This power supply uses a slightly different configuration from what we’ve seen to date, so we drew a simplified schematics of its secondary for a better understanding, see Figure 12.

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Figure 12: Cooler Master Real Power Pro 850 W secondary.

The +5 V and +3.3 V ouputs use the traditional configuration used by power supplies with a forward switching design. For the +5 V and +3.3 V outputs the two transformers are connected in parallel and each output uses two Schottky rectifiers in parallel each. Instead of sharing the same transformer output with the +5 V output, the +3.3 V line uses its own transformer output, which is great.

The +5 V output is produced by two STPS60L45CW Schottky rectifiers connected in parallel, which support up to 60 A (30 A per diode, measured at 135º C) each. 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 30 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 429 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 other two STPS60L45CW Schottky rectifiers connected in parallel, which support up to 60 A (30 A per diode, measured at 135º C) each. 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 30 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 283 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.

The +12 V output, on the other hand, uses a very unique design, using a partial synchronous configuration. On a synchronous configuration the two diodes (rectifying diode and freewheeling diode) are replaced by two power MOSFET transistors (called control MOSFET and synchronous MOSFET, respectively). This power supply continues using rectifying diodes (four in parallel, to be exact), adding two power MOSFET transistors to do the freewheeling part. Two freewheeling diodes were kept to make sure the power supply is avoiding cross-conduction (i.e., the rectifying diodes and the syncrhonous MOSFETs are not conducting at the same time).

The diodes are provided by three 40CPQ06 Schottky rectifiers, which can deliver up to 40 A (20 A per diode measured at 120º C) each. The two synchronous MOSFETs are IFRS3207, capable of delivering up to 130 A at 100º C each.

In order to calculate the maximum theoretical current and power the +12 V can deliver, we need to consider the side (rectifying or freewheeling) that provides the lower current limit. That would be rectifying side with the four 20 A diodes connected in parallel. Using the same math shown before, this gives a maximum theoretical current of 114 A or 1,371 W. Really impressive.

The +12V filtering stage from this power supply is also different from other power supplies: it provides two separated filtering sections, one for the +12V1, +12V2 and +12V3 rails and another for the +12V4, +12V5 and +12V6 rails. This is great.

We could also clearly see that each virtual rail was really connected to the monitoring integrated circuit (a PS232S), which is in charge of the power supply protections, like OCP (over current protection). OCP was really activated, as we will talk about later.

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

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Figure 14: +3.3 V rectifier, +5 V rectifier and +12 V rectifier.

As you can see in Figure 14 this power supply has two thermal sensors attached to its secondary heatsink. One of them is used to control the fan speed according to the power supply internal temperature and the other is used on the power supply over temperature protection (OTP) circuit. We will talk more about this circuit later.

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 has (like over temperature) is implemented outside this integrated circuit.

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Figure 15: PS232S monitoring integrated circuit.

On this power supply the big electrolytic capacitors from the active PFC circuit are Japanese from Chemi-Con and rated at 85º C, while the electrolytic capacitors from the secondary are Taiwanese from Teapo and rated at 105º C.