Chapter 14: Power Supply and Electrical Issues^315
Switching AC to DC
Electricity has two current types: AC (alternating current) and DC (direct current): AC electricity This is the type of electricity available from the electrical
outlets in a home or business in North America. AC current changes directions
about 60 times per second, moving first one way, then the other. This causes
the current to switch its flow direction in the wire as well. AC power has
advantages for the power company and your household electrical appliances,
but these advantages are of little value on a low-voltage system like a PC.
DC electricity This is the type of electricity used inside the PC. Direct current
electricity flows in only one direction at a constant level. In a DC circuit,
negatively charged particles seek out and flow toward positively charged
particles, creating a direct electrical current flow. DC current has a constant level.
For example, if you were to wire a light bulb to a battery, the current flows from
the negative terminal to the positive terminal through the light bulb, where the
electrical current causes heat and light and the light bulb glows.Has it been mentioned that the computer runs on DC power? The PC’s power supply
converts AC power from the wall socket to DC power for the computer. Even the devices
outside the computer case use DC power. Peripheral devices, such as printers, external
modems, and disk drives, use AC power converters to convert AC power to DC power.Figure 14-2. A digital multimeter combines several electricity measurement tools