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Electronic Devices & Circuits Lab Experiments

Experiment to Study the Characteristics of Uni Junction Transistor

Jun 25 2023


Title

To Plot and study the characteristics of UJT & determine it’s intrinsic standoff Ratio.

Apparatus Required:

S.No. Name Range Type Qty
1 R.P.S (0-30)V 2
2 Ammeter (0–30)mA 1
3 Voltmeter (0–30)V/(0–10)V 1

Components Required:

S.No. Name Range Type Qty
1 UJT 2N2646 1
2 Resistor 1KΩ 2
3 Breadboard 1

Theory:

UJT(Double base diode) consists of a bar of lightly doped n-type silicon with a small piece of heavily doped P type material joined to one side. It has got three terminals. They are Emitter(E), Base1(B1),Base2(B2).Since the silicon bar is lightly doped, it has a high resistance & can be represented as two resistors, rB1& rB2. When VB1B2 = 0, a small increase in VE forward biases the emitter junction. The resultant plot of VE & IE is simply the characteristics of forward biased diode with resistance. Increasing VEB1 reduces the emitter junction reverse bias. When VEB1 = VrB1 there is no forward or reverse bias. & IE = 0. Increasing VEB1 beyond this point begins to forward bias the emitter junction. At the peak point, a small forward emitter current is flowing. This current is termed as peak current(IP). Until this point UJT is said to be operating in cutoff region. When I Eincreases beyond peak current the device enters the negative resistance region. In which the resistance rB1 falls rapidly & V E falls to the valley voltage.Vv. At this point I E= Iv. A further increase of I Ecauses the device to enter the saturation region.

Procedure:

  1. Connect the circuit as per the circuit diagram.
  2. Set VB1B2= 0V, vary V EB1,& note down the readings of I E&VEB1
  3. Set VB1B2= 10V , vary VEB1,& note down the readings of IE& VEB1
  4. Plot the graph : I E Versus V EB1 for constant V B1B2
  5. Find the intrinsic standoff ratio.

Formula for Intrinsic Standoff Ratio:

η=V P-V D/ V B1B2, where V D= 0.7V.

Procedure:

  1. Give the circuit connections as per the circuit diagram.
  2. The dc input voltage is set to 20 V in RPS.
  3. The output sweep waveform is measured using CRO.
  4. The graph of output sweep waveform is plotted

Result:

  1. Thus the characteristics of given UJT was Plotted & its intrinsic standoff Ratio = ----.
circuit-diagram

Pin Diagram:

bottom-view-of-2N2646

Specification for 2N2646:

* Inter base resistance R BBBB = 4.7 to 9.1 KΩ

* Minimum Valley current = 4 mA

* Maximun Peak point emitter current 5 μA

*Maximum emitter reverse current 12 μA.

model-graph

Tabular Column:

V B1B2= 0V/V EB1(V)/I E(mA) V B1B2= 10V/V EB1(V)/I E(mA)
1
2
3
4
5
6
7









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