OCZ EliteXStream 1000 W Power Supply Review

Secondary Analysis

On this power supply the first transformer and part of the second transformer are used to produce the +12 V outputs. The second transformer is also in charge of producing the +5 V and +3.3 V outputs.

This power supply uses synchronous topology for rectifying the +12 V output. On this topology the rectifying diodes are replaced by power MOSFET transistors. In theory this design offers a higher efficiency, as the voltage drop added by each transistor is of only 0.1 V or less, while a typical Schottky rectifier presents a voltage drop of 0.5 V. In other words, less conduction loss (wasted power) is introduced, thus increasing efficiency. The four power MOSFET transistors used for rectifying the +12 V output are FDP047AN08A0, which support a maximum current of up to 80 A at 144° C each and a far higher current at pulse mode, which is the case (we would need to know the frequency at which the switching transistors operate to make the proper calculation, so let’s consider the maximum continuous current for our math below).

The maximum theoretical current the +12 V line can deliver is given by the formula I / (1 – D), where D is the duty cycle used and I is the maximum current supported by the rectifying diode (which in this case is made by two 80 A transistors in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 229 A or 2,743 W for the +12 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used. As you can see the design used is clearly overspec’ed.

The +5 V output is produced by two STPS30L45CT Schottky rectifiers, each one capable of handling up to 30 A (15 A per internal diode) at 135° C. The maximum theoretical current the +5 V line can deliver is given by the formula I / (1 – D), where D is the duty cycle used and I is the maximum current supported by the rectifying diode (which in this case is made by two 15 A diodes in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 43 A or 214 W for the +5 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.

The +3.3 V output is produced by two STPS30L30CT Schottky rectifiers, each one capable of handling up to 30 A (15 A per internal diode) at 140° C. The maximum theoretical current the +3.3 V line can deliver is given by the formula I / (1 – D), where D is the duty cycle used and I is the maximum current supported by the rectif
ying diode (which in this case is made by two 15 A diodes in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 43 A or 141 W for the +3.3 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.

It is interesting to note that the +5 V and +3.3 V lines don’t share the same output from the transformer, as usually happens.

On the secondary heatsink we also found the rectifier for the +5VSB (“standby power”) output, a SBL1060CT. This device can handle up to 10 A (5 A per internal diode). This explains the higher current limit this power supply has for its +5VSB output (4 A) compared to other products (this is in fact the highest limit we’ve ever seen; most high-end power supplies can deliver up to 3 A or 3.5 A on the +5VSB output).

Another component found on the secondary heatsink is a voltage regulator integrated circuit for the -12 V output (LM7912). This device has a current limit of 1.5 A. The use of this integrated circuit explains why the -12 V output was so stable during our tests (usually manufacturers use cheaper solutions for the -12 V output, which results in a tremendous ripple on this output). We will talk more about this later.

Figure 12: Power MOSFET transistors in charge of the +12 V rectification.

Figure 13: Rectifiers for the +5VSB output, +3.3 V output (two), +5 V output (two) and the voltage regulator from the -12 V output.

The outputs are monitored by a PS232 integrated circuit, which supports the following protections: over current (OCP), under voltage (UVP) and over voltage (OVP). Any other protection that this unit may have is implemented outside this integrated circuit.

Talking about protections, notice how this power supply has two thermal sensors on the secondary heatsink. Usually this means that the product has over temperature protection (OTP), but there is no reference to this protection on OCZ’s website and since the montoring integrated circuit does not implement this protection we would need to analyze the circuit in more details to confirm this suspicion.

Figure 14: PS232S monitoring integrated circuit.

The electrolytic capacitors from the secondary are from Teapo, a Taiwanese company. It would be great if the manufacturer also used Japanese caps here.