Description
The UJT Characteristics Apparatus and UJT as Relaxation Oscillator provide a practical platform to study and demonstrate the unique properties of the Unijunction Transistor (UJT) and its application as a relaxation oscillator.
UJT Characteristics Apparatus
This apparatus typically includes a mounted UJT device, regulated DC power supplies for biasing, and terminals for measuring emitter and base voltages and currents. It enables plotting the voltage-current (V-I) characteristics exhibiting three regions — cutoff, negative resistance, and saturation. The negative resistance region, where voltage decreases as current increases, is particularly important for relaxation oscillator function.
UJT as Relaxation Oscillator
A relaxation oscillator circuit uses the UJT, resistor, and capacitor connected such that the capacitor charges through the resistor until the voltage reaches the UJT peak voltage (Vp). At this point, the UJT switches “on,” rapidly discharging the capacitor until the voltage falls to the valley voltage (Vv), turning the UJT “off.” This cycle repeats continuously, producing a sawtooth or non-sinusoidal waveform.
The frequency of the oscillator depends on the RC time constant and the intrinsic standoff ratio (η) of the UJT, and is given approximately by the formula:
f
=
1
R
C
ln
(
1
1
−
η
)
f=
RCln(
1−η
1
)
1
Applications of this oscillator include waveform generation, triggering SCRs or TRIACs in phase control circuits, blinkers, pulse generators, and timer circuits.
This combined apparatus and oscillator study assist in understanding UJT behavior and practical electronic circuit design utilizing UJT relaxation oscillators.