This power supply uses a DC-DC converter design on the secondary, meaning that this 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 25º C or up to 190 A at 100º C in continuous mode, or up to 1,080 A at 25º 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. MODU87+ definitely gives “overspecification” a total new meaning!
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Figure 14: +12 V transistors (the diode on the right is used for the +5VSB output).
A unique feature from MODU87+ 700 W is the configuration of the filtering stage of the +12 V line. It 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, plus a very high-end filtering coil.
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Figure 15: Configuration of the filtering capacitors.
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.
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Figure 16: One of the DC-DC modules.
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Figure 17: One of the DC-DC modules.
The outputs are monitored by a PS231 integrated circuit, plus an LM339 voltage comparator is also used.
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Figure 18: Monitoring integrated circuit.
