Tektronix 175, Руководство пользователя

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SECTION 3
CIRCUIT
DESCRIPTION
Block Diagram
The Block Diagram shows the relationship of the Collector
Sweep, the Step Generator, the Step Amplifier, and the CRT
Deflection Amplifiers to the transistor under test. The Step
Generator is driven by the 60-cycle line voltage and the
waveform from the Step Amplifier is applied to the input of
the transistor under test. The Collector Sweep Generator
supplies the full-wave rectified pulses that are applied to the
collector of the transistor. Notice that the pulsations occur
at twice the line frequency. The crt deflection amplifiers are
shown connected for a display of the transistor l c - V c char ­
acteristic curves.
The three possible time relationships between waveforms of
the Collector Sweep and the Step Generator are shown in
Fig. 3-1. In waveform (b), each voltage step begins at a time
when the Collector Sweep voltage is zero. In waveform (c),
each step begins at a time when the Collector Sweep volt­
age is at its maximum value. In waveform (d), steps begin
both at times when the Collector Sweep voltage is at its
maximum value and when it is at its minimum value.
Collector Sweep
The Collector Sweep circuit rectifies the 60-cycle line volt­
age (full-wave circuit) to produce 120 sweeps per second for
the collector of the transistor under test.
The primary voltage of T702 is variable from 0 to 140
volts rms by the variable autotransformer T701 (PEAK VOLTS
control). The secondary of T702 provides output voltages up
to 20 volts and 200 volts, peak, depending on the setting of
the PEAK VOLTS control and the PEAK VOLTS RANGE switch
SW706. The collector-supply primary is protected by a cir ­
cuit breaker, set to trip within 30 seconds at 1.2 ampere rms
current but to hold on a rms current of 1 ampere. The turns
ratio of the transformer for the 20-v range is such that a
maximum peak current of 15 amperes is available with 1
ampere rms in the primary. Because the current pulses for
transistors are not sinusoidal nor of constant amplitude, and
their duty cycle is dependent upon the characteristics of the
device being tested, it is difficult to say what maximum col ­
lector-current curves can be plotted. Generally, a family of
collector-current curves can be plotted to 20 amperes or more
b. Upper 120 position of STEPS/SEC switch
COLLECTOR SWEEP
waveform
STEP GENERATOR
waveform
f
Lower 120 position of STEPS/SEC switch c
d. 240 position of STEPS/SEC switch
Fig. 3-1. The time relationship between waveforms of the Collector Sweep circuit
and the Step Generator.
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3-1