Secondary Analysis
Contents
Even though Sentey officially sells the SD850-SS as having the standard 80 Plus certification, it uses a synchronous design, where the Schottky rectifiers are replaced with MOSFETs, and a DC-DC design, which means that the power supply is basically a +12 V unit, with the +5 V and +3.3 V outputs produced by two smaller power supplies connected to the main +12 V rail. Both designs are used to increase efficiency, and are usually only seen on high-efficiency power supplies with at least the 80 Plus Bronze certification.
The +12 V output uses four IPP040N06N MOSFETs, each one supporting up to 80 A at 100° C in continuous mode, or up to 320 A at 25° C in pulse mode, with a maximum RDS(on) of 4 mΩ.
Figure 15: The +12 V transistors
As explained, the +5 V and +3.3 V outputs are produced by two DC-DC converters, which are located on a single printed circuit board located in the secondary section of the power supply. Each converter is controlled by one NCP1587A integrated circuit and uses two IPD060N03L MOSFETs, which support up to 50 A at 100° C in continuous mode and up to 43 A at 25° C in pulse mode, with a maximum RDS(on) of 6 mΩ.
Figure 16: The DC-DC converters
Figure 17: The DC-DC converters
We did not see an integrated circuit for monitoring the power supply outputs. Since the Power Good wire and sensors were connected to the small printed circuit board where the resonant controller was attached, our best guess is that the enigmatic SF29601 controller, with the aid of four operational amplifiers provided by an LM324 integrated circuit, does the trick.
The electrolytic capacitors available in the secondary are also from CapXon and labeled at 105° C, except for the electrolytic capacitor used on the +5VSB output, which is from Su’scon.
Figure 18: Capacitors
