Enermax Platimax 850 W Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of the Enermax Platimax 850 W. For a better understanding, please read our “Anatomy of Switching Power Supplies” tutorial.

This power supply uses one LL25XB60 rectifying bridge, whic
h is attached to an individual heatsink. This bridge supports up to 25 A at 113° C, so in theory, you would be able to pull up to 2,875 W from a 115 V power grid. Assuming 80% efficiency, the bridge would allow this unit to deliver up to 2,300 W without burning itself out (or 2,587.5 W at 90% efficiency). Of course, we are only talking about this particular component. The real limit will depend on all the components combined in this power supply. This is the same bridge used by the 600 W model.

Figure 10: Rectifying bridge

The active PFC circuit uses three TK20J60U MOSFETs, each one supporting up to 20 A at 25° C or 40 A at 25° C in pulse mode. Unfortunately, the manufacturer doesn’t state  the current limit at 100° C. These transistors present a 165 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. This configuration is different from the one used in the 600 W model, which has two different transistors.

Figure 11: The active PFC transistors and diode

The active PFC is managed by a CM6502S active PFC controller.

Figure 12: Active PFC controller

The output of the active PFC circuit is filtered by two 390 µF x 400 V electrolytic capacitors connected in parallel. (This configuration is equivalent of one 780 µF x 400 V capacitor.) These capacitors are Japanese, from Matsushita (Panasonic), labeled at 105° C. The 600 W model uses only one capacitor here.

In the switching section, another two TK20J60U MOSFETs are employed using a resonant configuration. The specifications for these transistors were already discussed above. The transistors used in the 600 W model are different.

Figure 13: The switching transistors

The switching transistors are controlled by a CM6901 resonant controller.

Figure 14: Resonant controller

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