Civil Engineering Reference
In-Depth Information
FIGURE 11-1
Basic semiconductor switching devices.
used circuit symbols in
Figure 11-1
.
The two power terminals 1 and 0 are
connected in the main power circuit, and one control terminal G. In normal
conducting operation, terminal 1 is generally at higher voltage than terminal
0. Terminal G, known as the gate terminal, is connected to the auxiliary
control circuit.
Since the devices are primarily used for switching power on and off as
required, they are functionally represented by the gate-controlled switch
shown in (f). In absence of the control signal at the gate, the device resistance
between the power terminals is large, with the functional equivalence of an
open switch. When the control signal is applied at the gate, the device
resistance approaches zero, making the device behave like a closed switch.
The device in this state lets the current flow freely through its body.
The voltage and current ratings of the switching devices available in the
market vary. The presently available ratings are listed in
Table 11-1
.
The switch is triggered periodically on and off by a train of gate signals
of suitable frequency. The gate signal may be of rectangular or other wave
shape, and is generated by a separate triggering circuit, which is often called
