Primary Analysis

On this page we will take an in-depth look at the primary stage of Corsair HX850W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU1506 rectifying bridge in its primary, supporting up to 15 A at 100° 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 out. Of course we are only talking about this component and the real limit will depend on all other components from the power supply.

Two SPW35N60C3 power MOSFETs are used on the active PFC circuit, each one capable of delivering up to 34.6 A at 25° C or 21.9 A at 100° C in continuous mode (note the difference temperature makes) or up to 103.8 A at 25° C in pulse mode.

Corsair HX850W power supplyFigure 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 HX850W uses two 390 µF x 400 V connected in parallel; this is equivalent of one 780 µF x 400 V capacitor.

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

In the switching section, two SPW20N60C3 power MOSFET transistors are used on the traditional two-transistor forward configuration. Each transistor supports up to 20.7 A at 25° C or 13.1 A at 100° C (note the difference temperature makes) or 62.1 A in pulse mode at 25° C.

Corsair HX850W power supplyFigure 10: Active PFC diode and switching transistors.

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

Corsair HX850W power supplyFigure 11: Active PFC/PWM combo controller.

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

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.