TM 11-6125-261-30
CHAPTER 2
FUNCTIONING OF EQUIPMENT
Section I. BASIC OPERATION
2-1. Overall Functional Description
is fed through the integrator to the primary center tap of
the main transformer. The end taps of the transformer
a. As an aid in understanding the operation of the
primary are alternately switched to ground at a 400 hertz
inverter described in this chapter, refer to the detailed
rate by the inverter switches. A 400 hertz sine wave is
block diagram, figure FO-1. schematics, FO-2 through
formed in the tuned secondary of the transformer for
output power. This is duplicated for each phase.
NOTE
Circuit function titles can be used to cross
2-2. Repetitive Circuits
reference the block diagram, schematics, and
Since the three phases of the inverter function basically the
theory description.
same way, the detailed functional description discusses
b. The operation of the inverter is demonstrated by
primarily phase A. Phase B and phase C are discussed
reviewing the block diagram (fig. FO-1) and referring to
separately only where they differ. In all cases where there
the waveform illustrations (fig. 3-1) referenced on the block
is a duplicate function, the reference designators for phase
diagram. The inverter in its simplest form is demonstrated
B and phase C follow the reference designator for phase
by referring to the pulser, the integrator, the inverter
A. The detailed description begins with the input filter
switches, and the main transformer. The 28 V dc input is
and proceeds logically to the output.
changed to a pulse controlled current source (pulser) which
Section II. DETAILED FUNCTIONAL DESCRIPTION
voltage for the oscillator at its emitter. The output will vary
2-3. 28 V Dc Filter
from about 8 V dc to about 14 V dc.
The +28 V dc filter has three purposes. The filter prevents
external high frequency noise from entering the unit, it
prevents internal high frequency noise from leaving the
unit, and it serves as a surge current storage bank to
2-7. Vout Voltage Divider and Error Detector
compensate for very high current requirements of the
a The output voltage feedback is first applied to a
inverter. The first two functions are performed by the A44
voltage divider A24R29 and A24R31 (fig. FO2) for phase
filter assembly and A3L1 (fig. FO-2). The current storage
A. The feedback output is reduced to approximately 55 V
bank consists of A 13C1 through A 13C17. The filter A44 is
ac. This voltage is then rectified, filtered and reduced by an
a sealed, encapsulated unit.
additional voltage divider. The Vout feedback is applied to
2-4. +16.5 V Dc Regulator
the error detector transistor A22Q103 (fig. FO-3). Since the
emitter bias of QI03 is determined by a 6.2 V zener diode,
The regulator is a standard series regulator. Zener diodes
A22CR104, the transistor will not turn on until the
A22CR102 and A22CR 103 (fig. FO-3) provide a reference
feedback signal exceeds 6-8 V (6.2 V 0.6 V for Q103
of 18 volts 0.9 vo1ts. A22Q101 and A22Q102are the series
emitter-base junction). The voltage at the collector is the
pass transistors. The bias supply output at the emitter of
bias for the oscillator control. A22CR104 provides the
Q102 is + 16.5 volts 0.9 volts.
reference voltage for all three phases.
b. Phase B and phase C operated slightly different.
2-5. +16.5 V Dc Requlator
Phase B feedback is applied through stepdown transformer
The +16.5 V dc output serves as the bias voltage for the
A24T5 (fig. FO-2). Phase C feedback is applied through
stepdown transformer A24T6. The reduced signals are
higher current +16 V dc pass transistor A24Q16 which
then fed through A24U28, a temperature compensation
provides the +16 V dc output at the emitter. This bias
module. Duplicate circuit action resumes at this point.
supply serves phase B and C circuits.
c. As the feedback voltage increases, the voltage at the
2-6. Oscillator Control
collector of A22Q103 (fig. FO-3) decreases, and the voltage
at the emitter of Ql04 (oscillator supply voltage) also
The oscillator control, transistor A22Q104 (fig. FO-2)
decreases. Potentiometer A22R109(OB-A21RI101, OC-
(OB-A21Q110, 0C-A21Q10) is also a series regulator.
A21R1) controls the feedback signal until the point
However the bias is provided by the Vout error detector
of output voltage regulation is reached.
(para. 2-7). The oscillator control provides the supply
2-1
