Ultra X4 850 W Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of Ultra X4 850 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBJ2506 rectifying bridge in its primary, which can deliver up to 25A at 100° C  if a heatsink is used, which is the case. This component is clearly overspec’ed: at 115 V this unit would be able to pull up to 2,875 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 2,300 W without burning this component. 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 SPW21N50C3 power MOSFET transistors are used, each one capable of delivering up to 21 A at 25° C or 13.1 A at 100° C in continuous mode (note the difference temperature makes), or up to 63 A in pulse mode at 25° C. These transistors present a resistance of 190 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.

This power supply uses a Japanese capacitor from Matsushita (Panasonic) labeled at 85° C to filter the output from the active PFC circuit.

In the switching section, another two SPW21N50C3 power MOSFET transistors are used on the traditional two-transistor forward configuration. The specs for these transistors were already published above.

Figure 11: Switching transistors.

The primary is controlled by the famous CM6800 PFC/PWM combo controller.

Figure 12: PFC/PWM combo controller.

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