Page 1001 - Basic Electrical Engineering

Figure 14.38 Two-transistor analogy of an SCR. (a) Block diagram; (b) equivalent circuit

14.10.3 Applications of SCR

SCR is a members of the thyristor family. DIAC (bidirectional diode

thyristor), TRIAC (bidirectional triode thyristor), etc. are some of the other
members. An SCR is often referred to as a thyristor. Thyristors find wide

applications in the field of industrial electronics and control. They are
extensively used as controlled rectifiers, as inverters, converters,

cycloconverters, in ac and dc motor control circuits, dc circuit breakers, in
electronic control of heating and welding circuits, etc. We will discuss the use
of SCR as a controlled rectifier.

Single-phase half-wave-controlled rectifier

We have known earlier that a diode can be used as a half-wave rectifier. The
circuit for a half-wave rectifier is shown again in Fig. 14.39 with the input

and output voltage wave. When the input terminal A is positive, current flows
through the diode and the load. When terminal B is negative the diode is

reverse biased and no current flows through it and the load. The output