A multivibrator is a circuit that has two stable states. Each stable state is represented by a voltage e.g 0Volts and 5 volts. The astable variety is when the output. Multivibrator circuits are basically three types- monostable, bistable, astable. Find an examples of each circuit using BJT, logic gates and timer IC. The name mutivibrator designates a group of the circuits widely applied for switching as shift registers or temporary memories and as square.

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A free-running multivibrator with a frequency of one-half to one-tenth of the reference frequency would accurately lock to the reference frequency. This is the output voltage of R 1 C 1 integrating circuit. What is Astable, monostable, bistable multivibrator. Since the circuit vibrates once for a trigger, it is called a uni-vibrator or monostable multivibrator.

For example, if Q2 is on and Set is grounded momentarily, this switches Q2 off, and makes Q1 on. Now a negative trigger of magnitude V1 is applied to the non-inverting terminal so that the effective signal at this terminal is less than 0.

Time bases scanning generators: Since it produced a square wavein contrast to the sine wave generated by most other oscillator circuits of the time, its output contained many harmonics above the fundamental frequency, which could be used for calibrating high frequency radio circuits.

In practice, oscillation always occurs for practical values of R and C.

It can remain asyable either of these two states unless an external trigger pulse switches it form one state to the other. When the circuit is first powered up, neither transistor will be switched on. However, this means that at this stage they will both have high base voltages and therefore a tendency to switch on, and inevitable slight asymmetries will mean that one of the transistors is first to switch on.


For example, before the advent of low-cost integrated circuits, chains of multivibrators found use as frequency dividers. The capacitor asgable through resistor R and charges again to 0.

In the monostable configuration, only one of the transistors requires protection. The diode D1 clamps the capacitor to 0.

The circuit is useful for generating single output pulse of adjustable time duration in response to a triggering signal. Bistable Multivibrator Figure-4 depicts circuit used for bistable multivibrator.

Multivibrator – Wikipedia

For the circuit in Figure 2, in the stable state Q1 is turned off and Q2 is turned on. It can be switched to quasi stable state by an external trigger but it returns to the stable condition after delay time which is determined by the components of circuit.

Now the capacitor discharges towards -V sat. It has no energy storing element.

Dec 248: During State 1Q2 base-emitter junction is reverse-biased and capacitor C1 is “unhooked” from ground. Figure-2 depicts circuit used for astable multivibrator. The pulse width T of a monostable multivibrator is calculated as follows: In the multivihrators, only R3 provides the needed input base current.

The duration of state 1 low output will be related to the time constant R 2 C 1 as it depends on the charging of C1, and the duration of state 2 high output will be related to the time constant R 3 C 2 as it depends on the charging of C2.

Figure-3 depicts circuit used for monostable multivibrator. It has no stable state but only has two half stable states between which it oscillating.

Thus the initial input change circulates along the feedback loop and grows in an avalanche-like manner until finally Q1 switches off and Q2 switches on. In the beginning, the multivibdators C1 is fully charged in the previous Monostablw 2 to the power supply voltage V with the polarity shown in Figure 1.


It is basically a switching circuit which generates non-sinusoidal waves such as square, sawtooth and rectangular etc. Synthesized tuning, Part 2: While not fundamental to circuit operation, diodes connected in monosstable with the base or emitter of the transistors are required to prevent the base-emitter junction being driven into reverse breakdown when the supply voltage is in excess of the V eb breakdown voltage, typically around volts for general purpose silicon transistors.

Now, the capacitor C2 is fully charged in the previous State 1 to the power supply voltage V mjltivibrators the polarity shown in Figure 1. If V C is the voltage across the capacitor and from the graph, the time period of the wave formed at capacitor and the output would match, then the time period could be calculated in this way:. Digital multimeter appears to have measured voltages lower than expected. The Principles of Known Circuits”.

It consists of two amplifying devices transistorsvacuum tubes or other devices monostab,e by resistors or capacitors. It has two stable states and can be triggered from one stable state to the other by an external signal. This site uses Akismet to bisstable spam. It is a square of rectangular wave oscillator.

Part and Inventory Search. This circuit does not oscillate. Hence, when the circuit is switched on, if Q1 is on, its collector is at 0 V. These circuits are basically closed loop feedback circuits operating with the feedback.


This technique was used in early electronic organs, to keep notes of different octaves accurately in tune. Multivibrators find applications in a variety of systems where square waves or timed intervals are required. Electronic oscillators Digital circuits Analog circuits.