Zalman ZM850-HP Plus Power Supply Review

Secondary Analysis

This power supply has three Schottky rectifiers and four MOSFET transistors 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 uses a synchronous design. In this kind of design, the manufacturer replaces the rectifiers with MOSFET transistors in order to increase efficiency. In this power supply, four AOT480 transistors are used, each one capable of handling up to 180 A at 25° C or up to 134 A at 100° C in continuous mode, or up to 500 A at 25° C in pulse mode, with an RDS(on) of only 4.5 mΩ.

The +5 V output uses one STPS60L45CW Schottky rectifier (60 A, 30 A per internal diode at 135° C, maximum voltage drop of 0.73 V), giving us a maximum theoretical current of 43 A or 214 W for this output.

The +3.3 V output uses another STPS60L45CW Schottky rectifier, giving us a maximum theoretical current of 43 A or 141 W for this output.

Figure 13: +12 V transistors, +5 V, +3.3 V, and +5VSB rectifiers

The third Schottky rectifier is used by the +5VSB output.

The secondary is monitored by a PS232S integrated circuit. This chip supports over voltage protection (OVP), under voltage protection (UVP), over temperature protection (OTP), and six over current protection (OCP) channels (four +12 V, one +5 V and one +3.3 V), matching the number of +12 V rails advertised by the manufacturer (four). We could clearly see shunts (current sensors) attached to each +12 V rail.

Figure 14: Monitoring circuit

All electrolytic capacitors used in the secondary are from Teapo and labeled at 105° C.