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## Secondary Analysis

The XFX PRO 650 W XXX Edition uses a DC-DC design in its secondary. This means that the power supply is basically a +12 V unit, with the +5 V and +3.3 V outputs produced by two smaller power supplies connected to the main +12 V rail. This design is used to increase efficiency.

The maximum theoretical current that each line can deliver is given by the formula I / (1 – D) where D is the duty cycle used and I is the maximum current supported by the rectifying diode. As an exercise, we can assume a duty cycle of 30 percent.

The +12 V output uses four SBR30A50CT Schottky rectifiers, each supporting up to 30 A (15 A per internal diode at 110° C with a 0.55 V maximum voltage drop). From the eight available diodes (two per rectifier pack), three are used in the direct rectification and five are used in the “freewheeling” part of the rectification. The PRO 650 W Core Edition uses the same rectifiers, with the same configuration.

Figure 16: The +12 V rectifiers

As explained, the +5 V and +3.3 V outputs are produced by two DC-DC converters, which are located on the same daughterboard and controlled by the same integrated circuit, an APW7159. The +5 V converter uses four IPD060N03L G MOSFETs, while the +3.3 V converter uses three of them. Each of these transistors supports up to 50 A at 100° C in continuous mode or up to 350 A at 25° C in pulse mode, with a maximum RDS(on) of 6 mΩ. The PRO 650 W Core Edition uses different transistors here.

Figure 17: The DC-DC converters

Figure 18: The DC-DC converters

This power supply uses a PS223 monitoring integrated circuit, which supports over voltage (OVP), under voltage (UVP), over current (OCP), and over temperature (OTP) protections. This integrated circuit has two +12 V OCP channels, but the manufacturer decided to use only one of them, resulting in this unit having a single +12 V rail.

Figure 19: Monitoring circuit

The electrolytic capacitors that filter the outputs are also Japanese, from Chemi-Con, and labeled at 105° C, as usual. See Figure 20.

Figure 20: Capacitors

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Gabriel Torres is a Brazilian best-selling ICT expert, with 24 books published. He started his online career in 1996, when he launched Clube do Hardware, which is one of the oldest and largest websites about technology in Brazil. He created Hardware Secrets in 1999 to expand his knowledge outside his home country.