Primary Control Circuits

TM 11-6130-429-40

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

protection.

event of an overvoltage condition, transistor Q14 is

g. Primary Control Circuits (fig. 1-7).

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

1-13