relay contacts in the proper configuration to indicate
(2) The components inside the dashed lines are
faults in the AN/TCC-38 and AN/TYC-39 systems.
mounted on PCB A1. Operation is as follows: An
The switch must be positioned in accordance with
independent voltage reference for the undervoltage
the system in which the converter is used.
and overvoltage circuits is generated by series drop-
ping resistor R58, variable zener reference U8, and
(4) Light-coupled transistor U4 is normally acti-
resistive divider R56 (undervoltage/overvoltage ad-
vated through R4 and CR 17 when the converter is
on. Under short circuit conditions U4 turns off. This
just R57). It is normally set to approximately 2.8V.
tells the current limit circuits in the primary regula-
The overvoltage comparison is performed by U3A
tor that the power supply is shorted, which in turn
which compares the output voltage as monitored on
generates the foldback current-limiting short circuit
resistive divider R59-R60 with the reference. In the
event of an overvoltage condition, transistor Q14 is
turned on, which in turn activates light-coupled tran-
sistor U5. CR19, in conjunction with C8 and R53,
(1) The primary control circuits include a volt-
age regulated power supply to assure proper opera-
assures that overvoltage will not be erroneously ac-
tion; an integrated circuit which is a combined clock,
tuated by spurious noise.
pulse width generator, voltage reference and appro-
(3) Network CR23-CR24-R52 goes to the gate
priate operational amplifiers to generate the drives
of the overvoltage SCR crowbar Q7, which simulta-
to the half wave forward converter; and appropriate
neously crowbars the output voltage downward. It
start-up (soft start), overvoltage, current limiting,
should be noted that the contacts of fault indicating
and fault circuits. All of these components are lo-
relay K1 are brought to the output through a toggle
cated on PCB A1.
switch (not shown on fig. 1-6), which connects the