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Secondary Analysis

As you can see in Figure 12 in the previous page, the first transformer drives the +5 V output and the +12 V output used on the cables that are connected on the motherboard (labeled “CPU,” i.e., +12V1 and +12V2 virtual rails), while the second transformer drives the +3.3 V output and the +12 V output used by peripherals (i.e., +12V3, +12V4 and +12V5 rails). Think of this power supply as having two independent power supplies inside.

This is the first time we’ve seen this approach. The main advantage of this achitecture is that the +12 V line connected on the motherboard (i.e., +12V1 and +12V2 rails) is not connected to the +12 V line used for peripherals (i.e., +12V3, +12V4 and +12V5), so any electrical noise produced by peripherals are not replicated to the CPU. The disadvantage is that since the +12 V outputs from each transformer are not connected together you can face a situation where one of the internal power supplies is overloaded while the other is idle, if power isn’t very well balanced (we will explain more about this in the next page).

The first +12 V output (+12V1 and +12V2 rails) is produced by two 40CPQ060 Schottky rectifiers connected in parallel, which can also deliver up to 40 A at 120° C each (20 A per internal diode). The maximum theoretical current the +12 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 20 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 57 A or 684 W for this +12 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.

The second +12 V output (+12V3, +12V4 and +12V5 rails) is identical and thus offering a maximum theoretical current of 57 A or 684 W. Thus the maximum combined is 1,368 W. But since these two outputs are not connected together they cannot "borrow" power to each other. We will explain more about this in the next page.

The +5 V output is produced by two 40CPQ045 Schottky rectifiers connected in parallel, each one supporting up to 40 A at 120° C (20 A per internal diode). 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 20 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 57 A or 286 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 two more 40CPQ045 Schottky rectifiers connected in parallel. Using the same math this output can deliver up to 57 A or 189 W.

This power supply +5VSB output (a.k.a. “standby power”) is pretty strong as well. As it happens on all ATX power supplies (even on low-end ones), it uses a separated transformer, however on this Enermax unit an F20SC6 Schottky rectifier is used, which can handle up to 20 A (10 A per internal diode).

And the –12 V output is produced by a 7912 voltage regulator, which can handle up to 1.5 A, so this output provides a maximum theoretical power of 18 W.

On the pictures below you can check all the rectifiers used on the two secondary sections of this power supply.

Enermax Galaxy 1000 WFigure 16: Secondary rectifiers used on this power supply.

Enermax Galaxy 1000 WFigure 17: Secondary rectifiers used on this power supply.

You can see again the small ferrite beads Enermax used on the terminal of all components, acting like a filter and thus decreasing noise.

This power supply has a temperature sensor attached to the heatsink used by the secondary rectifiers, in charge of controlling the fan speed.

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Gabriel Torres is a Brazilian best-selling ICT expert, with 24 books published. He started his online career in 1996, when he launched Clube do Hardware, which is one of the oldest and largest websites about technology in Brazil. He created Hardware Secrets in 1999 to expand his knowledge outside his home country.