Contents Introduction History Astable multivibrator Operation Multivibrator period Monostable multivibrator circuit Bistable mutlivibrator circuit Application Reference

Introduction A multivibrators is a basically a two stage R-C coupled amplifier with positive feedback from the output of one amplifier to the input of the other. As shown in figure- Multivibrators is a switching ckt and may be define as an electronic ckt that generates non sinusoidal wave such as rectangular waves,sawtooth waves square waves.

Basic configuration of a multivibrator

History The classic multivibrator circuit is first described by H Abraham at 1919.The multivibrator also called a ‘Plate-coupled multivibrator’. Types of multivibrator circuits- Depending upon coupling n/w- Astable multivibrator Bistable multivibrator. Monostable multivibrator.

Astable multivibrator In an astable multivibrator,both coupling network provide AC coupling capacitor. The astable multivibrator is also called ‘Free-running multivibrator& collector-coupled astable multivibrator. The circuit of an astable multivibrator using to similar transmission is depicted in fig:

Fig:BJT astable multivibrator

Waveform of astable multivibrator

Operation: The circuit operation is based on the fact that the forward-biased base emitter junction of the switched-on BJT can provide a path for the capacitor restoration. The circuit has two stable state- -Q1 is switched on,Q2 is switched off, -Q1 is switched off,Q2 is switched on.

Monostable multivibrator Monostable multivibrator is a two-stage amplifier with two states-one stable state & another quasi state. The MMV generates one output pulse for every trigger pules so it is also called single-shot multivibrator. fig: shows the circuit of a MMV-

BJT monostable multivibrator

Waveform of monostable multivibrator

Bistable multivibrator circuit In the bastable multivibrator,both resistive-capacitive n/w are replace by resistive networks. The bistable multivibrator,also called a two-shot multivibrator,requires application of two trigger to return the ckt to its original state. Because two triggers are required .bistable ckt are sometimes called flip-flops. fig-show the bistable multivibrator ckt :

Bistable multivibrator circuit

Application In astable multivibrator- Frequency adjustment is easy. Synchronization is easy. In monostable multivibrator- It can be employed to generate new pulse. In bistable multivibrator- As frequency divider Binary information.

References ^ Multivibrator in IEEE Std. 100 Dictionary of Standards Terms 7th ed.,IEEE Press, 2000 ISBN 0-7381-2601-2 page 718 ^ William Henry Eccles and Frank Wilfred Jordan, "Improvements in ionic relays" British patent number: GB 148582 (filed: 21 June 1918; published: 5 August 1920). ^ a b Donald Fink (ed), Electronics Engineers' Handbook, McGraw Hill, 1975 ISBN 070209804, page 16-40

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