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[nextpage title=”Introduction”]

HX620W (also known as CMPSU-620HX) is a power supply that Corsair claims can deliver its rated power at 50° C, and featuring a modular cabling system, a big 120 mm fan, active PFC, high efficiency and two video card power cables for you to feed your SLI or CrossFire system. We completely disassembled this power supply to see the components and design used and also tested to see if it can really deliver its labeled 620 W.

Corsair HX620W Power SupplyFigure 1: Corsair HX620W.

Corsair HX620W Power SupplyFigure 2: Corsair HX620W.

HX620W features high-efficiency and active PFC. According to Corsair this power supply has an efficiency of at least 80% (compare to less than 70% on regular power supplies), meaning less power loss – an 80% efficiency means that 80% of the power pulled from the power grid will be converted in power on the power supply outputs and only 20% will be wasted. This translates into less consumption from the power grid (as less power needs to be pulled in order to generate the same amount of power on its outputs), meaning lower electricity bills.

Active PFC (Power Factor Correction), on the other hand, provides a better usage of the power grid and allows this power supply to be comply with the European law, making Corsair able to sell it in that continent (you can read more about PFC on our Power Supply Tutorial). In Figure 1, you can see that this power supply doesn’t have an 110V/220V switch, feature available on power supplies with active PFC.

This power supply uses a very good cooling solution. Instead of having a fan on its back, its fan is located at the bottom of the unit, as you can see in Figure 1 (the power supply is upside down). A mesh replaced the back fan, as you can see. Since the fan used is bigger than fans usually used on power supply units, this unit is not only quieter than traditional power supplies, but also provides a better airflow.

In Figure 3, you can see this power supply modular cabling system, used by its peripheral cables. In Figure 4, you can see the peripheral cables that come with this unit.  Corsair made a minor change to the cables that come with this unit since the first time we looked at it (Sep 2006), upgrading the video card power cables from 6-pin connectors to 6/8-pin connectors.

Corsair HX620W Power SupplyFigure 3: Modular cabling system.

Corsair HX620WFigure 4: Peripheral cables that come with this unit.

This power supply comes with 11 peripheral power cables: two 6/8-pin PCI Express auxiliary power cables for video cards (6-pin on older units); peripheral power cables containing two standard peripheral power connectors each; two peripheral power cables containing three standard peripheral power connectors each; two Serial ATA power cables containing three SATA power connectors each; one Serial ATA power cable containing two SATA power connectors; one floppy disk drive "Y" adapter containing one standard power connector at one end and two floppy disk drive power connectors at the other end; and one fan “Y” adapter allowing you to connect two fans to a single peripheral power connector.

[nextpage title=”Introduction (Cont’d)”]

All wires used on all peripheral cables are black instead of using colored wires (black, yellow, red and orange), as you can see in Figure 4. On each cable the wires are stuck together, which is great, as you won’t have loose wires inside your case blocking the PC internal airflow.

Corsair HX620W Power SupplyFigure 5: On each cable all wires are stuck together.

Like power supplies from Enermax, this unit comes with a plastic pouch for you to store the peripheral cables that aren’t being used at the moment.

Corsair HX620W Power SupplyFigure 6: Plastic pouch for storing the peripheral cables.

From the power supply comes three cables: the main motherboard cable with a 20/24-pin connector, an ATX12V cable and an EPS12V cable. A plastic sleeving protects all cables.

The 24-pin motherboard connector can be easily transformed into a 20-pin one, as you can see in Figure 7.

Corsair HX620W Power SupplyFigure 7: Transforming its 24-pin power connector into a 20-pin one.

The gauge of all main wires is 18 AWG.

This power supply is really manufactured by Seasonic, as we found out reading its UL number. Taking a look at Seasonic’s website, we couldn’t find any model that matched HX620W, however it seems that HX620W is actually a model from Seasonic S12 series.

We decided to fully disassemble this power supply to take a look inside.

[nextpage title=”A Look Inside The HX620W”]

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.

In this page, we will have an overall look, while in the next page we will discuss in details the quality and rating of the components used.

We can point out several differences between this power supply and a low-end (a.k.a. “generic”) one: the construction quality of the printed circuit board (PCB); the use of more components on the transient filtering stage; the active PFC circuitry; the power rating of all components; the design; etcetera.

On Figures 8 and 9 you can have an overall look from inside this power supply.

Corsair HX620W Power SupplyFigure 8: Inside HX620W.

Corsair HX620W Power SupplyFigure 9: Inside HX620W.

[nextpage title=”Transient Filtering Stage”]

As we mentioned in other articles, 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 than that, usually removing the MOV, which is essential for cutting spikes coming from the power grid, and the first coil.

