Enermax PRO87+ 500 W Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of the Enermax PRO87+ 500 W For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU8J rectifying bridge on its primary, which is attached to an individual heatsink. This component supports up to 8 A at 100° C, so in theory, you would be able to pull up to 920 W from a 115 V power grid. Assuming 80% efficiency, the bridge would allow this unit to deliver up to 736  without burning itself out. Of course, we are only talking about this component, and the real limit will depend on all the other components in this power supply. The MODU87+ 700 W uses one 20 A bridge here.

Figure 9: Rectifying bridge

The active PFC circuit uses two SiHG20N50C MOSFETs, each one capable of delivering up to 20 A at 25° C or up to 11 A at 100° C (note the difference temperature makes) in continuous mode, or up to 80 A in pulse mode at 25° C. These transistors present a 225 mΩ resistance when turned on, a characteristic called RDS(on). The lower this number the better, meaning that the transistors will waste less power and the power supply will have a higher efficien
cy. The MODU87+ 700 W uses different transistors here, but with similar specs.

Figure 10: Active PFC transistors and diode

The active PFC circuit is controlled by a CM6502 PFC controller.

Figure 11: Active PFC controller

The output of the active PFC circuit is filtered by one Japanese electrolytic capacitor, from Matsushita (Panasonic), labeled at 85° C.

In the switching section, two 2SK4107 power MOSFETs are used. They are capable of handling up to 15 A at 25° C in continuous mode, or up to 60 A at 25° C in pulse mode, with an RDS(on) of 330 mΩ. Unfortunately the manufacturer doesn’t say the maximum current at 100° C. The MODU87+ 700 W uses more powerful transistors here.

Figure 12: Switching transistors

The switching transistors are connected using a design called “LLC resonant,” also known as a series parallel resonant converter, being controlled by a CM6901 integrated circuit, which operates under PWM (Pulse Width Modulation) mode when the power supply is operating under light load but under FM (Frequency Modulation) mode under other loads.

Figure 13: Controller

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