OCZ StealthXStream 600 W Power Supply Review

Primary Analysis

We were very curious to check what components were chosen for the power section of this power supply and also how they were set together, i.e., the design used. We were willing to see if the components could really deliver the power announced by OCZ.

From all the specs provided on the databook of each component, we are more interested on the maximum continuous current parameter, given in ampères or amps for short. To find the maximum theoretical power capacity of the component in watts we need just to use the formula P = V x I, where P is power in watts, V is the voltage in volts and I is the current in ampères.

We also need to know under which temperature the component manufacturer measured the component maximum current (this piece of information is also found on the component databook). The higher the temperature, the lower current semiconductors can deliver. Currents given at temperatures lower than 50° C are no good, as temperatures below that don’t reflect the power supply real working conditions.

Keep in mind that this doesn’t mean that the power supply will deliver the maximum current rated for each component as the maximum power the power supply can deliver depends on other components used – like the transformer, coils, the PCB layout, the wire gauge and even the width of the printed circuit board traces – not only on the specs of the main components we are going to analyze.

For a better understanding of what we are talking here, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses two GBU606 rectifying bridges in its primary stage, which can deliver up to 6 A each one (rated at 100° C), so the total current the rectifying section of this power supply can handle is of 12 A. These are the same components used by Zalman ZM600-HP. OCZ GameXstream 700 W uses two GBU605 bridges, but they have the same specs. This stage is clearly overspec’ed: at 115 V this unit would be able to pull up to 1,380 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 1,104 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.

The active PFC circuit from this power supply uses three power MOSFET transistors (20N60C3 – the same one used by several other power supplies we took a look, like Antec Neo 550 HE, Cooler Master iGreen Power 430 W, Corsair HX620W, Thermaltake Toughpower 750 W, OCZ GameXstream 700 W and Zalman ZM600-HP), just like OCZ GameXstream 700 W and Zalman ZM600-HP. Zalman ZM600-HP, OCZ GameXstream 700 W and OCZ StealthXstream 600 W are the only power supplies we’ve seen using such design. All other high-end power supplies we’ve seen to date use only two transistors (except Enermax Galaxy 1000 W, which uses four transistors). Each 20N60C3 can handle up 300 A @ 25° C each in pulse mode (which is the case).

The active PFC transistors and the PFC diode are installed on the same heatsink.

Figure 9: Active PFC transistors and PFC diode.

In the switching section two FQPF18N50V2 power MOSFET transistors in two-transistor forward configuration are used. Each transistor has a maximum rated current of 18 A at 25° C or 12.1 A at 100° C in continuous mode (note the difference temperature makes) or 72 A at 25° C in pulsating mode, which is the mode used, as the PWM circuit feeds these transistors with a square waveform. Interesting to note that these are the same transistors used by Zalman ZM600-HP, OCZ GameXstream 700 W and Corsair HX620W power supplies.

The two rectifying bridges are installed on the same heatsink used by the switching transistors.

Figure 10: Switching transistors and rectifying bridges.

The primary section from power supply is controlled by a CM6800 integrated circuit, which is an active PFC and PWM controller combo. It is located on a small printed circuit board shown in Figure 11.

Figure 11: Active PFC and PWM controller integrated circuit.