Figures 5-2. Regulated power supply, simplified schematic diagram.

TM 11-6625-539-14-4

EL6625-539-14-4-TM-5

Figures 5-2. Regulated power supply, simplified schematic diagram.

5-3. Beta Function Circuit

d. Meter sense amplifier AR3 forces the re-

quired base current from the device under test to

a. A simplified schematic diagram of the beta

flow through resistor R30. The output voltage at

function circuit is shown in figure 5-3. The circuit

AR3, therefore, is proportional to the base current

is shown for the NPN transistor, but it also

of the device. When this voltage is applied to

applies to a PNP when the polarity is reversed

meter amplifier AR4, it drives the meter to indi-

through POLARITY switch S2.

cate the beta of the device under test. RANGE

switch S3 selects the required sensitivity level to

b. The beta circuits are automatically energized

provide full-scale deflection at 5 mV, 50 mV, and

w h e n the BETA is selected on FUNCTION

500 mV to correspond with full scale beta ranges

SWITCH S1. No additional front panel adjust-

of 100, 1000, and 10,000.

ments are required.

e. Since beta is an inverse function, and the

c. The 1-kHz multivibrator Z2 drives analog

higher beta transistors read less than full scale,

switches Z1A and Z1B to produce a square wave

transistors with betas from 1 to 10,000 may accu-

at C6. The square-wave peak-to-peak level is equal

rately be tested.

to the difference between circuit common and the

output of AR2 through CR6. Amplifier AR2 ampli-

5-4. Ohms Function Circuit

fies the square wave and drives the emitter of the

a. A simplified schematic diagram of the ohms

device under test to produce a collector current

function circuit is shown in figure 5-4. A voltage

which flows through resistors R4 and R6. The

divider consisting of resistors R10, R13, R15, R16,

values of R4 and R6 are such that the input of the

and R20 produces a 10 mV source for the meter.

sense amplifier AR1 is satisfied when an average

I CES ZERO/OHMS ADJ controls are adjusted to

collector current of 1mA flows. In this manner,

provide full-scale meter deflection when the unit

the sense amplifier AR1 controls the emitter drive

is not connected to the equipment under test.

signal, forcing the device under test to conduct at

RANGE resistors R19, R22, and R25 provide ohms

1mA. Variable resistor R6 provides an adjustment

ranges of 100 ohms, 1 kilohm, and 10 kilohms at

of the current level during NPN calibration. Vari-

center scale. The meter amplifier AR4 monitors

able resistor R3 provides the adjustment during

the voltage divider formed by the range resistor

PNP calibration.

5-2