Power Supply Voltage-Regulating Circuit.

TM 11-6665-209-40

(2) Power Supply Voltage-Regulating Circuit.

Transistors Q103, Q104 and their associated resistors, together with ger-

manium diode CR106, resistor R109 and glow tube V101, form a voltage-

regulating circuit to keep power supply output constant regardless of variations

in battery supply voltage and load, initially, S102 is turned to an ON position,

V101 remains extinguished and a negative potential is applied to the base

resistor R104 and to the base of Q103 through the emitter of Q104. This results

in Q103 being biased into full conduction and the total battery voltage is ap-

plied to the primary circuit of T101. The secondary voltage will now rise until

V101 is ignited causing the base potential of Q104 and the Q103 to become

more positive, bringing Q103 into a region of lower conduction and causing a

voltage drop to appear across Q103. This lowers the input voltage to the

primary circuit and thus the secondary voltage causing the current through

V101 to decrease. This, in turn, causes the base potential of Q104 and Q103 to

become less positive, increasing the conduction through Q103 and lowering

the voltage drop across it which again increases the input voltage to the

primary circuit of T101. The circuit will then stabilize so that a constant voltage

of approximately 6 volts is applied to the primary circuit, the difference bet-

ween this voltage and the battery voltage appearing as a drop across Q103.

This action keeps the input voltage constant with battery voltage changes.

Changes in load current are reflected as changes in the average current

through V101 which, in turn, cause a restoring voltage change at the input

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