Bistable Multivibrator Working And Signal Waveform

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 I_C1 is greater than I_C2 and V_C1 is less than V_C2. 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 V_C1 =Low, V_C2 high, V_B1 = less pos­i­tive and V_B2 = ‑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, V_C2 = low, V_B1 = ‑V_BB and V_B2 = 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.