Power supply control unit

TM 9-1240-369-34

(1) Power supply control unit. The power supply

The gate also ensures the system is not in the test

mode, because it is not desired that the laser actually be

unit consists of the following circuits; PFN charge power

fired during routine testing. If these conditions are all

supply, low voltage power supply, --1600 V power supply.

met, the fire signal is developed. The fire logic applies a

reply gating, select logic, counters, interface circuits,

turnoff signal to the PFN control logic to inhibit PFN

preregulator, and a pulse forming network. Each circuit

charging during the time the laser is fired, and a charged

is explained in the following paragraphs.

(a) PFA charge power supply module. The

signal to the range light flasher logic. Prior to firing, the

reset flip-flop causes that logic circuit to apply range light

PFN charge power supply is a plug-in module which

signals to the red RANGE backlights so that they are

draws a constant current from the power source during

continuously on. When the charged signal is applied

the PFN charge cycle and, after the energy storage

with the manual reset signal, it opens a gate for the

capacitors in the PFN are charged, provides a repeaking

range light oscillator so that the backlights will flash.

operation to maintain the voltage until the laser is fired.

This indicates that the laser is ready to fire. After firing, a

The charging cycle is controlled by a linear amplifying

reset signal developed in the transmitter logic circuit card

charging sense circuit that includes a multivibrator and

assembly resets the charge logic flip-flop. It cannot

four amplifiers. This circuit develops a pulsating, rather

operate subsequently until the reset flip-flop has been

than a continuous. recharging cycle. PFN voltage adjust

reset by the SCR trigger signal, generated with the firing

(R 10) enables field adjustment of the PFN voltage and,

of the flashtube, so that it can accept the manual reset

consequently, the energy that may be stored in the PFN.

signal generated by pressing the RESET switch, or the

If R10 is set for too high an energy level. the laser flash

manual reset that occurs when the system is turned on.

can be intense enough to severely damage the

The PFN charge power supply also develops +400 V

transmitting optics; if set too low, insufficient energy will

from the + 1600 V supply for the flashtube trigger circuit.

be directed on the target to permit detection by the

(b) Bias power supply cards. A DC to DC

receiver. A thermistor is provided in this circuit to correct

converter in the preregulator converts the prime power

the PFN voltage for laser temperature changes. A high

from the battery power supply unit to + 15 V. The + 1.5

voltage DC to AC converter functions as a regenerative

V is then applied to a regulator whose output is + 10 V.

oscillator. developing a square-wave output that turns

A DC to DC converter in the low voltage power supply

two power transistors on and off to provide a constant

utilizes a square-loop oscillator to develop + 5, --5. and

current PFN charging and repeaking function. The PFN,

+ 29 V from the + 15 V output to the preregulator. Only

consisting of capacitors and inductors is charged to

the +5 V output of the low voltage power supply is

about + 1200 V. It provides the current and voltage to

regulated. The -1600 V power supply converts the + 15

maintain the desired duration of flashtube firing. Power

V regulated voltage to -1600 V required for the

supply protection is provided by a circuit that utilizes a

photomultiplier tube (PMT) bias network. DC to DC

differential amplifier and silicon controlled rectifier to

conversion. with a driven squarewave generator and full-

prevent excessive current in the power drive by turning it

wave rectification, develops these voltages.

off before the end of half cycle. or in the event of a short

in the PFN. The circuit also detects high overvoltage

processing begins in the reply gating circuit card

transients and cuts off the power drive to prevent

assembly. Some of the circuitry on this card is devoted

excessive collector voltage buildup. Further protection is

exclusively to test circuits. With the LASER MODE

provided by a differential amplifier that senses

CONTROL switch set to TEST, the laser cannot be fired.

overvoltage and acts through the PFN control logic circuit

Built-in test circuits in the reply gating card allow

to cause the SCR to cut off the power drive. .A dump

simulated range signals to be processed to verify the

relay forms a discharge path for the PFN when power is

various logic elements. Pressing the R/T control unit

removed from the receiver/transmitter unit. to eliminate

RANGE switch in test mode simulates firing and

the safety hazard of a residual charge. Activation of the

processing of one, two, three, or four replies, which are

RANGE switch on the R/T control unit initiates the firing

displayed on the commander's unit RANGE (METERS)

of the laser. The range signal is applied to the fire logic

and RETURNS indicators. The simulation logic test

circuit.

which contains a flip-flop driven by the

circuitry on the reply gating card develops simulated

multivibrator in the charging sense circuit. and a gate to

video, simulated A-trigger, and simulated reset signals

determine that the PFN is charged, the system has been

manually reset, and the RANGE switch is being pressed.

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