+100 V Rectifier Circuits

TM 11-5820-695-35

if an excessive temperature develops.

The circuit description for the +100 V and +28 V rectifier

circuits are provided in the following subparagraphs.

(1) Within control circuit 3A6A2 (fig. 5-105) develops a

corrective lator 3A6A2Q1 develops the pass transistor

a. +100 V Rectifier Circuits. The lO0-volt rectifier

control voltage and current limiting control signals; and

produces approximately 126 VDC. In this circuit, power

transistor stage 3A6A2Q1 provides the overvoltage trip

from transformer windings 3-4 (95 VRMS) is applied to

signal. Power to operate the control circuit is derived by

the fullwave bridge rectifier formed by diodes 3A6CR1

a bridge rectifier (A2CR1-A2CR4), which is energized by

through 3A6CR4. Parallel connected filter capacitors

a separate secondary winding (pins 3A7T1-5 and

3A6C1 through 3A6C4 smooth the rectifier ripple, and

3A7T1-6) on 3A7 transformer 3A7T1. Voltage regulator

Darlington connected transistors 3A6Q1 and 3A6Q2 act

3A6A2U1 contains a reference voltage amplifier, a

as the regulator series pass transistors.

Silicon

differential error amplifier, a current limiting transistor,

controlled rectifier 3A6Q3 forms an overvoltage crowbar

and a series pass output transistor. The reference

circuit across the rectifier output terminals, pins 5, 6, 7

amplifier output of 7.15 volts appears at pin 3A6A2U1-6.

and 8 of connector 3A6P2. The crowbar circuit short-

This voltage is connected to the voltage sensing

circuits the regulated output in the event of a regulator

network formed by resistors 3A6A2R4 and 3A6A2R5,

failure, or momentary overvoltage condition. Control

potentiometer 3A6A2R3, and 6.3 volt zener diode

voltages for the series regulator and crowbar circuits are

3A6A2VR2.

The divider network establishes a

obtained from +100 V regulator printed wiring board

reference level at the noninverting input to the error

assembly 3A6A2 through terminals 3A6A2E3 through

amplifier (pin 3A6A2U1-5). The tap on potentiometer

3A6A2E7. The output voltage of the regulator is sensed

3A6A2R3 picks off a voltage which is proportionate to

by the control circuit through terminals 3A3E5 and

the regulator output, and therefore causes changes in

3A3E6. In turn, the control circuit (fig. 5-105) precision

the output voltage to be proportionately applied to the

voltage regu-voltage at terminal 3A3E3, which varies

inverting input (pin 3A6A2U1-4) of the error amplifier. If

the voltage across the series pass transistors (3A6Q1

a rise in output voltage occurs due to a change in load,

and 3A6Q2) so a constant output voltage is maintained.

the output of the error amplifier proportionately becomes

Resistor 3A6R2 provides a path for any low level base

more positive. This causes the series pass transistor in

to emitter current through pass transistor 3A5Q1 and

regulator 3A6A2U1 to conduct less and thereby

3A6Q2 when they are cut off. This assures that the

decreases the voltage at terminal 3A6A2E3. In turn,

pass transistors will not conduct due to noise in the

conduction through Darlington pair 3A6Q1-3A6Q2 is

control circuits. Current limiting is initiated by the action

reduced, causing the regulator output voltage to

of sensing resistor 3A6R3 which causes a voltage

decrease to the nominal level determined by the setting

representative of the load current to be applied to the

of potentiometer 3A6A2R3. Decreases in the supply

current sensing terminals (3A6A2E4 and 3A6A2E6) of

output voltage create the opposite reaction to that

the control circuit. Thermal protection for the regulator

explained above.

components is provided by switch 3A6S2. This switch

senses the heat sink temperature of the Darlington pair

(2) Foldback current limiting is provided by

between the limits of 230 and 260 degrees F, and opens

the current limiting transistor within voltage regulator

Change 6 2-133