3-40
Figure 3-44B.—Unijunction sawtooth generator. EMITTER WAVEFORM.
The circuit operation from now on is just a continuous repetition of the actions between T2 and T4.
The capacitor charges until the emitter becomes forward biased, the unijunction conducts and C1
discharges, and Q1 becomes reverse biased and C1 again starts charging.
Now, let's determine the linearity, electrical length, and amplitude of the output waveform. First, the
linearity: To charge the circuit to the full 20 volts will take 5 time constants. In the circuit shown in figure
3-44, view (B), C1 is allowed to charge from T2 to T3. To find the percentage of charge, use the equation:
This works out to be about 57 percent and is far beyond the 10 percent required for a linear sweep
voltage. The linearity is very poor in this example.
