4-1OVERALL BLOCK DIAGRAM DISCUSSION
4-2 The major circuits of the power supply are shown on the overall block diagram of Figure 4-1.The ac input voltage is first applied to the prereg- ulator triac which operates in conjunction with the preregulator control circuit to form a feedback loop. This feedback loop minimizes the power dissipated by the series regulator by keeping the voltage drop across the regulator at a low and constant level.
4-3 To accomplish this, the preregulator control circuit issues a phase adjusted firing pulse to the triac once during each half cycle of the input ac.
The control circuit continuously samples the output voltage, the input line voltage (from A3T2), and the voltage across the series regulator and, on the
basis of these inputs, determines at what time each firing pulse is generated.
4-4 The phase adjusted output of the triac is applied to the power transformer where it is stepped- down and coupled to a full-wave rectifier and filter. The preregulated dc current is applied next to the series reguIator which varies its conduction to provide a regulated voltage or current at the output terminals.
4-5 The series regulator is part of another feedback loop consisting of the error and driver amplifiers and the constant voltage/constant current compactors. The series regulator feedback loop provides rapid, low magnitude regulation of the output while the preregulator feedback loop handles large, relatively slow, regulation demands.