TM 5-6675-316-14
(1) Terminal regulators.
U3, U4 and U6 use an unregulated ac supply from a
30 V ac center-tapped secondary winding on the main power transformer. This ac
voltage is rectified by the bridge rectifier and filtered by capacitors C16 and C17.
Regulators U3, U4 and U6 convert this unregulated dc voltage to fixed dc voltages
according to the output specifications. The unregulated dc input does in fact
provide a minimum of 13 V under full-load conditions. Regulator U4 is provided with
an adjustable resistor-trimmer network R36-R37 to set the output at -12 V. Diodes
CR7 through CR14, between the input, output and return lines, protect the regulators
from reverse voltages that may be caused by external system faults or transient
conditions.
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