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Figure 2-1. Block Diagram.
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TM-11-6125-259-30 Inverter Power Static PP-7274C/A Manual
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Static Inverter Circuit Description
TM 11-6125-259-30
CHAPTER 2
FUNCTIONING OF EQUIPMENT
2-1. Static Inverter Block Diagram Functional
ground (referred to as a short to ground in the text)
Description
for the center tap of the two input chokes, which
The inverter, consists of the following subassem-
with this high current flow stores energy. During
the next cycle of operation the choke energy is
blies and sections (see block diagram, fig. 2-1): In-
discharged into the power capacitors.
put and Output EMI Filters. Start Up Regulator,
e. Power Capacitors. The power capacitors are
Boost Regulation Control, Input Chokes, Power
charged by the energy stored in the input chokes.
Capacitors, Logic, Overvoltage Sense, Overcurrent
The 37 vdc output of the power capacitors is used by
Sense, Major and Minor Drive, Major and Minor
the major and minor drive circuits, the major and
Bridge Converters, Output Voltage Sense, and Out-
minor bridge converter circuits and initially for
put Filter.
power for the start up regulator.
a. Input EMI (Electromagnetic Interference)
f. Logic. The logic circuit functions as follows:
Filter. The EMI filter reduces conducted and
logic to prduce major and minor drive waveforms,
radiated energy.
turn-on time delay logic, input overvoltage logic and
b. Start Up Regulator. The start up regulator
output overcurrent sense logic. The drive logic
p r o v i d e s regulated +5 vdc and +15 vdc bias
develops waveforms from a 9.6 KHz oscillator that
v o l t a g e s to the logic circuits and the boost
are fed to the major and minor drive circuits to
r e g u l a t i o n control. At turn-on, the start up
f i n a l l y produce major and minor quasi sine
regulator receives its input power from the power
waveforms that are fed to output voltage trans-
capacitors. After turn-on the start up regulator
formers T1 and T2. At inverter turn-on, the +15 V
receives its input from rectified voltages from the
comes on at once and the turn-on time delay logic
minor bridge converter transformer T2.
generates a signal which allows the other circuits to
c. Boost Regulation Control. This overall
stabilize before the drive waveforms and the +5 vdc
regulation circuit consists of part of the A2 assem-
and 37 vdc supplies are energized. The input
bly (high level boost) and A3 assembly (low level
overvoltage logic generates inverter shutdown
boost) and the entire A7 assembly (boost regulator).
signals for the major and minor bridges (cuts off the
The A2 and A3 assemblies function in an identical
drive waveforms) and turns off the 37 vdc supply.
way in this circuit; each one servicing an input
The output overcurrent sense logic maintains a 7.5
choke (L201, L301). The overall circuit regulates the
amp inverter output current for five seconds after
37 vdc supply. The regulation is accomplished by
an overload current of 200% or greater (output short
changing the duty cycle ratio (choke charge time to
circuit) is detected. The inverter output is then
choke discharge-into-power-capacitors time) of the
cycled off and on until overcurrent condition is
t w o input chokes which feed into the power
removed.
capacitors to form the 7 vdc supply. The duty cycle
g. Overvoltage Sense. The overvoltage sense
ratio is proportional to the input voltage and the in-
circuit detects an excessive (44 vdc) level of inverter
verter output load. The A7 boost regulator alter-
input voltage or 37 vdc supply voltage in the form of
nately acts to charge and discharge the two input
transient or static potentials. The overvoltage sense
chokes into the power capacitors in order to create a
circuit will shut down the inverter output and the 37
push-pull effect. The circuit also makes use of a
vdc supply for the duration of the overvoltage.
power ratio transfer (low voltage_high current ver-
h. Overcurrent Sense. The overcurrent sense
sus high voltage_low current) and, in addition, the
circuit provides inverter protection from overloads
circuit receives an error signal from the output
greater than 200% and support output short circuit
voltage sense circuit and this back-loop regulation
current at 2.5 times the rated current for a duration
enables fine control of the 37 vdc and the output ac
of five seconds following the application of a short.
voltage.
The current sense circuit monitors the output of
d. Input Chokes. The two input chokes are con-
each phase through current transformers. Each
nected to the inverter input voltage on one end and
transformer output is rectified by diodes to produce
to the power capacitors on the other end. The boost
an equivalent dc voltage that is fed into the output
regulator alternately provides a low impedance to
2-1

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