PC Hardware —

DC Power (Direct Current)

Alternating current is used for transporting low-cost power to end users. But a computer's electronic components won't run on AC power-they need a steady stream of direct current. The PC's power supply performs several tasks, but the main function is to convert AC into DC. A computer's power supply combines two components to handle this job: a step-down transformer and an AC/DC converter. The AC adapters used for laptop computers, many low-cost ink-jet printers, and many other consumer electronics do the same thing-turn alternating current into lower-voltage direct current.

As we have seen, DC is electrical energy that travels in a single direction within a circuit. (The electrical energy in a thunderstorm is another example, but not very practical in electronic applications.) DC current flows from one pole to another, hence it is said to have polarity (see Figure 13.4). The polarity indicates the direction of the flow of the current and is signified by the "+" and "-" signs (see Figure 13.5).

Figure 13.4 DC power

Figure 13.5 DC voltage

Measuring Electricity

A computer professional should know how to use a multimeter-sometimes called a VOM (Volt-Ohm Meter) or a DVOM (Digital Volt-Ohm Meter). An electrical test meter is probably the best (and most practical) tool for troubleshooting electrical problems. It is not necessary to be an "electronic technician" to use this tool effectively.