Monostable Circuit Multivibrator And Signal Waveform

Monostable Circuit

Mono­stable Cir­cuit Mul­ti­vi­bra­tor is below the picture

Mono­stable mul­ti­vi­bra­tor con­tains only one sta­ble state. The oth­er state is qua­si sta­ble state. Hence it is also called as one shot mul­ti­vi­bra­tor. It is used to gen­er­ate pre­cise time delays 

When a suf­fi­cient mag­ni­tude of pos­i­tive pulse is applied to its trig­ger input the base Q1 is for­ward biased and it starts con­duc­tion. The cur­rent I_C1 starts flow­ing through the col­lec­tor of Q₁. The volt­age of V_C1 decreases. 

The regen­er­a­tive feed­back also increas­es the con­duc­tion of Q₁ and also decreas­es the con­duc­tion of Q₂. Final­ly Q₁ goes to sat­u­ra­tion and Q₂ goes to cutoff. 

The volt­ages V_C1 is low and V_C2 is high. The volt­age already placed at the col­lec­tor of Q₁ is ful­ly dropped across the capac­i­tor C₁. Hence the volt­age now occurred at the base of Q₁ is less pos­i­tive and the volt­age occurred at the base of Q₁ is less pos­i­tive and the volt­age occurred at the base of Q₂ is ‑V_cc. This state is a qua­si-sta­ble state because it is auto­mat­i­cal­ly changed by the charg­ing effect of capac­i­tor C₁.

Now the capac­i­tor C₁ is going to charge towards V_CC through the resis­tor R_B2. When the capac­i­tor C₁ attains a suf­fi­cient volt­age to switch ON the tran­sis­tor Q₂ it starts conduction. 

By the regen­er­a­tive feed­back actions the con­duc­tion of Q₂ increas­es and the con­duc­tion of Q₂ increas­es and the con­duc­tion of Q₁ decreases. 

Final­ly Q₂ goes to sat­u­ra­tion and Q₁ goes to cut­off. Now the base volt­age of Q₁ goes to ‑V_BB and the base volt­age of Q₂ goes to less positive. 

This state is a sta­ble state. This state is con­vert­ed only by apply­ing trig­ger pulse to the trig­ger cir­cuit. The ON peri­od of Q₁ or the OFF peri­od of Q₂ depends upon the val­ue of C₁ and R_B2