State the working principle of UJT

State the working principle of UJT
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Answer :

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Figure shows the equivalent circuit of a unijunction transistor with voltage source VEE connected across emitter and base 1 and VBB connected across base 1 and base 2. Hence the Emitter diode is reversed biased by a voltage drop across the rB1 and its own barrier potential VD. Thus total reverse bias voltage across a diode is equal to sum of ȵVBB and VD. 

As long as the VEE is below the total reverse bias voltage across the diode, it remains reverse biased and there is no emitter current.

However if the VEE voltage reaches or exceeds the value equal to (ȵVBB + VD),the diode conducts VEE, which causes the diode to conduct ,is called peak point voltage. 

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When the emitter current begins to flow ,the UJT is said to be fired, triggered or turned on.

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