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TO 31R2-2GRC171-2
TM 11-5820-815-14
NAVELEX 0967-LP-544-5010
A5T1 while A5Q4/Q6 is on induces a positive-to-negative
4-216. +12-V SERIES REGULATOR. Refer to figure 4-
voltage pulse across terminals 5 and 2 of A5T3. This
8. A 26-V dc input voltage is applied to transistor Q3 of
positive voltage appears at low-pass filter A5L1-A10C14
the +12-V series regulator.  To develop the +12-V dc
through forward-biased rectifier diode A5CR16.
output voltage, a sample of the output voltage is
developed across resistors R12 and R13 of voltage
4-210. Since the variable edge of the 40-kHz variable
divider R11-R12-R13 and applied to the inverting input of
duty cycle waveform controls the off-time switch, voltage
the error amplifier of U2. A stable reference voltage of
is only applied to the low-pass filter during the time when
about 7.15 V dc is developed by U2 and applied to the
output transistor switch A5Q2/Q3 or A5Q4/Q6 is turned
noninverting input of the error amplifier.  The error
on. No voltage is applied for the remainder of the 40-
amplifier compares the sample of the output voltage
kHz period. This results in a voltage in the form 40-kHz
developed across R12 and R13 to the reference voltage
pulses, but due to the filter action of filter choke A5L1
and applies the result to the base of the series pass
and chassis A10 filter capacitor C14, the voltage pulses
transistor of U2.  The series pass transistor controls
appear at the load as an average dc voltage level that is
base current to transistor Q3 to control the output
a function of the voltage pulse width. Through remote
voltage. Resistors R12 and R13 are test selected to set
sensing, the dc-dc converter varies the width of the
the output voltage to about +12 V dc.  To achieve
voltage pulse to maintain an average +26-V dc output
regulation, small changes in output voltage are amplified
by the error amplifier to control base current to Q3. If the
output voltage tries to increase, the error amplifier output
4-211. Zener diodes A5A3VR11 and A5A3VR2 across
decreases to reduce base current to Q3. This causes
output transistor switches A5Q2/Q3 and A5Q4/Q6 limit
Q3 to conduct less to bring the output voltage back to
the voltage applied across these transistors to about 140
+12 V dc.  The opposite occurs if the output tries to
V dc when they are turned off.  Resistor-capacitor
networks A5A3R59-C15, A5A3R57-C4, A5A3R60-C16,
A5A3R58-C5, A5A3R1-C8, and A5A3R2-C9 suppress
4-217.  Current limiting resistor R10 limits the output
switching transients to protect the transistors from
current from the +12-V series regulator to approximately
damage that could result from overvoltage conditions.
1.6 amperes.  Current flow through R10 develops a
voltage drop which is applied between the base and
emitter of the current limiting transistor of U2. When the
crowbar A5A1Q16 shuts the output switching circuit off if
output current begins to exceed approximately 1.6
the output voltage exceeds approximately 30 V dc.
amperes, the voltage drop across R10 begins to forward
Zener diode A5A1VR13 conducts when the output
bias the current limiting transistor and turn it on. When
voltage exceeds the zener voltage of about 30 volts.
on, the current limiting transistor shunts base current
This develops a voltage across resistor A5A1R60 which
from the series pass transistor causing it to reduce base
fires SCR A5A1Q16. When A5A1Q16 fires, it grounds
current to Q3. This decreases collector current through
the primary winding of current base drive transformer
Q3 to limit the current through resistor R10 to
A5T3.  This squelches base drive to A5Q2/Q3 and
approximately 1.6 amperes.
A5Q4/Q6 causing whichever transistor pair is turned on,
to turn off.
4-218. -12-V SERIES REGULATOR. Circuit operation
of the -12-V series regulator is similar to that of the +12-
V series regulator (paragraph 4-216). Resistors R17 and
R18 are test selected to set the output voltage to
4-214.  GENERAL.  Refer to figure FO-23.  Voltage
approximately -12 V dc. Voltage sensed across resistor
regulator module A6 consists of four series regulators, a
R16 limits the output current to about 1.6 amperes.
zener diode regulator, and a 1-diode-drop voltage
source. The four series pass regulators receive 10-, 26-
4-219. +5.1-V SERIES REGULATOR. Circuit operation
and 17-V dc unregulated voltage from dc-dc converter
of the +5.1-V series regulator is similar to that of the +12-
module A5 and provide 5.1-, 12-, -12-, and 22-V dc
V dc series regulator (paragraph 4-216) with the
regulated voltage to circuits of the receiver-transmitter.
exception that voltage divider R4-R5-R6 divides down
The zener diode (VR1) regulator develops about +14 V
the internal reference voltage of U1 to set the output
dc from the 26-V dc input.  The 1-diode-drop voltage
voltage. Resistors R4 and R5 are test selected to set the
source (A6A2R1-R2-CR1) develops about -1.0 V dc from
output voltage of the +5.1-V series regulator to
the -12-V dc output. This output is named -0.7 V dc
approximately +5.1 V dc. Voltage sensed across resistor
throughout the radio set. Diode A6A2CR2 prevents the
R3 limits the output current to about 5.3 amperes.
voltage from going positive by more than about +0.7 V dc
4-220. +22-V SERIES REGULATOR. Circuit operation
4-215. Since circuit operation of all four series regulators
of the +22-V series regulator is similar to that of the +12-
is functionally the same, only the +12-V dc series
regulator will be discussed in detail.

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