Secondary Analysis

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 a small printed circuit board inside the unit. This design is called DC-DC converter and is also used by Corsair HX1000W, Antec Signature 650 W and Seasonic M12D 750 W.

Five STP160N75F3 are used, each one capable of delivering up to 120 A at 100° C in continuous mode, or up to 480 A at 25° C in pulse mode. 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).

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%.

For our math we need to assume the path that has the lower limit, which is the “freewheeling” path. This would give us a maximum theoretical current of 343 A (120 A x 2 / 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 343 A was solely pulled from the +12 V outputs, this would give us 4,114 W.

Corsair HX850W power supplyFigure 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, and they use solid capacitors.

Corsair HX850W power supplyFigure 13: DC-DC converters in charge of generating +5 V and +3.3 V outputs from the +12 V output.

Corsair HX850W power supplyFigure 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.

Corsair HX850W power supplyFigure 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 (and unusual).

Gabriel Torres is a Brazilian best-selling ICT expert, with 24 books published. He started his online career in 1996, when he launched Clube do Hardware, which is one of the oldest and largest websites about technology in Brazil. He created Hardware Secrets in 1999 to expand his knowledge outside his home country.