3.1 State the difference between a monostable multivibrator and an astable multivibrator with reference to their output states - NSC Electrical Technology Digital - Question 3 - 2022 - Paper 1

C2 serves to stabilize the voltage and determine the timing characteristics based on its charge and discharge cycles, while R3 limits the current flowing through the circuit, protecting the components and ensuring proper functioning by controlling the discharge timing of C2.

When C2 is fully charged to 9 V, the non-inverting voltage (Vb) will also be at 9 V because the capacitor holds the voltage equal to the supply voltage in a stable state with no current flowing.

The moment a positive pulse is applied to the inverting input, the output voltage transitions from a high state (e.g., +9 V) to a low state (e.g., -9 V), resulting in a change in output state for the duration of the pulse, due to the inverter behavior of the op-amp.

The required waveform should show the output initially at a positive voltage, and then dropping to negative voltage during the duration of the input pulse, returning to positive once the pulse is removed.

When the output is positive, the polarity of Vb is also positive, indicating that the non-inverting input is receiving a higher voltage than the inverting input.

The output transitions from +9 V to -9 V as soon as Va becomes greater than Vb, indicating that the non-inverting input is surpassing the inverting reference level.

Increasing the value of RF will increase the time constant of the circuit, making the capacitor charge more slowly. This leads to a decrease in the frequency of the output waveform, changing the timing characteristics of the astable multivibrator.

The saturation voltages of the Schmitt trigger are typically referenced to the supply voltage levels, specifically +9 V and -9 V, depending on the configuration and reference points utilized.

RF and R1 are used to set the trigger voltage level at the non-inverting terminal, determining how the Schmitt trigger response will operate based on the input voltage levels.

Both RF and R1 help in establishing the feedback loop that defines the operating threshold levels, effectively determining how sensitive the circuit will be to input voltage changes.