What is UJT (Uni Junction Transistor)?

Hello friends! Today I will read you about what is UJT?, its structure, and procedure in this post. So let's start:-

what is UJT?

The full name of UJT is uni-junction transistor. It is a three terminal semiconductor device. There is only one pn junction in it, hence it is called unijunction transistor.

Construction of Unijunction Transistor

In UJT a low doped n-type silicon rod is used. The heavily doped p type material is diffused on one side of this rod.

The terminal which is connected to the p type region is called the emitter terminal (E) and the two terminals which are connected to the opposite ends of the n type region are called base1(B1) and base2(B2).


operation of UJT

When the voltage between emitter and base1 is zero, the UJT does not conduct and the n-type rod acts as a resistor. But we see that a small leakage current flows due to the reverse bias junction.

When we increase the emitter voltage gradually, the resistance between emitter and base1 decreases. When the emitter voltage increases so much that the junction becomes forward biased, then the emitter current starts flowing. This happens because the holes in the heavily doped p-type region enter the n-type region and combine with the electrons in the n-type region. In this way the trend of uni junction transistor starts.

applications of UJT

Its applications are as follows:-

  1. It is used as triggering device in SCR and TRAIC.
  2. UJT is used to generate non sinusoidal waves in relaxation oscillator.
  3. It is used to control the speed of AC and DC motors.
  4. UJT is used in saw tooth wave generator and phase control circuits.

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