How many Types of Multivibrators Are There? The name mutivibrator designates a group of the circuits widely applied for switching as shift registers or temporary memories and as square were timing oscillator or clocks. These circuits are basically closed loop feedback circuits operating with the feedback. Types of multivibrators There are three general types of multivibrators, which are: The astable or free running mutivibrator which has no stable states. It continuously switched between two limits without application of an external signal it is a square wave oscillator.

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A multivibrator, is basically two amplifier circuits arranged with regenerative feedback. Multivibrators Introduction The type of circuit most often used to generate square or rectangular waves is the multivibrator. One of the amplifiers is conducting while the other is cut off When an input signal to one amplifier is large enough, the transistor can be driven into cutoff, and its collector voltage will be almost V CC.

However, when the transistor is driven into saturation, its collector voltage will be about 0 volts. A circuit that is designed to go quickly from cutoff to saturation will produce a square or rectangular wave at its output. This principle is used in multivibrators. Multivibrators are classified according to the number of steady stable states of the circuit. A steady state exists when circuit operation is essentially constant; that is, one transistor remains in conduction and the other remains cut off until an external signal is applied.

The astable circuit has no stable state. With no external signal applied, the transistors alternately switch from cutoff to saturation at a frequency determined by the RC time constants of the coupling circuits.

The monostable circuit has one stable state; one transistor conducts while the other is cut off. A signal must be applied to change this condition. After a period of time, determined by the internal RC components, the circuit will return to its original condition where it remains until the next signal arrives.

The bistable multivibrator has two stable states. It remains in one of the stable states until a trigger is applied. Astable Multivibrator A multivibrator which generates square waves of its own i. It is also called free ramming multivibrator. It has no stable state but only two quasi-stables half-stable makes oscillating continuously between these states.

Thus it is just an oscillator since it requires no external pulse for its operation of course it does require D. C power. In such circuit neither of the two transistors reaches a stable state. It switches back and forth from one state to the other, remaining in each state for a time determined by circuit constants.

In other words, at first one transistor conducts i. ON state and the other stays in the OFF state for some time. After this period of time, the second transistor is automatically turned ON and the first transistor turned OFF. Thus the multivibrator will generate a square wave of its own. The width of the square wave and it frequency will depend upon the circuit constants. Here we like to describe. In that case , the circuit is known as symmetrical astable multivibrator.

The transistor Q1 is forward biased by the Vcc supply through resistor R2. Similarly the transistor Q2 is forward biased by the Vcc supply through resistor R1. The output of transistor Q1 is coupled to the input of transistor Q2 through the capacitor C2. Similarly the output of transistor Q2 is coupled to the input of transistor Q1 through the capacitor C1.

It consists of two common emitter amplifying stages. Each stage provides a feedback through a capacitor at the input of the other. Since the amplifying stage introduces a o phase shift and another o phase shift is introduced by a capacitor, therefore the feedback signal and the circuit works as an oscillator. In other words because of capacitive coupling none of the transistor can remain permanently out-off or saturated, instead of circuit has two quasi-stable states ON and OFF and it makes periodic transition between these two states.

The output of an Astable multivibrator is available at the collector terminal of the either transistors as shown in figure a. However, the two outputs are o out of phase with each other. Therefore one of the outputs is said to be the complement of the other.


How many Types of Multivibrators Are There?








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