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TX750W belongs to the latest power supply series from Corsair, TX. It is the power supply with the highest wattage from Corsair today – rated at 50° C, by the way, which is great – and also the only one featuring four power connectors for video cards – even the 650 W model from TX series doesn’t have four connectors. Another technical feature of this new series is the use of a single high current +12 V rail instead of several virtual rails with lower currents – units from their HX series have three virtual rails, but models from their VX series also feature a single +12V rail. It doesn’t feature a modular cabling system like HX series, but it has a 140 mm fan, high efficiency and active PFC. Let’s take an in-depth look inside this power supply and see if it can truly deliver its rated power.
This power supply comes inside a bag and also comes with 10 cable holders for fastening the power supply cables and thus improving the airflow inside your computer.
As you can see on Figures 2 and 3 this unit uses a 140 mm fan on its bottom (the power supply is upside down on Figures 2 and 3) and a mesh on its rear side, where traditionally we have an 80 mm fan. This cooling solution provides a better airflow and lower noise level, since bigger fans can rotate at a lower speed in to generate the same airflow as smaller fans. It is important to note that the 650 W model from TX series uses a smaller 120 mm fan.
It also has the two standard features, active PFC and high efficiency (80%).
The higher the efficiency the better – 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 – compare to below 70% on regular power supplies.
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). As you can see in Figure 2 this power supply doesn’t have an 110V/220V switch, feature available on power supplies with active PFC.
This power supply comes with seven peripheral power cables: four auxiliary power cables for video cards with 6/8-pin connectors (see Figure 4), two cables containing four standard peripheral power connectors and one floppy disk drive power connector each and two cables containing four SATA power connectors each.
We have one constructive criticism regarding the peripheral power cables though. Instead of using a long cable with a lot of connectors, we think the manufacturer should have added more cables with fewer connectors each – for example, three cables with three SATA connectors each instead of two cables with four SATA connectors. In our opinion this provides a better power distribution.
As we mentioned, all video card power connectors can be transformed into an 8-pin connectors, meaning that with this power supply you can install all kinds of high-end video cards.
The plastic sleeving used by the cables don’t come from inside the power supply (see Figure 3), which is something we don’t like for esthetic reasons.
This power supply has one EPS12V connector that can be transformed in two ATX12V connectors and the main power supply connector can be used both on older 20-pin motherboards and on current 24-pin motherboards.
All wires used on this power supply are 18 AWG, but for this power range we think we should see at least some thicker wires (i.e., 16 AWG) around. Cheap power supplies use 20 AWG wires or even 22 AWG, which are thinner.
Even though Corsair paid to have its own UL number, this power supply is really manufactured by CWT, as you can see in Figure 5.
[nextpage title=”A Look Inside The TX750W”]
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.On 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.
As soon as we opened the power supply we had a déjà vu feeling. The layout was very similar to the one used by Thermaltake Toughpower 750 W, which is also manufactured by CWT. However, after a closer inspection on the printed circuit board we could find enough differences to say for sure that even though they have the same labeled power and are manufactured by the same company, they are definitely different products (also Thermaltake’s product has three 18 A +12 V rails while Corsair’s has a single 60 A rail).
[nextpage title=”Transient Filtering Stage”]
As we mentioned on other articles, the fir
st 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.
On this section this power supply is flawless, as it has more components than the necessary – one extra X capacitor, four extra Y capacitors and one extra coil. This power supply also features an X capacitor after the rectifying bridge.
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. As you can see on Figures 6, 7 and 9 all coils used on this power supply are also protected by the same material.
In the next page we will have a more detailed discussion about the components used in the TX750W.
[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, the wire gauge and even the width of the printed circuit board traces – 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 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.
The active PFC circuit from this power supply uses two power MOSFET transistors (20N60C3 – the same one used by several other power supplies we took a look). Some other power supplies like OCZ StealthXStream 600 W and Zalman ZM600-HP use three transistors here instead of two. Each 20N60C3 can handle up 300 A @ 25° C each in pulse mode (which is the case) or 45 A @ 25° C or 20 A @ 110° C in continuous mode.
In the switching section, another two 20N60C3 power MOSFET transistors in two-transistor forward configuration are used. Here lies one of the main differences between Corsair TX750W and Thermaltake Toughpower 750 W: this model from Corsair uses transistors with far higher current limits, which is great (300 A vs. 80 A in pulsating mode, both rated at 25° C). In other words, at least in theory the primary stage can deliver more current (and thus power) to the secondary stage.
The primary is controlled by a CM6800 integrated circuit, which is a very popular active PFC and PWM controller combo. It is located on a small printed circuit board shown in Figure 12.
[nextpage title=”Secondary Analysis”]
This power supply uses four Schottky rectifiers on its secondary, the same models used on Thermaltake Toughpower 750W.
The +12 V output is produced by two STPS60L45CW Schottky rectifiers connected in parallel, which can deliver up to 60 A each (30 A per internal diode, measured at 135° 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 this section is highly overspec’ed.
