Electronic Components

As a computer professional, you should be familiar with the more common types of electronic components within a power supply. Here is a description of the basic components found on circuit boards inside a computer.

Before the advent of the circuit breaker, fuses were common in the home and office. A fuse serves one purpose-to fail-and thus cut the flow of power in the event of a current load that has exceeded the safe capacity of the system components to absorb. While fuses come in many shapes and sizes, a PC fuse is almost always a small, clear glass tube with metal caps on each end and a wire inside the tube to electrically connect the two caps (see Figure 13.10). In general, the thicker the wire, the more current it can conduct before failing. When a fuse fails, the wire will melt or be broken. You can check for a “blown” fuse by seeing if the wire is intact or broken. The amperage (A) rating (stamped on the metal cap) indicates the maximum current the wire is rated to conduct. Be sure not to exceed to the rated limits of the PC design for a fuse, because an excess power load can damage or destroy the system.


A capacitor is an electrical component used to hold an electrical charge. In photography, electronic flashes use capacitors to build up power before a picture is taken and to vary the amount of power used in a flash to control the exposure. In PCs, they are often used to regulate the flow of current to areas of the system circuits for a short period of time. Some are fixed-capacity models, whereas others can absorb or hold variable amounts of power. The amount of electrical current a capacitor can control is called capacitance, measured in microfarads.

Most PC power supplies employ an electrolytic capacitor. These devices are able to retain a significant charge for long periods. You should work with such components only if you are properly trained to know how to release any residual charge before disconnecting, testing, removing, or replacing one. Failure to follow safe procedures can result in injury or death to you, and damage to the system. These capacitors have a distinct polarity (negative and positive) to their two leads.

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