1 W (86.8 mV).

BFG LS-550 (New) power supplyFigure 16: +12V2 rail with power supply delivering 531.1 W (79.6 mV).

BFG LS-550 (New) power supplyFigure 17: +5V rail with power supply delivering 531.1 W (31.4 mV).

BFG LS-550 (New) power supplyFigure 18: +3.3 V rail with power supply delivering 531.1 W (32.4 mV).

Now let’s see if we could pull more than 550 W from this unit.

[nextpage title=”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.

In order to do that we increased current on the +12 V rail until the power supply shut down. This happened when we tried to pull more than 47 A from it.

Manufacturers always leave a margin between what is written on the label (42 A in this case) and the level the OCP circuit is really configured (47 A in this case). We always like to see this margin as tight as possible.

Then starting from test five we increased currents to the maximum we could with the power supply still running inside ATX specs. The results are below. When we tried to increase one more amp at any output ripple and noise at +12 V would increase above the maximum allowed (120 mV).

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 during our overload tests.

Input Maximum
+12V1 23 A (276 W)
+12V2 23 A (276 W)
+5V 9 A (45 W)
+3.3 V 9 A (29.7 W)
+5VSB 2.5 A (12.5 W)
-12 V 0.5 A (6 W)
Total 624.8 W
% Max Load 113.6%
Room Temp. 43.8° C
PSU Temp. 41.6° C
AC Power 804.0 W
Efficiency 77.7%
AC Voltage 108.2 V
Power Factor 0.980

[nextpage title=”Main Specifications”]

BFG LS-550 (New) power supply specs include:

  • ATX12V 2.2
  • Nominal labeled power: 550 W at 40° C.
  • Measured maximum power: 624.8 W at 43.8° C.
  • Labeled efficiency: 80% minimum (80 Plus certified)
  • Measured efficiency: Between 80.3% and 85.7% at 115 V (nominal, see complete results for actual voltage).
  • Active PFC: Yes.
  • Modular Cabling System: No.
  • Motherboard Power Connectors: One 24-pin 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.
  • SATA Power Connectors: Six in two cables.
  • Peripheral Power Connectors: Six in two cables.
  • Floppy Disk Drive Power Connectors: One.
  • Protections: Over current (OCP, tested and working), over voltage (OVP, not tested) and short-circuit protection (SCP, tested and working).
  • Warranty: Five years if registered 30 days after purchase, otherwise warranty if only of 2 years.
  • More Information: https://www.bfgtech.com
  • Average price in the US: N/A.

[nextpage title=”Conclusions”]

The LS-550 (New) proved to be a good mainstream 550 W unit, providing a decent efficiency between 84.5% and 85.7% if you pull between 20% and 60% (between 110 W and 330 W) from its labeled wattage. Delivering 80% from its labeled capacity (440 W) efficiency dropped to 82.7%, still a very decent number. At full load (550 W) efficiency dropped to 80.3%, still above the 80% mark.

Ripple and noise we
re always below the maximum allowed.

Compared to LS-450, even though they are based on the same project, all main components were upgraded on LS-550. This is really nice to see, because some manufacturers when releasing a power supply with a higher wattage only replaces the secondary rectifiers, not upgrading the primary.

A very important thing to keep in mind if you buy this unit: 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.

The only problem right now is finding this power supply for sale; it looks like it is on its final days.