Draw and explain free running multivibrator.

Free-Running Multivibrator

A free-running multivibrator is a relaxation oscillator circuit that produces a continuous, square-wave output waveform without the need for an external trigger signal. It consists of two amplifying devices (typically transistors) connected in a positive feedback loop, along with resistors and capacitors to set the frequency and duty cycle of the output waveform.

Circuit Diagram

Operation

The free-running multivibrator operates based on the principle of regenerative feedback. When power is applied to the circuit, one of the transistors (Q1 or Q2) is initially turned on, while the other is turned off. This is due to the positive feedback loop, where the output of one transistor is fed back to the input of the other, causing it to turn on and off in a regenerative manner.

As Q1 turns on, it pulls its collector voltage low. This low voltage is fed back to the base of Q2 through R2, causing Q2 to turn off. With Q2 turned off, its collector voltage rises high. This high voltage is fed back to the base of Q1 through R1, causing Q1 to remain turned on.

This regenerative feedback loop continues until one of the transistors (Q1 or Q2) reaches saturation, at which point the loop is broken and the transistor switches states. The transistor that was on turns off, and the transistor that was off turns on. The process then repeats itself, generating a continuous square-wave output.

Frequency and Duty Cycle

The frequency and duty cycle of the output waveform are determined by the values of the resistors and capacitors in the circuit. The frequency (f) is given by:

f = 1 / (2.2 * R1 * C1)

The duty cycle (D) is given by:

D = R2 / (R1 + R2)

Applications

Free-running multivibrators are used in a wide variety of applications, including:

• Clock generators
• Signal generators
• Pulse generators
• Timers
• Flip-flops
• Logic gates

Advantages and Disadvantages

Advantages:

• Simple circuit design
• Stable operation
• Wide range of frequency and duty cycle adjustment

Disadvantages:

• Limited frequency range
• Temperature sensitivity
• Susceptible to noise and interference