Seventeam ST-620PAF Power Supply Review

Secondary Analysis

This power supply uses four Schottky rectifiers on its secondary.

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 SBL3060PT (30 A, 15 A per internal diode at 95° C, voltage drop of 0.70 V) connected in parallel. This gives us a maximum theoretical current of 43 A or 514 W for the +12 V output.

By the way, we are now talking about the voltage drop presented by the rectifiers. This parameter shows how much voltage is wasted by the rectifier. The lower this number is, the better, as less voltage is wasted, increasing efficiency.

The +5 V output is produced by one SBL6040PT Schottky rectifier (60 A, 30 A per internal diode at 100° C, voltage drop of 0.55 V), giving us a maximum theoretical current of 43 A or 214 W for this output.

The +3.3 V output is produced by another SBL6040PT Schottky rectifier, giving us a maximum theoretical current of 43 A or 141 W for this 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.

The -12 V is regulated by a 7912 integrated circuit.

Figure 11: -12 V integrated circuit and rectifiers.

The outputs are monitored by a PS223 integrated circuit, which supports under voltage (UVP), over voltage (OVP), over current (OCP) and over temperature (OTP, not implemented on this power supply) protections. Any other protection that this unit may have is implemented outside this integrated circuit.

Figure 12: Monitoring integrated circuit.

Most electrolytic capacitors from the secondary are from Samxon, a Chinese company.