Astable Multivibrator Using 741 Op-Amp

Posted on Feb 6, 2014

The positive feedback comparator circuit increases the gain ofthe op-amp, which helps to switch very fast between the two states of a multivibrator. The positive feedback also provides hysteresis to the circuit. A capacitor `C` is connected to the inverting terminal of the Op-Amp with its other end grounded. The capacitor along with the resistor `R`

Astable Multivibrator Using 741 Op-Amp
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acts as a RC integrator. The vol;tage across the capacitor is given by Vc. Thebelow figure demonstrates the working of an Astable Multivibrator using IC 741 Operationalamplifier, consisting of a comparator circuit having a positive feedback with a feedback factor. Now, the op-amp has a voltage of `Vc` at the inverting terminal and [R2/(R1+R2)]Vo atthe non-inverting terminal, giving rise to a voltage equal to+Vsat or -Vsat at the output. On the other hand at the inverting terminal, the capacitor tries to charge to +Vsat, which is available to the capaciror through `R`. but on the way to +Vsat, when the capacitor reaches at a potential equal to the potential at the non-inverting terminal of the op-amp. Since the op-amp behaves as a comparator circuit, the output changes from +Vsat to -Vsat, because the inverting potential is greater than non-inverting potential.

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