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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*