Section III. PRINCIPLES OF OPERATION

TM 11-5820-554-12

Section III. PRINCIPLES OF OPERATION

current until it is signaled to do so by a pulse on its

8-7. General (fig. 8-4)

third terminal gate). It latches on, when the anode-to-

The output voltage is regulated to 5 percent by the

cathode current exceeds a certain small value Ih, and

solatron autotransformer network in response to a

turns off when the current falls below this value. When

signal applied to the magnetic amplifier control

it is off, it will withstand full circuit voltages; when on,

windings by the control amplifier.

The control

its voltage drop is about 1 volt. It will withstand circuit

amplifier amplifies the difference between the output

voltages in the reverse direction.

voltage signal from the feedback circuit and the

8-10. Unijunction Transistor Firing Circuit

reference source signal. This amplified difference

This circuit supplies a pulse to get the scr's in response

voltage is applied to the control windings. The control

to a d.c. voltage signal from the difference amplifier. A

amplifier is comprised of three main stages: transistor

unijunction transistor (ujt) is a single-junction, three-

difference amplifier; unijunction transistor firing

terminal, silicon semiconductor device.

circuit; and silicon controlled rectifier (scr) power

8-11. Difference Amplifier

amplifier. Three internal harmonic filters reduce the

The difference amplifier is a two-transistor circuit. Its

harmonics in the output to less than 12 percent. The

output is approximately proportional to the difference

regulated d.c. supply provides operating voltages to the

between its two inputs. Its two outputs are the

reference source, transistor difference amplifier, and

reference voltage source and the signal voltage from the

unijunction transistor firing circuit.

output voltage feedback circuit.

8-8. Solatron Autotransformer Network

8-12. Reference Circuit

The solatron autotransformer network is a magnetic

The reference circuit is comprised of a Zener diode and

assembly which acts as a variable autotransformer. It

a resistor. The voltage developed across the Zener

is controlled by direct current and can either add to, or

diode is very stable because the d.c. voltage supplied to

subtract from, the input voltage. It is comprised of an

this circuit is preregulated by the main d.c. supply

autotransformer, a linear reactor and a two-component

regulator. The reference voltage

saturable reactor. The load is connected to the output

of the autotransformer.

One side of the

autotransformer is common to both the input power and

output loads. The other side of the input line is

connected to two taps on the autotransformer. One tap

is a step-up which has the saturable reactors connected

in series, the other tap is a stepdown and has the linear

reactor connected in series. With no d.c. control

current, power is applied through the linear reactor and

stepdown tap. Increasing the d.c. in the saturable

reactors increases the power drawn through them until

maximum step-up is reached. In operation, the d.c. in

the control windings is controlled by semiconductor

circuitry.

8-9. Silicon Controlled Rectifier Circuit

The d.c. control current for the solatron

autotransformer network is produced by a transformer

and two scr's in a full wave center-tapped rectifier

configuration. A silicon controlled rectifier is a four-

ELOD0024

Figure 8-4. Regulator,Voltage , CN-1146/FRC -95,

layer, three-terminal, semiconductor device. It acts

block diagram

both as a rectifier (it carries current in one direction

only) and as a latching switch (it will not conduct

8-5