This power supply from Corsair uses one MOV, four ceramic capacitors, one metalized polyester capacitors and three ferrite coils, plus a ferrite bead on the main power cord, so it has one coil more than required.

Corsair HX620W Power SupplyFigure 10: Transient filtering stage (part 1).

Corsair HX620W Power SupplyFigure 11: Transient filtering stage (part 2).

[nextpage title=”Primary Analysis”]

We were very curious to check what components were chosen for the power section of this power supply and also how they were set together, i.e., the design used. We were willing to see if the components could really deliver the power announced by Corsair.

From all the specs provided on the databook of each component, we are more interested on the maximum continuous current parameter, given in ampères or amps for short. To find the maximum theoretical power capacity of the component in watts we need just to use the formula P = V x I, where P is power in watts, V is the voltage in volts and I is the current in ampères.

We also need to know under which temperature the component manufacturer measured the component maximum current (this piece of information is also found on the component databook). The higher the temperature, the lower current semiconductors can deliver. Currents given at temperatures lower than 50° C are no good, as temperatures below that don’t reflect the power supply real working conditions.

Keep in mind that this doesn’t mean that the power supply will deliver the maximum current rated for each component as the maximum power the power supply can deliver depends on other components used – like the transformer, coils, the PCB layout and the wire gauge – not only on the specs of the main components we are going to analyze.

For a better understanding of what we are talking here, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBJ1506 rectifying bridge in its primary stage, which can deliver up to 15 A (rated at 100° C). This component is clearly overspec’ed: at 115 V this unit would be able to pull up to 1,725 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 1,380 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.

Four power MOSFET transistors are used on this power supply primary, two on the active PFC circuit and two on the switching section. On the active PFC circuit two 20N60C3 are used. These transistors have a maximum rated current of 45 A each at 25° C or 20 A at 110° C in continuous mode, or up to 300 A at 25° C in pulsating mode.

On the switching section two FQPF18N50V2 power MOSFET transistors in two-transistor forward switcher configuration are used, and each one has a maximum rated current of 72 A in pulsating mode, which is the mode used, as the PWM circuit feeds these transistors with a square waveform. In continuous mode they can deliver up to 18 A @ 25° C or up to 12.1 A @ 100° C.

Corsair HX620W Power SupplyFigure 12: MOSFET transistors used on the primary.

For a better understanding on the relationship between these transistors, we drew a simplified diagram of this section of HX620W power supply, see Figure 13.

Corsair HX620W Power SupplyFigure 13: Simplified diagram of this power supply showing the location of its four MOSFET transistors.

A very interesting feature from this power supply is that its fuse is inside a fireproof rubber protection. So this protection will prevent the spark produced on the minute the fuse is blown from setting the power supply on fire.

The primary section is controlled by a UCC28515 integrated circuit, which is an active PFC and PWM controller combo. It is located on a small printed circuit board shown in Figure 14.

Corsair HX620W Power SupplyFigure 14: Active PFC and PWM controller integrated circuit.

[nextpage title=”Secondary Analysis”]

This power supply uses four Schottky rectifiers on its secondary. 

The +12 V output is produced by two STPS6045CW Schottky rectifiers connected in parallel, which can deliver up to 60 A each (30 A per internal diode, measured at 130° C). 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 30 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 86 A or 1,029 W for the +12 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used. As you can see the rectifiers are highly overspec’ed.

The +5 V output is produced by one STPS60L30CW Schottky rectifier, also supporting up to 60 A (30 A per internal diode, measured at 130° C). 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 30 A diode). Just as an exercise, we ca
n assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 43 A or 214 W for the +5 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.

And the +3.3 V output is produced by one STPS30L30CT Schottky rectifier, supporting up to 30 A (15 A per internal diode, measured at 140° C). Using the same math this would equal 21 A or 71 W. As mentioned, the maximum current this line can really deliver will depend on other factors.

Even though the +5 V line and the +3.3 V line have separated rectifiers, they share the same transformer output. So the maximum current both lines can deliver will depend a lot on the transformer.

On Figures 15 and 16 you can see the four power Schottky rectifiers used on the secondary section of this power supply and a 7805 voltage regulator which is probably used to simulate a load and allow the power supply to turn on.

Corsair HX620W Power SupplyFigure 15: Power rectifiers used on the secondary.

Corsair HX620WFigure 16: Power rectifiers used on the secondary.

This power supply uses a semiconductor thermal sensor, which is very small and installed on the solder side of the printed circuit board, right below the transformer ground outputs. This sensor is used to control the fan speed according to the power supply internal temperature.

Corsair HX620WFigure 17: Thermal sensor.

On this power supply all electrolytic capacitors are rated at 105° C and the capacitors from the secondary are Japanese, from Chemi-Con.

[nextpage title=”Power Distribution”]

In Figure 18, you can see HX620W label stating all its power specs.

