In Win GreenMe 750 W Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of the In Win GreenMe 750 W. For a better understanding, please read our “Anatomy of Switching Power Supplies” tutorial.

This power supply uses two GBU805 rectifying bridges, which are attached to the same heatsink as the active PFC and switch transistors. Each bridge supports up to 8 A at 100° C. So, in theory, you would be able to pull up to 1,840 W from a 115 V power grid. Assuming 80% efficiency, the bridges would allow this unit to deliver up to 1,472 W without burning themselves out. Of course, we are only talking about these particular components. The real limit will depend on all the components combined in this power supply.

Figure 10: Rectifying bridges

The active PFC circuit uses two SPW21N50C3 MOSFETs, each supporting up to 21 A at 25° C or 13.1 A at 100° C in continuous mode (see the difference temperature makes) or 63 A at 25° C in
pulse mode. These transistors present a 190 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.

The output of the active PFC circuit is filtered by one 470 µF x 450 V Japanese electrolytic capacitor, from Panasonic, labeled at 105° C.

In the switching section, two TK20J50D MOSFETs are employed using the traditional two-transistor forward configuration. Each of these transistors supports up to 20 A at 25° C in continuous mode or up to 80 A at 25° C in pulse mode, with a maximum RDS(on) of 270 mΩ. Unfortunately, the manufacturer doesn’t publish the current limits at 100° C.

Figure 11: One of the active PFC transistors and the two switching transistors

The primary is managed by a CM6802 active PFC/PWM combo controller.

Figure 12: Active PFC/PWM combo controller

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