Antec EarthWatts 500 W Power Supply Review

Secondary Analysis

This power supply uses four Schottky rectfiers on its secondary.

The +12 V output is produced by two SBR30A50CT Schottky rectifiers connected in parallel, which can deliver up to 30 A each (15 A per internal diode, measured at 110° 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 15 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 43 A or 514 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 STPS30L30CT Schottky rectifier, which supports up to 30 A (15 A per internal diode, measured at 140° 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 15 A diode). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 21 A or 107 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 STPS30L30CT Schottky rectifier, which supports up to 30 A (15 A per internal diode, measured at 140° C). Using the same math this would translate into a maximum current of 21 A or 71 W.

Even though this power supply has a separated rectifier for the +3.3 V output, this rectifier is connected to the same transformer output as the +5 V line, so the maximum current +5 V and +3.3 V can pull together is limited by the transformer.

Figure 11: Three of the four Schottky rectifiers used on the secondary. The other rectifier is on the other side of the heatsink.

This power supply uses a semiconductor thermal sensor, which is very small and installed on the solder side of the printed circuit board, between the transformer and the +12 V rectifiers. This sensor is used to control the fan speed according to the power supply internal temperature.

Figure 12: Thermal sensor.

On this power supply the active PFC capacitor is rated at 85° C, while the electrolytic capacitors from the secondary are rated at 105° C and are manufactured by OST, a Taiwanese company.