Corsair HX620W Power SupplyFigure 18: Power supply label.

As you can see the label says this power supply has three +12V rails. These rails are “virtual” as all of them are connected together to the single +12 V “real” rail coming from the +12 V rectifiers through a series of jumpers (a.k.a. “shunts”).

Each virtual rail, at least in theory, has its own over current protection (OCP) and that is why they are listed as individual rails even though they are all connected to the same place inside the power supply. From what the label says the over current protection is configured to shut down the power supply if you pull more than 18 A in any of the three rails (usually the over current protection circuit is set with a value a little bit higher than what is written on the label). At least in theory, as during our tests we pulled a lot more than 18 A on +12V1 rail and the power supply didn’t shut down (but let’s not get ahead of ourselves; more about this in the next page).

This power supply, however, has only two virtual rails (+12V1 and +12V2), not three, as you can see on Figures 19, 20 and 21 (Figures 19 and 20 were taken with the version of Corsair HX620W we looked in Sep 2006; the version currently on the market – Feb 2008 – uses a  slight different wire configuration, as shown in Figure 21). Corsair explained to us that the OCP connection wasn’t being made on the printed circuit board like it is normally done, but directly on the +12 V wires, and that we shouldn’t consider what was on the printed circuit board. We, however, couldn’t find any evidence of this happening (if OCP was connected to the +12 V wires instead of to the jumpers located on the PCB we should see one wire connecting each claimed +12 V virtual rail to the OCP circuit, which we couldn’t find).

Corsair HX620W Power SupplyFigure 19: +12 V wires are separated into two groups (there is no 12V3 virtual rail inside the PSU).

Corsair HX620W Power SupplyFigure 20: But they are connected to the same +12 V line on the PCB.

Corsair HX620WFigure 21: +12 V wire distribution on the model currently on the market (Feb 2008).

On the model currently on the market, +12V distribution is the following:

  • +12V1: Modular cabling system, EPS12 V.
  • +12V2: Main motherboard connector, ATX12V.

Unless, of course, Corsair is right and there are three virtual rails using an exotic configuration we weren’t able to figure out. If we are right, we would like to see EPS12V on the second rail for better power distribution.

[nextpage title=”Load Tests”]

We conducted several tests with this power supply, as described in the article Hardware Secrets Power Supply Test Methodology. All the tests described below were taken with a room temperature between 45.5° and 50° C. During our tests the power supply temperature was between 50° and 56° C.

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.

+12V2 is the second +12V input of our load tester and on this test it was connected to the power supply EPS12V connector.

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.

Input Test 1 Test 2 Test 3 Test 4 Test 5
+12V1 5 A (60 W) 10 A (120 W) 14 A (168 W) 18.5 A (222 W) 25.5 A (306 W)
+12V2 4 A (48 W) 8.5 A (102 W) 13 A (156 W) 18 A (216 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) 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) 0.8 A (9.6 W)
Total 128 W 250 W 374 W 498 W 618 W
% Max Load 20.6% 40.3% 60.3% 80.3% 99.7%
Result Pass Pass Pass Pass Pass
Voltage Regulation Pass Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power 149 W 284 W 432 W 585 W 745 W
Efficiency 85.9% 88.0% 86.6% 85.1% 82.9%

Corsair HX620W proved to be an outstanding power supply. As you can see, it could deliver its rated power with a room temperature of 50° C, which is impressive. This power supply also provides one of the best efficiencies on the market. At full load it presented an 83% efficiency and at 40% load (250 W) it presented an amazing 88% efficiency.

Voltage stability was also one of the highlights during our tests. All outputs were within 3% of the nominal voltage during all tests, which is outstanding, as ATX spec states that regulation should be within 5%. Translation: the voltages were closer to their nominal values than what is stated by the ATX standard.

Electrical noise was also at a very low level (always below 40 mV on +12 V, below 8 mV on +5 V and below 7 mV on +3.3 V – ATX spec states a maximum noise level of 120 mV for +12 V and 50 mV for both +5 V and +3.3 V outputs), and we really impressed by that, because the Corsair TX750W power supply we reviewed recently had a very high noise level. The reason of the difference is probably due to the different manufacturer of the power supply – HX620W is manufactured by Seasonic, while TX750W is manufactured by CWT.

Just to put things into perspective, the noise level achieved by Corsair HX620W was lower than PC Power and Cooling Silencer 610 EPS12V, a product that has a very low noise level. This is simply fantastic.

Below we show the noise level we found on the power supply outputs while the unit was operating at its full load (test number five): +12V1 input was at 38.6 mV, +12V2 input was at 34.4 mV, +5 V input was at 7.8 mV and +3.3 V input was at 6.8 mV. Great numbers.

Corsair HX620WFigure 22: Noise level at +12V1 input of the load tester.

