OCZ ZX Series 850 W Power Supply Review

Secondary Analysis

This power supply uses a synchronous design in its secondary, meaning that the Schottky rectifiers were replaced by MOSFET transistors in order to increase efficiency. On top of that, this unit uses a DC-DC design, meaning that this unit is basically a +12 V power supply, with the +5 V and +3.3 V outputs being generated by two small power supplies attached to the +12 V output.

The +12 V output is rectified by four IPP034NE7N3 MOSFETs, each one capable of handling up to 100 A at 100° C in continuous mode or up to 400 A at 25° C in pulse mode, with an RDS(on) of only 3.4 mΩ. This would give a maximum theoretical current of 286 A or 3,429 W for the +12 V rail.

Figure 14: Two of the four +12 V transistors and +5VSB rectifier

As already explained, the +5 V and +3.3 V outputs are obtained by installing two smaller switch-mode power supplies to the +12 V output, each one available on an individual daughterboard. Each converter is managed by an APW7073 PWM controller, and uses four IPD060N03L MOSFETs, each one capable of handling up to 50 A at 100° C in continuous mode, or 350 A at 25° in pulse mode, with an RDS(on) of only 6 mΩ.

Figure 15: One of the DC-DC converters

Figure 16: One of the DC-DC converters

The secondary is monitored by a PS223 integrated circuit. This chip supports OCP (over current protection), over voltage protection (OVP), under voltage protection (UVP) and over temperature protection (OTP). This circuit has four OCP channels (+3.3 V, +5 V and two +12 V), but the manufacturer decided to use only one for the +12 V output, making this power supply a single-rail unit.

Figure 17: Monitoring circuit