On this page we will take an in-depth look at the primary stage of Corsair HX750W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU1506 rectifying bridge in its primary (the same one used on Corsair HX850W), supporting up to 15 A at 100º C if a heatsink is used (which is the case), so in theory, you 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 itself. Of course we are only talking about this component and the real limit will depend on all other components from the power supply.

Two SPW20N60C3 power MOSFETs are used on the active PFC circuit, each one capable of delivering up to 20.7 A at 25º C or 13.1 A at 100º C in continuous mode (note the difference temperature makes) or up to 62.1 A at 25º C in pulse mode. These transistors present a maximum resistance of 190 mΩ when turned on, a characteristic called RDS(on). This number indicates the amount of power that is wasted, so the lower this number the better, as less power will be wasted thus increasing efficiency. The 850 W version uses more powerful transistors here (34.6 A at 25º C or 21.9 A at 100º C in continuous mode, 103.8 A in pulse mode).

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Figure 9: Rectifying bridge and active PFC transistors.

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. Corsair HX750W uses two 330 µF x 420 V connected in parallel; this is equivalent of one 660 µF x 420 V capacitor (HX850W uses two 390 µF x 400 V capacitors).

These capacitors are Japanese, from Chemi-Con and are labeled at 105º C. This is good for two reasons, first, Japanese capacitors do not leak; and second, usually manufacturers use 85º C capacitors here, so it is good to see a manufacturer using a capacitor with a higher temperature rating.

In the switching section, two IRFP460A power MOSFET transistors are used on the traditional two-transistor forward configuration. Each transistor is capable of delivering up to 20 A at 25º C or 13 A at 100º C in continuous mode (note the difference temperature makes), or up to 80 A in pulse mode at 25º C, with a 270 mΩ RDS(on). Corsair HX850W uses different transistors here but with similar specs.

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Figure 10: Switching transistors.

This power supply uses a CM6802 active PFC/PWM combo controller.

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Figure 11: Active PFC/PWM combo controller.

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