Dale - Computer Science Illuminated 124

Dale - Computer Science Illuminated 124 - 4.3 Constructing...

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4.3 Constructing Gates 97 Figure 4.8 The connections of a transistor Ground Source Output Base Before tackling the details of transistors, let’s discuss some basic prin- ciples of electricity. An electrical signal has a source, such as a battery or an outlet in your wall. If the electrical signal is grounded , it is allowed to flow through an alternative route to the ground (literally) where it can do no harm. A grounded electrical signal is pulled down, or reduced, to 0 volts. A transistor has three terminals: a source, a base, and an emitter. The emitter is typically connected to a ground wire, as shown in Figure 4.8. For computers, the source produces a high value, approximately 5 volts. The base value regulates a gate that determines whether the connection between the source and ground is made. If the source signal is grounded, it is pulled down to 0 volts. If the base does not ground the source signal, it stays high. An output line is usually connected to the source line. If the source
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