Enermax MODU87+ 700 W Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of Enermax MODU87+ 700 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU2006 rectifying bridge in its primary, which can deliver up to 20 A at 100° C if a heatsink is used, which is the case. At 115 V this unit would be able to pull up to 2,300 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 1,840 W without burning this component. That is what we call overspecification! Of course we are only talking about this component and the real limit will depend on all other components from the power supply.

Figure 9: Rectifying bridge.

On the active PFC circuit two TK20J60T power MOSFET transistors are used, each one capable of delivering up to 20 A at 25° C (unfortunately the manufacturer doesn’t say the limit at 100° C) in continuous mode, or up to 40 A in pulse mode at 25° C. These transistors present a resistance of 165 mΩ when turned on, a characteristic called RDS(on). This number indicates the amount of power that is wasted, so the lower this number the better, as less power will be wasted thus increasing efficiency.

Figure 10: Active PFC transistors and diode.

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

Figure 11: Active PFC controller.

This power supply uses a Japanese capacitor from Rubycon labeled at 85° C to filter the output from the active PFC circuit. For a “Gold” power supply we expected to see a 105° C capacitor here.

In the switching section, two SiHG20N50C power MOSFET transistors are used. Each of the transistors is capable of delivering up to 20 A at 25° C or 11 A at 100° C in continuous mode, or up to 80 A at 25° C in pulse mode, with an RDS(on) of 225 mΩ.

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. This is the same design on the other 80 Plus Gold power supply we’ve reviewed, Seasonic X-Series 650 W.

Figure 13: Controller.

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