Page 1004 - Basic Electrical Engineering

Figure 14.41 SCR controlled single-phase full-wave-controlled rectifier bridge

Figure 14.42 Static switching circuit using SCRs and diodes

If we used four diodes in the bridge circuit, the output voltage would have

been a full-wave-rectified dc. By using two SCRs T and T we are able to
2
1
vary the magnitude of the average output voltage by changing the firing angle
α of the two SCRs. The output voltage is variable dc because the angle α can
be changed by changing the time at which the gate current will be made

available to the two SCRs. With this variable dc we can control the speed of a
dc motor, for example. In Fig. 14.41, the gate control circuit for the SCRs

have not been shown.

Static switching circuit using SCR-diode combinations