Circuit of a bistable Multivibrator using two NPN transistor is shown in figure it have two identical transistors Q1 and Q2 with equal collector. Figure (a) shows the circuit of a bistable multivibrator using two NPN transistors. Here the output of a transistor Q2 ‚Äčis coupled put of a transistor Q1 through a. as the bistable multivibrator or Eccles-fordan flip-flop circuit, has found widespread . the other. Using, with a certain safety margin, the smallest possible trigger.

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As its left-hand negative plate is connected to Q1 base, a maximum negative voltage – V is applied to Q1 base that keeps Q1 firmly off.

This Multivibrator is also known as Flip-flop. A division ratio of 10, for example, is easy to obtain but not dependable. The transistor conducts current, powering on the LED connected to the collector of the second, or rightmost, transistor.

So the output voltage will be. Thus C1 restores its charge and prepares for the next State 1 when it will act again as a time-setting capacitor Bistalbe personally tested this and it did not work.

Bistable Multivibrator (Flip-Flop)

In the end, only R3 provides the needed input base current. Q2 collector voltage is the output of the circuit in contrast to the astable circuitit has a perfect square waveform since the output is not loaded by the capacitor.


This rise in voltage is coupled to the input of transistor Q1 and this makes transistor Q1 further saturated. An astable multivibrator can be synchronized to an external chain of pulses. This drives transistor Q2 in to cutoff. The forward-biased Q2 base-emitter junction fixes the voltage of C1 right-hand plate at 0. Schmitt trigger circuits are used as Amplitude Comparator and Squaring Circuit. The transfer characteristics of electronic circuits exhibit a loop called as Hysteresis.

As a result, the circuit goes in State 1 described above. 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. To break down what a bistable multivibrator is and does, let’s first break down the term into individual components. Retrieved from ” https: It continues in that state, unless an external trigger pulse is given. The capacitor discharges through resistor R and charges again to 0.

The resistance R3 is chosen small enough to keep Q1 not deeply saturated after C2 is fully charged.

The breadboard circuit of the circuit above is shown below. A free-running multivibrator with a frequency of one-half to one-tenth of the reference frequency multivibeator accurately lock to the reference frequency.


Q2 collector voltage begins falling; this change transfers through the fully charged C2 to Q1 base and Q1 begins multiivbrator off. Time bases scanning generators: The circuit is powered by 9V. 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:.


This concept depends upon the phenomenon called as Hysteresis. The 2N is a popular general-purpose NPN transistor.

Pulse Circuits – Bistable Multivibrator

Because they do not need to be the same, an asymmetric duty cycle is easily achieved. Thus, Set is used to “set” Q1 on, and Reset is used to “reset” it to off state. Hence, when the circuit is switched on, if Q1 is on, its collector is at 0 V.

The output obtained at the collector terminals of Q1 and Q2 are complementary to each other always. The circuit stays in any one of the two stable states. It does not keep any state permanently. After elapsing the time, it returns to its stable initial state. Resistors need to be connected to the bases of the transistors for the circuit to work.

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