Corsair HX750W Power Supply Review

Secondary Analysis

Like Corsair HX850W and HX1000W, this power supply uses a synchronous design, where the rectifiers are replaced with transistors. Also this power supply basically produces only the +12 V output. +5 V and +3.3 V outputs are generated from the +12 V output by two little power supplies located on two small printed circuit boards inside the unit. This design is called DC-DC converter and is also used by several other power supplies on the market, as mentioned on the introduction.

Five IPP037N08N are used, each one capable of delivering up to 100 A at 100° C in continuous mode, or up to 400 A at 25° C in pulse mode, with a maximum RDS(on) of 3.5 mΩ, which is impressively low. Three of them are in charge of the direct rectification, while the remaining two are in charge of the “freewheeling” part of the rectification process (i.e., discharging the coil). Corsair HX850W also uses five transistors, but models with a higher current limit (120 A).

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%.

This would give us a maximum theoretical current of 428.5 A (100 A x 3 / 0.70). This maximum theoretical current limit is for the whole secondary, since +5 V and +3.3 V are also produced from the +12 V output. The practical limit will depend on other factors, but mainly on the coils used and on the design from the small DC-DC converters used to generate the +5 V and +3.3 V outputs. If this 428.5 A was solely pulled from the +12 V outputs, this would give us 5,142 W. Talk about overspecification!

Figure 12: Transistors used on the +12 V rectification.

This power supply has two separated DC-DC converters, one for +5 V and another for +3.3 V. Each one uses one APW7073 controller and three APM2556N MOSFETs (which present a maximum RDS(on) of only 7.2 mΩ), using solid capacitors.

Figure 13: One of the DC-DC converters.

Figure 14: One of the DC-DC converters.

This power supply uses a PS229 monitoring integrated circuit, which is in charge of the power supply protections. Unfortunately there is no information about this circuit on the manufacturer’s website.

Figure 15: Monitoring circuit.

Electrolytic capacitors from the secondary are also Japanese, from Chemi-Con and labeled at 105° C. We could find some capacitors installed on the modular cabling system, which is great.