# Circuit Simulator - Bistable Multivibrator (Flip-Flop)

Bistable Multivibrator (Flip-Flop)
Circuit Description:
This circuit is a bistable multivibrator, or flip-flop. Click on the "set" input at lower left to bring the output high (5V). Click on the "reset" input at lower right to bring the output low (ground).

The transistors are cross-coupled in such a way that the circuit has two stable states. Initially, Q2 is on and Q1 is off. Since Q1 is off, no current is flowing through it, and its collector voltage is close to 5V. This allows current to flow through into the base of Q2, which keeps Q2 switched on. Q2 is in saturation mode, keeping the collector voltage close to ground; this prevents any current from flowing into the base of Q1 to switch it on.

If you click the "set" input momentarily, this provides base current to Q1, switching it on, bringing its collector low, which stops the base current flowing to Q2. So the circuit switches to the opposite state. Clicking the "reset" input switches back.

Discussion:
6 comments Page 1 of 1.

What happen if positive pulse is given to transistor in bistable multivibrator?
(4)

Veer said:   10 years ago
When positive pulse given to the transistor which is in "off state". This pulse forward biased the transistor and starts conducting. So there is voltage drop across the collector of transistor. Which is fed to the base of transistor which is on state. Via resistor instantly. Makes transistor cutt off.

So voltage at collector increase which fed to the base of transistor which is conducting. And makes it more forward bias :D this is stable state.
(7)

Jadhav yogesh said:   9 years ago
Why we give the trigger of the transistor?
(4)

Roshan ahire said:   8 years ago
I'm trying to operate this bistable circuit with op amp comparator, its not working. Op-amps LOW voltage is not been considered as GND for our multivibrator.
(3)

Zahoor said:   8 years ago
Define bi stable multivibarator.
(7)

Abdullah akhtar said:   8 years ago
Bistable, in which the circuit is stable in either state. It can be flipped from one state to the other by an external trigger pulse. This circuit is also known as a flip-flop. It can be used to store one bit of information.
(3)