Spire BlackDragon 400 W Power Supply Review

Primary Analysis

On this page, we will take an in-depth look at the primary stage of the Spire BlackDragon 400 W. For a better understanding, please read our “Anatomy of Switching Power Supplies” tutorial.

This power supply uses one GBU808 rectifying bridge, which is attached to the same heatsink used by the components from the active PFC circuit. This bridge supports up to 8 A at 100° C. In theory, you would be able to pull up to 920 W from a 115 V power grid. Assuming 80% efficiency, the bridge would allow this unit to deliver up to 736 W without burning itself out. Of course, we are only talking about this particular component. The real limit will depend on all the components combined in this power supply.

Figure 11: Rectifying bridge

The active PFC circuit uses two FDPF18N50 MOSFETs, each one supporting up to 18 A at 25° C or 10.8 A at 100° C in continuous mode (note the difference temperature makes), or 72 A at 25° C in pulse mode. These transistors present a 265 mΩ maximum 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.

Figure 12: The active PFC transistors and diode

The output of the active PFC circuit is filtered by one 220 µF x 420 V electrolytic capacitor from CapXon, labeled at 85° C.

Figure 13: Capacitor

In the switching section, two FQPF12N60 MOSFETs are employed using the traditional two-transistor forward configuration. Each transistor supports up to 5.8 A at 25° C or 3.7 A at 100° C in continuous mode or up to 23 A at 25° C in pulse mode, with a maximum RDS(on) of 700 mΩ.

Figure 14: The switching transistors

The switching transistors and active PFC circuit are controlled by the omnipresent CM6800 controller.

Figure 15: Active PFC/PWM controller

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