Install guide

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