Corsair HX620WFigure 23: Noise level at +12V2 input of the load tester.

Corsair HX620WFigure 24: Noise level at +5V input of the load tester.

Corsair HX620WFigure 25: Noise level at +3.3V input of the load tester.

[nextpage title=”Overload Tests”]

After these tests we tried to pull even more power from Corsair HX620W. Below you can see the maximum amount of power we could extract from this unit keeping it working with its voltages and electrical noise level within the proper working range. During this test room temperature was of 48° C and the power supply was working at 58° C.

Input Maximum
+12V1 28 A (336 W)
+12V2 27 A (324 W)
+5V 8 A (40 W)
+3.3 V 8 A (26.4 W)
+5VSB 3 A (15 W)
-12 V 0.8 A (9.6 W)
Total 746 W
% Max Load 120%
AC Power 901 W
Efficiency 82.8%

Under this extreme condition noise level continued very low, at 43 mV on +12V1 and 38.2 mV on +12V2, as you can see below. This is really good.

Corsair HX620WFigure 26: Noise level at +12V1 input from the load tester at 750 W.

Corsair HX620WFigure 27: Noise level at +12V2 input from the load tester at 750 W.

We tried to push this unit above 750 W but the unit started working outside its specs, or the ripple all of the sudden would do far above 120 mV or the voltages would drop to values outside the working range.

We didn’t see over power protection or over current protection in action, as the power supply turned on with values that were making it to work outside its specs. For testing over current protection (OCP) we pulled 33 A from EPS12V (the maximum we could configure using our load tester) putting all other connectors to pull a low value (5 A) and the power supply worked just fine, and the power supply didn’t shut down as it should. At least it didn’t burn, which is another good thing about this power supply.

Short-circuit protection worked just fine.

During our tests 3, 4 and 5 the power supply generated a not so loud high pitch noise.

Another great feature about this power supply is its fan. When the power supply is cool, it runs very slowly, making almost no noise. But even when it was operating at full load and the fun spinning at its full speed, noise level was very low, making this power supply one of the most silent power supplies we have reviewed to date.

[nextpage title=”Main Specifications”]

Corsair HX620W power supply specs include:

  • ATX12V 2.2
  • Nominal labeled power: 620 W at 50° C.
  • Measured maximum power: 746 W at 48° C.
  • Labeled efficiency: minimum 80%.
  • Measured efficiency: 82.9% to 88.0% at 115 V.
  • Active PFC: Yes.
  • Motherboard Connectors: One 20/24-pin connector, one ATX12V connector and one EPS12V connector.
  • Peripheral Connectors: two 6/8-pin PCI Express auxiliary power cables; two peripheral power cables containing two standard peripheral power connectors each; two peripheral power cables containing three standard peripheral power connectors each; two Serial ATA power cables containing three SATA power connectors each; one Serial ATA power cable containing two SATA power connectors; one “Y” adapter for floppy disk driv
    es containing one standard power connector at one end and two floppy disk drive power connectors at the other end; and one fan “Y” adapter allowing you to connect two fans to a single peripheral power connector.
  • Protections: short-circuit (SCP), over current (OCP), over voltage (OVP), over power (OPP) and under voltage (UVP).
  • Warranty: 5 years.
  • More Information: https://www.corsair.com
  • Real Model: Seasonic S12
  • Average price in the US*: USD 160.00

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

[nextpage title=”Conclusions”]

Corsair HX620W is a terrific power supply and won’t let you down. In our tests it could really deliver its labeled power at 50° C, showed a terrific voltage regulation, it was very quiet, produced a very low electrical noise level and its efficiency was of at least 83%, peaking 88%. And the best of all: we could extract up to 746 W from it. So you will be basically paying for a 620 W product and bringing home a 740 W power supply.

We like modular cabling systems as you can add only the cables you will really use, keeping your computer organized and helping the PC internal airflow – the fewer things on the way, the better. And this unit provides more cables and connectors than you probably need.

First it has two video card power cables – now with 8-pin option, saving you headaches if the 8-pin plug becomes standard on forthcoming video cards –, which is required if you have or are thinking of an SLI or CrossFire system. Second, it provides a total of eight SATA power connectors – even the most hardcore enthusiast will find this number more than enough. Third, it provides 10 peripheral power connectors, way beyond what you will ever need. And fourth, it comes with two “Y” adapters, one for converting any peripheral power plug into two floppy disk drive power plugs and the other to transform any peripheral power connector into two connectors, facilitating the installation of fans that use this kind of connector.

Finally we have the five-year warranty in the US.

In conclusion, Corsair HX620W is one of the best power supplies you can find on the market, pleasing both average users and enthusiasts.

The only “bad thing” we can find about this product is its price. Unfortunately it isn’t the cheapest power supply around.