OCZ Fatal1ty 700 W Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of Fatal1ty 700 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBJ1506 rectifying bridge in its primary, capable of delivering up to 15 A at 100° C. EliteXstream 1,000 W uses a 20 A component here. This component is clearly overspec’ed: at 115 V this unit would be able to pull up to 1,725 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 1,380 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 10: Rectifying bridge.

The active PFC circuit uses two 20N60C3 power MOSFET transistors (EliteXstream 1,000 W uses three), the same used by several other power supplies we looked. Each one is capable of handling up to 300 A @ 25° C in pulse mode (which is the case) or up to 45 A @ 25° C or 20 A @ 110° C (note the difference temperature makes).

An unusual thing about the active PFC circuit from this power supply is the use of three Japanese electrolytic capacitors from Hitachi rated at 105° C connected in parallel. When capacitors are connected in parallel the value of their capacitances are added. So three 180 µF capacitors connected in parallel is equivalent as one single 540 µF capacitor. This is a very smart trick to achieve a higher capacitance without using a physically bigger component. It is interesting to note that EliteXStrem 1,000 W, which is based on the same printed circuit board, uses three 330 µF, for a total capacitance of 990 µF.

Figure 11: The active PFC capacitors.

On the switching section this power supply uses another 20N60C3 transistors, on the traditional two-transistor forward configuration. The specs for these transistors are published above. As you can see in Figure 12, all main semiconductors from the primary side are installed on the same heatsink.

Figure 12: Active PFC diode, two active PFC transistors and two switching transistors.

This power supply uses a discrete active PFC/PWM controller instead of using an integrated circuit that has this circuit already ready to use. On this power supply this circuit was built using one LM339 comparator, one UC3845B current mode controller and one ICE2PCS02 PFC controller.

Figure 13: Active PFC/PWM controller circuit.