The +5 V output is produced by one STPS40L45CW Schottky rectifier, supporting up to 40 A (20 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 20 A diode). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 29 A or 143 W for the +5 V output. The maximum current this line can really deliver will depend on ot
her components, in particular the coil used. As you can see this section is highly overspec’ed.
The +3.3 V output is also produced by another STPS40L45CW Schottky rectifier, supporting up to 40 A (20 A per internal diode, measured at 130° C). Using the same math this would equal 29 A or 94 W.
Even though this power supply has a separated rectifier for the +3.3 V output, this rectifier is connected to the same transformer output as the +5 V line, so the maximum current +5 V and +3.3 V can pull together is limited by the transformer.
In Figure 14, you can see the thermal sensor used by this power supply, in charge of changing the fan speed according to the power supply internal temperature.
This power supply uses only Japanese capacitors, all rated at 105° C. The active PFC capacitor is from Matushita (Panasonic) while the smaller ones are from Chemi-Con.
[nextpage title=”Power Distribution”]
In Figure 15, you can see TX750W label stating all its power specs.
As you can see Corsair labeled this unit as having only one +12 V rail. If you open the power supply, however, you will see that the +12 V wires are separated in four groups (+12V1 through +12V4) and may think that this power supply has in fact four virtual rails (see Figure 16).
Here is the deal. As we have exhaustively explained on other articles, on power supplies with more than one rail these +12 V “virtual rails” are connected to the single +12 V real rail the power supply has – there is only +12 V output coming from the rectifiers. The exact same thing happens on this power supply from Corsair. The difference lies on the OCP (Over Current Protection) mechanism. On power supplies with multiple rails, the OCP circuit has several inputs and is set to shut down the power supply whenever any of the rails pulls more than a given current – 16 A, 18 A, 20 A are some good examples. So on power supplies with four rails, for example, the OCP circuit will be monitoring the four rails.
On this power supply, however, the OCP circuit monitors the entire current pulled by all +12 V wires, so it has only one input. If your system pulls more than 60 A (actually the OCP circuit is usually set a little higher than the current printed on the power supply label), then your unit will shut down.
There is a lot of discussion of what design is the best, but we will leave this discussion to a tutorial we are planning to write.
So even though you see four labels on the printed circuit board this unit uses in fact a single rail design.
What is important is that the power and currents labeled are inside the specs from the semiconductors used on this power supply.
Once again we’d like to remind that this power supply is labeled at 50° C, which is outstanding. Usually when no temperature is stated, the manufacturers assume 25° C, which is a temperature far below the power supply real working temperature. Keep in mind that the maximum power a power supply can deliver drops as its internal temperature increases. We have a suggestion to Corsair, to post this information on their website, because it is printed only on the product box. Anyway, we will see if this power supply can really deliver its labeled power in the next page.
The only thing we really didn’t like about this power supply is how the +12 V wires from the video card cables are connected. As you can see in Figure 17 each video card cable has three +12 V wires but two of them are connected together to a single wire. We think that the three wires should be connected directly to the printed circuit board without any splitting in the middle of the way, as the configuration used can limit the maximum amount of current (and thus power) the power supply can deliver to each video card, theoretically speaking.
[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° and 49° C. During our tests the power supply temperature was between 47° and 53° 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. Keep in mind that power supply uses a single rail design.
|Input||Test 1||Test 2||Test 3||Test 4||Test 5|
|+12V1||5 A (60 W)||11 A (132 W)||17 A (204 W)||24 A (288 W)||33 A (396 W)|
|+12V2||5 A (60 W)||10 A (120 W)||15 A (180 W)||20 A (240 W)||22 A (264 W)|
|+5V||2 A (10 W)||4 A (20 W)||6 A (30 W)||8 A (40 W)||8 A (40 W)|
|+3.3 V||2 A (6.6 W)||4 A (13.2 W)||6 A (19.8 W)||8 A (26.4 W)||8 A (26.4 W)|
|+5VSB||1 A (5 W)||1 A (5 W)||1.5 A (7.5 W)||2 A (10 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||148 W||296 W||447 W||610 W||751 W|
|% Max Load||19.7%||39.5%||59.6%||81.4%||100%|
|Ripple and Noise||Pass||Pass||Pass||Pass||Pass|
|AC Power||177 W||368 W||728 W||920 W|
We were very impressed by these results. Corsair TX750W could not only deliver its labeled power under between 45° C and 50° C but it could maintain its efficiency at 80% (the only test where its efficiency was below 80% was at test number two, where we were pulling around 40% of the power supply maximum labeled capacity and even then it was almost 80%).
