This power supply uses a DC-DC design on the secondary. This means that this power supply is basically a +12 V unit, with +5 V and +3.3 V outputs being produced by two smaller power supplies connected to the main +12 V output. Most high-efficiency power supplies use this design nowadays, which is proving to be a winner.

The main +12 V power supply uses a synchronous design, i.e. instead of using Schottky diodes it uses MOSFETs to perform the rectification. Four IPD036N04L MOSFETs are used, each one being able to handle up to 90 A at 25º C or up to 87 A at 100º C in continuous mode or up to 400 A at 25º C in pulse mode, with an RDS(on) of only 3.6 mΩ. Seasonic decided to use the power supply housing as a heatsink for these transistors.

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Figure 13: +12 V MOSFETs.

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Figure 14: The power supply housing is used as a heatsink.

What is unique about this power supply is that the DC-DC converters for the +5 V and +3.3 V outputs are not located on small daughter boards attached to the secondary. Instead, Seasonic opted in putting this circuit on the printed circuit board from the modular cabling system. This drastically reduced the number of wires connecting the main printed circuit to the modular cabling system, since only the +12 V wires are needed (plus thin +12 V, +5 V and +3.3 V wires for the monitoring circuit). Also there is no need for thick or several +12 V wires because half of the modular cabling system – the connectors that carry only +12 V outputs and are connected to the most power-hungry devices like the CPU and video cards – is installed directly on the main printed circuit board.

The +5 V and +3.3 V converters are controlled by an APW7159 integrated circuit, with each output being driven by two APM2510N (maximum of 50 A at 25º C or 35 A at 100º C, RDS(on) of only 8.5 mΩ) and two APM2556N (maximum of 160 A at 25º C or 90 A at 100º C, RDS(on) of only 4.5 mΩ) MOSFETs.

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Figure 15: +5 V and +3.3 V power supplies located on the modular cabling system.

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Figure 16: Modular cabling system.

This power supply uses a PS223 monitoring integrated circuit, which is in charge of the power supply protections, like OCP (over current protection), over voltage protection (OVP), under voltage protection (UVP) and over temperature protection (OTP, not implemented on this unit).

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Figure 17: Monitoring circuit.

As mentioned before, all capacitors used on the secondary are solid and made in Japan.