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 

Monostable Circuit
Mono­stable Circuit

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 IC1 starts flow­ing through the col­lec­tor of Q1. The volt­age of VC1 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 VC1 is low and VC2 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 ‑Vcc. 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 VCC through the resis­tor RB2. 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. 

Monostable Circuit
Mono­stable Circuit

Final­ly Q2 goes to sat­u­ra­tion and Q1 goes to cut­off. Now the base volt­age of Q1 goes to ‑VBB 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 RB2

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