Primary Analysis

On this page we will take an in-depth look at the primary stage of the Enermax NAXN 82+ 750 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses two GBU1005 rectifying bridges connected in parallel on its primary, which are attached to an individual heatsink. These components support up to 10 A at 100° C each, so in theory, you would be able to pull up to 2,300 W from a 115 V power grid. Assuming 80% efficiency, the bridges would allow this unit to deliver up to 1,840 W without burning themselves out. Of course, we are only talking about these components, and the real limit will depend on all the other components in this power supply.

Enermax NAXN 82+ 750 W power supplyFigure 10: Rectifying bridge

The active PFC circuit uses two IPW60R125P MOSFETs, each supporting up to 25 A at 25° C or 16 A at 100° C in continuous  mode (note the difference temperature makes), or 82 A in pulse mode at 25° C. These transistors present a 125 mΩ resistance when turned on, a characteristic called RDS(on). The lower the number the better, meaning that the transistor will waste less power, and the power supply will have a higher efficiency.

Enermax NAXN 82+ 750 W power supplyFigure 11: Active PFC transistors

The electrolytic capacitor that filters the output of the active PFC circuit is Japanese, from Chemi-Con, and labeled at 105° C.

In the switching section, two SPP20N60C3 MOSFETs are used, installed in the two-transistor forward configuration. Each one is capable of delivering up to 20.7 A at 25° C or 13.1 A at 100° C in continuous mode, or 62.1 A in pulse mode at 25° C. These transistors present an RDS(on) of 190 mΩ.

Enermax NAXN 82+ 750 W power supplyFigure 12: Switching transistors

The primary is controlled by the omnipresent CM6800 active PFC/PWM combo controller.

Enermax NAXN 82+ 750 W power supplyFigure 13: Active PFC/PWM combo controller

Let’s now 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.