
142 10 ◊ Phase Control
10.7. Gate Drive Circuits
Many arrangements have been used to derive the phase references for
SCR gate drives. These include phase shifters, phase locked loops,
ramp intercepts, cosine intercepts, and programmable counters,
among others. Most can be implemented in either hardware or soft-
ware. A simple R/C phase shifter may be suitable when a limited
range of phase control is satisfactory, although cascaded sections will
provide a larger range. The programmable counter relies on a high-
frequency reference signal that is initiated at a reference point in the
line voltage. The control then counts cycles of the reference to estab- ...