TM 11-6625-1683-15
filter circuit approximates 100 volts dc and
flop switching effect, resistor R77 is connected
from the +100-volt supply to the base of Q1.
activates the inverter section of the power con-
verter.
This places a slight positive bias on the base
of Q1 in contrast to the zero bias on the base
d. The function of the inverter is to trans-
of Q2. Under these conditions, Q1 is in a con-
late the 100-volt dc supply into a square-wave
ductive state while Q2 is nonconductive.
]ow-voltage ac. The components of the inverter
circuit are: resistors R77, R78, and R79; satu-
j. With the application of voltage to the
rable transformer T1; and transistors Q1 and
circuit, current flow through Q1 takes place.
Q2, both of which are type DTS-431.
The impedance of the associated half of the
primary winding under current carrying con-
e. The + 100 volts applied to transformer
ditions develops a voltage drop, making the
T1 is connected to the center tap of the pri-
collector end of the winding negative with re-
mary (terminal 2). The collector of transistor
spect to the center tap. This induces a negative
Q1 is connected to primary terminal 3, while
signal into the base end of the feedback wind-
the collector of transistor Q2 is connected to
ing, reducing the biasing potential on the base
primary terminal 1.
to the cutoff point.
f. Two feedback windings are incorporated
k. Simultaneously, the opposite end of the
as part of transformer T1. Terminal 6 of one
primary winding feeding the collector of Q2
winding is connected to the base of Q1 through
assumes a positive character, inducing a posi-
resistor R78, while terminal 7 at the other end
tive signal into the base of Q2. This cause Q2
of this feedback winding is connected to the
to become conductive. As the voltage drop
emitter of Ql, which is held at the negative
through its half of the primary winding be-
potential of the inverter circuit. Terminal 5 of
comes effective, cutoff takes place and the
the other feedback winding is connected to the
switching cycle repeats. This cyclic change
base of Q2 through resistor R79. Terminal 4
occurs at a rate of approximately 1 kHz and
of this winding is brought to the emitter of
is basically governed by the parameters of
Q2 which, in the same manner as the emitter
transformer T1.
of Ql, is maintained at the negative potential.
l. A secondary winding coupled to the pri-
g. Resistors R78 and R79 limit the current
mary is proportioned to provide an unloaded
flow in the base circuits of Q1 and Q2. Without
voltage output of approximately 8 volts ac on
these current-limiting resistors, excessive cur-
each side of the center tap. To assist in main-
rent flow could develop with a consequent de-
taining frequency, the secondary is tuned with
structive effect on the transistors
capacitor C9. This capacitor aids in removing
transient spikes that tend to appear in the out-
h. The feedback windings are phased with
put waveshape (fig. 51).
relation to the primary winding so that posi-
tive, or in-phase, feedback will occur. This
m. The square-wave ac secondary output is
implies that a positive impulse appearing at
rectified by a pair of 1N1199 diodes, CR5 and
the Q1 collector will be reflected by a positive
impulse at the base of this transistor. Simi-
tion. The dc resultant is fed to a capacitive
larly, the same relative polarization will occur
input filter consisting of input capacitor C10,
in transistor Q2. This phase relationship is gov-
series inductor L2, and output capacitors C11
erned by the direction of the windings.
and C12. The 6 volt dc filtered output is passed
through rf filter FL3 within the converter
i. In a quiescent state, the collectors of Q1
shield. This serves as a safeguard against ex-
and Q2 could be equipotential in terms of ap-
t e r n a l radiation of rf signal components
plied dc. This would inhibit essential oscillatory
generated within the converter.
action. To avoid this state and to insure a flip-
AGO 7918A
5-2
Previous Page
