The gate drive that phase
controls the four parallel SCRs is accomplished with complementary MOS hex gate MC14572
and two bipolar transistors. This adjustable line-synchronized driver permits SCR
conduction from near zero to 180 degrees. A Schmitt trigger clocks a delay monostable
multivibrator that is followed by a pulse-width monostable multivibrator. Line
synchronization is achieved through the half-wave section of the secondary winding of the
full-wave, center-tapped transformer. This winding also supplies power to the circuit
through rectifiers Dl and D2. |