16.6 UNIJUNCTION TRANSISTORS

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,

ch16-ueq42

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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