HEC WinPower 480 W Power Supply

Secondary Analysis

This power supply uses four Schottky rectifiers on its secondary.

The +12 V output is produced by two MBR20100CT Schottky rectifiers, which can deliver up to 20 A each (10 A per internal diode, measured at 133° C). The maximum theoretical current the +12 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 343 W for the +12 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.

The +5 V output is produced by one MBR6045PT Schottky rectifier, supporting up to 60 A (30 A per internal diode, measured at 125° C). The maximum theoretical current the +5 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 one 30 A diode). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 43 A or 214 W for the +5 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.

The +3.3 V output is produced by another MBR6045PT Schottky rectifier. Using the same math this output has a maximum theoretical current of 43 A or 141 W.

Even though the +5 V line and the +3.3 V line have separated rectifiers, they share the same transformer output. So the maximum current both lines can deliver will depend a lot on the transformer.

The problem here is that apparently this unit uses an outdated design. As you can see the +12 V output has a far lower current limit compared to the +5 V and +3.3 V outputs, a scenario that was typical several years ago. Nowadays PCs pull more current/power from +12 V and we want see a higher limit on this output.

On Figures 12 and 13 you can see the four power Schottky rectifiers used on the secondary section of this power supply. As you can see, a copper plate is used between the +5 V rectifier and the heatsink in order to provide a better heat dissipation.

Figure 12: Power rectifiers used on the secondary.

Figure 13: Power rectifiers used on the secondary.

This power supply uses Taiwanese electrolytic capacitors from Teapo and CapXon. The two big capacitors from the voltage doubler are rated 85° C while all other smaller capacitors are rated 105° C.