BFG MX-550 Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of MX-550. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU1006 rectifying bridge in its primary, capable of delivering up to 10 A at 100° C if a heatsink is used, which is the case. This is more than adequate rating for a 500 W power supply. The reason why is that at 115 V this unit would be able to pull up to 1,150 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 920 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.

MX-550 uses two SPP16N50C3 power MOSFET transistors on its active PFC circuit, each one capable of delivering up to 10 A at 100° C (or 16 A at 25° C, see the difference temperature makes) in continuous mode, or up to 48 A in pulse mode.

The active PFC capacitor is Japanese from Matsushita (Panasonic) and labeled at 85° C.

Figure 10: Active PFC transistors and diode.

This power supply uses two SPA16N50C3 power MOSFET transistors on the traditional two-transistor forward configuration on its switching section. These transistors are identical to the ones used on the active PFC circuit except for the packaging (TO220 vs. TO220FP).

Figure 11: Switching transistors.

The primary is controlled by a CM6800 integrated circuit installed on a small printed circuit board. This component is the most popular PWM/PFC combo controller.

Figure 12: PFC/PWM controller.