A multivibrator is an electronic circuit with two active devices (such as transistors or vacuum tubes) that oscillate between two states. It is a type of relaxation oscillator, meaning that it operates by repeatedly charging and discharging a capacitor. Multivibrators can be used to generate a variety of waveforms, including square waves, triangle waves, and sawtooth waves.
The most common type of multivibrator is the astable multivibrator. An astable multivibrator is a free-running oscillator, meaning that it does not require an external trigger to start oscillating. It is typically used to generate a square wave output.
Working principle of an astable multivibrator:
The astable multivibrator circuit consists of two transistors (Q1 and Q2), two capacitors (C1 and C2), and four resistors (R1, R2, R3, and R4). The transistors are cross-coupled, meaning that the output of one transistor is connected to the input of the other transistor. The capacitors are connected in parallel with the base-emitter junctions of the transistors.
The circuit works as follows:
Initially, transistor Q1 is conducting and transistor Q2 is off. This is because capacitor C1 is charged and capacitor C2 is discharged.
As capacitor C1 discharges, the voltage at the base of transistor Q1 decreases. This causes transistor Q1 to start turning off.
As transistor Q1 turns off, the voltage at the collector of transistor Q1 increases. This increase in voltage is coupled to the base of transistor Q2 through capacitor C2.
As the voltage at the base of transistor Q2 increases, transistor Q2 starts turning on.
As transistor Q2 turns on, the voltage at the collector of transistor Q2 decreases. This decrease in voltage is coupled to the base of transistor Q1 through capacitor C1.
This process continues to repeat itself, with the transistors switching back and forth between on and off states.
The frequency of oscillation of the astable multivibrator is determined by the values of the capacitors and resistors. The larger the values of the capacitors, the slower the frequency of oscillation. The larger the values of the resistors, the faster the frequency of oscillation.
Applications of astable multivibrator:
Astable multivibrator used in a wide variety of electronic applications, including:
Oscillators: Multivibrators can be used to generate a variety of waveforms, including square waves, triangle waves, and sawtooth waves. These waveforms can be used for a variety of purposes, such as driving clocks, generating tones, and modulating signals.
Timers: Multivibrators can also be used to create timers. A timer is a circuit that generates a single pulse or a train of pulses after a certain delay. Multivibrators can be used to create timers with a wide range of delays.
Flip-flops: Flip-flops are digital circuits that have two stable states. Multivibrators can be used to create flip-flops. Flip-flops are used in a wide variety of digital circuits, such as memory devices, counters, and registers.
Multivibrators are one of the most fundamental types of electronic circuits. They are used in a wide variety of applications, from simple oscillators to complex digital circuits.