UJT Interview Question Answer

State the full form of UJT.

Unijunction transistor

Which are the three main terminals of the UJT?

UJT terminals
  • Base 1
  • Base 2
  • Emitter

How many PN junction diode the UJT consists of?


Whether two base terminals are interchangeable in the UJT?


What do you mean by inter base resistance?

Inter base resistance
  • The resistance between two terminal base 1 and base 2 is called as inter base resistance. 
  • It is resistance of the N type material.

Explain the term : Intrinsic stand off ratio

Intrinsic stand off ratio
  • It is defined as the ratio of resistance between base 1 to emitter  ( RB1 ) to the inter base resistance RBB. Its symbol is eta ( η ).                                                                                 η = RB1 / RBB

State the operating region of the UJT.

The UJT operates in the peak point to the valley point region.

Define : Valley current

Valley current
  • The valley current is similar to holding current in the SCR. It is minimum current requires to keep the UJT in on condition. 
  • The UJT turns off when the emitter current reduces below valley current.

Define : Peak voltage in the UJT

Peak voltage
  • It is an emitter voltage at which the UJT operates or turn on.

       VP = ηVBB + VD
       VP =  Peak point voltage
       VBB  = Voltage between base 1 and emitter
        VD = Voltage across diode and
         η =  Intrinsic stand off ratio

Which types of pulses are generated in the UJT relaxation oscillator circuit at terminal B1 and B2?

Positive train of pulses at terminal B1 whereas negative pulses at terminal B2

Which parameters greatly affect the oscillator frequency in the UJT relaxation oscillator?

UJT relaxation oscillator
  • The oscillator frequency in the UJT relaxation oscillator depends upon the RC time constant circuit. 
  • The time period of the relaxation oscillator is given by       T = RC loge [ 1 / ( 1 – η )] 
        ( Where η = Intrinsic stand off ratio )

State the application of the UJT.

  • Timing circuits
  • Relaxation oscillators
  • Trigger circuits
  • Non sinusoidal oscillators
  • Saw tooth generators
  • Timing circuits

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