5.1 State ONE effect of switch bounce in electronic circuits - NSC Electrical Technology Electronics - Question 5 - 2024 - Paper 1

Feedback in this circuit refers to the process where a portion of the output voltage is fed back to the non-inverting input through the voltage divider R2 and R3. This feedback helps stabilize the operation of the bistable multivibrator by maintaining the desired output state.

When a positive trigger pulse is applied, the capacitor charges immediately to the applied voltage. This rapid change causes the output to switch to a high state, indicating that the circuit has been triggered.

Upon receiving a negative trigger pulse, the op-amp compares the voltages at its inverting and non-inverting terminals. If the voltage on the inverting input becomes greater than that on the non-inverting input, the output transitions to its lower state, reflecting the reset of the multivibrator.

The output does not change during the application of trigger pulse 2 when the voltage on the non-inverting input is lower than the inverting input. In this case, the conditions required for a state change are not met.

The multivibrator circuit identified in FIGURE 5.3 is a monostable multivibrator.

Resistor R2 serves to maintain pin 2 of the 555 timer (the trigger pin) in a stable state, thus helping to keep the monostable circuit in its steady state until interrupted by a trigger.

The output waveform will consist of a single pulse whose duration is determined by the external resistors and capacitor connected to the 555 timer.

The circuit will reset to its resting state at 6 V, as that is the threshold at which the capacitor C1 charges to two-thirds of Vcc, allowing the output to return to its low state.

The output changes state continually as both trigger pin 2 and threshold pin 6 are interconnected to the timing capacitor. As the capacitor charges and discharges through the resistors, it causes repeated resets and triggers, resulting in a continuous output stream.

The times t1 and t2 are not equal because the capacitor charges through R1 but discharges through R1 and R2 combined, leading to different time constants for charging and discharging.

The frequency can be calculated using the formula: f = rac{1}{T}

Where T is the total period including both t1 and t2, leading to the calculation based on resistor values and capacitance.

The reference voltage, V_ref, can be calculated using the voltage divider principle applied to the resistors. Substituting the values gives: $V_{ref} = 4,5 V$

The resistance of R1 can be influenced by the desired gain of the amplifier. A higher resistance will lead to a lower current through R1, affecting the output voltage as per Ohm's law.

The output voltage will follow the input voltage, switching levels at the reference threshold, producing a triangle output resulting from the comparator action.

An increase in the value of R1, assuming fixed input voltages, will lead to a higher voltage drop across R1. This causes the voltage across R2 to decrease, as R2 will have less voltage available to drop.

A summing amplifier integrates multiple input signals to provide a single output voltage, representing the sum of the scaled inputs. It can combine different signal voltages into one output.

The output voltage can be computed using the formula: $V_{out} = -(V_1 R_f/R_1 + V_2 R_f/R_2 + V_3 R_f/R_3)$

When R5 is set to a low value like 200 Ω, the amplifier operates at unity gain, resulting in the output voltage closely approximating the input, which in this case falls to 0.6 V.

The output waveform will be a variation mirroring the input, with specific characteristics depending on the RC timing elements of the circuit.

During the first positive square wave, the capacitor charges rapidly to the potential of the input while the other plate remains at ground, causing the output to transition significantly towards the positive supply.

The circuit can be modified into a passive integrator by rearranging the resistor and capacitor in the configuration that allows continuous charging based on input signal variation, smoothing the signal output.