Corsair TX850 V2 Power Supply Review

Secondary Analysis

This power supply uses a DC-DC project in its secondary, meaning that this unit is basically a +12 V power supply, with the +5 V and +3.3 V outputs produced by two smaller switching power supplies connected to the +12 V rail. This design is used in order to increase efficiency.

The +12 V output makes use of six SBR30A50CT Schottky rectifiers (30 A, 15 A per internal diode at 110° C, 0.55 V maximum voltage drop). From the available 12 diodes (two per rectifier pack), eight are used in the direct rectification, and four are used in the “freewheeling” part of the rectification. The 750 W model has five Schottky rectifiers here.

Figure 14: The +12 V rectifiers

As explained, the +5 V and +3.3 V outputs are generated using two DC-DC converters (i.e., two switching power supplies). Usually, power supplies using this design have these two converters installed on separate daughterboards, but in the Corsair TX850 V2 they are available on the same board, shown in Figures 15 and 16. The two converters are managed by the same PWM chip (APW7159) and use seven APM2556N MOSFET transistors, each one being able to handle up to 160 A at 25° C or 90 A at 100° C with an RDS(on) of only 4.5 mΩ. This board is identical to the one used in the 750 W version.

Figure 15: The +5 V and +3.3 V DC-DC converters

Figure 16: The +5 V and +3.3 V DC-DC converters

The secondary is monitored by a PS223 integrated circuit, which supports over voltage protection (OVP), under voltage protection (UVP), over current protection (OCP), and over temperature protection (OTP). This integrated circuit has four OCP channels (+3.3 V, +5 V and two +12 V), but the manufacturer decided to use only one of the +12 V channels, making this a single-rail power supply.

Figure 17: Monitoring circuit

All electrolytic capacitors used in the secondary are also Japanese, from Chemi-Con, and labeled at 105° C.