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Circuit Simulator - Bistable Multivibrator (Flip-Flop)

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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.

Credits: Mr. Paul Falstad.




Neetika said: (Thu, Jun 5, 2014 01:36:47 PM)    
 
What happen if positive pulse is given to transistor in bistable multivibrator?

Veer said: (Fri, Sep 26, 2014 12:37:26 AM)    
 
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.

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