Zalman ZM750-HP Power Supply Review

Secondary Analysis

Zalman ZM750-HP has eight Schottky rectifiers on its secondary, four for the +12 V output, two for the +5 V output and two for the +3.3 V output. This configuration is identical to the one used by other power supplies based on the same project of ZM750-HP, like ZM600-HP, OCZ StealthXStream 600 W and OCZ GameXStream 700. But let’s see whether or not the components are identical.

The +12 V output is produced by four SBR30A45CT Schottky Rectifiers, each one capable of handling up to 30 A at 110° C (15 A per internal diode). The maximum theoretical current the +12 V 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 (which in this case is made by four 15 A diodes in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 86 A or 1,029 W for the +12 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.

The +5 V output is produced by two MBR3045CT Schottky Rectifiers, which is basically the same component with a different name (different vendor). The maximum theoretical current the +5 V 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 (which in this case is made by two 15 A diodes in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 43 A or 214 W for the +5 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.

The +3.3 V output is produced by another two MBR3045CT Schottky Rectifiers. The maximum theoretical current the +3.3 V 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 (which in this case is made by two 15 A diodes in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 43 A or 141 W for the +3.3 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.

As you can see, the rectifiers are clearly overspec’ed, especially the ones in charge of the +12 V outputs.

Figure 12: +12 V rectifiers, +5 V rectifier and +3.3 V rectifier.

Figure 13: +3.3 V rectifier, +5 V rectifier and +12 V rectifiers.

These are the same rectifiers used on Zalman ZM600-HP and OCZ GameXStream 700 W, while OCZ StealthXStream 600 W uses rectifiers with lower current limits (20 A per device, 10 A per internal diode) on the +12 V output.

So the main difference between Zalman ZM750-HP and ZM600-HP is on the primary side, not on the secondary.

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.

All the electrolytic capacitors from the secondary are Taiwanese from Capxon and Teapo, and labeled at 105° C as usual.