Figure 1-46.-Phase shift of gate pulse.

on for a greater or smaller portion of the half cycle.

The SCRs accomplish power control because they

Figure 1-46 shows how power can be increased as the

are rectifiers and in an ac circuit conduct only during

firing point is moved along the phase time axis.

half of each cycle and then only after being turned on

by a positive gate pulse (from the trigger amplifier).

The firing point is determined by the position (or

timing) of a spiked gate pulse. When applied to the SCR,

Power control is accomplished by switching the power

Figure 1-46.-Phase shift of gate pulse.

1-42