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TO 31R2-2GRC171-2
TM 11-5820-815-14
NAVELEX 0967-LP-544-5010
A5A1C25 to reverse bias on-time switch A5A1Q10. This
cycle signal, both output transistor switches are off. The
keeps A5A1Q10 turned off. When A5A1Q11 turns on, a
40-kHz timing signal assures both output transistors are
pulse of current (startup pulse current) flows through
turned off for approximately 4 microseconds out of each
winding 4-3 of A5T3 to ground. This induces a positive
switching cycle. This is dead zone time which allows the
voltage across A5T3 winding 7-6 (plus at 7) and a
output switching circuit to settle.  The voltage monitor
negative voltage across winding 8-9 (negative at 8). The
output, when logic 0, shuts down the dc-dc converter by
positive-induced voltage turns A5Q2/Q3 on.
causing the output of A5A1U5A to remain at logic 1.
negative-induced voltage charges capacitors A5A3C3,
A5A3C13, and A5A3C14 through resistor to develop a
4-204. OUTPUT SWITCHING CIRCUIT. Refer to figure
negative voltage at the base of A5Q4,/Q6. This assures
FO-22.  The dc-dc converter output switching circuit
A5Q4/Q6 remains turned off while A5Q2/Q3 is turned on.
consists of the following functional circuits:  on-time
When A5Q2,/Q3 turns on, current flow through winding
switches  A5A1QO1,  A5A1Q11;  off-time  switch
11-10 of A5T3 induces a positive voltage across winding
A5A1Q17/Q12; current base drive transformer A5T3;
7-6 (plus to 7) to keep A5Q2/Q3 turned on once the
output transistor switches A5Q2/Q3 and A5Q4/Q5; step-
startup pulse terminates.  Transistor switch A5Q2/Q3
up autotransformer A5T2, and rectifier/filter A5CR15-
remains on until off-time switch A5A1Q17/Q12 turns it
CR16, A5L1-A10C14 (capacitor A10C14 is located on
the chassis). Because of their interrelationship, these
circuits will be discussed as one unit.
4-207.  In the off-time switching circuit, the logic 1 to
logic 0 transition from pulse width gate A5A1U5A that
4-205. In general, the output switching circuit functions
turned A5A1Q11 on, also applies a ground to the
as follows: On-time switch A5A1Q11 controls the turn-
cathode end of diode A5A1CR42.  This back-biases
on time of output transistor switch A5Q2/Q3. On-time
diode A5A1CR43 causing A5A1Q17/Q12 to be turned off
switch A5A1Q10 controls the turn-on time of output
as long as the signal is at logic 0. When the output of
transistor switch A5Q4/Q6. Only one transistor is on at
pulse width gate A5A1U5A changes from logic 0 to logic
any one time. Off-time switch A5A1Q17/Q12 controls
1, the ground is removed from A5A1CR42. This results
the turnoff time of both A5Q2/Q3 and A5Q4/Q6. Current
in the reverse biasing of A5A1CR42 and forward biasing
base drive transformer A5T3 couples start and stop base
of A5A1CR43 to turn A5A1Q17/Q12 on.  When on,
drive signals from the on-time and off-time switches to
A5A1Q12 shorts winding 1-5 to A5T3 to ground through
the base circuits of A5Q2/Q3 and A5Q4/Q6 to switch
diodes A5A1CR45 and A5A1CR46. The shorted primary
them on and off. In addition, A5T3 couples back a base
winding of A5T3 squelches the induced voltage in the
drive signal to sustain base drive once A5Q2/Q3 or
secondary winding causing A5Q2/Q3 to turn off.
A5Q4/Q6 is turned on. Step-up auto-transformer A5T1
combines the current flow through A5Q2/Q3 and
4-208.  This completes one-half cycle of the output
A5Q4/Q6 into a stepped up ac voltage (actually a series
switching sequence.  For one complete cycle of the
of variable width, voltage pulses).  Rectifier diodes
variable duty cycle waveform (output of A5A1U5A),
A5CR15 and A5CR16 and low-pass filter A5L1-A10C14
output transistor switch A5Q2/Q3 turns on, then off, to
rectify and filter the ac voltage into an average dc output
allow current flow through winding 1-2 of step-up auto-
voltage from the dc-dc converter.
transformer A5T1. This induces a positive-to- negative
voltage pulse across winding 4-2 of A5T1 that appears at
4-206.  The variable duty cycle waveform from pulse
low-pass filter A5L1-A10OC14 through forward-biased
width gate A5A1U5A is fed to both the on-time switching
rectifier diode A5CR15.
circuit (A5A1U1B, A5A1Q10, and A5A1Q11) and off-time
switching circuit (A5A1Q17/Q12).
In the on-time
4-209. In a similar manner, the next cycle of the variable
switching circuit, each logic 1 to logic 0 transition applied
duty cycle waveform controls the on time of output
to the clock input of flip-flop A5A1U15 causes its outputs
transistor switch A5Q4/Q6.  The logic 1 to logic 0
to change state. This results in a 20-kHz square wave at
transition causes flip-flop A5A1U1B to change state.
the true and false outputs of A5A1U1B. Because of the
The resulting logic 1 to logic 0 transition from the true
frequency division, one complete cycle of the output
output of A5A1U1B turns on-time switch A5A1Q10 on
switching circuit requires two cycles of the variable duty
allowing a pulse of current to flow through winding 2-3 of
cycle waveform. As a starting point, assume that the first
A5T3. The induced positive voltage across winding 8-9
logic 1 to logic 0 transition causes the false output of
(plus at 8) turns A5Q4/Q6 on. Once A5Q4/Q6 turns on,
A5A1U1B to change from logic 1 to logic 0.  The
current flow through winding 12-13 of A5T3 induces a
negative-going transition is coupled through capacitor
positive voltage across winding 8-9 to keep A5Q4/Q6
A5A1C26 causing base current to flow in on-time switch
turned on. Off-time switch A5A1Q17/Q12 turns A5Q4/-
A5A1Q11. This turns A5A1Q1 on for the length of time
Q6 off when the variable duty cycle waveform changes
required for A5A1C26 to charge. At the same time, the
from logic 0 to logic 1.  The current flow through
logic 0 to logic 1 transition from the true output of

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