Operational amplifier bistable multivibrator

- a circuit for a bistable multivibrator using an operational amplifier, op amp

Op-amp circuits include:
    •  Operational amplifier circuits
    •  Inverting op-amp
    •  Non-inverting op-amp
    •  Op-amp high pass filter
    •  Op-amp low pass filter
    •  Op-amp bandpass filter
    •  Op-amp variable gain amplifier
    •  Op-amp notch filter circuits
    •  Operational amplifier multivibrator
    •  Op-amp bistable
    •  Op-amp comparator
    •  Op-amp Schmitt trigger
    •  Op-amp integrator
    •  Op-amp differentiator

It is easy to use an operational amplifier as a bistable multivibrator. An incoming waveform is converted into short pulses and these are used to trigger the operational amplifier to change between its two saturation states. To prevent small levels of noise triggering the circuit, hysteresis is introduced into the circuit, the level being dependent upon the application required. The operational amplifier bistable multivibrator uses just five components, the operational amplifier, a capacitor and three resistors.

The bistable circuit has two stable states. These are the positive and negative saturation voltages of the operational amplifier operating with the given supply voltages. The circuit can then be switched between them by applying pulses. A negative going pulse will switch the circuit into the positive saturation voltage, and a positive going pulse will switch it into the negative state.

It is very easy to calculate the points at which the circuit will trigger. The positive going pulses need to be greater than Vo-Sat through the potential divider, i.e. Vo-Sat x R3 / (R2 + R3), and similarly the negative going pulses will need to be greater than Vo+Sat through the potential divider, i.e. Vo+Sat x R3 / (R2 + R3). If they are not sufficiently large then the bistable will not change state.

By Ian Poole

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