In this note, we discuss the applications of Unijunction Transistors like UJT Relaxation Oscillators and Overvoltage Detector. Welcome to Poly Notes Hub, a one-stop solution for Diploma Engineering Notes.
Author Name: Arun Paul.
Introduction
A special kind of semiconductor, the unijunction transistor, or UJT, has several uses in technology and electronics. This page examines the many uses for UJTs in a variety of industries, including oscillators, pulse generators, and more.
Unijunction Transistors are used extensively in the oscillator, pulse generator, and voltage-sensing circuits. Some of the important applications of UJT are discussed below:
Applications of Unijunction Transistor
UJT Relaxation Oscillator
The below figure shows the UJT relaxation oscillator where the discharging of a capacitor through UJT can develop a saw-tooth output as shown in the below picture.
When battery V-BB is turned on, the capacitor C charges through resistor R1. During the charging period, the voltage across the capacitor rises exponentially until it reaches the peak -point Volta. At this instant of time, the UJT switches to its low-resistance conducting mode, and the capacitor is discharged between E and B1. As the capacitor voltage flies back to zero, the emitter ceases to conduct and the UJT is switched off. The next cycle then begins, allowing capacitor C to charge again. The frequency of the output saw-tooth wave can be varied by changing the value of R1 since this controls the time constant R1-C of the capacitor charging circuit.
The period and hence the frequency of the saw -tooth, wave can be calculated as follows. Assuming that the capacitor is initially unchanged, the voltage across the capacitor before breakdown is given by:
Overvoltage detector
Fig shows a simple d.c. over-voltage indicator. A warning pilot -lamp L is connected between the emitter and the B1 circuit. So long as the input voltage is less than the peak-point voltage of the UJT, the device remains switched off. However, when the input voltage exceeds peak-point voltage, the UJT is switched on and the capacitor discharges through the low resistance path between terminals E and B1. The current flowing in the pilot-lamp L lights it, thereby indicating the overvoltage in the circuit.
Conclusion | Diploma Engineering Notes | Poly Notes Hub
Above the note, we are discussing the Applications of Unijunction Transistor or UJT. The applications like UJT Relaxation Oscillator and Overvoltage Detector. Our Poly Notes Hub provides syllabus-wise notes for polytechnic or diploma engineering students of streams like Electrical Engineering, Electronics Engineering, Electrical and Electronics Engineering, Electronics & Instrumentation Engineering, and Computer Science & Technology. Our website is updating day by day so keep in touch with us for new and syllabus-wise notes and topic which helps you all to do any task regarding diploma engineering.