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Functional Description of Inverter Drive Circuit Board A1A2 (1974 Model Only)
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TM-11-6130-377-14 Inverter Power Static PP-7078/U Manual
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Shunt Trip Relay Driver
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
j.
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

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