Equivalent Circuit :

The equivalent circuit of a UJT is shown in fig. The P - N junction represented in the emitter by a diode. Silicon bar being lightly doped has a high resistance and can be represented as two resistors connected in series RB from base 1 to point A and RB2 from base 2 to point A, as shown in fig. the resistance RB is shown as a variable resistor since its magnitude varies with the emitter current IE. In fact, for a typical UJT, RB may vary from 5 k down to 50. For a corresponding change of emitter current IE from 0 to 50 n A. the total resistance of silicon bare from one end to the other end i.e., the resistance between B2 and B1 with emitter terminal E open is called the inter base resistance RBB. From the equivalent circuit shown in fig. it is obvious that with a voltage VBB applied between B2 and B1 as shown in the figure, the voltage at the junction of RB1 and RB2 is.