ASUS U-65GA 650 W Power Supply Review

Secondary Analysis

ASUS U-65GA uses four Schottky rectifiers on the secondary, plus an LM7912 voltage regulator to regulate the -12 V output.

The maximum theoretical current 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. Just as an exercise, we can assume a typical duty cycle of 30%.

The +12 V output is produced by two S60SC6M Schottky rectifiers (60 A, 30 A per internal diode at 118° C, 0.67 V voltage drop) connected in parallel, giving us a maximum theoretical current of 86 A or 1,029 W for the +12 V output. Talk about overspecification!

The +5 V output is produced by one STPS40L45CW Schottky rectifier (40 A, 20 A per internal diode at 130° C, maximum forward voltage of 0.49 V). This gives us a maximum theoretical current of 29 A or 143 W for the +5 V output.

The +3.3 V output is produced by another STPS40L45CW Schottky rectifier, giving us a maximum theoretical current of 29 A or 94 W for the +3.3 V output.

Figure 12: -12 V voltage regulator and rectifiers.

Instead of using a monitoring integrated circuit this power supply implements a discrete solution, so we couldn’t check what protections this power supply really has. The daughterboard located on the secondary is in charge of providing the protections, controlling the fan, generating the power good signal and turning the power supply on and off.

Figure 13: Secondary daughterboard.

Some electrolytic capacitors from the secondary are Japanese from Rubycon and Chemi-Con, but not all; some are from Ltec and CapXon. They are all labeled at 105° C, as usual.