Oscillator Circuit

TM 11-6130-377-14

transients that may be present at the turn-on of the

b. Oscillator Circuit (fig. 5-2 and FO-2). The crystal

inverter.

oscillator consists of transistors Q1 through Q5 and

crystal Y1 (transistors Q1 and Q3 operate as a relaxation

g. Soft-Start Generator. (fig. 5-2G and FO-2). The

oscillator). The 480 KHz output to the frequency divider

soft-start generator (bypass SCR driver) consists of

is buffered by transistor Q5.

transistor Q15 and Q16. During the 350 millisecond

power-on delay, transistor Q15 is off and transistor Q16 is

c. Frequency Divider Circuit (fig. 5-2 and FO-2).

on, grounding the gate of the bypass SCR through

The frequency divider consists of divide-by-ten counters

connector J1 pin 1. The bypass SCR is off, causing the

U3, U4 and U5; divide-by-four counter U6; and divide-by-

inverter input circuitry to come up to full power at a

two counter U8. The output to the SCR driver is a 60-Hz

gradual rate. When transistor Q9 turns on, transistor Q15

squarewave through connector J2 pin 2.

turns on, transistor Q16 turns off, and the bypass SCR

d. SCR Driver Circuit (fig. 5-2D and FO-2). The

turns on for normal operation.

SCR driver consists of phase-splitter U9 and transistors

h. AC Output Relay Driver (fig. 5-2H and FO-2).

Q20 and Q21. The 60 Hz input to transistor Q21 is

The AC output relay driver consists of transistor Q18.

inverted by one gate and the input to transistor Q20 is

During the 350-millisecond power-on delay, transistor Q18

double-inverted by two gates of integrated circuit U9

is turned off. This caused the AC output relay (through

which is connected as a phase-splitter. The comple-

connector P1 pin 6) to be deenergized, disconnecting the

mentary 60 Hz signals cause transistors Q20 and Q21 to

inverter AC output circuit breaker from the output

drive output transformer T1. Transformer T1 provides

terminals. When transistor Q9 turns on, transistor Q18

gate drive for the inverter power SCRs through connector

turns on and energizes the AC output relay. This

J1 pins 3, 9 and 12.

connects the AC output circuit breaker of the inverter to

e. Power-on Delay (fig. 5-2E and FO-2). When the

the output terminal for normal operation.

system input circuit breaker CB1 is closed, + 110 vdc

i. Low Voltage Fault Sensor (fig. 5-21 and FO-2).

INPUT VOLTAGE is applied to connector J1 pin 2 and

The voltage fault sensors monitor the +110 vdc INPUT

thus to the power-on delay circuit which consists of

VOLTAGE at connector J1 pin 2 through a voltage divider

transistors Q7, Q9 and Q10. When +110 vdc is first

consisting of resistors R8 and R11. The low voltage fault

applied, transistors Q7, Q9 and Q10 are off until capacitor

sensor consists of operational amplifies U2 and transistor

C9 charges through resistor R23. When the charge on

Q6 and Q8. A reference voltage is setup at the + input of

capacitor C9 exceeds approximately 7.4 volts (the voltage

the operational amplifier by potentiometer R15 and

of Zener diode CR3 plus the base-emitter drop of

resistors R14 and R16. Potentiometer R15 is set so that

transistor Q7), transistor Q7 turns on. This delay is

the voltage of the + input is below the-input as long as the

approximately 350 milliseconds after turn-on of the

+110

vdc

INPUT

VOLTAGE

remains

above

inverter input circuit breaker. When transistor Q7 turns

approximately 95 vdc. If the + 110 vdc INPUT VOLTAGE

on, transistors Q9 and Q10 turn on. Transistor Q9, in

drops to approximately 95 vdc, a voltage potential is

turn, pulls up a line that is connected to the sensor delay,

created across the + and -inputs of the amplifier. This

soft-start generator, and AC output relay driver circuits,

causes the amplifier output to rise which turns off

which are subsequently described below.

transistors Q6 and Q8. When transistor Q8 turns off, the

f. Sensor Delay (fig. 5-2F and FO-2). The sensor

line through diode CR7 rises and causes the shunt trip

delay consists of transistors Q11 and Q13. During the

relay driver to operate as described below.

350-millisecond power-on delay, transistor Q1 is off and

High Voltage Fault Sensor (fig. 5-2J and FO-2).

capacitor C12 charges through resistors R34 and R35.

The high voltage fault sensor consists of operational

The charge on capacitor C12 holds transistor C13 on,

amplifier U7 and transistors Q12 and Q14. The high

which inhibits the voltage fault sensor circuits. Transistor

voltage fault sensor operates in a manner similar to the

Q9 turning on causes transistor Q11 to turn on and

low voltage fault sensor except that the amplifier inputs

provide a discharge path for capacitor C12 through

are reversed. Potentiometer R30 is set so that the

resistor R35 and transistor Q11 to common. When

voltage of the minus (-) input of the amplifier is above the

capacitor C12 discharges to a voltage below the cut-off

voltage of the positive (+) input as long as the +110 VDC

point of transistor Q13 (approximately 50 milliseconds),

INPUT VOLTAGE remains below approximately 142

the transistor turns off and removes the inhibit command

VDC. If the +110 VDC INPUT VOLTAGE rises to

from the voltage fault sensors. The total delay of

approximately 142 VDC, transistor Q14 turns off and

approximately 400 milliseconds (power-on delay plus

sensor delay) prevents the fault sensors from reacting to

5-5