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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How to Build a Bistable Multivibrator Circuit with Transistors

CS1 French-language sources fr Pages with citations lacking titles All usint with failed verification Articles with failed verification from December Articles with failed verification from February Articles needing additional references from January All articles btj additional references Commons category link is on Wikidata. Chains of bistable flip-flops provide more predictable division, at the cost of more active elements.

After elapsing the time, it returns to its stable initial state. By using this site, you agree to the Terms of Use and Privacy Policy.

How to Build an Bistable Multivibrator Circuit with Transistors

The capacitor discharges through resistor R and charges again to 0. However, this means that at this stage they will both have multiivbrator base voltages and therefore a tendency to usijg on, and inevitable slight asymmetries will mean that one of the transistors is first to switch on. This is the second stable state of the Multivibrator.

The same Multivibrators are designed using operational amplifiers and also IC timer circuits, which are discussed in further usibg. To understand the operation, let us consider the switch to be in position 1. 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. If we don’t change the switch, the outputs remain what they are until we do so.


This reduces the reverse bias on transistor Q2 and drives it in to saturation. It explains that the output values depends upon both the present and the past values of the input.

During State 1Q2 base-emitter junction is reverse-biased and capacitor C1 is “unhooked” from ground. Then the voltage at the collector of Q1 drops to minimum and this reduced voltage is coupled to the base of transistor Q2 through resistor R1. Schmitt trigger circuits are used as Amplitude Comparator and Squaring Circuit. For example, before the advent of low-cost integrated circuits, chains of multivibrators found use as frequency dividers. 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.

Bistable Multivibrator (Flip-Flop)

Similarly, Q2 remains on continuously, if it happens to get switched on first. The transfer characteristics of electronic circuits exhibit a loop called as Hysteresis. It can be powered with as little as about 6V but the LED will not be as bright.

A division ratio of 10, for example, is easy to obtain but not dependable. So this is our circuit above.

I personally tested this and it did not work. If the voltage is already greater than V 1then it remains there until the input voltage reaches V 2which is a low level transition. 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 will quickly put the circuit into one of the above states, and oscillation will ensue. Simultaneously, C1 that is fully discharged and even slightly charged to 0. During State 2Q2 base-emitter junction is forward-biased and capacitor C1 is “hooked” to ground.

The forward-biased Q2 base-emitter junction fixes the voltage of C1 right-hand plate at 0. The Principles of Known Circuits”. Mltivibrator C1 restores its charge and prepares for the next State bjtt when it will act again as a time-setting capacitor Now the capacitor discharges towards -V sat.


This latch circuit is similar to an astable multivibrator, except that there is no charge or discharge time, due to the absence of capacitors.

For this reason Abraham and Bloch called it a multivibrateur. Compare this to comparison to an astable multivibrator circuit, which doesn’t stay permanently bishable any state. This rise in voltage is coupled to the input of transistor Q1 and this makes transistor Q1 further saturated.

So multivibdator circuit is set up so that only one LED is on at a time. The bistable circuit is a bistablle of a flip flop. Q2 collector voltage begins falling; this change transfers through the fully charged C2 to Q1 base and Q1 begins cutting off.

This is another stable state of the Multivibrator. It is a predecessor of the Eccles-Jordan trigger [7] which was derived from the circuit a year later.

Q2 begins conducting and this starts the avalanche-like positive feedback process as follows. And if both bases were grounded at the same multicibrator, both LEDs would be on. Hence, when the circuit is switched on, if Q1 is on, its collector is at 0 V. This repeats and forms a free-running oscillator or an astable multivibrator.

Pulse Circuits – Bistable Multivibrator

Now, the capacitor C2 is fully charged in the previous State 1 to the power supply voltage V with the polarity shown in Figure 1. Two transistors are connected in feedback with two resistors, bbistable one collector connected to the base of the other. In this circuit, we build a bistable circuit with transistors and a few resistors and our output LEDs.