Young Year YP-AB Transparent Power Supply

Secondary Analysis

This power supply uses three power Schottky rectifiers on its secondary section, one for each positive output: +3.3 V, +5 V and +12 V. The only advantage of this power supply compared to 100% “generic” units is that on this unit the +3.3 V output has a separated rectifier – sharing, however, the same transformer output as the +5 V output. In old ATX power supplies, a voltage regulator connected to the +5 V output provided the +3.3 V output.

Since this power supply is based on the half-bridge configuration, to calculate the maximum theoretical current is easy: all we need to do is add the maximum currents from the diodes.

The +12 V output uses one STPR1020CT Schottky rectifier, which supports up to 10 A (at 110° C, 5 A per internal diode). So the +12 V output has a maximum theoretical power of 120 W, an outrageous discrepancy from what is printed on the power supply label (we will talk more about this in the next page). The maximum current this line can really deliver will depend on other components, especially the transformer, the coil, the wire gauge and even the width of the printed circuit board traces used.

The +5 V output uses one SBL3040PT Schottky rectifier, which supports up to 30 A (at 95° C, 15 A per internal diode). So the +5 V output has a maximum theoretical power of 150 W, another discrepancy from what is written on the power supply label that we will talk about in the next page.

The +3.3 V output also uses one SBL3040PT Schottky rectifier (30 A at 95° C, 15 A per internal diode), so the +3.3 V output has a maximum theoretical power of 99 W, another discrepancy we will talk about in the next page.

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.

Figure 12: Power rectifiers used on the secondary.

In Figure 13, you can see a thermal sensor touching the secondary heatsink, which controls the fan speed.

Figure 13: Secondary thermal sensor.