The Case and Power Supply - Anatomy of an ATX Power Supply
(Page 6 of 9 )
Before you’re ready to select a power supply, it might help you to understand exactly what goes into one. Figure 1-6 shows a naked power supply. A typical ATX power supply contains an integrated circuit board with the necessary capacitors, resistors, coils, and other electrical components needed to perform its duties. There’s no need to go into detail here for two reasons: one, the power supply’s printed circuit board (PCB) isn’t considered a serviceable part, so if you blow a power supply or if it otherwise becomes damaged, it’s best to replace it rather than tinker with its electronic innards; and two, it would take pages upon pages of explanation that would be better suited for an Electrical Engineering 101 textbook.
Figure 1-6 An ATX power supply sans cover
Internal Fan Wiring
Fan Switch Power Connector
Figure 1-7 An ATX power supply and its parts
Some power supplies may contain an on/off switch that can be used to kill the PS_ON, along with other small, ambient currents the power supply maintains when the computer is off. It contains a female power receptacle for a standard PC power cord. On the inside of the computer, it contains a jumble of wires and connectors, each of which we’ll look at individually, and each of which is labeled in Figure 1-7.
If you look at the rear (external) panel of the power supply (as shown in Figure 1-5), along with the possibility of an on/off switch, you’ll see a female AC power connector, a fan blowhole for ventilation, and a switch to toggle between 115v and 230v input. In the United States, power is supplied at a level of 115v, but to make the power supply interchangeable so it can be used in Europe and elsewhere around the world, it also accepts the European standard of 230v.
Most computer power supplies are of a type called switching power supplies. These supplies not only try to put out constant DC voltage required by the PC no matter what kind of situation the incoming AC line is coughing up, but they also draw only the amount of current needed at a given time. This makes a switching power supply an efficient power source that uses a minimum of electricity.
ATX power supplies have two fans: a rear exhaust fan that blows air out of the back of the system, and an internal fan on the bottom of the power supply that blows air from the system into the power supply. This creates a negative flow cooling system (meaning that more air flows out of the system than into it, which creates a vacuum and draws air through the case’s ambient holes).
This chapter is from Build Your Own High Performance Gamers' Mod PC, by Chen and Durham (McGraw-Hill/Osborne, 2004, ISBN: 0072229012). Check it out at your favorite bookstore today. Buy this book now.
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