Enermax PRO87+ 500 W Power Supply Review
Secondary Analysis
Contents
This power supply uses a synchronous design on 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 produced by four IRFB3206 MOSFETs, two for the direct rectification and two for the “freewheeling” part of the rectification. Each transistor has a maximum RDS(on) of only 2.5 mΩ and can deliver up to 270 A at 25° C or up to 190 A at 100° C in continuous mode, or up to 1,080 A at 25° C in pulse mode. Good Lord! This would give us a maximum theoretical current of 266 A for the whole +12 V bus; if all this current would be pulled from the +12 V outputs, this unit would be able to deliver up to 3,192 W! Of course other parts of this power supply would burn way before we could be even close to this theoretical value. These are the same transistors used in the MODU87+ 700 W.
Figure 14: Transistors of the +12 V rail
The +5 V and +3.3 V outputs are generated by two small power supplies available on small daughterboards attached to the +12 V rail. Each of these power supplies is comprised of three APM2556 MOSFETs and one APW7073 PWM controller.
Figure 15: One of the DC-DC converters
Figure 16: One of the DC-DC converters
This power supply uses a PS231 monitoring integrated circuit, which supports over voltage (OVP), under voltage (UVP) and over current (OCP) protections. The over current protection circuit available in this integrated circuit has five channels, one for +3.3 V, one for +5 V, and three for +12 V. This matches the number of +12 V rails advertised by the manufacturer.
Figure 17: Monitoring circuit
The electrolytic capacitors available in the secondary are from also Japanese, from Chemi-Con, and labeled at 105° C. The secondary also has some solid capacitors.