Write a note on multivibrator.

Q.) Write a note on multivibrator.

 Subject: electronic devices and circuit

Multivibrator

Definition:

A multivibrator is an electronic circuit used to generate a non-sinusoidal periodic waveform. It consists of two amplifying devices (transistors, vacuum tubes, etc.) cross-coupled by resistors and capacitors, and sometimes by an inductor. The output waveforms of a multivibrator are square-wave or rectangular-wave signals, which are periodic in nature. Multivibrators are used in various applications such as timers, frequency generators, flip-flops, and logic gates.

Types of Multivibrators:

  1. Astable Multivibrator:

An astable multivibrator is a free-running multivibrator that continuously generates a square-wave or rectangular-wave output without any external trigger. It has no stable state and keeps oscillating continuously. The output waveforms of an astable multivibrator are symmetrical.

  1. Monostable Multivibrator:

A monostable multivibrator is a one-shot multivibrator that produces a single output pulse of a specific duration in response to a trigger pulse. It has one stable state and one quasi-stable state. When triggered, the circuit transitions to the quasi-stable state for a predetermined time duration and then returns to the stable state.

  1. Bistable Multivibrator:

A bistable multivibrator, also known as a flip-flop, is a two-state multivibrator that has two stable states. It can be switched from one stable state to another by applying a trigger pulse. Bistable multivibrators are used in memory elements, registers, and counters.

Working Principle:

The working principle of a multivibrator is based on the regenerative feedback mechanism. The amplifying devices (transistors or vacuum tubes) are connected in a cross-coupled configuration, where the output of one device is fed back to the input of the other device. This feedback loop creates a positive feedback effect, causing the circuit to oscillate continuously.

In astable multivibrators, the feedback network is designed to provide the necessary conditions for continuous oscillation. The values of resistors and capacitors determine the frequency and duty cycle of the output waveform.

In monostable multivibrators, the feedback network is designed to provide a single output pulse when triggered. The duration of the output pulse is determined by the values of resistors and capacitors in the circuit.

In bistable multivibrators, the feedback network is designed to provide two stable states. The circuit can be switched from one stable state to another by applying a trigger pulse.

Applications:

Multivibrators are widely used in various electronic circuits and systems. Some of the common applications of multivibrators include:

  1. Timers: Multivibrators are used in timers to generate time delays and intervals.

  2. Frequency Generators: Multivibrators can generate square-wave or rectangular-wave signals of specific frequencies.

  3. Flip-Flops: Bistable multivibrators are used as flip-flops, which are essential memory elements in digital systems.

  4. Logic Gates: Multivibrators can be used to implement logic gates such as AND, OR, NOT, XOR, and NAND.

  5. Pulse Generators: Multivibrators can generate pulses of various shapes and durations.

  6. Signal Conditioning: Multivibrators can be used for signal conditioning and shaping.

  7. Instrumentation: Multivibrators are used in various instruments and testing equipment.

  8. Automotive Electronics: Multivibrators are used in automotive electronics for controlling ignition systems, fuel injection systems, and other electronic components.