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ELECTRICIAN - CITS

EXERCISE 65 : Construct UJT triggering circuit

Objectives

At the end of this exercise you shall be able to:
• construct UJT relaxation oscillator circuit
• test UJT triggering circuit.
Requirements

Tools/Equipments/Instruments
• DC power supply 0-15V,1A -1 No. • Diode 1N4007 -1 No.
• UJT 2N2646 -1 No. • Trainee tool kit -1 No.
• Resistor 12K1, POT 470K1/2w, • Dual channel oscilloscope -1 No.
200E,100E -1 No. 20 MHZ
• Capacitors 0.01μF -1 No. • Power supply unit 0-15V, -1 No.
• General purpose PCB -1 No. 1A variable

Procedure

TASK 1: Construct UJT triggering circuit
1 Assemble the circuit as per diagram in Fig 1 in general purpose PCB.
2 Get the assembled circuit checked by instructor

Fig 1

TASK 2: Test UJT triggering circuit
1 Connect +12V dc power supply at their indicated position from external source.
2 Adjust the potentiometer 470k to reduce the frequency.
2 Switch ON the power supply.

3 Connect the oscilloscope CHI between output and ground and CHII between tp1 and ground and observe the
waveform of pulse output and RC time constant.
4 Vary the potentiometer P1 so as to increase the frequency of the output.

5 calculate Time seconds = (R1 + R2) x C where R1 = 12K1, PI= 0 At start, C=0.01μF
6 calculate frequency = 1/T
7 Observe the pulse output wave form in CRO

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