What is the UJT| UJT construction| Application of UJT|

UJT ( Uni junction transistor )

As  a show in figure it is a three terminals device. A uni junction transistor (UJT) is an electronic semiconductor device that has only one junction .

Construction of UJT

 It has three terminals an emitter (E) and two bases (B1and B2). The base is formed by lightly doped n-type bar of silicon. Two ohmic contacts B1 and B2 are attached at its ends. The emitter is of p-type and it is heavily doped. The resistance between B1 and B2, when the emitter is open-
circuit is called interbase resistance. The original UJT, is a simple device that is essentially a bar of N type semi-conductor material into which P type material has been diffused somewhere along its length.
RBB = RB1 + RB2
RB1= Resistance of base B1
RB2=Resistance of base B2
N- channel is lightly doped , therefore RBB is relatively high typical 5 to 10k ohm.

Intrinsic stand of ration;

                                                  V1= ( RB1/RBB) VBB
                                                   η = ( RB1/RB1+RB2)
The ratio η is a property of UJT and it is always lass than one and usually between 0.4 and 0.85.


1. Trigger device for SCR and UJT.
2. Non sinusoidal oscillator .
3. Saw tooth generator.
4. Timing circuit .
5. Tuning circuit.


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