LEPA G 500 W Power Supply Review

Secondary Analysis

This power supply uses a DC-DC converter design in its secondary, meaning that it is basically a +12 V power supply where the +5 V and +3.3 V outputs are produced by two separated power supplies connected to the +12 V line. This design is proving to be the best solution for achieving high efficiency. On top of that, the +12 V power supply uses a synchronous design. On this kind of design the rectifiers are replaced by transistors (MOSFETs) for higher efficiency.

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.

Figure 15: +12 V transistors (the diode on the right is used for the +5VSB output)

Like other all members of the MODU87+ family, the filtering stage of the +12 V line uses a mix of solid capacitors and Japanese caps, from Chemi-Con, installed on small printed circuit boards attached to the main power supply board.

Figure 16: Filtering circuit

The +5 V and +3.3 V outputs are produced by two separated DC-DC modules, which are connected to the main +12 V line to produce these two voltages. Each module uses three APM2556 MOSFETs, controlled by an APW7073 integrated circuit, and only solid caps.

Figure 17: One of the DC-DC modules

Figure 18: One of the DC-DC modules

The secondary is monitored by a PS231S integrated circuit, which supports over voltage protection (OVP), under voltage protection (UVP) and over current protection (OCP). This integrated circuit has five OCP channels (+3.3 V, +5V and three +12 V), correctly matching the number of +12 V rails advertised by the manufacturer.

Figure 19: Monitoring circuit

The secondary of the LEPA G 500 W (Enermax MODU87+ 500 W) is identical to the secondary of the 700 W model (Enermax MODU87+ 700 W).