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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This reduces the reverse bias on transistor Q2 and drives it in to saturation.

Two transistors are connected in feedback with two resistors, having one collector connected to the base of the other. An astable multivibrator can be synchronized to an external chain of pulses. Compare this to comparison to an astable multivibrator circuit, which doesn’t stay permanently in any state.

When the switch is altered, the base of transistor Q 2 is grounded turning it to OFF state. A division ratio of 10, for example, is easy to obtain but not dependable. Then the voltage at the collector of Q1 rises towards Vcc and this rise in voltage is fed to the base of transistor Q2 through resistor R1. The output voltage of the switched-off transistor Q1 changes exponentially from low to high since this relatively high resistive output is loaded by a low impedance load capacitor C1.

The feedback resistors are shunted by capacitors C1 and C2. It is implemented by the coupling capacitors that instantly transfer voltage changes because the voltage across a capacitor cannot suddenly change. For the circuit in Figure 2, in the stable state Q1 is turned off and Q2 is turned on. The capacitor discharges through resistor R and charges again to 0.

The diode D1 clamps the capacitor to 0. Bistabel this voltage gets applied at the emitter of Q 1. This technique was used in early electronic organs, to keep notes of different octaves accurately in tune. It’s able to store bits indefinitely unless desired to be changed. The figure below bisable the circuit diagram of a fixed-bias binary. The circuit has two astable unstable states that change alternatively with maximum transition rate because of the “accelerating” positive feedback.


By using this site, you agree to the Terms of Use and Privacy Policy. The circuit operation is based on the fact that the forward-biased base-emitter junction of the switched-on bipolar transistor can provide a path for the capacitor restoration.

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. The main difference in the construction of this circuit is that the coupling from the output C 2 of the second transistor to the base B1 of the first transistor is missing and that feedback is obtained now through the resistor R e.

The transistor Q 1 is given a trigger input at the base through the capacitor C 3 and the transistor Q 2 is given a trigger input at multivibratir base through the capacitor C 4. The resistance R3 is chosen small enough to keep Q1 not deeply saturated after C2 is fully charged. This is the other stable state.

How to Build a Bistable Multivibrator Circuit with Transistors

At the same time, the other empty capacitor quickly charges thus restoring its charge the first capacitor acts as a time-setting capacitor and the second prepares to play this role in the next state. Chains of bistable flip-flops bidtable more predictable division, at the cost of more active elements. As the input bistwble continues to rise, the voltage at the points C 1 and B 2 continue to fall and E 2 continues to rise.

This switch allows us to switch logic states of the outputs. The output waveforms at the collectors of Q 1 and Q 2 along with the trigger inputs given at the bases of Q W and Q 2 are shown in the following figures.

Simultaneously, C1 that is fully discharged and even slightly charged to 0. Another type of binary circuit which is ought to be discussed multivkbrator the Emitter Coupled Binary Circuit.

The circuit is useful for generating single output pulse of adjustable time duration in response to a triggering signal. In other projects Wikimedia Commons.

Multivibrator – Wikipedia

A single pair of active devices can be used to divide a reference by a large ratio, however, the stability of the technique is poor owing to the variability of the power supply and the circuit elements. So this is our circuit above. How manual control is achieved in the circuit is through a SPDT switch.


The bistable circuit is a function of a flip flop. It can be used basically for any circuit in where you want manual control over outputs which you want to keep stable states unless you trigger it to change.

In the charging capacitor equation above, substituting:. We do not use any integrated circuit such multicibrator a timer. After elapsing the time, it returns to its stable initial state.

Pulse Circuits – Bistable Multivibrator

Thus, the circuit remains stable in a single state continuously. Suppose transistor Q1 conducts more and it drives in to saturation mode. Accordingly, one fully charged capacitor discharges reverse charges slowly thus converting the time into an exponentially changing voltage. Bistable means that the outputs can be stably either in the HIGH state or the LOW state, without changing unless manually triggered to change to the opposite state.

This concept depends upon the phenomenon called as Hysteresis. The change of switch to position 2, works as a trigger. If the voltage is already greater than V 1then it remains there until the input voltage reaches V 2which is a low level transition.

The datasheet for the 2N transistor can be found at the following link: 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:. Since it produced a square wavein contrast to the sine wave generated by mmultivibrator other oscillator circuits of the usjng, its output contained many harmonics above the fundamental frequency, which could be used for calibrating high frequency radio circuits.

And if both bases were grounded at the same time, both LEDs would be on.