Draw the circuit and explain the operation of UJT relaxation oscillator.

Draw the circuit and explain the operation of UJT relaxation oscillator. 
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1 Answer

Answer :

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Working: When the supply voltage (VCC) is switched ON, the capacitor charges through resistor (R), till the capacitor voltage reaches the voltage level (VP) which is called as peak point voltage. At this voltage the UJT turns ON. As a result of this, the capacitor (C) discharges rapidly through resistor (R1). When that capacitor voltage drops to level Vv (called valley- point voltage) the uni- junction transistor switches OFF allowing the capacitor (C) to charge again. In this way because of the charging and discharging of capacitor the exponential sweep voltage will be obtained at the emitter terminal of UJT. The voltage developed at base 1(VB1) terminal is in the form of narrow pulses commonly known as trigger pulses. The sweep period depends upon time constant (R.C) and the sweep frequency can be varied by changing value of either resistance (R) or capacitor (C). Due to this fact, the resistor R is shown as a variable resistor.

The sweep period is given by the relation

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