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Characteristics of a UJT

2018-01-31 22:25  
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UJT Characteristics

UJT Characteristics

The static emitter char-acteristic (a curve showing the relation between emitter voltage VEand emitter current IE) of aUJTat a given inter base voltage VBBis shown in figure. ?From figure it is noted that for emitter potentials to the left of peak point, emitter current IEnever exceeds IEo. The current IEocorresponds very closely to the reverse leakage current ICoof the conventional BJT. This region, as shown in the figure, is called the cut-off region. Once con-duction is established at VE= VPthe emitter po-tential VEstarts decreasing with the increase in emitter current IE. This Corresponds exactly with the decrease in resistance RBfor increasing cur-rent IE. This device, therefore, has a negative resistance region which is stable enough to be used with a great deal of reliability in the areas of applications listed earlier. Eventually, the valley point reaches, and any further increase in emitter current IEplaces the device in the saturation region, as shown in the figure. Three other important parameters for the UJT are IP, VVand IVand are defined below:

Peak-Point Emitter Current. Ip. It is the emitter current at the peak point. It repre-sents the rnimrnum current that is required to trigger the device (UJT). It is inversely proportional to the interbase voltage VBB.

Valley Point Voltage VVThe valley point voltage is the emitter voltage at the valley point. The valley voltage increases with the increase in interbase voltage VBB.

Valley Point Current IVThe valley point current is the emitter current at the valley point. It increases with the increase in inter-base voltage VBB.

Special Features of UJT.The special features of a UJT are :

A stable triggering voltage (VP)— a fixed fraction of applied inter base voltage VBB.A very low value of triggering current.A high pulse current capability.A negative resistance characteristic.Low cost.
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