This power supply uses six Schottky rectifiers on its secondary, using an unusual configuration for its +12 V output, as shown on Figure 8. As we could understand, the +12 V output "steals" current from the +5 V line.

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Figure 8: Schematics for the secondary used on this power supply.

Let's first analyze the +3.3 V output, which is the easiest one to understand. It uses two STPS2045CT Schottky rectifiers connected in parallel, with a maximum current limit of 20 A (10 A per internal diode, rated at 125º C). The maximum theoretical current the +3.3 V 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 (which in this case is made by two 10 A diodes in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 29 A or 94 W for the +3.3 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used. Even though this power supply has separated rectifiers for its +3.3 V output, this output is generated from the same transformer output used for the +5 V output. Thus the maximum current +5 V and +3.3 V outputs can provide are limited by the maximum current this transformer output can provide.

The +5 V output is generated by two STPS4045CW Schottky rectifiers connected in parallel, each one with a maximum current limit of 40 A at 150º C (20 A per internal diode). The maximum theoretical current the +5 V output can deliver can be calculated using the same math. In this case we have two 20 A diodes in parallel, so the maximum theoretical current will be of 57 A or 286 W.

The +12 V output is generated by two BYW51-200 Schottky rectifiers connected in parallel, each one with a maximum current limit of 20 A at 120º C (10 A per internal diode). The maximum theoretical current the +12 V output can deliver can be calculated using the same math, but for the value of the diode we have to consider the path with the lower current limit. In this case this is the freewheeling path, i.e. the path where current flows when the diodes connected directly to the transformer are not conducting and energy is flowing from the coil. On this path we have the diode with an arrow on Figure 8 conducting, which has a 20 A limit (two 10 A diodes in parallel). This gives a maximum current of 29 A or 343 W for the +12 V output.

If our calculations are correct, it seems that this power supply uses components with values too close to the unit's maximum labeled power. As explained unfortunately at this moment we don't have a load tester yet, equipment that would say if this power supply can deliver or not its labeled power.

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Figure 9: The six Schottky rectifiers used on the secondary (three on each side of the heatsink).

As we said earlier, the maximum power the power supply can deliver depends on other components used – like the transformer, coils, the PCB layout, the wire gauge and even the width of the printed circuit board traces.

This power supply uses Taiwanese electrolytic capacitors from OST. The big electrolytic capacitors from the passive PFC circuit is rated 85º C while all other smaller capacitors are rated at 105º C.