This power supply has nothing less than 13 components attached to its secondary heatsink. From these, one in a 7912 voltage regulator integrated circuit used for the -12 V output, and one is an STPS2045CT used by the standby (+5VSB) circuit. This leaves us with 11 Schottky rectifiers in charge of the main positive voltages.
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 four S60SC6M Schottky rectifiers, each one capable of delivering up to 60 A (30 A per internal diode at 121º C). Two are used for the rectification while two are used for the “freewheeling” part of the rectification (i.e. discharging the coil). This gives us a maximum theoretical current of 171 A (60 A x 2 / 0.70) or 2,057 W for the +12 V output. Talk about overspecification!
The +5 V output is produced by three STPS30L45CT Schottky rectifiers, each one capable of delivering up to 30 A (15 A per internal diode at 110º C). One has its two internal diodes connected in parallel and is in charge of the rectification. The other two are connected in parallel and are in charge of the “freewheeling” part of the rectification (i.e. discharging the coil). For our math we need to consider only the path with the lower current limit, which is the rectification part with 30 A limit, giving us a maximum theoretical current of 43 A or 214 W for the +5 V output.
The +3.3 V output is produced by another three STPS30L45CT Schottky rectifiers, each one capable of delivering up to 30 A (15 A per internal diode at 110º C). One has its two internal diodes connected in parallel and is in charge of the rectification. The other two are connected in parallel and are in charge of the “freewheeling” part of the rectification (i.e. discharging the coil). For our math we need to consider only the path with the lower current limit, which is the rectification part with 30 A limit, giving us a maximum theoretical current of 43 A or 141 W for the +3.3 V output.
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Figure 15: Some of the semiconductors installed on the secondary heatsink.
Instead of using a monitoring integrated circuit, this power supply implements a discrete solution, using a timer and comparator integrated circuits.
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Figure 16: Monitoring circuit.
Electrolytic capacitors from the secondary are manufactured by Aishi, Ltec and Rubycon and labeled at 105º C.
