Page 176 - Power Electronics Handbook

168 Static switches

A.C. line timing
voltage
\, ,Variabletrigger
Constant voltage

(0) to tl
Figure 8.12 Phase-delay circuits: (a) and (b) simple R-C phase shift; (c) and (d) extended R-C
phase shift; (e) and (f) ramp and pedestal; (g) variable trigger threshold

8.3 A.C. chopper regulation

Regulation of the a.c. power to a load by phase-control methods, as
described in the previous section, has several disadvantages, one being the
high harmonic content in the output, which is especially evident at large
delay angles. An alternative to phase control is chopper regulation, which
is illustrated in Figure 8.13.