Unijunction Transistor

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Unijunction Transistor

Transcript of Unijunction Transistor

  • Unijunction Transistor

  • UJT

  • UJT Equivalent Circuit

  • UJT Equivalent Circuit DetailsRB1 - Internal dynamic resistance of the Si bar between B1 & emitter junction. This resistance is variable because its value depends upon the bias voltage across the pn junctionRB2 - Internal dynamic resistance of the Si bar between B2 & emitter junctionThe pn junction is represented in the emitter by a diode D

  • UJT Equivalent Circuit DetailsWith no voltage applied to the UJT, the inter- base resistance is given by

    whose value lies b/w 4 k & 10 k2. If a voltage VBB is applied b/w the bases with emitter open (IE =0), the voltage across RB1 is

  • UJT Equivalent Circuit Details3. Intrinsic Stand-off Ratio ()

    whose value usually lies between 0.51 & 0.82 Therefore voltage across RB1, V1 = VBB with IE = 0

  • UJT Characteristic Curve

  • Peak Point Voltage Equation

  • UJT Characteristic Curve for different VBB Values

  • Cont

  • Application of UJTUsed as a trigger device for SCR & triacsUsed as Non-sinusoidal oscillatorUsed as Sawtooth generatorUsed in phase control & timing circuits

  • UJT Relaxation Oscillator

  • UJT Relaxation OscillatorWaveforms for UJT Relaxation Oscillator

  • UJT Relaxation OscillatorCondition for Turn ON UJTCondition for Turn OFF UJT

  • UJT Relaxation Oscillator

  • ReferenceElectronic Devices & Circuits by David A BellElectronic devices by Floyd

    RB1 varies inversely with emitter current IE (check it) *Refer lab manual*