Thermaltake Purepower 500 W Power Supply Review

Secondary Analysis

This power supply has four Schottky rectifiers attached to its secondary heatsink.

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 STPS20H100CT Schottky rectifiers connected in parallel, each one supporting up to 20 A (10 A per internal diode at 160° C, 0.88 V maximum voltage drop). This gives us a maximum theoretical current of 29 A or 343 W for the +12 V output – a value that is simply too low for a model labeled as being a 500 W unit.

The +5 V output is produced by one STPS30L45CT Schottky rectifier, which is capable of delivering up to 30 A (15 A per internal diode at 135° C, 0.74 V maximum voltage drop), giving us a maximum theoretical current of 21 A or 107 W for the +5 V output.

The +3.3 V output is produced by a STPS3045CT Schottky rectifier, which is capable of delivering up to 30 A (15 A per internal diode at 155° C, 0.57 V typical voltage drop and 0.84 V maximum voltage drop), giving us a maximum theoretical current of 21 A or 71 W for the +3.3 V output.

All these numbers are theoretical. The real amount of current/power each output can deliver is limited by other components, especially by the coils used on each output.

Figure 12: +12 V and +3.3 V rectifiers.

Figure 13: +5 V and +12 V rectifiers.

The outputs are monitored by a PS229 integrated circuit. Unfortunately no datasheet is available for this chip.

Figure 14: Monitoring integrated circuit.

All capacitors from the secondary are from Teapo.