Solid State Electronic Devices, 7th Edition

7.6 Switching

In a switching operation a transistor is usually controlled in two conduction states, which can be referred to loosely as the “on” state and the “off” state. Ideally, a switch should appear as a short circuit when turned on and an open circuit when turned off. Furthermore, it is desirable to switch the device from one state to the other with no lost time in between. Transistors do not fit this ideal description of a switch, but they can serve as a useful approximation in practical electronic circuits. The two states of a transistor in switching can be seen in the simple common-emitter example of Fig.  7–12. In this figure the collector current i_C is controlled by the base current i_B over most of the family of characteristic curves. ...