Secondary Analysis
Contents
While RX-6300 (630 W) used a partial synchronous design on its secondary, RX-8500 uses a standard design with six 40CPQ045 Schottky rectifiers, each one supporting up to 40 A (20 A per internal diode at 120° C, voltage drop of 0.43 V).
As mentioned before, this power supply uses two transformers. The first transformer is used to generate half of the +12 V main rail and the +5 V output, while the second transformer is used to generate the other half of the +12 V main rail and the +3.3 V output.
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 using four of the available rectifiers, leaving us with a maximum theoretical current of 114 A or 1,371 W.
The +5 V output is produced by one the rectifiers, giving us a maximum theoretical current of 29 A or 143 W.
The +3.3 V output is produced by the last rectifiers, giving us a maximum theoretical current of 29 A or 94 W.
Figure 12: Rectifiers.
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. As you can clearly see in Figure 13, this unit has a thermal sensor in addition to the one present on the secondary heatsink, which usually means that the power supply has over temperature protection (OTP).
Figure 13: Monitoring circuit.
Electrolytic capacitors from the secondary are also Taiwanese, from Teapo and labeled at 105° C.
