ARMY TM 5-6675-308-34
MARINE CORPS TM 08837A-34/2
28V power supply
d. DC-to-AC Sine Wave Inverter. The inverter, a
class B push-pull amplifier, produces 26V and 115V,
Ambient temperature control DC power supply
400 Hz sine waves and is driven by a 400-Hz constant
amplitude sine wave oscillator. Voltage feedback. is
DC-to-AC sine wave inverter
from the 26 VAC output terminal. An overcurrent
DC-to-AC square wave inverter
protection circuit senses the DC current into the center
tap and each leg of the inverter transformer primary
Power supply monitor and control
and controls the DC driving signal level to prevent
Battery charger
transformer saturation.
Battery monitor and control
e. DC-to-AC Square Wave Inverter. The inverter
produces a 115V, 400-Hz square wave unregulated
a. RFI Filters. Two RFI filters make up this assem-
output. This square wave voltage lags the sine wave
bly. The first is located at vehicle input power and
inverter 26 VAC is differentiated to provide the 90-
smooths current transients when input power is
degree phase shift and clipped to form a square wave.
switched between vehicle power and PADS. The second
The driving signal is passed through a two-pole filter to
filter attenuates current ripple that is felt by the input
increase the rise time of the output square wave and
power source due to pulse currents drawn by DC
minimize EMI. The rest of the driving circuit is the
regulators and AC inverters.
same as described for the sine-wave inverter.
b. 28V Power Supply. The 28V power supply is
f. Power Supply Monitor and Control. This circuit
a 25-kHz switching regulator. This circuit supplies 28,
senses and controls power supply output voltages.
+2, 20, and 14V for the assembly control circuits
When the outputs exceed specified limits, the on/off
and + 3V boosting voltages for three switching regula-
control circuit shuts down all power supplies and the
tors. The + 28V is sensed and compared to a reference
power fault indicator is operated. If a power supply
voltage at the error amplifier input. The error amplifier
fails and bus voltage is below + 20V, the battery fault
output voltage is fed into a pulse width modulator that
indicator is also operated. Overvoltage or undervoltage
controls the on-off duty cycle of the power switching
signal (IMU inhibit) causes the power supplies to shut
transistor in the switching regulator. The switching
down.
regulator output voltage is sensed by the power supply
monitor and control circuit. If the output voltage of the
g. Battery Charger. This circuit charges the PADS
switching regulator or DC-to-DC converter exceeds the
batteries via the vehicle power. A DC-to-DC converter
specifed amplitude, the on/off control is turned off and
boosts the vehicle power by + 6V. The voltage is then
shuts down the switching regulator,
regulated to + 28V to charge the PADS battery. Charg-
ing current is sensed and controlled to 6 amps maxi-
c. Ambient Temperature Control DC Power Supply.
mum by the battery monitor and control circuit on the
The ambient temperature control DC power supply
sequence monitor circuit and assembly.
consists of a 40-kHz switching regulator and tempera-
ture control circuit. The operation of the switching
h. Battery Monitor and Control This circuit turns
regulator is similar to that described for 28V power
the power supply assembly on or off, and controls the
supply except that the reference voltage to the error
battery charge and SCR firing circuits.
amplifier equals the absolute value of the ambient
(1) Power Supply On-Off Circuit. The power sup-
temperature error signal from the IMU. The ambient
ply assembly operates when either circuit breaker CB1
temperature error signal, therefore, determines the out-
or CB2 is closed and when the CDU ON-OFF switch-
put voltage level of the switching regulator. The regula-
indicator is set to ON. After a delay, power relay K2 is
tor output voltage is connected to the heater through
energized and the power supplies are turned on. The
relay K3. When the ambient temperature error signal is
power supply assembly is shut off when the CDU ON-
negative, signifying an increase in internal IMU temper-
OFF switch-indicator is set to OFF, or upon detection
ature, relay K3 is energized, switching the regulator
of an overvoltage or overcurrent condition or presence
output voltage to the IMU thermoelectric coolers to
of an IMU overtemperature signal.
reduce the internal temperature. When system power is
turned on, the control circuit applies power to the
(2) Battery Charger Control This circuit senses
transient heaters through relay K1. When the IMU
bus voltage levels, SCR current levels, circuit breakers
internal temperature reaches a given level, this control
CB1 and CB2 on-and-off conditions, and controls bat-
circuit deenergizes relay Kl, removing power from the
tery charging current. If the SCR current falls below 0.5
transient heaters. A gain and polarity sensing circuit
amps, a power transistor is turned on and vehicle power
checks the power supply voltage gain and the heater-
is applied to the charger converter. Charging of the
cooler relay connection. If the gain or polarity is not
PADS battery will be initiated if all the following
proper, the checking circuit signals the power supply
conditions are met:
monitor and control circuit to turn the power supply
off.
PADS battery is connected.
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