UJT is used for which of the following applications?

Question

Question

This question was previously asked in

ALP CBT 2 Electrician Official Paper (Held On: 23 Jan 2019 Shift 3)

Answer 1

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 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; It exhibits a negative resistance characteristic and so it can be employed as an oscillator