LEPA G 500 W Power Supply Review

Primary Analysis

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

This power supply uses one GBU10J rectifying bridge in its primary, 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 1,150 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
component, and the real limit will depend on all the other components in this power supply. The Enermax MODU87+ 700 W uses a more powerful bridge here (20 A).

Figure 10: Rectifying bridge

The active PFC circuit uses two SiHG20N50C MOSFETs, which are 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, each. 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 achieve a higher efficiency. It is interesting to note that the Enermax MODU87+ 700 W uses different transistors here, but with the same specs.

Figure 11: Active PFC transistors and diode

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

Figure 12: Active PFC controller

The capacitor used to filter the output of the active PFC circuit is Japanese, from Matsushita (Panasonic), and labeled at 105° C.

In the switching section, two 2SK4107 MOSFET transistors are used, each one supporting up to 15 A at 25° C in continuous mode (unfortunately the manufacturer doesn’t say the limit at 100° C), and up to 60 A at 25° C in pulse mode, with an RDS(on) of 330 mΩ. The Enermax MODU87+ 700 W uses more powerful transistors here (20 A).

Figure 13: Switching transistors

The switching transistors are connected using a design called LLC resonant, being controlled by a CM6901 integrated circuit, which operated 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 14: LLC resonant controller

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