VOLTAGE REGULATOR MODULE A6.

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

voltage.

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

decrease.

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

4-212.

OVERVOLTAGE CROWBAR.

Overvoltage

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-

4-213. VOLTAGE REGULATOR MODULE A6.

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

series

regulator

(paragraph

4-216).

regulator will be discussed in detail.

4-39