Bistable Multivibrator Working
Bistable multivibrator working
Bistable Multivibrator Working contains two stable states. Both states are converted only by applying external trigger pulses. It is also known as Flip Flop multivibrator.
When the supply is switched ON due to the slight mismatch between the two transistors the conduction of one transistor is more than other.
We assume that the conduction of Q1 is more than Q2. Hence IC1 is greater than IC2 and VC1 is less than VC2. By the regenerative feedback actions the conduction of Q1 again increases and Q2 decreases. Finally Q1 goes to saturation and Q2 goes to cutoff. Now the voltages of VC1 =Low, VC2 high, VB1 = less positive and VB2 = ‑VBB
This state is a stable state. It is converted only by applying positive trigger pulse to the base of Q2 or a negative trigger pulse to the base of Q1.
When a proper trigger pulse is applied the conduction of Q2 increases and the conduction of Q1 decreases.
By the regenerative feedback actions Q1 goes to cutoff and Q2 goes to saturation. Now the voltages of VC1 = high, VC2 = low, VB1 = ‑VBB and VB2 = less positive
This state is also a stable state. It is again converted either by applying a positive pulse to the base of Q1 or a negative pulse to the base of Q2. The capacitors C1 and C2 are called speed up capacitors used for increasing the speed of operation.
Hence in bistable multivibrators both states are converted only by applying proper external trigger pulses.