The only thing we didn’t like about this power supply during our test was electrical noise at the +12 V rail, too high compared to other power supplies we’ve seen so far. For example, on test number four, where we were pulling 610 W from this power supply, noise level was at 60 mV at +12V1 and 68 mV at +12V2. On our tests with PC Power & Cooling Silencer 610 EPS12V pulling the same amount of power (and working at 100%, usually where we see the maximum noise level the power supply produces) we saw only 44 mV and 42 mV on these two inputs. With the power supply operating at its full load, noise level was of 90.6 mV at 12V1 input and 103 mV at +12V2 input. Even though these numbers are still inside the 120 mV limit, we’d like to see lower figures here, around 60 mV. Noise levels for the +5 V output and +3.3 V were of 8.8 mV and 16 mV, respectively, within the 50 mV limit for these outputs.
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).
[nextpage title=”Overload Tests”]
After these tests we tried to pull even more power from Corsair TX750W. 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 45° C and the power supply was working at 45° C.
|+12V1||33 A (396 W)|
|+12V2||33 A (396 W)|
|+5V||10 A (50 W)|
|+3.3 V||10 A (33 W)|
|+5VSB||3 A (15 W)|
|-12 V||0.8 A (9.6 W)|
|% Max Load||120%|
|AC Power||1,111 W|
Here noise level at +12 V output reached 112 mV, a value that is touching the 120 mV limit, showing us that this power supply obviously wasn’t designed to operate under such high specs.
We were not only impressed by the fact that a power supply labeled as a 750 W product could deliver 900 W but also because it could maintain an efficiency over 80% under this circumstance. But, as we mentioned, we were not happy with the electric noise level.
Another thing worth mentioning is the thermal dissipation of this power supply. Even under this extreme condition the power supply temperature was only two degree Celsius higher than the room temperature inside our “hot box,” showing that the 140 mm fan used by this product works very well. During our tests we could see its speed changing as the power supply temperature increased. Another very important feature present on this power supply is the fact that its fan will continue spinning even after the computer is turned off – assuming that you don’t turn off the power supply master switch –, which is really great, as it will keep cooling down the power supply until it reaches a “safe” temperature. The fan will spin at a lower speed, so you can’t even hear it spinning when this happens. In theory this feature increases the life span of the product.
Short-circuit protection for both +5 V and +12 V outputs worked just fine, but it seems, however, that this power supply doesn’t have over current protection (OCP), or it is set way over 66 A (the maximum amount of current we pulled from the +12 V output) – while according to the power supply label the limit for the single +12 V rail is of 60 A.
As for the over power protection (OPP), we pulled way over the maximum power supply labeled power and the power supply didn’t shut down. In fact, when we tried to pull even more power from this unit (i.e., when we tried to pull more than 10 A from +5 V and +3.3 V) the circuit breaker here at our lab disarmed. We wanted to see our power supply disarming, not the circuit breaker.
[nextpage title=”Main Specifications”]
Corsair TX750W power supply specs include:ATX12V 2.2
- Nominal labeled power: 750 W.
- Measured maximum power: 900 W at 45° C.
- Labeled efficiency: 80%.
- Measured efficiency: Between 78.8% and 84.3% at 115 V.Active PFC: Yes.
- Motherboard Connectors: One 20/24-pin connector and one ATX12V/EPS12V connector.
- Peripheral Connectors: four video card power cables (all with 6/8-pin connectors), two cables containing four standard peripheral power connectors and one floppy disk drive power connector each and two cables containing four SATA power connectors each.
- Protections: short-circuit (SCP), over current (OCP), over voltage (OVP), over power (OPP), under voltage (UVP) and over temperature (OTP).
- Warranty: 5 years.
- More Information: https://www.corsair.com
- Real manufacturer: CWT
- Average price in the US*: USD 170.00
* Researched at Shopping.com on the day we published this review.
This is a great 750 W power supply for users willing to install up to four high-end video cards on their systems. What is really great about this power supply is the fact that all its video card power connectors can be transformed into 8-pin ones, so you won’t need to upgrade your power supply in the future if the 8-pin connector becomes standard. Or you can use this power supply to connect two Radeon HD 2900 XT in parallel, as each one of them requires t
wo power cables, one with six pins and another with eight pins. It also has eight SATA power connectors and eight peripheral power connectors, more than enough for even the übergeek with two or more DVD burners and a big RAID array and extra hard drives – even though we think we could see a better distribution of the connectors, i.e., three cables with three connectors each instead of two cables with four connectors each.
This unit also has all the basic stuff everyone is looking for nowadays: high efficiency, active PFC, excellent cooling solution, enough power to feed high-end video cards, five-year warranty and the best of all: it can really deliver its rated 750 W at 50° C. Not only that. During our tests we could pull up to 900 W at 45° C. So you will be basically buying a 900 W power supply paying the price of a 750 W one. What is sweeter than that?
The only thing we didn’t like about it is its electrical noise level. Even though noise level was within ATX specs we expected that this unit would produce a lower noise level. This “problem” should not worry Average Joe, but if you are an extreme enthusiast looking for a flawless power supply you should look for another 750 W model with lower electric noise level.
Don’t get us wrong, this power supply is a terrific product and we do recommend it, all we want to say is that it isn’t flawless. And that is why we are giving it our “Silver Award” instead of “Golden.”