A unijunction transistor as discussed in chapter-12 exhibits a V–I characteristic as shown in Fig. 16.28. The device is ON when v = VP and OFF when v = VV. The device is used as a switch.

16.6.1 An Astable Multivibrator Using a UJT

The Fig. 16.29(a) gives an astable multivibrator using an UJT. Let initially the diode D be ON. Then its forward resistance is small. Thevenizing the circuit at E,


Here, VEE is the Thevenin source and RE is its internal resistance. The circuit shown in Fig. 16.29(a) can now be redrawn as shown in Fig. 16.29(b), when D is ON.

Initially, when the UJT is OFF, the capacitor tries to charge ...

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