Enermax NAXN 82+ 550 W Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of the Enermax NAXN 82+ 550 W. For a better understanding, please read our “Anatomy of Switching Power Supplies” tutorial.

This power supply uses one GBU1006 rectifying bridge, which is attached to an individual heatsink. This bridge supports up to 10 A at 100° C, so in theory, you would be able to pull up to 1,115 W from a 115 V power grid. Assuming 80% efficiency, the bridge would allow this unit to deliver up to 920 W without burning itself out. Of course, we are only talking about this particular component. The real limit will depend on all the components combined in this power supply.

Figure 10: Rectifying bridge

The active PFC circuit uses two FDP18N50 MOSFETs, each one supporting up to 18 A at 25° C or 10.8 A at 100° C in continuous mode (note the difference temperature makes), or 72 A at 25° C in pulse mode. These transistors present a 265 mΩ resistance when turned on, a characteristic called RDS(on). The lower the number is, the better, meaning that the transistor will waste less power, and the power supply will have a higher efficiency.

Figure 11: The active PFC transistors and diode

The output of the active PFC circuit is filtered by a 270 µF x 400 V electrolytic capacitor, from Samxon, labeled at 85° C.

In the switching section, two MDF18N50 MOSFETs are employed using the traditional two-transistor forward configuration. These transistors are similar to the ones used in the active PFC circuit, except they are from a different manufacturer. Therefore, the specifications for them were already discussed above.

Figure 12: The switching transistors

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

Figure 13: Active PFC/PWM controller

The primary of the Enermax NAXN 82+ 550 W is identical to the one from the Enermax NAXN 80+ 600 W.

Let’s now take a look at the secondary of this power supply.