BISTABLE MULTIVIBRATOR THEORY PDF

A Bistable multivibratior is used in a many digital operations such as counting and the storing of binary information. It is also used in the generation and processing of pulse-type waveform. They can be used to control digital circuits and as frequency dividers. There are two outputs available which are complements of one another. When VCC is applied, one transistor will start conducting slightly more than that of the other, because of some differences in the characteristics of a transistor. The potential at the collector of Q 1 increases which in turn further increases the base to emitter voltage at the base of Q 2.

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The bistable multivibrator has two absolutely stable states. It will remain in whichever state it happens to be until a trigger pulse causes it to switch to the other state. If left to itself, the bistable multivibrator will stay in this position for ever. However, if an external pulse is applied to the circuit in such a way that Q 1 is cut-off and Q 2 is turned on, the circuit will stay in the new position.

Another trigger pulse is then required to switch the circuit back to its original state. In other words a multivibrator which has both the state stable is called a bistable multivibrator. It is also called flip-flop, trigger circuit or binary. The output pulse is obtained when, and why a driving triggering pulse is applied to the input. A full cycle of output is produced for every two triggering pulses of correct polarity and amplitude.

Figure a shows the circuit of a bistable multivibrator using two NPN transistors. Similarly, the output of a transistor Q 1 is coupled to the base of transistor Q 2 through a resistor R 1. The capacitors C 2 and C 1 are known as speed up capacitors. Their function is to increase the speed of the circuit in making abrupt transition from one stable state to another stable state.

The output of a bistable multivibrator is available at the collector terminal of the both the transistor Q 1 and Q 2. However, the two outputs are the complements of each other. Suppose, now a positive pulse is applied momentarily to R. It will cause Q 2 to conduct. To change the stable state of the binary it is necessary to apply an appropriate pulse in the circuit, which will try to bring both the transistors to active region and the resulting regenerative feedback will result on the change of state.

In asymmetrical triggering, there are two trigger inputs for the transistors Q 1 and Q 2. Each trigger input is derived from a separate triggering source. To induce transition among the stable states, let us say that initially the trigger is applied to the bistable. For the next transition, now the identical trigger must appear at the transistor Q 2. Thus it can be said that the asymmetrical triggering the trigger pulses derived from two separate source and connected to the two transistors Q 1 and Q 2 individually, sequentially change the state of the bistable.

Thus measurement of time interval is facilitated. There are various symmetrical triggering methods called symmetrical collector triggering, symmetrical base triggering and symmetrical hybrid triggering.

Here we would liked to explain only symmetrical base triggering positive pulse only as given under symmetrical Base Triggering. Figure c shows the circuit diagram of a binary with symmetrical base triggering applying a positive trigger pulses. Diodes D 1 and D 2 are steering diodes. On the arrival of the next trigger pulse now the diode D 2 will be forward biased and ultimately with regenerative feedback it will be in the ON state.

Main menu. Uses: In timing circuits as frequency divider In counting circuits In computer memory circuits Bistable Multivibrator Triggering To change the stable state of the binary it is necessary to apply an appropriate pulse in the circuit, which will try to bring both the transistors to active region and the resulting regenerative feedback will result on the change of state.

Figure b shows the circuit diagram of an asymmetrically triggered bistable multivibrator. II Symmetrical Triggering There are various symmetrical triggering methods called symmetrical collector triggering, symmetrical base triggering and symmetrical hybrid triggering. Log in to post comments. Search Search.

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Pulse Circuits - Bistable Multivibrator

A Bistable Multivibrator has two stable states. The circuit stays in any one of the two stable states. It continues in that state, unless an external trigger pulse is given. This Multivibrator is also known as Flip-flop.

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The circuit can be built using a variety of different types of semiconductor device. In this instance an op amp or comparator is used. Flip flop or bistable circuits can be used for many applications, and whwn associated with analogue circuitry, the use of a comparator or op amp can be convenient. A bistable is an electronic circuit also referred to as a flip-flop or latch. It is a circuit that has two stable states and can be used to store state information.

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Multivibrator

The bistable multivibrator has two absolutely stable states. It will remain in whichever state it happens to be until a trigger pulse causes it to switch to the other state. If left to itself, the bistable multivibrator will stay in this position for ever. However, if an external pulse is applied to the circuit in such a way that Q 1 is cut-off and Q 2 is turned on, the circuit will stay in the new position.

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Op Amp Bistable Multivibrator Circuit Design

It will flipped from one stable state to another stable state by external trigger pulse. It requires two trigger pulses. In the application of first trigger pulse circuit will switches from one state another and continue the state till another trigger pulse is applied. The output of transistor Q1 is coupled to the input of transistor Q2 through resistor R1 and the output of transistor Q2 is coupled to the input of transistor Q1 through Resistor R2. The feedback resistors are shunted by capacitors C1 and C2. These capacitors are known as commutating capacitor and is employed to improve the switching characteristics of the circuit. Thus the transition time is reduced and distortionless output is obtained.

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