A unijunction transistor (UJT) is used to generate a ____ wave

Uni Junction Transistor (UJT):

• The uni-junction transistor is a solid-state three-terminal device that can be used in gate pulse, timing circuits, and trigger generator applications to switch and control both thyristors and triacs for AC power control type applications.
• When a UJT is used for triggering an SCR, the wave shape of the voltage obtained from the UJT circuit is a saw-tooth wave.

• The UJT is a three-terminal, semiconductor device which exhibits negative resistance and switching characteristics for use as a relaxation oscillator in phase control applications.

• The device has only one junction, so it is called the unijunction device
• The device, because of one P-N junction, is quite similar to a diode but it differs from an ordinary diode as it has three terminals
• The structure of a UJT is quite similar to that of an N-channel JFET
• The main difference is that P-type (gate) material surrounds the N-type (channel) material in the case of JFET and the gate surface of the JFE T is much larger than the emitter junction of UJT
• In a unijunction transistor, the emitter is heavily doped while the N-region is lightly doped, so the resistance between the base terminals is relatively high, typically 4 to 10 kilo Ohm when the emitter is open
• The N-type silicon bar has a high resistance and the resistance between emitter and base1 is larger than that between emitter and base2; It is because emitter is closer to base2 than base1
• UJT is operated with emitter junction forward- biased while the JFET is normally operated with the gate junction reverse-biased
• UJT does not have the ability to amplify but it has the ability to control a large AC power with a small signal. So that it is not used for amplification purposes. 

Applications of UJT:

• Uses negative oscillator resistance property for the generation of the sawtooth waveform
• Used as a Relaxation oscillator.
• Used as a Voltage regulator.
• Used as a switching circuit.
• Widely used as a triggering device for silicon control rectifiers (SCR).
• Used as a phase control circuit.
• Used as a timing circuit.
• Used in a sawtooth generator.
• Used to generate magnetic flux.