Which of the following device is used as a relaxation oscillator?

Explanation:

Relaxation Oscillator

Definition: A relaxation oscillator is an electronic oscillator that generates a non-sinusoidal repetitive waveform, such as a square wave or a triangle wave. It operates based on the charging and discharging of a capacitor through a resistor or other nonlinear device, leading to the periodic switching of the circuit between two states.

Working Principle: In a relaxation oscillator, a capacitor is charged through a resistor until the voltage across the capacitor reaches a certain threshold. At this point, a nonlinear device, such as a Unijunction Transistor (UJT) or other switching element, rapidly discharges the capacitor. This cycle of charging and discharging generates the desired oscillatory waveform.

Advantages:

• Simple design and easy to construct.
• Can generate various waveforms such as square, triangle, and sawtooth waves.
• Useful in timing and waveform generation applications.

Disadvantages:

• Less frequency stability compared to other types of oscillators.
• May produce more harmonic distortion in the output waveform.

Applications: Relaxation oscillators are commonly used in applications such as flashing lights, clock generation, waveform generation, and time delay circuits.

Correct Option Analysis:

The correct option is:

Option 3: UJT (Unijunction Transistor)

This option is correct because the Unijunction Transistor (UJT) is a well-known component used in the construction of relaxation oscillators. The UJT's unique characteristic of having a negative resistance region allows it to effectively switch between high and low resistance states, facilitating the rapid charging and discharging cycles needed for oscillation.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: JFET (Junction Field-Effect Transistor)

While JFETs are versatile components used in various electronic circuits, they are not typically used as the primary switching element in relaxation oscillators. JFETs are more commonly employed in amplification and switching applications where linear characteristics are desired.

Option 2: BJT (Bipolar Junction Transistor)

BJTs can be used in oscillator circuits, but they are not as commonly used in relaxation oscillators as UJTs. BJTs are more suitable for linear amplification and switching applications, and while they can be used to create oscillations, they lack the specific characteristics that make UJTs ideal for relaxation oscillators.

Option 4: Diode

Diodes are primarily used for rectification, voltage regulation, and signal modulation. While they can be part of oscillator circuits, they are not typically used as the main switching component in relaxation oscillators. Diodes lack the necessary negative resistance region that UJTs have, which is crucial for the operation of relaxation oscillators.

Conclusion:

Understanding the specific characteristics and applications of electronic components is crucial for identifying their roles in various circuits. The Unijunction Transistor (UJT) is particularly suited for use in relaxation oscillators due to its unique switching properties, making it the correct choice for generating non-sinusoidal waveforms in timing and waveform generation applications.