Figure 1-44.-Voltage regulator, simplified schematic.

applied via R8, which is a factory set and locked

Voltage-Sensing Circuit

reference voltage adjustment.

The voltage-sensing circuit (fig. 1-44) steps down

Resistor R9 is the voltage dropping resistor for CR7,

the 3-phase generator 440-volt ac output through volt-

and capacitor C3 reduces the ripple and noise voltages

age-sensing transformer T1 to 25-volt ac. Each phase is

across CR7 to provide a clean dc reference voltage.

rectified by diodes CR1 through CR6 and filtered by C1

Resistors R6 and R7 are load resistors for transistor Q2.

and C2. This dc voltage is proportional to the generator

Any difference between the input voltage at the base

output voltage. The dc voltage is applied to voltage

of Q1 and the reference voltage at the base of Q2 will

divider network R1 through R4 (R3 can be adjusted to

produce an error signal (a change in collector current).

develop the amount of voltage desired as the

If the input voltage is higher than the reference voltage,

representative generator output) for comparison to the

Q1 conducts heavier than Q2 and vice versa when the

reference voltage in the error voltage detector circuit.

reference voltage is higher than the input. The voltage

drop across R6 is the error voltage that is applied to the

base of the modulator Q3.

Error Voltage Detector Circuit

Modulator Circuits

Transistors Q1 and Q2 (fig. 1-44) forma differential

amplifier to compare the base voltages of the two

transistors. The signal from the voltage-sensing circuit

The modulator circuit (fig. 1-44) modifies the time

is applied to the base of Q1, while the reference voltage

constant of the RC circuit (C4, R10, and the Q3

collector-emitter resistance). (The collector-emitter

is applied to the base of Q2. The reference voltage is

Figure 1-44.-Voltage regulator, simplified schematic.

1-40