TM 11-6625-2958-14&P
SECTION IV
PRINCIPLES OF OPERATION
Figure 4-1. Overall Block Diagram
4-1 OVERALL 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 ap-
plied 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 pro-
vide a regulated voltage or current at the output
terminals.
4-5 The series regulator is part of another feed-
back loop consisting of the error and driver ampli-
fiers and the constant voltage/constant current
compactors. The series regulator feedback loop
provides rapid, low magnitude regulation of the out-
put while the preregulator feedback loop handles
large, relatively slow, regulation demands.
4-1
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