Zalman ZM770-XT Power Supply Review

Secondary Analysis

This power supply has eight Schottky rectifiers attached to the 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 four 40CPQ060 Schottky rectifiers connected in parallel, each one supporting up to 40 A (20 A per internal diode at 120° C, 0.49 V voltage drop). This gives us a maximum theoretical current of 114 A or 1,371 W.

The +5 V output is produced by two STPS60L45CW Schottky rectifiers connected in parallel, each one supporting up to 60 A (30 A per internal diode at 135° C, 0.50 V maximum voltage drop). This gives us a maximum theoretical current of 86 A or 429 W.

The +3.3 V output is produced by another two STPS60L45CW Schottky rectifiers, giving us a maximum theoretical current of 86 A or 283 W.

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 11: +12 V, +5 V and +3.3 V rectifiers.

As mentioned earlier, the heatsinks are made of aluminum, even though its color reminds copper. The rounded component shown in Figure 11 is another LED that glows blue when the unit is on.

The outputs are monitored by a PS232 integrated circuit, which supports the following protections: over current (OCP), under voltage (UVP) and over voltage (OVP). Any other protection that this unit may have is implemented outside this integrated circuit.

Figure 12: Monitoring circuit.

Electrolytic capacitors from the secondary are from Teapo and labeled at 105° C.